central engines and radiation mechanisms of gamma …veresp.web.elte.hu/stuff/veres_hsv16.pdfcentral...

Central engines and radiation mechanismsof gamma-ray bursts

Peter Veres

CSPAR, University of Alabama in Huntsville

collaborators: Rob Preece, Adam Goldstein, Valerie Connaughton, Peter Meszaros,Alessandra Corsi, Bin-Bin Zhang, J. Michael Burgess and Eric Burns

8th Huntsville gamma-ray burst symposiumOctober 26, 2016

Peter Veres (UAH) Central engines and emission mechanism HSV 10/26/16 1 / 19

Gamma-ray Bursts - Overview

• Random directions on the sky(∼ few per week)

• Short/long divide in duration

• Broad non-thermal spectrumemerging complex picture

• Afterglow visible for ∼ week(s)

• Prompt: keV to . MeV,AG: radio to .TeV

• Deduce: compact object,Γ > 100, θjet ≈few ◦,Eiso = 1051 − 1055 erg

128-channel CSPEC or TTE data, are more reliable for suchweak events.

5. DISCUSSION

Figure 4 shows the sky distribution of GBM-triggered GRBsin Galactic coordinates. Crosses indicate long GRBs(T90>2 s) and asterisks indicate short GRBs. Both the longand short GRB locations do not show any obvious anisotropy,which is consistent with an isotropic distribution of GRBarrival directions. Also shown are the locations of GRBs thattriggered Swift-BAT in coincidence with GBM. Many of theseSwift coincident GRBs also have redshifts estimated bydetecting the optical afterglows with ground-based telescopes.

The histograms of the logarithms of GBM-triggered GRBdurations (T50 and T90) are shown in Figure 5. Using the

conventional division between the short and long GRB classes(T90�2 s and T90>2 s, respectively), we find that during thefirst 6 years there were 229 short GRBs and 1175 long GRBs.The short and long GRBs, as defined by their T90 in50–300 keV, may belong to two different classes (Kouveliotouet al. 1993). However, from the T90 distribution shown inFigure 5, the distinction seems to be less than obvious. Thereare also several claims in the literature concerning the existenceof three types of GRBs based on multiple GRB parameters likeduration, fluence, spectrum, spectral lag, peak-count rate, etc.,from the BATSE sample (Mukherjee et al. 1998; Horváthet al. 2006), Swift sample (Veres et al. 2010), and RHESSIsample (Ripa et al. 2012). The three groups are the familiarshort-hard GRBs, long-soft GRBs, and soft-intermediateduration GRBs bridging the other two groups. Hence, wedecided to independently assess the number of groups in the

Table 8GRB Fluence and Peak Flux (50–300 keV)

Trigger Fluence PF64 PF256 PF1024ID (erg cm−2) (ph cm−2 s−1) (ph cm−2 s−1) (ph cm−2 s−1)

bn080714086 3.54E-07±1.73E-08 1.52±0.74 0.91±0.36 0.43±0.18bn080714425 9.79E-07±1.36E-08 1.03±0.45 0.71±0.19 0.46±0.08bn080714745 3.26E-06±6.03E-08 4.41±1.66 3.27±0.71 2.82±0.36bn080715950 2.54E-06±3.52E-08 10.70±0.95 6.61±0.45 3.83±0.22bn080717543 2.37E-06±4.51E-08 2.14±1.03 1.30±0.47 1.05±0.23bn080719529 3.88E-07±1.47E-08 0.59±0.18 0.32±0.08 0.23±0.04bn080720316 3.88E-07±1.47E-08 0.59±0.18 0.32±0.08 0.23±0.04bn080723557 3.92E-05±1.15E-07 21.19±1.79 19.81±1.09 15.14±0.48bn080723913 7.45E-08±5.19E-09 2.62±0.66 2.14±0.32 0.69±0.13bn080723985 1.57E-05±1.07E-07 5.92±1.23 5.17±0.54 4.85±0.28

(This table is available in its entirety in machine-readable form.)

Figure 4. Sky distribution of GBM-triggered GRBs in celestial coordinates. Crosses indicate long GRBs (T90>2 s) and asterisks indicate short GRBs. Also shownare the GBM GRBs simultaneously detected by Swift (red squares).

12

The Astrophysical Journal Supplement Series, 223:28 (18pp), 2016 April Bhat et al.

