prompt emission mechanisms of grbs - max planck societygrb07/presentations/giannios.pdfprompt...
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Prompt emission mechanisms ofGRBsDimitrios Giannios
Max Planck Institute for Astrophysics
Structure of the talk Main properties of the prompt emission
Models for the GRB flow Fireballs Poynting-flux dominated flows
Reconnection model
Dissipative mechanisms for the prompt emission Internal shocks vs Magnetic reconnection
Radiative mechanisms Thomson thin vs photospheric emission
Summary
1 MeV
The prompt emission spectrum
The typical GRB spectrum hasnon-thermal appearanceBand et al 1993 Kaneko et al 2006
Low energy power law slope α High energy power law slope β Connected at ~a few hundred
keV (spectral peak)
Short bursts are harder probablybecause of steeper low energyslopePaciesas et al 2003 Ghirlanda et al 2004
E (MeV)
E f(E
) (er
gcm
2 s)
E
f(E)
GRB Variability
Short
t
N (t
)
Variability detected to as short as sub-msec timescales
Variable lightcurves composed bypulses Fenimore et al 1995 Norris et al 1996
The typical pulse width is δt~1sec(~01 sec) for long (short) bursts
Summary for the prompt emission Clues
The prompt emission has non-thermal spectral appearance Band et al 1993 Preece et al 1998
Rapid variability
The GRB-emitting flow is ultrarelativistic (γgt100)eg Piran 1999
Big questions How is the flow accelerated What processes result in the observed spectral and
temporal properties of GRBs
Can we learn something about the central engine
General considerations Acceleration Important quantities of the flow
luminosity L mass flux Efficient acceleration can lead to γsr~η
Depending on the energy extraction mechanism the flow canbe dominated by
Thermal energy rarr thermal acceleration (Fireball) Paczynski 1986 Goodman 1986 Sari amp Piran 1991 Magnetic energy rarr magnetic acceleration (Poynting-flux dominated
flow) Usov 1992 Thompson 1994 Meacuteszaacuteros amp Rees 1997 Drenkhahn amp Spruit 2002 Lyutikon amp
Blandford 2003
21
L
Mc = gtgt
ampMampBaryon loading
Fireballs
Parameters L η initial radius ro
Go through fast acceleration Converting thermal energy into kinetic
Saturation takes place when almost all thermal energy is used γsr η at the photospheric crossing γsr lt η
Radiation and matter decouple whenτ ~ 1 Photospheric emission takes place
r
[Notation (L= L521052 ergs)]
Magnetic (Poynting) models The field can be
axisymmetric (DC flow) Vlahakis amp Koumlnigl 2003 Lyutikov amp Blandford 2003
McKinney 2005 Uzdensky amp MacFadyen 2006
highly asymmetric (AC flow)Drenkhahn amp Spruit 2002 Thompson 2006
Acceleration is more gradualDrenkhahn amp Spruit 2002 Vlahakis amp Koumlnigl 2003
Here I focus more on AC flow
DC
AC
The reconnection (AC) model
1 3
sr sr
4 3
7 3
23
diss
diss
( )
( ) 8
r r
B r
n r
BP r
t
=
$
$
= $
Magnetic field changes polarityon small scales λ = 2πcω
Magnetic reconnection proceedswith a fraction ε ~ 01 of theAlfveacuten speed Lyubarsky 2005
The dynamics of the flow havebeen worked out in detailDrenkhahn 2002 and Denkhahn amp Spruit 2002see also Lyubarsky amp Kirk 2001 for pulsar winds
Parameters L η (εω)
rsr
rph
Log(r [cm])
These are all fineWhere are the γ-rays in this picture
Which processes power the prompt emission
Where (at which radii) is it produced
General considerationsenergy source of the prompt emission The rapid GRB variability argues against the forward shock for
the prompt emissioneg Sari amp Piran 1997 see however Dermer 2007 for a different point of view
Observationally transition from the prompt to the early afterglowemission Zhang et al 2006
The prompt emission most likely comesfrom internal dissipation of energy in the fast flow
This can take place by Internal shocks Rees amp Meacuteszaacuteros 1994 Sari amp Piran 1997
Magnetic dissipation Thompson 1994 Denkhahn amp Spruit 2002 Lyutikov amp Blandford 2003-see Fan et al 2004 for a combination of the two
Internal shocks vs Magnetic dissipation Internal shocks
Unsteady flow composed bymany fast shells
A fast shell with γ2gtγ1 collideswith a slower one dissipatingtheir relative kinetic energythrough shock waves
Magnetic dissipation Magnetic fields carry most of the
energy of the flow The magnetic energy is
dissipated internally throughreconnection
g-rays
Fk
FB
Fk
variability and dissipation are separateingredients in magnetic dissipationmodels
γ2υ2 γ1υ1
FB
γυ
Where is the prompt emission produced anywhere between the Thomson photosphere rph and the
deceleration radius rd
Typically rph~1011cm and rd ~1017cm in this range of radii density ~12 orders of magnitude optical depth ~6 orders of magnitude
Different radiative mechanisms dependingon the location of the energy dissipation
Case 1 Thomsonthin dissipation
Case 2 Photosphericdissipation
Case 1Internal shocks in the Thomson thin regime Internal shocks
The collision of the shells takes place at rcol~γ2ctv tv related to the central engine activity (not trivially Janka et al 2005 Aloy amp
Rezolla 2006) Each collision results in an observed pulse of gamma-rays
shocks cross the shells
In the shock front Particle acceleration takes place Magnetic field amplification due to plasma instabilitites (see next talks)
Parameters fractions єe ζe єB power-law N(γe) ~ γe-p pgt2
Fast particles + magnetic fields Synchrotron self-Compton emission
Thin synchrotron emission may explain the observed spectrum
~
Case 1Can thin Synchrotron emission explain the spectra
Pros For tv~1 s the characteristic pulse duration and separation can be reproduced
Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002
The peak of the synchrotron spectrum can be in the ~a few 100 keV range
Flat high-energy power law
Cons Low radiative efficiency (though uncertain)
~ єdiss єe єBand at the ~ level
Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004
jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair
creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002
Case 1Magnetic dissipation in the Thomson thin regime
In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006
Fast proper plasma motions lead to the rapid observed variability
AC model dissipation near photosphere as well as outside
Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005
Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004
Thin synchrotron emission may be responsible for the GRB
The B-field is given directly by the model At low densities particle distributions in reconnection uncertain
Case 2
Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin
Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000
Spectrum quasi thermal Goodman 1986
Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006
In the AC model DG 2006 DG amp Spruit 2007
For this range of η the model predicts a dissipative photosphere
1 48 3 23
ph 25 o7 52
2 3
52 o7
005 1000L r L
L L r
$ lt amp
(
15 15ph 15 1552 3
52 3
25
( )016 150 ( )
L LL
L
$
Dissipative Photosphere in a fireball Internal shocks take place below the
photosphere for tvltlt1 s
Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007
Injecting fast electrons Slow heating Ghisellini amp Celotti 1999
Studied the radiative transfer for variousvalues of єdiss єB єe τ
Big variety of spectra depending on τ
Dominant process Compton scattering ofphotons advected with the flow
τγe = 1
Our suggestion photospheric emission from the AC modelMain features
AC model gradual dissipation throughout the photosphere
If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering
Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007
Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes
Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~
rsrrph
Log(r [cm])
Radiative transfer analytical estimates+ Monte Carlo Comptonization
Deep in the flow radiation ampparticles are in thermal equilibrium
At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV
For r gt req balance in heating andcooling determined Te
Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering
Photospheric spectra Characteristic peak at ~1 MeV
(in the central engine frame)
Flat power law high energy tails(unsaturated Comptonization)
Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of
bursts Ryde 2004 2005
Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007
Inferences for the central enginethe stronger the cleaner
The Amati relation explainedif in different bursts
Variability in prompt emission Reflects changes in L η
Assumption relationholds during the GRB the model predicts the observed
narrowing of pulses withincreasing energyFenimore et al 1995
06L
06L
Summary Spectral and temporal properties of GRBs are very intriguing
The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation
Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB
Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them
The peak energy and the energetics
η30 100 300 1000
η30 100 300 1000
Comment
The temperature of the flow at the req in the observer frame is
The Ef(E) spectrum of this component peaks at ~4 times thisenergy
19 1 9 1 3 2 9
eq eqobs e1 52 3 25
eq
( ) ( )100 keV
1 1
r T f LT
z z
$
+ +
Structure of the talk Main properties of the prompt emission
Models for the GRB flow Fireballs Poynting-flux dominated flows
Reconnection model
Dissipative mechanisms for the prompt emission Internal shocks vs Magnetic reconnection
Radiative mechanisms Thomson thin vs photospheric emission
Summary
1 MeV
The prompt emission spectrum
The typical GRB spectrum hasnon-thermal appearanceBand et al 1993 Kaneko et al 2006
Low energy power law slope α High energy power law slope β Connected at ~a few hundred
keV (spectral peak)
Short bursts are harder probablybecause of steeper low energyslopePaciesas et al 2003 Ghirlanda et al 2004
E (MeV)
E f(E
) (er
gcm
2 s)
E
f(E)
GRB Variability
Short
t
N (t
)
Variability detected to as short as sub-msec timescales
Variable lightcurves composed bypulses Fenimore et al 1995 Norris et al 1996
The typical pulse width is δt~1sec(~01 sec) for long (short) bursts
Summary for the prompt emission Clues
The prompt emission has non-thermal spectral appearance Band et al 1993 Preece et al 1998
Rapid variability
The GRB-emitting flow is ultrarelativistic (γgt100)eg Piran 1999
Big questions How is the flow accelerated What processes result in the observed spectral and
temporal properties of GRBs
Can we learn something about the central engine
General considerations Acceleration Important quantities of the flow
luminosity L mass flux Efficient acceleration can lead to γsr~η
Depending on the energy extraction mechanism the flow canbe dominated by
Thermal energy rarr thermal acceleration (Fireball) Paczynski 1986 Goodman 1986 Sari amp Piran 1991 Magnetic energy rarr magnetic acceleration (Poynting-flux dominated
flow) Usov 1992 Thompson 1994 Meacuteszaacuteros amp Rees 1997 Drenkhahn amp Spruit 2002 Lyutikon amp
Blandford 2003
21
L
Mc = gtgt
ampMampBaryon loading
Fireballs
Parameters L η initial radius ro
Go through fast acceleration Converting thermal energy into kinetic
Saturation takes place when almost all thermal energy is used γsr η at the photospheric crossing γsr lt η
Radiation and matter decouple whenτ ~ 1 Photospheric emission takes place
r
[Notation (L= L521052 ergs)]
Magnetic (Poynting) models The field can be
axisymmetric (DC flow) Vlahakis amp Koumlnigl 2003 Lyutikov amp Blandford 2003
McKinney 2005 Uzdensky amp MacFadyen 2006
highly asymmetric (AC flow)Drenkhahn amp Spruit 2002 Thompson 2006
Acceleration is more gradualDrenkhahn amp Spruit 2002 Vlahakis amp Koumlnigl 2003
Here I focus more on AC flow
DC
AC
The reconnection (AC) model
1 3
sr sr
4 3
7 3
23
diss
diss
( )
( ) 8
r r
B r
n r
BP r
t
=
$
$
= $
Magnetic field changes polarityon small scales λ = 2πcω
Magnetic reconnection proceedswith a fraction ε ~ 01 of theAlfveacuten speed Lyubarsky 2005
The dynamics of the flow havebeen worked out in detailDrenkhahn 2002 and Denkhahn amp Spruit 2002see also Lyubarsky amp Kirk 2001 for pulsar winds
Parameters L η (εω)
rsr
rph
Log(r [cm])
These are all fineWhere are the γ-rays in this picture
Which processes power the prompt emission
Where (at which radii) is it produced
General considerationsenergy source of the prompt emission The rapid GRB variability argues against the forward shock for
the prompt emissioneg Sari amp Piran 1997 see however Dermer 2007 for a different point of view
Observationally transition from the prompt to the early afterglowemission Zhang et al 2006
The prompt emission most likely comesfrom internal dissipation of energy in the fast flow
This can take place by Internal shocks Rees amp Meacuteszaacuteros 1994 Sari amp Piran 1997
Magnetic dissipation Thompson 1994 Denkhahn amp Spruit 2002 Lyutikov amp Blandford 2003-see Fan et al 2004 for a combination of the two
Internal shocks vs Magnetic dissipation Internal shocks
Unsteady flow composed bymany fast shells
A fast shell with γ2gtγ1 collideswith a slower one dissipatingtheir relative kinetic energythrough shock waves
Magnetic dissipation Magnetic fields carry most of the
energy of the flow The magnetic energy is
dissipated internally throughreconnection
g-rays
Fk
FB
Fk
variability and dissipation are separateingredients in magnetic dissipationmodels
γ2υ2 γ1υ1
FB
γυ
Where is the prompt emission produced anywhere between the Thomson photosphere rph and the
deceleration radius rd
Typically rph~1011cm and rd ~1017cm in this range of radii density ~12 orders of magnitude optical depth ~6 orders of magnitude
Different radiative mechanisms dependingon the location of the energy dissipation
Case 1 Thomsonthin dissipation
Case 2 Photosphericdissipation
Case 1Internal shocks in the Thomson thin regime Internal shocks
The collision of the shells takes place at rcol~γ2ctv tv related to the central engine activity (not trivially Janka et al 2005 Aloy amp
Rezolla 2006) Each collision results in an observed pulse of gamma-rays
shocks cross the shells
In the shock front Particle acceleration takes place Magnetic field amplification due to plasma instabilitites (see next talks)
Parameters fractions єe ζe єB power-law N(γe) ~ γe-p pgt2
Fast particles + magnetic fields Synchrotron self-Compton emission
Thin synchrotron emission may explain the observed spectrum
~
Case 1Can thin Synchrotron emission explain the spectra
Pros For tv~1 s the characteristic pulse duration and separation can be reproduced
Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002
The peak of the synchrotron spectrum can be in the ~a few 100 keV range
Flat high-energy power law
Cons Low radiative efficiency (though uncertain)
