searching for gravitational waves bursts associated with...
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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
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Outline
Gamma-ray bursts astrophysicsGravitational wave unmodeled burst data analysisResults from 2005-2007
Michał Was (G1100070) Moriond, 2011 March 22 2 / 15
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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
Michał Was (G1100070) Moriond, 2011 March 22 3 / 15
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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
Michał Was (G1100070) Moriond, 2011 March 22 4 / 15
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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
Michał Was (G1100070) Moriond, 2011 March 22 5 / 15
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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
Michał Was (G1100070) Moriond, 2011 March 22 6 / 15
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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
Michał Was (G1100070) Moriond, 2011 March 22 7 / 15
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Coherent analysis
2
1
Vetotime of flight~10 ms
t
h(t) 1 2-
1 2+
Michał Was (G1100070) Moriond, 2011 March 22 8 / 15
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Time frequency maps
⇒ Concentrate signal energy ina small number of pixels
Michał Was (G1100070) Moriond, 2011 March 22 9 / 15
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Clusters of excess energy
Cluster pixels with highest energySum energy in pixels forming cluster→ detection statistic
⇒ GW triggers
Sum Difference
Michał Was (G1100070) Moriond, 2011 March 22 10 / 15
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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
Michał Was (G1100070) Moriond, 2011 March 22 11 / 15
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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
Michał Was (G1100070) Moriond, 2011 March 22 12 / 15
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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]
Michał Was (G1100070) Moriond, 2011 March 22 13 / 15
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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]
Michał Was (G1100070) Moriond, 2011 March 22 14 / 15
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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
Michał Was (G1100070) Moriond, 2011 March 22 15 / 15
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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