3rd GBM GRB catalog Bhat+16


http://arxiv.org/abs/1603.07612







• Deduce: compact object,Γ > 100, θjet ≈few ◦,Eiso = 1051 − 1055 erg 3rd GBM GRB catalog Bhat+16










100 101 102 103 104 105 106

E [keV]ν

Fν [

arb

itra

ry u

nit

s]

Comptonized

Band

Power law

Blackbody









10−3 10−2 10−1 100 101 102 103

Time from GBM trigger (d)

10−8

10−7

10−6

10−5

10−4

10−3

10−2

10−1

100

Flux

(Jy)

LAT 2−100 GeV (x1000)

LAT 0.1−2 GeV (x1000)

BAT 15−50 keV

XRT 0.2−10 keV

UVOT 180nm

P60/T100/GROND 0.6µm

UKIRT/GROND 2µmCARMA/PdBI 90 GHz

RTT/VLA 30 GHz (x10)

VLA 5.5 GHz (x100)

E1 E2 E3 E4 E5 E6 E7 E8 E9 E10 E11

Perley+14










credit: NASA/Swift/deWilde


Outline

• Central engine [Black hole and/or neutron star]

• Emission mechanism [thermal, synchrotron, Compton]

• Case studies [GRB 130427A, GW 150914-GBM]

• Jet composition [baryonic, magnetic]


Central engine sources

Black Hole

Neutron Star

BH-NS merger

Single

Binary

accreting BH

NS-NS merger (magnetar)

BH-BH merger?

Magnetar

Single

BinaryNeutron Star

• (Indirect) evidence:• Long GRB progenitor: collapsar• Short GRB progenitor: compact binary

• Invisible central engine: black hole + disc or magnetar

• (?) direct observations near → GW [see also talk by Bing Zhang]


Central engines: Black hole + accretion disk

• Hyper-accreting BH• Neutrino annihilation:νν → e± powers jet along rotaxis. E budget: disk material. 1054 erg

• Blandford Znajek: E budget:BH rotation ∼ 1054 erg

credit: Bartos+13



Magnetars

• Rapidly rotating (P∼ 1 ms) NS(near breakup speed)

• Highly magnetized (B∼1015 G)- to transfer NS energy to jet

• Observational signature: X-rayplateau + break / extendedemission

• Possible issue: Emax = Erot =2×1052R2

6P−2ms

M1.4M�

erg . EGRB

(talk by Fruchter) credit: Bartos+13



Binary Black hole mergers - unlikely progenitors

• For EM: mass stripped form NS to form acc. disk to tap BH energy→ need at least a NS component.

• Difficult to keep disk around BH binary for long time

• Considered after GW 150914-GBM

• Loeb15: Star /w massive He core forms 2 BHs

• Woosley16: need binary/ EM delayproblematic

• Perna+16: dead disk around one BH,re-energized by merger

• Zhang16: norm. charge: ∼ 10−5, links to FRB

• Lyutikov16: unreasonable magn. fieldrequired.

• ... and many more: Li+16, Yamazaki+16,Janiuk+16, Murase+16, Kimura+16,Veres+16

Shock-heateddisk,MRIactiveandactivelyaccretingontoBHS

Durationofaccretion(GRB)

Deaddisk

Tidallyheatedouterrim,MRIactive

BlackHoles

Catastrophic,fulldisk-heating

Steady-stateouterrimheating

Perna+16

• Are BBH mergers (short)GRB sources? → need more observations














Scenarii for GRB prompt emission

• Photospheric models (dissipative/non-dissipative)• Blackbody / shocks + synchrotron / geometry / τ � 1 dissipation

• Internal shocks• Shocks + Synchrotron / Self-Compton / magnetic fields

• External shock (?)• Synchrotron / Self-Compton


GRB dynamics and prompt emission models

Energy (Γ0 = E/Mc2 � 1) released in a volume ∼ R30 .

→ Jet expands/accelerates→ Reaches Γ ∼ Γ0

→ Dissipates (kinetic/magnetic) energy→ Decelerates

Γ(R) =

R/R0 if R < Rsat

Γ0 if Rsat < R < Rdec

(R/Rdec)−3/2 if Rdec < R.