~ єdiss єe єBand at the ~ level
Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004
jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair
creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002
Case 1Magnetic dissipation in the Thomson thin regime
In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006
Fast proper plasma motions lead to the rapid observed variability
AC model dissipation near photosphere as well as outside
Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005
Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004
Thin synchrotron emission may be responsible for the GRB
The B-field is given directly by the model At low densities particle distributions in reconnection uncertain
Case 2
Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin
Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000
Spectrum quasi thermal Goodman 1986
Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006
In the AC model DG 2006 DG amp Spruit 2007
For this range of η the model predicts a dissipative photosphere
1 48 3 23
ph 25 o7 52
2 3
52 o7
005 1000L r L
L L r
$ lt amp
(
15 15ph 15 1552 3
52 3
25
( )016 150 ( )
L LL
L
$
Dissipative Photosphere in a fireball Internal shocks take place below the
photosphere for tvltlt1 s
Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007
Injecting fast electrons Slow heating Ghisellini amp Celotti 1999
Studied the radiative transfer for variousvalues of єdiss єB єe τ
Big variety of spectra depending on τ
Dominant process Compton scattering ofphotons advected with the flow
τγe = 1
Our suggestion photospheric emission from the AC modelMain features
AC model gradual dissipation throughout the photosphere
If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering
Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007
Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes
Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~
rsrrph
Log(r [cm])
Radiative transfer analytical estimates+ Monte Carlo Comptonization
Deep in the flow radiation ampparticles are in thermal equilibrium
At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV
For r gt req balance in heating andcooling determined Te
Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering
Photospheric spectra Characteristic peak at ~1 MeV
(in the central engine frame)
Flat power law high energy tails(unsaturated Comptonization)
Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of
bursts Ryde 2004 2005
Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007
Inferences for the central enginethe stronger the cleaner
The Amati relation explainedif in different bursts
Variability in prompt emission Reflects changes in L η
Assumption relationholds during the GRB the model predicts the observed
narrowing of pulses withincreasing energyFenimore et al 1995
06L
06L
Summary Spectral and temporal properties of GRBs are very intriguing
The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation
Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB
Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them
The peak energy and the energetics
η30 100 300 1000
η30 100 300 1000
Comment
The temperature of the flow at the req in the observer frame is
The Ef(E) spectrum of this component peaks at ~4 times thisenergy
19 1 9 1 3 2 9
eq eqobs e1 52 3 25
eq
( ) ( )100 keV
1 1
r T f LT
z z
$
+ +
1 MeV
The prompt emission spectrum
The typical GRB spectrum hasnon-thermal appearanceBand et al 1993 Kaneko et al 2006
Low energy power law slope α High energy power law slope β Connected at ~a few hundred
keV (spectral peak)
Short bursts are harder probablybecause of steeper low energyslopePaciesas et al 2003 Ghirlanda et al 2004
E (MeV)
E f(E
) (er
gcm
2 s)
E
f(E)
GRB Variability
Short
t
N (t
)
Variability detected to as short as sub-msec timescales
Variable lightcurves composed bypulses Fenimore et al 1995 Norris et al 1996
The typical pulse width is δt~1sec(~01 sec) for long (short) bursts
Summary for the prompt emission Clues
The prompt emission has non-thermal spectral appearance Band et al 1993 Preece et al 1998
Rapid variability
The GRB-emitting flow is ultrarelativistic (γgt100)eg Piran 1999
Big questions How is the flow accelerated What processes result in the observed spectral and
temporal properties of GRBs
Can we learn something about the central engine
General considerations Acceleration Important quantities of the flow
luminosity L mass flux Efficient acceleration can lead to γsr~η
Depending on the energy extraction mechanism the flow canbe dominated by
Thermal energy rarr thermal acceleration (Fireball) Paczynski 1986 Goodman 1986 Sari amp Piran 1991 Magnetic energy rarr magnetic acceleration (Poynting-flux dominated
flow) Usov 1992 Thompson 1994 Meacuteszaacuteros amp Rees 1997 Drenkhahn amp Spruit 2002 Lyutikon amp
Blandford 2003
21
L
Mc = gtgt
ampMampBaryon loading
Fireballs
Parameters L η initial radius ro
Go through fast acceleration Converting thermal energy into kinetic
Saturation takes place when almost all thermal energy is used γsr η at the photospheric crossing γsr lt η
Radiation and matter decouple whenτ ~ 1 Photospheric emission takes place
r
[Notation (L= L521052 ergs)]
Magnetic (Poynting) models The field can be
axisymmetric (DC flow) Vlahakis amp Koumlnigl 2003 Lyutikov amp Blandford 2003
McKinney 2005 Uzdensky amp MacFadyen 2006
highly asymmetric (AC flow)Drenkhahn amp Spruit 2002 Thompson 2006
Acceleration is more gradualDrenkhahn amp Spruit 2002 Vlahakis amp Koumlnigl 2003
Here I focus more on AC flow
DC
AC
The reconnection (AC) model
1 3
sr sr
4 3
7 3
23
diss
diss
( )
( ) 8
r r
B r
n r
BP r
t
=
$
$
= $
Magnetic field changes polarityon small scales λ = 2πcω
Magnetic reconnection proceedswith a fraction ε ~ 01 of theAlfveacuten speed Lyubarsky 2005
The dynamics of the flow havebeen worked out in detailDrenkhahn 2002 and Denkhahn amp Spruit 2002see also Lyubarsky amp Kirk 2001 for pulsar winds
Parameters L η (εω)
rsr
rph
Log(r [cm])
These are all fineWhere are the γ-rays in this picture
Which processes power the prompt emission
Where (at which radii) is it produced
General considerationsenergy source of the prompt emission The rapid GRB variability argues against the forward shock for
the prompt emissioneg Sari amp Piran 1997 see however Dermer 2007 for a different point of view
Observationally transition from the prompt to the early afterglowemission Zhang et al 2006
The prompt emission most likely comesfrom internal dissipation of energy in the fast flow
This can take place by Internal shocks Rees amp Meacuteszaacuteros 1994 Sari amp Piran 1997
Magnetic dissipation Thompson 1994 Denkhahn amp Spruit 2002 Lyutikov amp Blandford 2003-see Fan et al 2004 for a combination of the two
Internal shocks vs Magnetic dissipation Internal shocks
Unsteady flow composed bymany fast shells
A fast shell with γ2gtγ1 collideswith a slower one dissipatingtheir relative kinetic energythrough shock waves
Magnetic dissipation Magnetic fields carry most of the
energy of the flow The magnetic energy is
dissipated internally throughreconnection
g-rays
Fk
FB
Fk
variability and dissipation are separateingredients in magnetic dissipationmodels
γ2υ2 γ1υ1
FB
γυ
Where is the prompt emission produced anywhere between the Thomson photosphere rph and the
deceleration radius rd
Typically rph~1011cm and rd ~1017cm in this range of radii density ~12 orders of magnitude optical depth ~6 orders of magnitude
Different radiative mechanisms dependingon the location of the energy dissipation
Case 1 Thomsonthin dissipation
Case 2 Photosphericdissipation
Case 1Internal shocks in the Thomson thin regime Internal shocks
The collision of the shells takes place at rcol~γ2ctv tv related to the central engine activity (not trivially Janka et al 2005 Aloy amp
Rezolla 2006) Each collision results in an observed pulse of gamma-rays
shocks cross the shells
In the shock front Particle acceleration takes place Magnetic field amplification due to plasma instabilitites (see next talks)
Parameters fractions єe ζe єB power-law N(γe) ~ γe-p pgt2
Fast particles + magnetic fields Synchrotron self-Compton emission
Thin synchrotron emission may explain the observed spectrum
~
Case 1Can thin Synchrotron emission explain the spectra
Pros For tv~1 s the characteristic pulse duration and separation can be reproduced
Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002
The peak of the synchrotron spectrum can be in the ~a few 100 keV range
Flat high-energy power law
Cons Low radiative efficiency (though uncertain)
~ єdiss єe єBand at the ~ level
Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004
jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair
creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002
Case 1Magnetic dissipation in the Thomson thin regime
In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006
Fast proper plasma motions lead to the rapid observed variability
AC model dissipation near photosphere as well as outside
Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005
Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004
Thin synchrotron emission may be responsible for the GRB
The B-field is given directly by the model At low densities particle distributions in reconnection uncertain
Case 2
Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin
Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000
Spectrum quasi thermal Goodman 1986
Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006
In the AC model DG 2006 DG amp Spruit 2007
For this range of η the model predicts a dissipative photosphere
1 48 3 23
ph 25 o7 52
2 3
52 o7
005 1000L r L
L L r
$ lt amp
(
15 15ph 15 1552 3
52 3
25
( )016 150 ( )
L LL
L
$
Dissipative Photosphere in a fireball Internal shocks take place below the
photosphere for tvltlt1 s
Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007
Injecting fast electrons Slow heating Ghisellini amp Celotti 1999
Studied the radiative transfer for variousvalues of єdiss єB єe τ
Big variety of spectra depending on τ
Dominant process Compton scattering ofphotons advected with the flow
τγe = 1
Our suggestion photospheric emission from the AC modelMain features
AC model gradual dissipation throughout the photosphere
If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering
Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007
Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes
Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~
rsrrph
Log(r [cm])
Radiative transfer analytical estimates+ Monte Carlo Comptonization
Deep in the flow radiation ampparticles are in thermal equilibrium
At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV
For r gt req balance in heating andcooling determined Te
Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering
Photospheric spectra Characteristic peak at ~1 MeV
(in the central engine frame)
Flat power law high energy tails(unsaturated Comptonization)
Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of
bursts Ryde 2004 2005
Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007
Inferences for the central enginethe stronger the cleaner
The Amati relation explainedif in different bursts
Variability in prompt emission Reflects changes in L η
Assumption relationholds during the GRB the model predicts the observed
narrowing of pulses withincreasing energyFenimore et al 1995
06L
06L
Summary Spectral and temporal properties of GRBs are very intriguing
The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation
Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB
Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them
The peak energy and the energetics
η30 100 300 1000
η30 100 300 1000
Comment
The temperature of the flow at the req in the observer frame is
The Ef(E) spectrum of this component peaks at ~4 times thisenergy
19 1 9 1 3 2 9
eq eqobs e1 52 3 25
eq
( ) ( )100 keV
1 1
r T f LT
z z
$
+ +
GRB Variability
Short
t
N (t
)
Variability detected to as short as sub-msec timescales
Variable lightcurves composed bypulses Fenimore et al 1995 Norris et al 1996
The typical pulse width is δt~1sec(~01 sec) for long (short) bursts
Summary for the prompt emission Clues
The prompt emission has non-thermal spectral appearance Band et al 1993 Preece et al 1998
Rapid variability
The GRB-emitting flow is ultrarelativistic (γgt100)eg Piran 1999
Big questions How is the flow accelerated What processes result in the observed spectral and
temporal properties of GRBs
Can we learn something about the central engine
General considerations Acceleration Important quantities of the flow
luminosity L mass flux Efficient acceleration can lead to γsr~η
Depending on the energy extraction mechanism the flow canbe dominated by
Thermal energy rarr thermal acceleration (Fireball) Paczynski 1986 Goodman 1986 Sari amp Piran 1991 Magnetic energy rarr magnetic acceleration (Poynting-flux dominated
flow) Usov 1992 Thompson 1994 Meacuteszaacuteros amp Rees 1997 Drenkhahn amp Spruit 2002 Lyutikon amp
Blandford 2003
21
L
Mc = gtgt
ampMampBaryon loading
Fireballs
Parameters L η initial radius ro
Go through fast acceleration Converting thermal energy into kinetic
Saturation takes place when almost all thermal energy is used γsr η at the photospheric crossing γsr lt η
Radiation and matter decouple whenτ ~ 1 Photospheric emission takes place
r
[Notation (L= L521052 ergs)]
Magnetic (Poynting) models The field can be
axisymmetric (DC flow) Vlahakis amp Koumlnigl 2003 Lyutikov amp Blandford 2003
McKinney 2005 Uzdensky amp MacFadyen 2006
highly asymmetric (AC flow)Drenkhahn amp Spruit 2002 Thompson 2006
Acceleration is more gradualDrenkhahn amp Spruit 2002 Vlahakis amp Koumlnigl 2003
Here I focus more on AC flow
DC
AC
The reconnection (AC) model
1 3
sr sr
4 3
7 3
23
diss
diss
( )
( ) 8
r r
B r
n r
BP r
t
=
$
$
= $
Magnetic field changes polarityon small scales λ = 2πcω
Magnetic reconnection proceedswith a fraction ε ~ 01 of theAlfveacuten speed Lyubarsky 2005
The dynamics of the flow havebeen worked out in detailDrenkhahn 2002 and Denkhahn amp Spruit 2002see also Lyubarsky amp Kirk 2001 for pulsar winds
Parameters L η (εω)
rsr
rph
Log(r [cm])
These are all fineWhere are the γ-rays in this picture
Which processes power the prompt emission
Where (at which radii) is it produced
General considerationsenergy source of the prompt emission The rapid GRB variability argues against the forward shock for
the prompt emissioneg Sari amp Piran 1997 see however Dermer 2007 for a different point of view
Observationally transition from the prompt to the early afterglowemission Zhang et al 2006
