searching for gravitational waves bursts associated with...

default

Searching for gravitational waves bursts associatedwith Gamma-ray bursts

Michał Was

for the Virgo collaboration and LIGO scientific collaboration

Moriond, 2011 March 22

Michał Was (G1100070) Moriond, 2011 March 22 1 / 15

default

Outline

Gamma-ray bursts astrophysicsGravitational wave unmodeled burst data analysisResults from 2005-2007


default

Gamma-ray bursts

Observational definition → a burst of γ-raysDiscovered in the 70’s by nuclear bomb test surveillancesatellites

2 sec

long GRB

short GRB

[Paciesas et al., 1999]

T90 - duration of 90% ofphoton countsTwo observationalpopulations:

I short-hard GRBs T90 . 2 sspectrum peaks at higherenergy

I long-soft GRBs T90 & 2 sspectrum peaks at lowerenergy

GRB time/position distributed through GCN with ∼ minuteslatencyGamma-ray burst Coordinates Network


default

Gamma-ray burst models

credit: Ute Kraus

Long GRBs⇒ Massive rapidly spinning star

collapse and explosion(hypernova)Short GRBs

⇒ Coalescence of a neutron starand a compact object

I small fraction is actuallyneutron star quakes

Both cases: asymmetric,compact, relativistic⇒ good GW sourceMeasured gamma emission:∼ 1051 erg = 10−3 M�c2

Problem:typical distance ∼ 1 Gpc


default

Associated gravitational waves

Binary coalescence

Waveform mostly known⇒ Template matched filtering

Hypernova

0 10 20 30 40

-1

0

1

2

h[1

0-21

at 1

0 kp

c]

0 10-10

-5

0

5

s11A1O07 s11A3O13

[Dimmelmeier et al., 2008]

Waveform, amplitude uncertainMain emission mechanismunknown

⇒�� “Unmodeled” search


default

Assumed astrophysical scenario

Gamma Ray Burst→ relativistic jet with photon production→ photons beamed inside the jet coneRelativistic jet point at Earth→ progenitor axis of rotation points at EarthProgenitors are extra-galactic:

I short GRBs⇒ NS-NS or BH-NS coalescence?

I long GRBs⇒ collapse of massive star with rapid

rotation?GW radiation

I Nearly face on inspiralI Bar modes / clumps in nearly face on diskI BH/NS oscillations

(ringdown, SASI excitation, ...)

EGW . 10−2 M�c2


default

Burst data analysis

Signal which we look forstrong rotation axis ⇒ nearly circular GW polarization

60-500 Hz bandI Include main GW radiation scenarios (binary and bar modes)I GW energy sensitivity degrades as ∝ f 4 above ∼ 200 HzI Excludes BH/NS normal modes (∼ 1 kHz)

→ For EGW = 0.01 M�c2 at this frequency, horizon < 1 Mpcinstead of > 10 Mpc

duration . 1 secMethod

“Look for same signal in several detectors”⇒ Linear combinations that add/subtract signal⇒ Simple time-frequency decomposition⇒ Search for excess energy


default

Coherent analysis

2

1

Vetotime of flight~10 ms

t

h(t) 1 2-

1 2+


default

Time frequency maps

⇒ Concentrate signal energy ina small number of pixels


default

Clusters of excess energy

Cluster pixels with highest energySum energy in pixels forming cluster→ detection statistic

⇒ GW triggers

Sum Difference


default

Searching GW in association with GRBs

Gamma-ray burst observed by satellites (Swift, Fermi, ...)⇒ GCN: Gamma-ray bursts Coordinates Network

Known position and timePosition → simplify coherent analysis(time delays between detectors known)Reduced time → reduced background

⇒ Better sensitivity by a factor ∼ 2

Time coincidence between GRB and GW: window [−10,+1]min→ dictated by long GRB astrophysics (several sec for short GRBs)-1.5 h +1.5 h-600 s +max(T90,60s)

GRB triggerPrecursor?

on-source off-sourceoff-source

Konus lightcurve


default

collapse

precursor jet?

jet launch

precursor γ?

Main γ emission

PNS

BH formation?

jet break-out

≲100s ≲100s ≲100s

Internalshocks ?

precursor

γ-ray burst

≲100s

≋GW! ≋GW!

≋GW! ≋GW!

≋GW!

600s 300smax(T90,60s)

Time window

γ light curve


default

Results 2005–2007

137 GRB triggers analyzedAmplitude ↔ Energy

hrss =√∫

(h2+(t) + h2

×(t))dt

1D2 '

π2c3

Gf 20 hrss

2

EGW

Exclusion distance ∼ 15 MpcExpected number of eventswithin horizon

I Long GRBs: ∼ 10−6

I Short GRBs: ∼ 2× 10−5

I Sub-luminous GRBs: ∼ 10−3

Distance lower limit assumingEGW = 0.01 M�c2 at 150 Hz

[Abbott et al., 2010]


default

GRB 070201

GRB070201 error box[Mazets et al., 2008]

Short GRBs, reconstructed skylocation overlap with M31,(Andromeda 770 kpc)no GW found

⇒ Binary coalescence in M31 excludedat >99% confidence levelCompatible with

I Neutron star quake in M31 (Softgamma-repeater)

I Coalescence in galaxy behind M31

[Abbott et al., 2008]


default

Conclusions

Triggered GW searchesfactor ∼ 2 more sensitive than blind all-skyImmediate astrophysical interpretation,even for null resultsBecoming astrophysically relevantAnalysis of current 2009-2010 data nearlyfinished⇒ gain ∼ 2 in sensitivityAdvanced detectors (∼ 2015)⇒ gain ∼ 10 in sensitivity


default

References

Abbott, B. P. et al. (2008).IMPLICATIONS FOR THE ORIGIN OF GRB 070201 FROM LIGO OBSERVATIONS.Astrophys. J 681, 1419.

Abbott, B. P. et al. (2010).Search for gravitational-wave bursts associated with gamma-ray bursts using data from LIGO Science Run 5 and VirgoScience Run 1.Astrophys. J. 715, 1438.

Dimmelmeier, H., Ott, C., Marek, A. and Janka, H.-T. (2008).Gravitational wave burst signal from core collapse of rotating stars.Phys. Rev. D 78, 0654056.

Mazets, E. P. et al. (2008).A GIANT FLARE FROM A SOFT GAMMA REPEATER IN THE ANDROMEDA GALAXY (M31).Astrophys. J. 680, 545.

Paciesas, W. S. et al. (1999).THE FOURTH BATSE GAMMA-RAY BURST CATALOG (REVISED).Astrophys. J. Suppl. Ser. 122, 465.

Michał Was (G1100070) Moriond, 2011 March 22 i

searching for gravitational waves bursts associated with...

Documents