• Photospheric models→ Dissipative photosphere (. 1010 cm)→ Non-dissipative photosphere (∼ 1010 cm)

• Internal shocks (∼ 1014 cm)

• External shocks (∼ 1016 cm)

107 108 109 1010 1011 1012 1013 1014 1015 1016 1017 1018

Radius approx. [cm]

101

102

Γ (

R)

Γ(R)∝R

Γ(R)∝R 0

∼Rphot

∼RIS

∼RES

Γ(R)∝R−3/2


Prompt emission models - Internal shocks

• Unsteady outflow → Γ & 100 shocks (τ � 1)→ accelerated particles,magnetic field, synchrotron

• Explains variability, broad nonthermal spectrum→ easy to calculate analytically

• Radiation from RIS ≈ tvarcΓ20 ≈ 3× 1014tvar,0Γ2

0,2 cm

• But: low efficiency, spectral index, dim photosphere → problems

• Zhang+11: ICMART: 2 step: highly magnetized ∼ RIS coll., thenmagnetic reconn. at . RES


https://arxiv.org/abs/1011.1197

Prompt emission models - Internal shocks

• Unsteady outflow → Γ & 100 shocks (τ � 1)→ accelerated particles,magnetic field, synchrotron

• Explains variability, broad nonthermal spectrum→ easy to calculate analytically

• Radiation from RIS ≈ tvarcΓ20 ≈ 3× 1014tvar,0Γ2

0,2 cm• But: low efficiency, spectral index, dim photosphere → problems• Zhang+11: ICMART: 2 step: highly magnetized ∼ RIS coll., then

magnetic reconn. at . RES

Credit: Bing Zhang



Prompt emission - photospheric models

• Energy released at the photosphere: τ = 1 ⇒Rphot = 6× 1012L52Γ−3

0,2 cm

• Non dissipative: geometry, Γ profile, fuzzy→ broadened Planck

• Fan+12: explains correlations

• Zhang+13: GRB 110721A: line of deathEp . 3.92kBT0 ≈ 4.7L

1/452 R

−1/20,7 MeV

• Rees+05: Dissipation below the photosphere (τ � 1)

• High efficiency, explains high Epeak & distr.

• Giannios08: magnetic dissipation• Beloborodov10, Vurm+11: n-p collisional

heating (+magnetic)• Meszaros+11: shocks @photosphere

• Jet simulations (Lazzati16) include more refined physicse-γ decoupling [see poster by Parsotan].

• Most likely model, but potentially violates emissionradius constraints Rdissip. > 1015−16 cm.

10-4 10-3 10-2 10-1 100 101 102 103100

101

102

103

104

10-6 10-5 10-4 10-3 10-2 10-1 100 101 102 103 104100

101

102

103

104

Black circles: Lv et al. 2012 sampleRed triangels: GRB 090902B

(a)

(b)

Black circles: Zhang et al. 2012 sampleRed triangles: GRB 090902B

L/1052 (erg/s)

E p (keV

)

50 51 52 53 54 550

1

2

3

4

5z=3.512

Log

Ep (1

+z) /

keV

Log Liso (erg s-1)

z=0.382




https://arxiv.org/abs/astro-ph/0412702






Prompt emission - photospheric models

• Energy released at the photosphere: τ = 1 ⇒Rphot = 6× 1012L52Γ−3

0,2 cm

• Non dissipative: geometry, Γ profile, fuzzy→ broadened Planck

• Fan+12: explains correlations

• Zhang+13: GRB 110721A: line of deathEp . 3.92kBT0 ≈ 4.7L

1/452 R

−1/20,7 MeV

• Rees+05: Dissipation below the photosphere (τ � 1)

• High efficiency, explains high Epeak & distr.

• Giannios08: magnetic dissipation• Beloborodov10, Vurm+11: n-p collisional

heating (+magnetic)• Meszaros+11: shocks @photosphere

• Jet simulations (Lazzati16) include more refined physicse-γ decoupling [see poster by Parsotan].

• Most likely model, but potentially violates emissionradius constraints Rdissip. > 1015−16 cm.

10-2 100 102 104 E [MeV]

1048

1049

1050

1051

E

L E

[

erg

s-1

]

εB=0

10−3

0.01

0.1

0.5

2

α=−1.2

Vurm+11

0

2×1052

4×1052

6×1052

8×1052

L iso

(erg

/s)

MCRaT light curveL13 approximation (/10)MCRaT peak energy

0

20

40

60

80

100

120

140

160

180

Peak

Frequency

(ke

V)

0 10 20 30 40 50Time since jet launch (s)

0.5

1.0

1.5

2.0

α

β

α 6

4

2

β

Lazzati+16










Prompt emission models - External shocks?

• Jet plows into ISM, decelerates, shocksform, B field enchanced, synchrotron

• Radiation fromRdec ≈ 6× 1016 E

1/353 n

−1/30 Γ

−2/30,2.5 cm

• Peak energy

Ep ∼ 800 ε2e,−1n

1/20 ε

1/2B,−1Γ4

0,2.5keV

• Invoked for afterglow

• Strong variability (tv ∼ 10−2 s) inprompt is difficult to explain

• May be relevant in unique cases(see talk by Yu)


Prompt emission models - External shocks?