The prompt emission most likely comesfrom internal dissipation of energy in the fast flow
This can take place by Internal shocks Rees amp Meacuteszaacuteros 1994 Sari amp Piran 1997
Magnetic dissipation Thompson 1994 Denkhahn amp Spruit 2002 Lyutikov amp Blandford 2003-see Fan et al 2004 for a combination of the two
Internal shocks vs Magnetic dissipation Internal shocks
Unsteady flow composed bymany fast shells
A fast shell with γ2gtγ1 collideswith a slower one dissipatingtheir relative kinetic energythrough shock waves
Magnetic dissipation Magnetic fields carry most of the
energy of the flow The magnetic energy is
dissipated internally throughreconnection
g-rays
Fk
FB
Fk
variability and dissipation are separateingredients in magnetic dissipationmodels
γ2υ2 γ1υ1
FB
γυ
Where is the prompt emission produced anywhere between the Thomson photosphere rph and the
deceleration radius rd
Typically rph~1011cm and rd ~1017cm in this range of radii density ~12 orders of magnitude optical depth ~6 orders of magnitude
Different radiative mechanisms dependingon the location of the energy dissipation
Case 1 Thomsonthin dissipation
Case 2 Photosphericdissipation
Case 1Internal shocks in the Thomson thin regime Internal shocks
The collision of the shells takes place at rcol~γ2ctv tv related to the central engine activity (not trivially Janka et al 2005 Aloy amp
Rezolla 2006) Each collision results in an observed pulse of gamma-rays
shocks cross the shells
In the shock front Particle acceleration takes place Magnetic field amplification due to plasma instabilitites (see next talks)
Parameters fractions єe ζe єB power-law N(γe) ~ γe-p pgt2
Fast particles + magnetic fields Synchrotron self-Compton emission
Thin synchrotron emission may explain the observed spectrum
~
Case 1Can thin Synchrotron emission explain the spectra
Pros For tv~1 s the characteristic pulse duration and separation can be reproduced
Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002
The peak of the synchrotron spectrum can be in the ~a few 100 keV range
Flat high-energy power law
Cons Low radiative efficiency (though uncertain)
~ єdiss єe єBand at the ~ level
Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004
jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair
creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002
Case 1Magnetic dissipation in the Thomson thin regime
In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006
Fast proper plasma motions lead to the rapid observed variability
AC model dissipation near photosphere as well as outside
Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005
Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004
Thin synchrotron emission may be responsible for the GRB
The B-field is given directly by the model At low densities particle distributions in reconnection uncertain
Case 2
Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin
Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000
Spectrum quasi thermal Goodman 1986
Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006
In the AC model DG 2006 DG amp Spruit 2007
For this range of η the model predicts a dissipative photosphere
1 48 3 23
ph 25 o7 52
2 3
52 o7
005 1000L r L
L L r
$ lt amp
(
15 15ph 15 1552 3
52 3
25
( )016 150 ( )
L LL
L
$
Dissipative Photosphere in a fireball Internal shocks take place below the
photosphere for tvltlt1 s
Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007
Injecting fast electrons Slow heating Ghisellini amp Celotti 1999
Studied the radiative transfer for variousvalues of єdiss єB єe τ
Big variety of spectra depending on τ
Dominant process Compton scattering ofphotons advected with the flow
τγe = 1
Our suggestion photospheric emission from the AC modelMain features
AC model gradual dissipation throughout the photosphere
If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering
Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007
Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes
Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~
rsrrph
Log(r [cm])
Radiative transfer analytical estimates+ Monte Carlo Comptonization
Deep in the flow radiation ampparticles are in thermal equilibrium
At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV
For r gt req balance in heating andcooling determined Te
Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering
Photospheric spectra Characteristic peak at ~1 MeV
(in the central engine frame)
Flat power law high energy tails(unsaturated Comptonization)
Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of
bursts Ryde 2004 2005
Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007
Inferences for the central enginethe stronger the cleaner
The Amati relation explainedif in different bursts
Variability in prompt emission Reflects changes in L η
Assumption relationholds during the GRB the model predicts the observed
narrowing of pulses withincreasing energyFenimore et al 1995
06L
06L
Summary Spectral and temporal properties of GRBs are very intriguing
The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation
Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB
Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them
The peak energy and the energetics
η30 100 300 1000
η30 100 300 1000
Comment
The temperature of the flow at the req in the observer frame is
The Ef(E) spectrum of this component peaks at ~4 times thisenergy
19 1 9 1 3 2 9
eq eqobs e1 52 3 25
eq
( ) ( )100 keV
1 1
r T f LT
z z
$
+ +
Summary for the prompt emission Clues
The prompt emission has non-thermal spectral appearance Band et al 1993 Preece et al 1998
Rapid variability
The GRB-emitting flow is ultrarelativistic (γgt100)eg Piran 1999
Big questions How is the flow accelerated What processes result in the observed spectral and
temporal properties of GRBs
Can we learn something about the central engine
General considerations Acceleration Important quantities of the flow
luminosity L mass flux Efficient acceleration can lead to γsr~η
Depending on the energy extraction mechanism the flow canbe dominated by
Thermal energy rarr thermal acceleration (Fireball) Paczynski 1986 Goodman 1986 Sari amp Piran 1991 Magnetic energy rarr magnetic acceleration (Poynting-flux dominated
flow) Usov 1992 Thompson 1994 Meacuteszaacuteros amp Rees 1997 Drenkhahn amp Spruit 2002 Lyutikon amp
Blandford 2003
21
L
Mc = gtgt
ampMampBaryon loading
Fireballs
Parameters L η initial radius ro
Go through fast acceleration Converting thermal energy into kinetic
Saturation takes place when almost all thermal energy is used γsr η at the photospheric crossing γsr lt η
Radiation and matter decouple whenτ ~ 1 Photospheric emission takes place
r
[Notation (L= L521052 ergs)]
Magnetic (Poynting) models The field can be
axisymmetric (DC flow) Vlahakis amp Koumlnigl 2003 Lyutikov amp Blandford 2003
McKinney 2005 Uzdensky amp MacFadyen 2006
highly asymmetric (AC flow)Drenkhahn amp Spruit 2002 Thompson 2006
Acceleration is more gradualDrenkhahn amp Spruit 2002 Vlahakis amp Koumlnigl 2003
Here I focus more on AC flow
DC
AC
The reconnection (AC) model
1 3
sr sr
4 3
7 3
23
diss
diss
( )
( ) 8
r r
B r
n r
BP r
t
=
$
$
= $
Magnetic field changes polarityon small scales λ = 2πcω
Magnetic reconnection proceedswith a fraction ε ~ 01 of theAlfveacuten speed Lyubarsky 2005
The dynamics of the flow havebeen worked out in detailDrenkhahn 2002 and Denkhahn amp Spruit 2002see also Lyubarsky amp Kirk 2001 for pulsar winds
Parameters L η (εω)
rsr
rph
Log(r [cm])
These are all fineWhere are the γ-rays in this picture
Which processes power the prompt emission
Where (at which radii) is it produced
General considerationsenergy source of the prompt emission The rapid GRB variability argues against the forward shock for
the prompt emissioneg Sari amp Piran 1997 see however Dermer 2007 for a different point of view
Observationally transition from the prompt to the early afterglowemission Zhang et al 2006
The prompt emission most likely comesfrom internal dissipation of energy in the fast flow
This can take place by Internal shocks Rees amp Meacuteszaacuteros 1994 Sari amp Piran 1997
Magnetic dissipation Thompson 1994 Denkhahn amp Spruit 2002 Lyutikov amp Blandford 2003-see Fan et al 2004 for a combination of the two
Internal shocks vs Magnetic dissipation Internal shocks
Unsteady flow composed bymany fast shells
A fast shell with γ2gtγ1 collideswith a slower one dissipatingtheir relative kinetic energythrough shock waves
Magnetic dissipation Magnetic fields carry most of the
energy of the flow The magnetic energy is
dissipated internally throughreconnection
g-rays
Fk
FB
Fk
variability and dissipation are separateingredients in magnetic dissipationmodels
γ2υ2 γ1υ1
FB
γυ
Where is the prompt emission produced anywhere between the Thomson photosphere rph and the
deceleration radius rd
Typically rph~1011cm and rd ~1017cm in this range of radii density ~12 orders of magnitude optical depth ~6 orders of magnitude
Different radiative mechanisms dependingon the location of the energy dissipation
Case 1 Thomsonthin dissipation
Case 2 Photosphericdissipation
Case 1Internal shocks in the Thomson thin regime Internal shocks
The collision of the shells takes place at rcol~γ2ctv tv related to the central engine activity (not trivially Janka et al 2005 Aloy amp
Rezolla 2006) Each collision results in an observed pulse of gamma-rays
shocks cross the shells
In the shock front Particle acceleration takes place Magnetic field amplification due to plasma instabilitites (see next talks)
Parameters fractions єe ζe єB power-law N(γe) ~ γe-p pgt2
Fast particles + magnetic fields Synchrotron self-Compton emission
Thin synchrotron emission may explain the observed spectrum
~
Case 1Can thin Synchrotron emission explain the spectra
Pros For tv~1 s the characteristic pulse duration and separation can be reproduced
Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002
The peak of the synchrotron spectrum can be in the ~a few 100 keV range
Flat high-energy power law
Cons Low radiative efficiency (though uncertain)
~ єdiss єe єBand at the ~ level
Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004
jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair
creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002
Case 1Magnetic dissipation in the Thomson thin regime
In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006
Fast proper plasma motions lead to the rapid observed variability
AC model dissipation near photosphere as well as outside
Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005
Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004
Thin synchrotron emission may be responsible for the GRB
The B-field is given directly by the model At low densities particle distributions in reconnection uncertain
Case 2
Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin
Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000
Spectrum quasi thermal Goodman 1986
Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006
In the AC model DG 2006 DG amp Spruit 2007
For this range of η the model predicts a dissipative photosphere
1 48 3 23
ph 25 o7 52
2 3
52 o7
005 1000L r L
L L r
$ lt amp
(
15 15ph 15 1552 3
52 3
25
( )016 150 ( )
L LL
L
$
Dissipative Photosphere in a fireball Internal shocks take place below the
photosphere for tvltlt1 s
Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007
Injecting fast electrons Slow heating Ghisellini amp Celotti 1999
Studied the radiative transfer for variousvalues of єdiss єB єe τ
Big variety of spectra depending on τ
Dominant process Compton scattering ofphotons advected with the flow
τγe = 1
Our suggestion photospheric emission from the AC modelMain features
AC model gradual dissipation throughout the photosphere
If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering
Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007
Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes
Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~
rsrrph
Log(r [cm])
Radiative transfer analytical estimates+ Monte Carlo Comptonization
Deep in the flow radiation ampparticles are in thermal equilibrium
At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV
For r gt req balance in heating andcooling determined Te
Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering
Photospheric spectra Characteristic peak at ~1 MeV
(in the central engine frame)
Flat power law high energy tails(unsaturated Comptonization)
Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of
bursts Ryde 2004 2005
Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007
Inferences for the central enginethe stronger the cleaner
The Amati relation explainedif in different bursts
Variability in prompt emission Reflects changes in L η
Assumption relationholds during the GRB the model predicts the observed
narrowing of pulses withincreasing energyFenimore et al 1995
06L
06L
Summary Spectral and temporal properties of GRBs are very intriguing
The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation
Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB
Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them
The peak energy and the energetics
η30 100 300 1000
η30 100 300 1000
Comment
The temperature of the flow at the req in the observer frame is
The Ef(E) spectrum of this component peaks at ~4 times thisenergy
19 1 9 1 3 2 9
eq eqobs e1 52 3 25
eq
( ) ( )100 keV
1 1
r T f LT
z z
$
+ +
General considerations Acceleration Important quantities of the flow
luminosity L mass flux Efficient acceleration can lead to γsr~η
Depending on the energy extraction mechanism the flow canbe dominated by
Thermal energy rarr thermal acceleration (Fireball) Paczynski 1986 Goodman 1986 Sari amp Piran 1991 Magnetic energy rarr magnetic acceleration (Poynting-flux dominated
flow) Usov 1992 Thompson 1994 Meacuteszaacuteros amp Rees 1997 Drenkhahn amp Spruit 2002 Lyutikon amp
Blandford 2003
21
L
Mc = gtgt
ampMampBaryon loading
Fireballs
Parameters L η initial radius ro
Go through fast acceleration Converting thermal energy into kinetic
Saturation takes place when almost all thermal energy is used γsr η at the photospheric crossing γsr lt η
Radiation and matter decouple whenτ ~ 1 Photospheric emission takes place
r
[Notation (L= L521052 ergs)]
Magnetic (Poynting) models The field can be
axisymmetric (DC flow) Vlahakis amp Koumlnigl 2003 Lyutikov amp Blandford 2003
McKinney 2005 Uzdensky amp MacFadyen 2006
highly asymmetric (AC flow)Drenkhahn amp Spruit 2002 Thompson 2006
Acceleration is more gradualDrenkhahn amp Spruit 2002 Vlahakis amp Koumlnigl 2003
