Transcript 2.6E-21 Hz -1/2

Search for Gravitational-Wave Bursts
(GWBs) Associated with GRBs Using
LIGO Detectors
Isabel Leonor (for the LIGO Scientific Collaboration)
University of Oregon
Outline of GRB-GWB search
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search for short-duration GW bursts coincident with GRBs
use GRB triggers observed by satellite experiments
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Swift, HETE-2, INTEGRAL, IPN, Konus-Wind
search 180 seconds of LIGO data surrounding each GRB trigger
(on-source segment)
waveforms of GW signals associated with GRB are not known
use crosscorrelation to search for associated GW signal
crosscorr
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
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i
2
x
j j
x i yi
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2
y
k k
target short-duration GW bursts, ~1 ms to ~100 ms
use crosscorrelation lengths of 25 ms and 100 ms to target shortduration GW bursts
April 25, 2006 Dallas, TX
April APS Meeting I. Leonor
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The S4/S3/S2 GRB Sample
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S4: 4 GRBs with at least double coincidence
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S3: 7 GRBs with at least double coincidence
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7 for LHO 4km – LHO 2km
0 for LHO 4km – LLO 4km
0 for LHO 2km – LLO 4km
S2: 28 GRBs with at least double coincidence
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4 for LHO 4km – LHO 2km
3 for LHO 4km – LLO 4km
3 for LHO 2km – LLO 4km
24 for LHO 4km – LHO 2km
9 for LHO 4km – LLO 4km
9 for LHO 2km – LLO 4km
only well-localized GRBs considered for LHO – LLO search
April 25, 2006 Dallas, TX
April APS Meeting I. Leonor
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LIGO
IFO 1
counts/sec
sample GRB
lightcurve
(Swift)
trigger
time
use 180-second
LIGO on-source
data surrounding
GRB trigger
crosscorrelate
output of two IFOs
LIGO
IFO 2
look for largest
crosscorrelation
within 180-second
on-source segment
Estimating probability of measured on-source statistic:
sample off-source distribution using 25-ms cc length
April 25, 2006 Dallas, TX
April APS Meeting I. Leonor
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local off-source distribution
determined for each IFO pair
for each GRB trigger
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distribution determined from
searches within science
segments occurring within
a few hours of GRB trigger
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use time shifts to get enough
statistics
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largest crosscorrelation found
in on-source search
indicated by black arrow
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probability is estimated using
this distribution
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Results: Cumulative distribution of local probabilities
25-ms crosscorrelation length
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April 25, 2006 Dallas, TX
April APS Meeting I. Leonor
59 entries -- includes all
GRBs, all IFO pairs
expected distribution of
probabilities under null
hypothesis is uniform from
0 to 1
no loud event from any GRB
test this distribution against
null hypothesis
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Results: Cumulative distribution of local probabilities
100-ms crosscorrelation length
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April 25, 2006 Dallas, TX
April APS Meeting I. Leonor
59 entries -- includes all
GRBs, all IFO pairs
expected distribution of
probabilities under null
hypothesis is uniform from
0 to 1
no loud event from any GRB
test this distribution against
null hypothesis
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Statistical tests
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statistical search: search for weak signals which, individually, would
not comprise a detection, but together could have a cumulative
effect
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use binomial test to search local probability distribution for excess
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ranksum test: test if medians of on-source crosscorrelation
distribution and off-source crosscorrelation distribution are
consistent with each other
April 25, 2006 Dallas, TX
April APS Meeting I. Leonor
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Testing a probability distribution:
25-ms crosscorrelation length
search 25% of distribution
(15 most significant events)
the binomial test finds the most
significant excess in the tail
of the distribution to be 9 events
with p ≤ 0.104
final significance
of excess:
P = 0.48
April 25, 2006 Dallas, TX
April APS Meeting I. Leonor
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Testing a probability distribution:
100-ms crosscorrelation length
search 25% of distribution
(15 most significant events)
the binomial test finds the most
significant excess in the tail
of the distribution to be 9 events
with p ≤ 0.112
final significance
of excess:
P = 0.58
April 25, 2006 Dallas, TX
April APS Meeting I. Leonor
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Ranksum test
Note: This plot needs to be updated.
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compare medians of
on-source and off-source
crosscorrelation
distributions
significance under null
hypothesis is 0.22
crosscorrelation
April 25, 2006 Dallas, TX
April APS Meeting I. Leonor
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S2/S3/S4 hrss 90% upper limits for sine-gaussians
hrss 
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

2
h( t ) dt
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April 25, 2006 Dallas, TX
April APS Meeting I. Leonor
GW waveforms not
known
inject simulated sinegaussians into data to
estimate search
sensitivity
S4 best hrss limit
(150 Hz):
 2.6E-21 Hz-1/2
S3 best hrss limit
(150 Hz):
 1.2E-20 Hz-1/2
S2 best hrss limit
(250 Hz):
 2.6E-20 Hz-1/2
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Relating hrss sensitivity to an astrophysical
quantity
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Energy radiated in gravitational waves:
EGW
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3
c
2
 Mc 2  DL2 hrss
G
If there is a nearby GRB trigger…
For example, at distance of GRB with smallest measured redshift:
z = 0.0084, DL = 35 Mpc (GRB 980425/SN1998bw), an S4 hrss
sensitivity of 3E-21 Hz-1/2 for 250-Hz, Q=8.9 sine-gaussian, will
correspond to an energy release in GW of
or
April 25, 2006 Dallas, TX
EGW ~ 15 M
at 35 Mpc
EGW ~ 1 M
at 9 Mpc
April APS Meeting I. Leonor
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S5 GRB-GWB Search: Preliminary Results
April 25, 2006 Dallas, TX
April APS Meeting I. Leonor
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S5 GRB sample
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53 GRB triggers in 5 months of LIGO S5 run (as
of April 10, 2006)
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most from Swift
16 triple-IFO coincidence
31 double-IFO coincidence
6 short-duration GRBs
11 GRBs with redshift
 z = 6.6, farthest
 z = 0.0331, nearest
performed GW burst search using same pipeline
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No loud events seen that are inconsistent with expected
probability distribution
April 25, 2006 Dallas, TX
April APS Meeting I. Leonor
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S5 GRB-GWB preliminary sensitivity: upper
limits on hrss at 250 Hz
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90% UL on hrss
Q = 8.9, f = 250 Hz
sine-gaussian
S5 best hrss (so far):
1.5E-21 Hz-1/2
EGW ~ 4 M at 35 Mpc
EGW ~ 1 M
April 25, 2006 Dallas, TX
April APS Meeting I. Leonor
at 17 Mpc
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Summary
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We have performed a search for short-duration GW bursts
associated with GRBs detected by satellite experiments during
dates of LIGO’s S2, S3, and S4 runs
We found no evidence for GW bursts associated with GRBs using
this sample
Using simulated sine-gaussian waveforms, we have estimated the
search sensitivity and set 90% upper limits on the root-sum-square
strain amplitude, with a best hrss limit for the S4 run of ≈3E-21 Hz-1/2
at 250 Hz (EGW ~ 1Msun at 9 Mpc)
We are using the same method to search for GW bursts associated
with GRBs detected by Swift (mostly) during LIGO’s ongoing S5 run
The S5 GRB-GWB sensitivity at 250 Hz, i.e. 90% hrss upper limit, is
≈1.5E-21 Hz-1/2 (EGW ~ 1Msun at 17 Mpc)
April 25, 2006 Dallas, TX
April APS Meeting I. Leonor
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