• Jet plows into ISM, decelerates, shocksform, B field enchanced, synchrotron

• Radiation fromRdec ≈ 6× 1016 E

1/353 n

−1/30 Γ

−2/30,2.5 cm

• Peak energy

Ep ∼ 800 ε2e,−1n

1/20 ε

1/2B,−1Γ4

0,2.5keV

• Invoked for afterglow

• Strong variability (tv ∼ 10−2 s) inprompt is difficult to explain

• May be relevant in unique cases(see talk by Yu)

101

Time [s]

102

103

Ep

[keV

]

Burgess+15



Case study 1 - GRB 130427A

• Preece+14: first pulse -synchrotron lab

• Ep ∝ t−1 curvature: OK, L ∝ E 1.5p not OK

• L ∝ E 1.5p expanding shell synch.: OK, ⇒

Ep ∝ t−4 not OK→ no single model can explain these relations

• Kouveliotou+13: synchrotron/ no SSC, butE synch.max violated

Ackermann+14: no SSCAliu+14: VHE upper limitsLiu+13, Fraija+16: FS/RS + SSCVurm+14: pairs: synch. + external Comptonde Pasquale+16: long term obs.




http://adsabs.harvard.edu/abs/2014Sci...343...42A






Case study 2. - GW 150914-GBM

Assume: GW 150914 and GW 150914-GBM are related.A binary black hole merger produced a GRB.Ask: What can we learn about GRB prompt emission models? Veres+16

• M1=36 M�, M2=29 M�, MBH=62 M�

• a ≈ 0.67, z ≈ 0.09

• Gravitational radius:RG = GMBH/c

2 = 9.2× 106 cm

• Innermost stable radius → GRB launchingradius: R0 ≈ 3.5RG = 3.2× 107 cm.

• Best explanation: untriggered, short GRB [seetalk by Goldstein]

• Best fit spectrum: power law

• T ≈ 1 s, ∆Tγ−GW ≈ 0.4 s



GW 150914-GBM - Spectrum

• Fluence 2.4× 107 erg/cm−2 (40precentile of short GBM GRBs)

• Weak signal: only 2 spectralparameters can be constrained

• Spectrum: power law→ needs a cutoff (3 param.)

• Fix 1 out of 3 parameters

• MC sim. spectral parametersconsistent with data

• Conclusion: Epeak & 1 MeV(∼ 95%)

2 1 0 1αComp

10-7

10-6

Fluence

(1

0-1

00

0 k

eV

) [e

rg c

m−

2]

Epeak=1 MeV (fixed)

102 103 104 105

Epeak [keV]

αComp=-0.42 (fixed)


GW 150914-GBM - testing prompt emission models

• Non-dissipative photosphere:

EPHpk . 3.92× kT0 ≈ 0.6

(L

Lobs

)1/4 (R0R∗

)−1/2MeV ∼not OK

• Diss. phot. Epk . 10 MeV (for Lobs) OK

• Int. sh.: E ISpk . 0.1

(L

Lobs

)1/6 (∆R0

)−5/6dt

1/6−3 ε

1/2B ε

4/3e MeV. ∼not OK

• External shocks:Synchrotron emission, atRdec assuming εB ,εe(=0.5) get:n ∼ 10−3 cm−3 andΓ ∼ 2000

102 103 104

Γ

10-6

10-5

10-4

10-3

10-2

10-1

100

n [

cm−

3]

B= 0.1 G

B= 1.0 G

B= 10.0 GB=100.0 G

B=1000.0 G

R=1.0e+17 cm

R=1.0e+16 cm

R=1.0e+15 cm

tdec =

0.01 s

tdec =

1.00 st

dec =0.40 s

tdec =

0.10 s

Fν, p= 124 µJy

Fν, p= 242 µJyFν, p= 171 µJy

Ep =

1.0 MeV

Ep =

3.0 MeV


Jet composition - What carries the energy?

• Multiple methods for hints on jetscomponents

• Bromberg+14: T90 plateau → jetbreakout timescale ∼ 10s → baryondom.