Here I focus more on AC flow
DC
AC
The reconnection (AC) model
1 3
sr sr
4 3
7 3
23
diss
diss
( )
( ) 8
r r
B r
n r
BP r
t
=
$
$
= $
Magnetic field changes polarityon small scales λ = 2πcω
Magnetic reconnection proceedswith a fraction ε ~ 01 of theAlfveacuten speed Lyubarsky 2005
The dynamics of the flow havebeen worked out in detailDrenkhahn 2002 and Denkhahn amp Spruit 2002see also Lyubarsky amp Kirk 2001 for pulsar winds
Parameters L η (εω)
rsr
rph
Log(r [cm])
These are all fineWhere are the γ-rays in this picture
Which processes power the prompt emission
Where (at which radii) is it produced
General considerationsenergy source of the prompt emission The rapid GRB variability argues against the forward shock for
the prompt emissioneg Sari amp Piran 1997 see however Dermer 2007 for a different point of view
Observationally transition from the prompt to the early afterglowemission Zhang et al 2006
The prompt emission most likely comesfrom internal dissipation of energy in the fast flow
This can take place by Internal shocks Rees amp Meacuteszaacuteros 1994 Sari amp Piran 1997
Magnetic dissipation Thompson 1994 Denkhahn amp Spruit 2002 Lyutikov amp Blandford 2003-see Fan et al 2004 for a combination of the two
Internal shocks vs Magnetic dissipation Internal shocks
Unsteady flow composed bymany fast shells
A fast shell with γ2gtγ1 collideswith a slower one dissipatingtheir relative kinetic energythrough shock waves
Magnetic dissipation Magnetic fields carry most of the
energy of the flow The magnetic energy is
dissipated internally throughreconnection
g-rays
Fk
FB
Fk
variability and dissipation are separateingredients in magnetic dissipationmodels
γ2υ2 γ1υ1
FB
γυ
Where is the prompt emission produced anywhere between the Thomson photosphere rph and the
deceleration radius rd
Typically rph~1011cm and rd ~1017cm in this range of radii density ~12 orders of magnitude optical depth ~6 orders of magnitude
Different radiative mechanisms dependingon the location of the energy dissipation
Case 1 Thomsonthin dissipation
Case 2 Photosphericdissipation
Case 1Internal shocks in the Thomson thin regime Internal shocks
The collision of the shells takes place at rcol~γ2ctv tv related to the central engine activity (not trivially Janka et al 2005 Aloy amp
Rezolla 2006) Each collision results in an observed pulse of gamma-rays
shocks cross the shells
In the shock front Particle acceleration takes place Magnetic field amplification due to plasma instabilitites (see next talks)
Parameters fractions єe ζe єB power-law N(γe) ~ γe-p pgt2
Fast particles + magnetic fields Synchrotron self-Compton emission
Thin synchrotron emission may explain the observed spectrum
~
Case 1Can thin Synchrotron emission explain the spectra
Pros For tv~1 s the characteristic pulse duration and separation can be reproduced
Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002
The peak of the synchrotron spectrum can be in the ~a few 100 keV range
Flat high-energy power law
Cons Low radiative efficiency (though uncertain)
~ єdiss єe єBand at the ~ level
Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004
jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair
creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002
Case 1Magnetic dissipation in the Thomson thin regime
In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006
Fast proper plasma motions lead to the rapid observed variability
AC model dissipation near photosphere as well as outside
Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005
Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004
Thin synchrotron emission may be responsible for the GRB
The B-field is given directly by the model At low densities particle distributions in reconnection uncertain
Case 2
Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin
Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000
Spectrum quasi thermal Goodman 1986
Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006
In the AC model DG 2006 DG amp Spruit 2007
For this range of η the model predicts a dissipative photosphere
1 48 3 23
ph 25 o7 52
2 3
52 o7
005 1000L r L
L L r
$ lt amp
(
15 15ph 15 1552 3
52 3
25
( )016 150 ( )
L LL
L
$
Dissipative Photosphere in a fireball Internal shocks take place below the
photosphere for tvltlt1 s
Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007
Injecting fast electrons Slow heating Ghisellini amp Celotti 1999
Studied the radiative transfer for variousvalues of єdiss єB єe τ
Big variety of spectra depending on τ
Dominant process Compton scattering ofphotons advected with the flow
τγe = 1
Our suggestion photospheric emission from the AC modelMain features
AC model gradual dissipation throughout the photosphere
If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering
Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007
Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes
Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~
rsrrph
Log(r [cm])
Radiative transfer analytical estimates+ Monte Carlo Comptonization
Deep in the flow radiation ampparticles are in thermal equilibrium
At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV
For r gt req balance in heating andcooling determined Te
Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering
Photospheric spectra Characteristic peak at ~1 MeV
(in the central engine frame)
Flat power law high energy tails(unsaturated Comptonization)
Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of
bursts Ryde 2004 2005
Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007
Inferences for the central enginethe stronger the cleaner
The Amati relation explainedif in different bursts
Variability in prompt emission Reflects changes in L η
Assumption relationholds during the GRB the model predicts the observed
narrowing of pulses withincreasing energyFenimore et al 1995
06L
06L
Summary Spectral and temporal properties of GRBs are very intriguing
The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation
Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB
Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them
The peak energy and the energetics
η30 100 300 1000
η30 100 300 1000
Comment
The temperature of the flow at the req in the observer frame is
The Ef(E) spectrum of this component peaks at ~4 times thisenergy
19 1 9 1 3 2 9
eq eqobs e1 52 3 25
eq
( ) ( )100 keV
1 1
r T f LT
z z
$
+ +
Fireballs
Parameters L η initial radius ro
Go through fast acceleration Converting thermal energy into kinetic
Saturation takes place when almost all thermal energy is used γsr η at the photospheric crossing γsr lt η
Radiation and matter decouple whenτ ~ 1 Photospheric emission takes place
r
[Notation (L= L521052 ergs)]
Magnetic (Poynting) models The field can be
axisymmetric (DC flow) Vlahakis amp Koumlnigl 2003 Lyutikov amp Blandford 2003
McKinney 2005 Uzdensky amp MacFadyen 2006
highly asymmetric (AC flow)Drenkhahn amp Spruit 2002 Thompson 2006
Acceleration is more gradualDrenkhahn amp Spruit 2002 Vlahakis amp Koumlnigl 2003
Here I focus more on AC flow
DC
AC
The reconnection (AC) model
1 3
sr sr
4 3
7 3
23
diss
diss
( )
( ) 8
r r
B r
n r
BP r
t
=
$
$
= $
Magnetic field changes polarityon small scales λ = 2πcω
Magnetic reconnection proceedswith a fraction ε ~ 01 of theAlfveacuten speed Lyubarsky 2005
The dynamics of the flow havebeen worked out in detailDrenkhahn 2002 and Denkhahn amp Spruit 2002see also Lyubarsky amp Kirk 2001 for pulsar winds
Parameters L η (εω)
rsr
rph
Log(r [cm])
These are all fineWhere are the γ-rays in this picture
Which processes power the prompt emission
Where (at which radii) is it produced
General considerationsenergy source of the prompt emission The rapid GRB variability argues against the forward shock for
the prompt emissioneg Sari amp Piran 1997 see however Dermer 2007 for a different point of view
Observationally transition from the prompt to the early afterglowemission Zhang et al 2006
The prompt emission most likely comesfrom internal dissipation of energy in the fast flow
This can take place by Internal shocks Rees amp Meacuteszaacuteros 1994 Sari amp Piran 1997
Magnetic dissipation Thompson 1994 Denkhahn amp Spruit 2002 Lyutikov amp Blandford 2003-see Fan et al 2004 for a combination of the two
Internal shocks vs Magnetic dissipation Internal shocks
Unsteady flow composed bymany fast shells
A fast shell with γ2gtγ1 collideswith a slower one dissipatingtheir relative kinetic energythrough shock waves
Magnetic dissipation Magnetic fields carry most of the
energy of the flow The magnetic energy is
dissipated internally throughreconnection
g-rays
Fk
FB
Fk
variability and dissipation are separateingredients in magnetic dissipationmodels
γ2υ2 γ1υ1
FB
γυ
Where is the prompt emission produced anywhere between the Thomson photosphere rph and the
deceleration radius rd
Typically rph~1011cm and rd ~1017cm in this range of radii density ~12 orders of magnitude optical depth ~6 orders of magnitude
Different radiative mechanisms dependingon the location of the energy dissipation
Case 1 Thomsonthin dissipation
Case 2 Photosphericdissipation
Case 1Internal shocks in the Thomson thin regime Internal shocks
The collision of the shells takes place at rcol~γ2ctv tv related to the central engine activity (not trivially Janka et al 2005 Aloy amp
Rezolla 2006) Each collision results in an observed pulse of gamma-rays
shocks cross the shells
In the shock front Particle acceleration takes place Magnetic field amplification due to plasma instabilitites (see next talks)
Parameters fractions єe ζe єB power-law N(γe) ~ γe-p pgt2
Fast particles + magnetic fields Synchrotron self-Compton emission
Thin synchrotron emission may explain the observed spectrum
~
Case 1Can thin Synchrotron emission explain the spectra
Pros For tv~1 s the characteristic pulse duration and separation can be reproduced
Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002
The peak of the synchrotron spectrum can be in the ~a few 100 keV range
Flat high-energy power law
Cons Low radiative efficiency (though uncertain)
~ єdiss єe єBand at the ~ level
Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004
jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair
creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002
Case 1Magnetic dissipation in the Thomson thin regime
In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006
Fast proper plasma motions lead to the rapid observed variability
AC model dissipation near photosphere as well as outside
Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005
Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004
Thin synchrotron emission may be responsible for the GRB
The B-field is given directly by the model At low densities particle distributions in reconnection uncertain
Case 2
Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin
Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000
Spectrum quasi thermal Goodman 1986
Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006
In the AC model DG 2006 DG amp Spruit 2007
For this range of η the model predicts a dissipative photosphere
1 48 3 23
ph 25 o7 52
2 3
52 o7
005 1000L r L
L L r
$ lt amp
(
15 15ph 15 1552 3
52 3
25
( )016 150 ( )
L LL
L
$
Dissipative Photosphere in a fireball Internal shocks take place below the
photosphere for tvltlt1 s
Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007
Injecting fast electrons Slow heating Ghisellini amp Celotti 1999
Studied the radiative transfer for variousvalues of єdiss єB єe τ
Big variety of spectra depending on τ
Dominant process Compton scattering ofphotons advected with the flow
τγe = 1
Our suggestion photospheric emission from the AC modelMain features
AC model gradual dissipation throughout the photosphere
If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering
Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007
Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes
Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~
rsrrph
Log(r [cm])
Radiative transfer analytical estimates+ Monte Carlo Comptonization
Deep in the flow radiation ampparticles are in thermal equilibrium
At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV
For r gt req balance in heating andcooling determined Te
Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering
Photospheric spectra Characteristic peak at ~1 MeV
(in the central engine frame)
Flat power law high energy tails(unsaturated Comptonization)
Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of
bursts Ryde 2004 2005
Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007
Inferences for the central enginethe stronger the cleaner
The Amati relation explainedif in different bursts
Variability in prompt emission Reflects changes in L η
Assumption relationholds during the GRB the model predicts the observed
narrowing of pulses withincreasing energyFenimore et al 1995
06L
06L
Summary Spectral and temporal properties of GRBs are very intriguing
The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation
Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB
Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them
The peak energy and the energetics
η30 100 300 1000
η30 100 300 1000
Comment
The temperature of the flow at the req in the observer frame is
The Ef(E) spectrum of this component peaks at ~4 times thisenergy
19 1 9 1 3 2 9
eq eqobs e1 52 3 25
eq
( ) ( )100 keV
1 1
r T f LT
z z
$
+ +
Magnetic (Poynting) models The field can be
axisymmetric (DC flow) Vlahakis amp Koumlnigl 2003 Lyutikov amp Blandford 2003
McKinney 2005 Uzdensky amp MacFadyen 2006
highly asymmetric (AC flow)Drenkhahn amp Spruit 2002 Thompson 2006
Acceleration is more gradualDrenkhahn amp Spruit 2002 Vlahakis amp Koumlnigl 2003
Here I focus more on AC flow
DC
AC
The reconnection (AC) model
1 3
sr sr
4 3
7 3
23
diss
diss
( )
( ) 8
r r
B r
n r
BP r
t
=
$
$
= $
Magnetic field changes polarityon small scales λ = 2πcω
Magnetic reconnection proceedswith a fraction ε ~ 01 of theAlfveacuten speed Lyubarsky 2005
The dynamics of the flow havebeen worked out in detailDrenkhahn 2002 and Denkhahn amp Spruit 2002see also Lyubarsky amp Kirk 2001 for pulsar winds
Parameters L η (εω)
rsr
rph
Log(r [cm])
These are all fineWhere are the γ-rays in this picture
Which processes power the prompt emission
Where (at which radii) is it produced
General considerationsenergy source of the prompt emission The rapid GRB variability argues against the forward shock for
the prompt emissioneg Sari amp Piran 1997 see however Dermer 2007 for a different point of view
Observationally transition from the prompt to the early afterglowemission Zhang et al 2006
The prompt emission most likely comesfrom internal dissipation of energy in the fast flow
This can take place by Internal shocks Rees amp Meacuteszaacuteros 1994 Sari amp Piran 1997
Magnetic dissipation Thompson 1994 Denkhahn amp Spruit 2002 Lyutikov amp Blandford 2003-see Fan et al 2004 for a combination of the two
Internal shocks vs Magnetic dissipation Internal shocks
Unsteady flow composed bymany fast shells
A fast shell with γ2gtγ1 collideswith a slower one dissipatingtheir relative kinetic energythrough shock waves
Magnetic dissipation Magnetic fields carry most of the
energy of the flow The magnetic energy is
dissipated internally throughreconnection
g-rays
Fk
FB
Fk
variability and dissipation are separateingredients in magnetic dissipationmodels
γ2υ2 γ1υ1
FB
γυ
Where is the prompt emission produced anywhere between the Thomson photosphere rph and the
deceleration radius rd
Typically rph~1011cm and rd ~1017cm in this range of radii density ~12 orders of magnitude optical depth ~6 orders of magnitude
Different radiative mechanisms dependingon the location of the energy dissipation
Case 1 Thomsonthin dissipation
Case 2 Photosphericdissipation
Case 1Internal shocks in the Thomson thin regime Internal shocks
The collision of the shells takes place at rcol~γ2ctv tv related to the central engine activity (not trivially Janka et al 2005 Aloy amp
Rezolla 2006) Each collision results in an observed pulse of gamma-rays
shocks cross the shells
In the shock front Particle acceleration takes place Magnetic field amplification due to plasma instabilitites (see next talks)
Parameters fractions єe ζe єB power-law N(γe) ~ γe-p pgt2
Fast particles + magnetic fields Synchrotron self-Compton emission
Thin synchrotron emission may explain the observed spectrum
~
Case 1Can thin Synchrotron emission explain the spectra
Pros For tv~1 s the characteristic pulse duration and separation can be reproduced
Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002
The peak of the synchrotron spectrum can be in the ~a few 100 keV range
Flat high-energy power law
Cons Low radiative efficiency (though uncertain)
~ єdiss єe єBand at the ~ level
Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004
jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair
creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002
Case 1Magnetic dissipation in the Thomson thin regime
In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006
Fast proper plasma motions lead to the rapid observed variability
AC model dissipation near photosphere as well as outside
Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005
Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004
Thin synchrotron emission may be responsible for the GRB
The B-field is given directly by the model At low densities particle distributions in reconnection uncertain
Case 2
Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin
Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000
Spectrum quasi thermal Goodman 1986
Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006
In the AC model DG 2006 DG amp Spruit 2007
For this range of η the model predicts a dissipative photosphere
1 48 3 23
ph 25 o7 52
2 3
52 o7
005 1000L r L
L L r
$ lt amp
(
15 15ph 15 1552 3
52 3
25
( )016 150 ( )
L LL
L
$
Dissipative Photosphere in a fireball Internal shocks take place below the
photosphere for tvltlt1 s
Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007
Injecting fast electrons Slow heating Ghisellini amp Celotti 1999
Studied the radiative transfer for variousvalues of єdiss єB єe τ
Big variety of spectra depending on τ
Dominant process Compton scattering ofphotons advected with the flow
τγe = 1
Our suggestion photospheric emission from the AC modelMain features
AC model gradual dissipation throughout the photosphere
If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering
Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007
Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes
Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~
rsrrph
Log(r [cm])
Radiative transfer analytical estimates+ Monte Carlo Comptonization
Deep in the flow radiation ampparticles are in thermal equilibrium
At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV
For r gt req balance in heating andcooling determined Te
Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering
Photospheric spectra Characteristic peak at ~1 MeV
(in the central engine frame)
Flat power law high energy tails(unsaturated Comptonization)
Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of
bursts Ryde 2004 2005
Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007
Inferences for the central enginethe stronger the cleaner
The Amati relation explainedif in different bursts
Variability in prompt emission Reflects changes in L η
Assumption relationholds during the GRB the model predicts the observed
narrowing of pulses withincreasing energyFenimore et al 1995
06L
06L
Summary Spectral and temporal properties of GRBs are very intriguing
The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation
Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB
Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them
The peak energy and the energetics
η30 100 300 1000
η30 100 300 1000
Comment
The temperature of the flow at the req in the observer frame is
The Ef(E) spectrum of this component peaks at ~4 times thisenergy
19 1 9 1 3 2 9
eq eqobs e1 52 3 25
eq
( ) ( )100 keV
1 1
r T f LT
z z
$
+ +
The reconnection (AC) model
1 3
sr sr
4 3
7 3
23
diss
diss
( )
( ) 8
r r
B r
n r
BP r
t
=
$
$
= $
Magnetic field changes polarityon small scales λ = 2πcω
Magnetic reconnection proceedswith a fraction ε ~ 01 of theAlfveacuten speed Lyubarsky 2005
The dynamics of the flow havebeen worked out in detailDrenkhahn 2002 and Denkhahn amp Spruit 2002see also Lyubarsky amp Kirk 2001 for pulsar winds
Parameters L η (εω)
rsr
rph
Log(r [cm])
These are all fineWhere are the γ-rays in this picture
Which processes power the prompt emission
Where (at which radii) is it produced
General considerationsenergy source of the prompt emission The rapid GRB variability argues against the forward shock for
the prompt emissioneg Sari amp Piran 1997 see however Dermer 2007 for a different point of view
Observationally transition from the prompt to the early afterglowemission Zhang et al 2006
The prompt emission most likely comesfrom internal dissipation of energy in the fast flow
This can take place by Internal shocks Rees amp Meacuteszaacuteros 1994 Sari amp Piran 1997
Magnetic dissipation Thompson 1994 Denkhahn amp Spruit 2002 Lyutikov amp Blandford 2003-see Fan et al 2004 for a combination of the two
Internal shocks vs Magnetic dissipation Internal shocks
Unsteady flow composed bymany fast shells
A fast shell with γ2gtγ1 collideswith a slower one dissipatingtheir relative kinetic energythrough shock waves
Magnetic dissipation Magnetic fields carry most of the
energy of the flow The magnetic energy is
dissipated internally throughreconnection
g-rays
Fk
FB
Fk
variability and dissipation are separateingredients in magnetic dissipationmodels
γ2υ2 γ1υ1
FB
γυ
Where is the prompt emission produced anywhere between the Thomson photosphere rph and the
deceleration radius rd
Typically rph~1011cm and rd ~1017cm in this range of radii density ~12 orders of magnitude optical depth ~6 orders of magnitude
Different radiative mechanisms dependingon the location of the energy dissipation
Case 1 Thomsonthin dissipation
Case 2 Photosphericdissipation
Case 1Internal shocks in the Thomson thin regime Internal shocks
The collision of the shells takes place at rcol~γ2ctv tv related to the central engine activity (not trivially Janka et al 2005 Aloy amp
Rezolla 2006) Each collision results in an observed pulse of gamma-rays
shocks cross the shells
In the shock front Particle acceleration takes place Magnetic field amplification due to plasma instabilitites (see next talks)
Parameters fractions єe ζe єB power-law N(γe) ~ γe-p pgt2
Fast particles + magnetic fields Synchrotron self-Compton emission
Thin synchrotron emission may explain the observed spectrum
~
Case 1Can thin Synchrotron emission explain the spectra
Pros For tv~1 s the characteristic pulse duration and separation can be reproduced
Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002
The peak of the synchrotron spectrum can be in the ~a few 100 keV range
Flat high-energy power law
Cons Low radiative efficiency (though uncertain)
~ єdiss єe єBand at the ~ level
Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004
jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair
creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002
Case 1Magnetic dissipation in the Thomson thin regime
In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006
Fast proper plasma motions lead to the rapid observed variability
AC model dissipation near photosphere as well as outside
Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005
Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004
Thin synchrotron emission may be responsible for the GRB
The B-field is given directly by the model At low densities particle distributions in reconnection uncertain
Case 2
Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin
Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000
Spectrum quasi thermal Goodman 1986
Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006
In the AC model DG 2006 DG amp Spruit 2007
For this range of η the model predicts a dissipative photosphere
1 48 3 23
ph 25 o7 52
2 3
52 o7
005 1000L r L
L L r
$ lt amp
(
15 15ph 15 1552 3
52 3
25
( )016 150 ( )
L LL
L
$
Dissipative Photosphere in a fireball Internal shocks take place below the
photosphere for tvltlt1 s
Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007
Injecting fast electrons Slow heating Ghisellini amp Celotti 1999
Studied the radiative transfer for variousvalues of єdiss єB єe τ
Big variety of spectra depending on τ
Dominant process Compton scattering ofphotons advected with the flow
τγe = 1
Our suggestion photospheric emission from the AC modelMain features
AC model gradual dissipation throughout the photosphere
If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering
Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007
Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes
Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~
rsrrph
Log(r [cm])
Radiative transfer analytical estimates+ Monte Carlo Comptonization
Deep in the flow radiation ampparticles are in thermal equilibrium
At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV
For r gt req balance in heating andcooling determined Te
Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering
Photospheric spectra Characteristic peak at ~1 MeV
(in the central engine frame)
Flat power law high energy tails(unsaturated Comptonization)
Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of
bursts Ryde 2004 2005
Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007
Inferences for the central enginethe stronger the cleaner
The Amati relation explainedif in different bursts
Variability in prompt emission Reflects changes in L η
Assumption relationholds during the GRB the model predicts the observed
narrowing of pulses withincreasing energyFenimore et al 1995
06L
06L
Summary Spectral and temporal properties of GRBs are very intriguing
The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation
Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB
Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them
The peak energy and the energetics
η30 100 300 1000
η30 100 300 1000
Comment
The temperature of the flow at the req in the observer frame is
The Ef(E) spectrum of this component peaks at ~4 times thisenergy
19 1 9 1 3 2 9
eq eqobs e1 52 3 25
eq
( ) ( )100 keV
1 1
r T f LT
z z
$
+ +
These are all fineWhere are the γ-rays in this picture
Which processes power the prompt emission
Where (at which radii) is it produced
General considerationsenergy source of the prompt emission The rapid GRB variability argues against the forward shock for
the prompt emissioneg Sari amp Piran 1997 see however Dermer 2007 for a different point of view
Observationally transition from the prompt to the early afterglowemission Zhang et al 2006
The prompt emission most likely comesfrom internal dissipation of energy in the fast flow
This can take place by Internal shocks Rees amp Meacuteszaacuteros 1994 Sari amp Piran 1997
Magnetic dissipation Thompson 1994 Denkhahn amp Spruit 2002 Lyutikov amp Blandford 2003-see Fan et al 2004 for a combination of the two
Internal shocks vs Magnetic dissipation Internal shocks
Unsteady flow composed bymany fast shells
A fast shell with γ2gtγ1 collideswith a slower one dissipatingtheir relative kinetic energythrough shock waves
Magnetic dissipation Magnetic fields carry most of the
energy of the flow The magnetic energy is
dissipated internally throughreconnection
g-rays
Fk
FB
Fk
variability and dissipation are separateingredients in magnetic dissipationmodels
γ2υ2 γ1υ1
FB
γυ
Where is the prompt emission produced anywhere between the Thomson photosphere rph and the
deceleration radius rd
Typically rph~1011cm and rd ~1017cm in this range of radii density ~12 orders of magnitude optical depth ~6 orders of magnitude
Different radiative mechanisms dependingon the location of the energy dissipation
Case 1 Thomsonthin dissipation
Case 2 Photosphericdissipation
Case 1Internal shocks in the Thomson thin regime Internal shocks
The collision of the shells takes place at rcol~γ2ctv tv related to the central engine activity (not trivially Janka et al 2005 Aloy amp
Rezolla 2006) Each collision results in an observed pulse of gamma-rays
shocks cross the shells
In the shock front Particle acceleration takes place Magnetic field amplification due to plasma instabilitites (see next talks)
Parameters fractions єe ζe єB power-law N(γe) ~ γe-p pgt2
Fast particles + magnetic fields Synchrotron self-Compton emission
Thin synchrotron emission may explain the observed spectrum
~
Case 1Can thin Synchrotron emission explain the spectra
Pros For tv~1 s the characteristic pulse duration and separation can be reproduced
Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002
The peak of the synchrotron spectrum can be in the ~a few 100 keV range
Flat high-energy power law
Cons Low radiative efficiency (though uncertain)
~ єdiss єe єBand at the ~ level
Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004
jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair
creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002
Case 1Magnetic dissipation in the Thomson thin regime
In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006
Fast proper plasma motions lead to the rapid observed variability
AC model dissipation near photosphere as well as outside
Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005
Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004
Thin synchrotron emission may be responsible for the GRB
The B-field is given directly by the model At low densities particle distributions in reconnection uncertain
Case 2
Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin
Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000
Spectrum quasi thermal Goodman 1986
Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006
In the AC model DG 2006 DG amp Spruit 2007
For this range of η the model predicts a dissipative photosphere
1 48 3 23
ph 25 o7 52
2 3
52 o7
005 1000L r L
L L r
$ lt amp
(
15 15ph 15 1552 3
52 3
25
( )016 150 ( )
L LL
L
$
Dissipative Photosphere in a fireball Internal shocks take place below the
photosphere for tvltlt1 s
Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007
Injecting fast electrons Slow heating Ghisellini amp Celotti 1999
Studied the radiative transfer for variousvalues of єdiss єB єe τ
Big variety of spectra depending on τ
Dominant process Compton scattering ofphotons advected with the flow
τγe = 1
Our suggestion photospheric emission from the AC modelMain features
AC model gradual dissipation throughout the photosphere
If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering
Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007
Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes
Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~
rsrrph
Log(r [cm])
Radiative transfer analytical estimates+ Monte Carlo Comptonization
Deep in the flow radiation ampparticles are in thermal equilibrium
At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV
For r gt req balance in heating andcooling determined Te
Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering
Photospheric spectra Characteristic peak at ~1 MeV
(in the central engine frame)
Flat power law high energy tails(unsaturated Comptonization)
Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of
bursts Ryde 2004 2005
Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007
Inferences for the central enginethe stronger the cleaner
The Amati relation explainedif in different bursts
Variability in prompt emission Reflects changes in L η
Assumption relationholds during the GRB the model predicts the observed
narrowing of pulses withincreasing energyFenimore et al 1995
06L
06L
Summary Spectral and temporal properties of GRBs are very intriguing
The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation
Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB
Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them
The peak energy and the energetics
η30 100 300 1000
η30 100 300 1000
Comment
The temperature of the flow at the req in the observer frame is
The Ef(E) spectrum of this component peaks at ~4 times thisenergy
19 1 9 1 3 2 9
eq eqobs e1 52 3 25
eq
( ) ( )100 keV
1 1
r T f LT
z z
$
+ +
General considerationsenergy source of the prompt emission The rapid GRB variability argues against the forward shock for
the prompt emissioneg Sari amp Piran 1997 see however Dermer 2007 for a different point of view
Observationally transition from the prompt to the early afterglowemission Zhang et al 2006
The prompt emission most likely comesfrom internal dissipation of energy in the fast flow
This can take place by Internal shocks Rees amp Meacuteszaacuteros 1994 Sari amp Piran 1997
Magnetic dissipation Thompson 1994 Denkhahn amp Spruit 2002 Lyutikov amp Blandford 2003-see Fan et al 2004 for a combination of the two
Internal shocks vs Magnetic dissipation Internal shocks
Unsteady flow composed bymany fast shells
A fast shell with γ2gtγ1 collideswith a slower one dissipatingtheir relative kinetic energythrough shock waves
Magnetic dissipation Magnetic fields carry most of the
energy of the flow The magnetic energy is
dissipated internally throughreconnection
g-rays
Fk
FB
Fk
variability and dissipation are separateingredients in magnetic dissipationmodels
γ2υ2 γ1υ1
FB
γυ
Where is the prompt emission produced anywhere between the Thomson photosphere rph and the
deceleration radius rd
Typically rph~1011cm and rd ~1017cm in this range of radii density ~12 orders of magnitude optical depth ~6 orders of magnitude
Different radiative mechanisms dependingon the location of the energy dissipation
Case 1 Thomsonthin dissipation
Case 2 Photosphericdissipation
Case 1Internal shocks in the Thomson thin regime Internal shocks
The collision of the shells takes place at rcol~γ2ctv tv related to the central engine activity (not trivially Janka et al 2005 Aloy amp
Rezolla 2006) Each collision results in an observed pulse of gamma-rays
shocks cross the shells
In the shock front Particle acceleration takes place Magnetic field amplification due to plasma instabilitites (see next talks)
Parameters fractions єe ζe єB power-law N(γe) ~ γe-p pgt2
Fast particles + magnetic fields Synchrotron self-Compton emission
Thin synchrotron emission may explain the observed spectrum
~
Case 1Can thin Synchrotron emission explain the spectra
Pros For tv~1 s the characteristic pulse duration and separation can be reproduced
Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002
The peak of the synchrotron spectrum can be in the ~a few 100 keV range
Flat high-energy power law
Cons Low radiative efficiency (though uncertain)
~ єdiss єe єBand at the ~ level
Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004
jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair
creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002
Case 1Magnetic dissipation in the Thomson thin regime
In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006
Fast proper plasma motions lead to the rapid observed variability
AC model dissipation near photosphere as well as outside
Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005
Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004
Thin synchrotron emission may be responsible for the GRB
The B-field is given directly by the model At low densities particle distributions in reconnection uncertain
Case 2
Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin
Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000
Spectrum quasi thermal Goodman 1986
Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006
In the AC model DG 2006 DG amp Spruit 2007
For this range of η the model predicts a dissipative photosphere
1 48 3 23
ph 25 o7 52
2 3
52 o7
005 1000L r L
L L r
$ lt amp
(
15 15ph 15 1552 3
52 3
25
( )016 150 ( )
L LL
L
$
Dissipative Photosphere in a fireball Internal shocks take place below the
photosphere for tvltlt1 s
Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007
Injecting fast electrons Slow heating Ghisellini amp Celotti 1999
Studied the radiative transfer for variousvalues of єdiss єB єe τ
Big variety of spectra depending on τ
Dominant process Compton scattering ofphotons advected with the flow
τγe = 1
Our suggestion photospheric emission from the AC modelMain features
AC model gradual dissipation throughout the photosphere
If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering
Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007
Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes
Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~
rsrrph
Log(r [cm])
Radiative transfer analytical estimates+ Monte Carlo Comptonization
Deep in the flow radiation ampparticles are in thermal equilibrium
At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV
For r gt req balance in heating andcooling determined Te
Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering
Photospheric spectra Characteristic peak at ~1 MeV
(in the central engine frame)
Flat power law high energy tails(unsaturated Comptonization)
Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of
bursts Ryde 2004 2005
Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007
Inferences for the central enginethe stronger the cleaner
The Amati relation explainedif in different bursts
Variability in prompt emission Reflects changes in L η
Assumption relationholds during the GRB the model predicts the observed
narrowing of pulses withincreasing energyFenimore et al 1995
06L
06L
Summary Spectral and temporal properties of GRBs are very intriguing
The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation
Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB
Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them
The peak energy and the energetics
η30 100 300 1000
η30 100 300 1000
Comment
The temperature of the flow at the req in the observer frame is
The Ef(E) spectrum of this component peaks at ~4 times thisenergy
19 1 9 1 3 2 9
eq eqobs e1 52 3 25
eq
( ) ( )100 keV
1 1
r T f LT
z z
$
+ +
Internal shocks vs Magnetic dissipation Internal shocks
Unsteady flow composed bymany fast shells
A fast shell with γ2gtγ1 collideswith a slower one dissipatingtheir relative kinetic energythrough shock waves
Magnetic dissipation Magnetic fields carry most of the
energy of the flow The magnetic energy is
dissipated internally throughreconnection
g-rays
Fk
FB
Fk
variability and dissipation are separateingredients in magnetic dissipationmodels
γ2υ2 γ1υ1
FB
γυ
Where is the prompt emission produced anywhere between the Thomson photosphere rph and the
deceleration radius rd
Typically rph~1011cm and rd ~1017cm in this range of radii density ~12 orders of magnitude optical depth ~6 orders of magnitude
Different radiative mechanisms dependingon the location of the energy dissipation
Case 1 Thomsonthin dissipation
Case 2 Photosphericdissipation
Case 1Internal shocks in the Thomson thin regime Internal shocks
The collision of the shells takes place at rcol~γ2ctv tv related to the central engine activity (not trivially Janka et al 2005 Aloy amp
Rezolla 2006) Each collision results in an observed pulse of gamma-rays
shocks cross the shells
In the shock front Particle acceleration takes place Magnetic field amplification due to plasma instabilitites (see next talks)
Parameters fractions єe ζe єB power-law N(γe) ~ γe-p pgt2
Fast particles + magnetic fields Synchrotron self-Compton emission
Thin synchrotron emission may explain the observed spectrum
~
Case 1Can thin Synchrotron emission explain the spectra
Pros For tv~1 s the characteristic pulse duration and separation can be reproduced
Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002
The peak of the synchrotron spectrum can be in the ~a few 100 keV range
Flat high-energy power law
Cons Low radiative efficiency (though uncertain)
~ єdiss єe єBand at the ~ level
Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004
jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair
creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002
Case 1Magnetic dissipation in the Thomson thin regime
In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006
Fast proper plasma motions lead to the rapid observed variability
AC model dissipation near photosphere as well as outside
Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005
Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004
Thin synchrotron emission may be responsible for the GRB
The B-field is given directly by the model At low densities particle distributions in reconnection uncertain
Case 2
Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin
Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000
Spectrum quasi thermal Goodman 1986
Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006
In the AC model DG 2006 DG amp Spruit 2007
For this range of η the model predicts a dissipative photosphere
1 48 3 23
ph 25 o7 52
2 3
52 o7
005 1000L r L
L L r
$ lt amp
(
15 15ph 15 1552 3
52 3
25
( )016 150 ( )
L LL
L
$
Dissipative Photosphere in a fireball Internal shocks take place below the
photosphere for tvltlt1 s
Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007
Injecting fast electrons Slow heating Ghisellini amp Celotti 1999
Studied the radiative transfer for variousvalues of єdiss єB єe τ
Big variety of spectra depending on τ
Dominant process Compton scattering ofphotons advected with the flow
τγe = 1
Our suggestion photospheric emission from the AC modelMain features
AC model gradual dissipation throughout the photosphere
If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering
Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007
Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes
Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~
rsrrph
Log(r [cm])
Radiative transfer analytical estimates+ Monte Carlo Comptonization
Deep in the flow radiation ampparticles are in thermal equilibrium
At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV
For r gt req balance in heating andcooling determined Te
Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering
Photospheric spectra Characteristic peak at ~1 MeV
(in the central engine frame)
Flat power law high energy tails(unsaturated Comptonization)
Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of
bursts Ryde 2004 2005
Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007
Inferences for the central enginethe stronger the cleaner
The Amati relation explainedif in different bursts
Variability in prompt emission Reflects changes in L η
Assumption relationholds during the GRB the model predicts the observed
narrowing of pulses withincreasing energyFenimore et al 1995
06L
06L
Summary Spectral and temporal properties of GRBs are very intriguing
The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation
Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB
Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them
The peak energy and the energetics
η30 100 300 1000
η30 100 300 1000
Comment
The temperature of the flow at the req in the observer frame is
The Ef(E) spectrum of this component peaks at ~4 times thisenergy
19 1 9 1 3 2 9
eq eqobs e1 52 3 25
eq
( ) ( )100 keV
1 1
r T f LT
z z
$
+ +
Where is the prompt emission produced anywhere between the Thomson photosphere rph and the
deceleration radius rd
Typically rph~1011cm and rd ~1017cm in this range of radii density ~12 orders of magnitude optical depth ~6 orders of magnitude
Different radiative mechanisms dependingon the location of the energy dissipation