• Zhang+10: BB non-detection in GRB080916C → σ & 20 [see also talk byRyde]

• Veres+14: modified initial acceleration:Γ ∝ Rµ, µ = 1/3-magnetic →µ = 1-baryonic jets










10−2

10−1

100

101

102

103

10−3

10−2

10−1

100

101

102

T90

dN

/dT

90

BATSE

Swi ft/3

Fermi/50










100 101 102 103 104 105 106 107

101

102

103

104

η = 200 T=1 keV σ= 15

η = 470 T=10 keV σ= 20

Tmax=50 keV; σ= 20

E [keV]

ν F ν

[keV

/cm

2 /s]

abcde










107 108 109 1010 1011 1012 1013 1014 1015 1016 1017 1018

Radius approx. [cm]

101

102

Γ (

R)

Γ(R)∝R

Γ(R)∝R 0

∼Rphot

∼RIS

∼RES

Γ(R)∝R−3/2

Drenkhahn+02,Meszaros+11,Bosnjak+12, McKinney+12,

Gao+15















107 108 109 1010 1011 1012 1013 1014 1015 1016 1017 1018

Radius approx. [cm]

101

102

Γ (

R)

Γ(R)∝R 1/3

Γ(R)∝R

Γ(R)∝R 0

∼Rphot

∼RIS

∼RES

Γ(R)∝R−3/2

Drenkhahn+02,Meszaros+11,Bosnjak+12, McKinney+12,

Gao+15










Jet composition from Epeak-T correlation

Observations:

• Ep ∝

L3µ−14µ+2 Γ

− 3µ−14µ+2

0 R

−5µ4µ+2

0 accel.

L−1/2 Γ30 coast

• T ∝

L14µ−5

12(2µ+1) Γ

2−2µ6µ+3

0 R− 10µ−1

6(2µ+1)0 accel.

L−5/12 Γ8/30 R

1/60 coast

• Ep ∝{

T6(3µ−1)(14µ−5) accel.

T 1.2 coast



Observations:

100 101 102 103

kT [keV]

100

101

102

103

104

Epeak

[keV

]

GRB 090719A

α=2.33±0.27µ=0.39±.01

100 101 102 103

kT [keV]

101

102

103

104

Epeak

[keV

]

GRB 130427A

α=1.02±0.05baryonic jet

• Ep ∝

L3µ−14µ+2 Γ

− 3µ−14µ+2

0 R

−5µ4µ+2

0 accel.

L−1/2 Γ30 coast

• T ∝

L14µ−5

12(2µ+1) Γ

2−2µ6µ+3

0 R− 10µ−1

6(2µ+1)0 accel.

L−5/12 Γ8/30 R

1/60 coast

• Ep ∝{

T6(3µ−1)(14µ−5) accel.

T 1.2 coast



Observations:

100 101 102 103

kT [keV]

100

101

102

103

104

Epeak

[keV

]

GRB 090719A

α=2.33±0.27µ=0.39±.01

100 101 102 103

kT [keV]

101

102

103

104

Epeak

[keV

]

GRB 130427A


Theory:

• Ep ∝

L3µ−14µ+2 Γ

− 3µ−14µ+2

0 R

−5µ4µ+2

0 accel.

L−1/2 Γ30 coast

• T ∝

L14µ−5

12(2µ+1) Γ

2−2µ6µ+3

0 R− 10µ−1

6(2µ+1)0 accel.

L−5/12 Γ8/30 R

1/60 coast

• Ep ∝{

T6(3µ−1)(14µ−5) accel.

T 1.2 coast



Observations:

100 101 102 103

kT [keV]

100

101

102

103

104

Epeak

[keV

]

GRB 090719A

α=2.33±0.27µ=0.39±.01

100 101 102 103

kT [keV]

101

102

103

104

Epeak

[keV

]

GRB 130427A


Theory:

• Ep ∝

L3µ−14µ+2 Γ

− 3µ−14µ+2

0 R

−5µ4µ+2

0 accel.

L−1/2 Γ30 coast

• T ∝

L14µ−5

12(2µ+1) Γ

2−2µ6µ+3

0 R− 10µ−1

6(2µ+1)0 accel.

L−5/12 Γ8/30 R

1/60 coast

• Ep ∝{

T6(3µ−1)(14µ−5) accel.

T 1.2 coast

GRB Name α (Ep ∝ Tα) Jet Type µ081224A 1.01± 0.14 baryonic −090719A 2.33± 0.27 magnetic 0.39±0.01100707A 1.77± 0.07 magnetic 0.42±0.01110721A 1.24± 0.11 baryonic −110920A 1.97± 0.11 magnetic 0.4±0.01130427A 1.02± 0.05 baryonic −

Veres+13, Burgess+14Peter Veres (UAH) Central engines and emission mechanism HSV 10/26/16 18 / 19



Conclusion

• Exciting times for GRB studies

• Direct information on central engine

• Confirm/reject binary BH CE

• GW obs. will constrain GRB models

• Jet composition


central engines and radiation mechanisms of gamma …veresp.web.elte.hu/stuff/veres_hsv16.pdfcentral...

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