Case 1 Thomsonthin dissipation
Case 2 Photosphericdissipation
Case 1Internal shocks in the Thomson thin regime Internal shocks
The collision of the shells takes place at rcol~γ2ctv tv related to the central engine activity (not trivially Janka et al 2005 Aloy amp
Rezolla 2006) Each collision results in an observed pulse of gamma-rays
shocks cross the shells
In the shock front Particle acceleration takes place Magnetic field amplification due to plasma instabilitites (see next talks)
Parameters fractions єe ζe єB power-law N(γe) ~ γe-p pgt2
Fast particles + magnetic fields Synchrotron self-Compton emission
Thin synchrotron emission may explain the observed spectrum
~
Case 1Can thin Synchrotron emission explain the spectra
Pros For tv~1 s the characteristic pulse duration and separation can be reproduced
Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002
The peak of the synchrotron spectrum can be in the ~a few 100 keV range
Flat high-energy power law
Cons Low radiative efficiency (though uncertain)
~ єdiss єe єBand at the ~ level
Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004
jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair
creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002
Case 1Magnetic dissipation in the Thomson thin regime
In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006
Fast proper plasma motions lead to the rapid observed variability
AC model dissipation near photosphere as well as outside
Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005
Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004
Thin synchrotron emission may be responsible for the GRB
The B-field is given directly by the model At low densities particle distributions in reconnection uncertain
Case 2
Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin
Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000
Spectrum quasi thermal Goodman 1986
Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006
In the AC model DG 2006 DG amp Spruit 2007
For this range of η the model predicts a dissipative photosphere
1 48 3 23
ph 25 o7 52
2 3
52 o7
005 1000L r L
L L r
$ lt amp
(
15 15ph 15 1552 3
52 3
25
( )016 150 ( )
L LL
L
$
Dissipative Photosphere in a fireball Internal shocks take place below the
photosphere for tvltlt1 s
Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007
Injecting fast electrons Slow heating Ghisellini amp Celotti 1999
Studied the radiative transfer for variousvalues of єdiss єB єe τ
Big variety of spectra depending on τ
Dominant process Compton scattering ofphotons advected with the flow
τγe = 1
Our suggestion photospheric emission from the AC modelMain features
AC model gradual dissipation throughout the photosphere
If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering
Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007
Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes
Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~
rsrrph
Log(r [cm])
Radiative transfer analytical estimates+ Monte Carlo Comptonization
Deep in the flow radiation ampparticles are in thermal equilibrium
At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV
For r gt req balance in heating andcooling determined Te
Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering
Photospheric spectra Characteristic peak at ~1 MeV
(in the central engine frame)
Flat power law high energy tails(unsaturated Comptonization)
Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of
bursts Ryde 2004 2005
Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007
Inferences for the central enginethe stronger the cleaner
The Amati relation explainedif in different bursts
Variability in prompt emission Reflects changes in L η
Assumption relationholds during the GRB the model predicts the observed
narrowing of pulses withincreasing energyFenimore et al 1995
06L
06L
Summary Spectral and temporal properties of GRBs are very intriguing
The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation
Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB
Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them
The peak energy and the energetics
η30 100 300 1000
η30 100 300 1000
Comment
The temperature of the flow at the req in the observer frame is
The Ef(E) spectrum of this component peaks at ~4 times thisenergy
19 1 9 1 3 2 9
eq eqobs e1 52 3 25
eq
( ) ( )100 keV
1 1
r T f LT
z z
$
+ +
Case 1Internal shocks in the Thomson thin regime Internal shocks
The collision of the shells takes place at rcol~γ2ctv tv related to the central engine activity (not trivially Janka et al 2005 Aloy amp
Rezolla 2006) Each collision results in an observed pulse of gamma-rays
shocks cross the shells
In the shock front Particle acceleration takes place Magnetic field amplification due to plasma instabilitites (see next talks)
Parameters fractions єe ζe єB power-law N(γe) ~ γe-p pgt2
Fast particles + magnetic fields Synchrotron self-Compton emission
Thin synchrotron emission may explain the observed spectrum
~
Case 1Can thin Synchrotron emission explain the spectra
Pros For tv~1 s the characteristic pulse duration and separation can be reproduced
Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002
The peak of the synchrotron spectrum can be in the ~a few 100 keV range
Flat high-energy power law
Cons Low radiative efficiency (though uncertain)
~ єdiss єe єBand at the ~ level
Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004
jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair
creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002
Case 1Magnetic dissipation in the Thomson thin regime
In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006
Fast proper plasma motions lead to the rapid observed variability
AC model dissipation near photosphere as well as outside
Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005
Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004
Thin synchrotron emission may be responsible for the GRB
The B-field is given directly by the model At low densities particle distributions in reconnection uncertain
Case 2
Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin
Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000
Spectrum quasi thermal Goodman 1986
Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006
In the AC model DG 2006 DG amp Spruit 2007
For this range of η the model predicts a dissipative photosphere
1 48 3 23
ph 25 o7 52
2 3
52 o7
005 1000L r L
L L r
$ lt amp
(
15 15ph 15 1552 3
52 3
25
( )016 150 ( )
L LL
L
$
Dissipative Photosphere in a fireball Internal shocks take place below the
photosphere for tvltlt1 s
Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007
Injecting fast electrons Slow heating Ghisellini amp Celotti 1999
Studied the radiative transfer for variousvalues of єdiss єB єe τ
Big variety of spectra depending on τ
Dominant process Compton scattering ofphotons advected with the flow
τγe = 1
Our suggestion photospheric emission from the AC modelMain features
AC model gradual dissipation throughout the photosphere
If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering
Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007
Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes
Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~
rsrrph
Log(r [cm])
Radiative transfer analytical estimates+ Monte Carlo Comptonization
Deep in the flow radiation ampparticles are in thermal equilibrium
At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV
For r gt req balance in heating andcooling determined Te
Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering
Photospheric spectra Characteristic peak at ~1 MeV
(in the central engine frame)
Flat power law high energy tails(unsaturated Comptonization)
Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of
bursts Ryde 2004 2005
Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007
Inferences for the central enginethe stronger the cleaner
The Amati relation explainedif in different bursts
Variability in prompt emission Reflects changes in L η
Assumption relationholds during the GRB the model predicts the observed
narrowing of pulses withincreasing energyFenimore et al 1995
06L
06L
Summary Spectral and temporal properties of GRBs are very intriguing
The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation
Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB
Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them
The peak energy and the energetics
η30 100 300 1000
η30 100 300 1000
Comment
The temperature of the flow at the req in the observer frame is
The Ef(E) spectrum of this component peaks at ~4 times thisenergy
19 1 9 1 3 2 9
eq eqobs e1 52 3 25
eq
( ) ( )100 keV
1 1
r T f LT
z z
$
+ +
Case 1Can thin Synchrotron emission explain the spectra
Pros For tv~1 s the characteristic pulse duration and separation can be reproduced
Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002
The peak of the synchrotron spectrum can be in the ~a few 100 keV range
Flat high-energy power law
Cons Low radiative efficiency (though uncertain)
~ єdiss єe єBand at the ~ level
Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004
jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair
creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002
Case 1Magnetic dissipation in the Thomson thin regime
In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006
Fast proper plasma motions lead to the rapid observed variability
AC model dissipation near photosphere as well as outside
Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005
Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004
Thin synchrotron emission may be responsible for the GRB
The B-field is given directly by the model At low densities particle distributions in reconnection uncertain
Case 2
Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin
Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000
Spectrum quasi thermal Goodman 1986
Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006
In the AC model DG 2006 DG amp Spruit 2007
For this range of η the model predicts a dissipative photosphere
1 48 3 23
ph 25 o7 52
2 3
52 o7
005 1000L r L
L L r
$ lt amp
(
15 15ph 15 1552 3
52 3
25
( )016 150 ( )
L LL
L
$
Dissipative Photosphere in a fireball Internal shocks take place below the
photosphere for tvltlt1 s
Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007
Injecting fast electrons Slow heating Ghisellini amp Celotti 1999
Studied the radiative transfer for variousvalues of єdiss єB єe τ
Big variety of spectra depending on τ
Dominant process Compton scattering ofphotons advected with the flow
τγe = 1
Our suggestion photospheric emission from the AC modelMain features
AC model gradual dissipation throughout the photosphere
If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering
Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007
Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes
Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~
rsrrph
Log(r [cm])
Radiative transfer analytical estimates+ Monte Carlo Comptonization
Deep in the flow radiation ampparticles are in thermal equilibrium
At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV
For r gt req balance in heating andcooling determined Te
Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering
Photospheric spectra Characteristic peak at ~1 MeV
(in the central engine frame)
Flat power law high energy tails(unsaturated Comptonization)
Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of
bursts Ryde 2004 2005
Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007
Inferences for the central enginethe stronger the cleaner
The Amati relation explainedif in different bursts
Variability in prompt emission Reflects changes in L η
Assumption relationholds during the GRB the model predicts the observed
narrowing of pulses withincreasing energyFenimore et al 1995
06L
06L
Summary Spectral and temporal properties of GRBs are very intriguing
The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation
Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB
Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them
The peak energy and the energetics
η30 100 300 1000
η30 100 300 1000
Comment
The temperature of the flow at the req in the observer frame is
The Ef(E) spectrum of this component peaks at ~4 times thisenergy
19 1 9 1 3 2 9
eq eqobs e1 52 3 25
eq
( ) ( )100 keV
1 1
r T f LT
z z
$
+ +
Case 1Magnetic dissipation in the Thomson thin regime
In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006
Fast proper plasma motions lead to the rapid observed variability
AC model dissipation near photosphere as well as outside
Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005
Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004
Thin synchrotron emission may be responsible for the GRB
The B-field is given directly by the model At low densities particle distributions in reconnection uncertain
Case 2
Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin
Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000
Spectrum quasi thermal Goodman 1986
Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006
In the AC model DG 2006 DG amp Spruit 2007
For this range of η the model predicts a dissipative photosphere
1 48 3 23
ph 25 o7 52
2 3
52 o7
005 1000L r L
L L r
$ lt amp
(
15 15ph 15 1552 3
52 3
25
( )016 150 ( )
L LL
L
$
Dissipative Photosphere in a fireball Internal shocks take place below the
photosphere for tvltlt1 s
Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007
Injecting fast electrons Slow heating Ghisellini amp Celotti 1999
Studied the radiative transfer for variousvalues of єdiss єB єe τ
Big variety of spectra depending on τ
Dominant process Compton scattering ofphotons advected with the flow
τγe = 1
Our suggestion photospheric emission from the AC modelMain features
AC model gradual dissipation throughout the photosphere
If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering
Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007
Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes
Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~
rsrrph
Log(r [cm])
Radiative transfer analytical estimates+ Monte Carlo Comptonization
Deep in the flow radiation ampparticles are in thermal equilibrium
At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV
For r gt req balance in heating andcooling determined Te
Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering
Photospheric spectra Characteristic peak at ~1 MeV
(in the central engine frame)
Flat power law high energy tails(unsaturated Comptonization)
Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of
bursts Ryde 2004 2005
Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007
Inferences for the central enginethe stronger the cleaner
The Amati relation explainedif in different bursts
Variability in prompt emission Reflects changes in L η
Assumption relationholds during the GRB the model predicts the observed
narrowing of pulses withincreasing energyFenimore et al 1995
06L
06L
Summary Spectral and temporal properties of GRBs are very intriguing
The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation
Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB
Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them
The peak energy and the energetics
η30 100 300 1000
η30 100 300 1000
Comment
The temperature of the flow at the req in the observer frame is
The Ef(E) spectrum of this component peaks at ~4 times thisenergy
19 1 9 1 3 2 9
eq eqobs e1 52 3 25
eq
( ) ( )100 keV
1 1
r T f LT
z z
$
+ +
Case 2
Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin
Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000
Spectrum quasi thermal Goodman 1986
Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006
In the AC model DG 2006 DG amp Spruit 2007
For this range of η the model predicts a dissipative photosphere
1 48 3 23
ph 25 o7 52
2 3
52 o7
005 1000L r L
L L r
$ lt amp
(
15 15ph 15 1552 3
52 3
25
( )016 150 ( )
L LL
L
$
Dissipative Photosphere in a fireball Internal shocks take place below the
photosphere for tvltlt1 s
Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007
Injecting fast electrons Slow heating Ghisellini amp Celotti 1999
Studied the radiative transfer for variousvalues of єdiss єB єe τ
Big variety of spectra depending on τ
Dominant process Compton scattering ofphotons advected with the flow
τγe = 1
Our suggestion photospheric emission from the AC modelMain features
AC model gradual dissipation throughout the photosphere
If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering
Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007
Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes
Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~
rsrrph
Log(r [cm])
Radiative transfer analytical estimates+ Monte Carlo Comptonization
Deep in the flow radiation ampparticles are in thermal equilibrium
At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV
For r gt req balance in heating andcooling determined Te
Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering
Photospheric spectra Characteristic peak at ~1 MeV
(in the central engine frame)
Flat power law high energy tails(unsaturated Comptonization)
Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of
bursts Ryde 2004 2005
Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007
Inferences for the central enginethe stronger the cleaner
The Amati relation explainedif in different bursts
Variability in prompt emission Reflects changes in L η
Assumption relationholds during the GRB the model predicts the observed
narrowing of pulses withincreasing energyFenimore et al 1995
06L
06L
Summary Spectral and temporal properties of GRBs are very intriguing
The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation
Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB
Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them
The peak energy and the energetics
η30 100 300 1000
η30 100 300 1000
Comment
The temperature of the flow at the req in the observer frame is
The Ef(E) spectrum of this component peaks at ~4 times thisenergy
19 1 9 1 3 2 9
eq eqobs e1 52 3 25
eq
( ) ( )100 keV
1 1
r T f LT
z z
$
+ +
Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000
Spectrum quasi thermal Goodman 1986
Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006
In the AC model DG 2006 DG amp Spruit 2007
For this range of η the model predicts a dissipative photosphere
1 48 3 23
ph 25 o7 52
2 3
52 o7
005 1000L r L
L L r
$ lt amp
(
15 15ph 15 1552 3
52 3
25
( )016 150 ( )
L LL
L
$
Dissipative Photosphere in a fireball Internal shocks take place below the
photosphere for tvltlt1 s
Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007
Injecting fast electrons Slow heating Ghisellini amp Celotti 1999
Studied the radiative transfer for variousvalues of єdiss єB єe τ
Big variety of spectra depending on τ
Dominant process Compton scattering ofphotons advected with the flow
τγe = 1
Our suggestion photospheric emission from the AC modelMain features
AC model gradual dissipation throughout the photosphere
If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering
Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007
Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes
Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~
rsrrph
Log(r [cm])
Radiative transfer analytical estimates+ Monte Carlo Comptonization
Deep in the flow radiation ampparticles are in thermal equilibrium
At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV
For r gt req balance in heating andcooling determined Te
Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering
Photospheric spectra Characteristic peak at ~1 MeV
(in the central engine frame)
Flat power law high energy tails(unsaturated Comptonization)
Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of
bursts Ryde 2004 2005
Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007
Inferences for the central enginethe stronger the cleaner
The Amati relation explainedif in different bursts
Variability in prompt emission Reflects changes in L η
Assumption relationholds during the GRB the model predicts the observed
narrowing of pulses withincreasing energyFenimore et al 1995
06L
06L
Summary Spectral and temporal properties of GRBs are very intriguing
The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation
Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB
Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them
The peak energy and the energetics
η30 100 300 1000
η30 100 300 1000
Comment
The temperature of the flow at the req in the observer frame is
The Ef(E) spectrum of this component peaks at ~4 times thisenergy
19 1 9 1 3 2 9
eq eqobs e1 52 3 25
eq
( ) ( )100 keV
1 1
r T f LT
z z
$
+ +
Dissipative Photosphere in a fireball Internal shocks take place below the
photosphere for tvltlt1 s
Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007
Injecting fast electrons Slow heating Ghisellini amp Celotti 1999
Studied the radiative transfer for variousvalues of єdiss єB єe τ
Big variety of spectra depending on τ
Dominant process Compton scattering ofphotons advected with the flow
τγe = 1
Our suggestion photospheric emission from the AC modelMain features
AC model gradual dissipation throughout the photosphere
If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering
Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007
Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes
Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~
rsrrph
Log(r [cm])
Radiative transfer analytical estimates+ Monte Carlo Comptonization
Deep in the flow radiation ampparticles are in thermal equilibrium
At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV
For r gt req balance in heating andcooling determined Te
Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering
Photospheric spectra Characteristic peak at ~1 MeV
(in the central engine frame)
Flat power law high energy tails(unsaturated Comptonization)
Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of
bursts Ryde 2004 2005
Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007
Inferences for the central enginethe stronger the cleaner
The Amati relation explainedif in different bursts
Variability in prompt emission Reflects changes in L η
Assumption relationholds during the GRB the model predicts the observed
narrowing of pulses withincreasing energyFenimore et al 1995
06L
06L
Summary Spectral and temporal properties of GRBs are very intriguing
The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation
Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB
Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them
The peak energy and the energetics
η30 100 300 1000
η30 100 300 1000
Comment
The temperature of the flow at the req in the observer frame is
The Ef(E) spectrum of this component peaks at ~4 times thisenergy
19 1 9 1 3 2 9
eq eqobs e1 52 3 25
eq
( ) ( )100 keV
1 1
r T f LT
z z
$
+ +
Our suggestion photospheric emission from the AC modelMain features
AC model gradual dissipation throughout the photosphere
If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering
Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007
Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes
Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~
rsrrph
Log(r [cm])
Radiative transfer analytical estimates+ Monte Carlo Comptonization
Deep in the flow radiation ampparticles are in thermal equilibrium
At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV
For r gt req balance in heating andcooling determined Te
Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering
Photospheric spectra Characteristic peak at ~1 MeV
(in the central engine frame)
Flat power law high energy tails(unsaturated Comptonization)
Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of
bursts Ryde 2004 2005
Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007
Inferences for the central enginethe stronger the cleaner
The Amati relation explainedif in different bursts
Variability in prompt emission Reflects changes in L η
Assumption relationholds during the GRB the model predicts the observed
narrowing of pulses withincreasing energyFenimore et al 1995
06L
06L
Summary Spectral and temporal properties of GRBs are very intriguing
The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation
Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB
Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them
The peak energy and the energetics
η30 100 300 1000
η30 100 300 1000
Comment
The temperature of the flow at the req in the observer frame is
The Ef(E) spectrum of this component peaks at ~4 times thisenergy
19 1 9 1 3 2 9
eq eqobs e1 52 3 25
eq
( ) ( )100 keV
1 1
r T f LT
z z
$
+ +
Radiative transfer analytical estimates+ Monte Carlo Comptonization
Deep in the flow radiation ampparticles are in thermal equilibrium
At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV
For r gt req balance in heating andcooling determined Te
Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering
Photospheric spectra Characteristic peak at ~1 MeV
(in the central engine frame)
Flat power law high energy tails(unsaturated Comptonization)
Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of
bursts Ryde 2004 2005
Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007
Inferences for the central enginethe stronger the cleaner
The Amati relation explainedif in different bursts
Variability in prompt emission Reflects changes in L η
Assumption relationholds during the GRB the model predicts the observed
narrowing of pulses withincreasing energyFenimore et al 1995
06L
06L
Summary Spectral and temporal properties of GRBs are very intriguing
The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation
Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB
Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them
The peak energy and the energetics
η30 100 300 1000
η30 100 300 1000
Comment
The temperature of the flow at the req in the observer frame is
The Ef(E) spectrum of this component peaks at ~4 times thisenergy
19 1 9 1 3 2 9
eq eqobs e1 52 3 25
eq
( ) ( )100 keV
1 1
r T f LT
z z
$
+ +
Photospheric spectra Characteristic peak at ~1 MeV
(in the central engine frame)
Flat power law high energy tails(unsaturated Comptonization)
Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of
bursts Ryde 2004 2005
Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007
Inferences for the central enginethe stronger the cleaner
The Amati relation explainedif in different bursts
Variability in prompt emission Reflects changes in L η
Assumption relationholds during the GRB the model predicts the observed
narrowing of pulses withincreasing energyFenimore et al 1995
06L
06L
Summary Spectral and temporal properties of GRBs are very intriguing
The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation
Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB
Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them
The peak energy and the energetics
η30 100 300 1000
η30 100 300 1000
Comment
The temperature of the flow at the req in the observer frame is
The Ef(E) spectrum of this component peaks at ~4 times thisenergy
19 1 9 1 3 2 9
eq eqobs e1 52 3 25
eq
( ) ( )100 keV
1 1
r T f LT
z z
$
+ +
Inferences for the central enginethe stronger the cleaner
The Amati relation explainedif in different bursts
Variability in prompt emission Reflects changes in L η
Assumption relationholds during the GRB the model predicts the observed
narrowing of pulses withincreasing energyFenimore et al 1995
06L
06L
Summary Spectral and temporal properties of GRBs are very intriguing
The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation
Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB
Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them
The peak energy and the energetics
η30 100 300 1000
η30 100 300 1000
Comment
The temperature of the flow at the req in the observer frame is
The Ef(E) spectrum of this component peaks at ~4 times thisenergy
19 1 9 1 3 2 9
eq eqobs e1 52 3 25
eq
( ) ( )100 keV
1 1
r T f LT
z z
$
+ +
Summary Spectral and temporal properties of GRBs are very intriguing
The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation
Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB
Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them
The peak energy and the energetics
η30 100 300 1000
η30 100 300 1000
Comment
The temperature of the flow at the req in the observer frame is
The Ef(E) spectrum of this component peaks at ~4 times thisenergy
19 1 9 1 3 2 9
eq eqobs e1 52 3 25
eq
( ) ( )100 keV
1 1
r T f LT
z z
$
+ +
The peak energy and the energetics
η30 100 300 1000
η30 100 300 1000
Comment
The temperature of the flow at the req in the observer frame is
The Ef(E) spectrum of this component peaks at ~4 times thisenergy
19 1 9 1 3 2 9
eq eqobs e1 52 3 25
eq
( ) ( )100 keV
1 1
r T f LT
z z
$
+ +
Comment
The temperature of the flow at the req in the observer frame is
The Ef(E) spectrum of this component peaks at ~4 times thisenergy
19 1 9 1 3 2 9
eq eqobs e1 52 3 25
eq
( ) ( )100 keV
1 1
r T f LT
z z
$
+ +