Документ взят из кэша поисковой машины. Адрес оригинального документа : http://zebu.uoregon.edu/~uochep/talks/talks05/G050216-00.pdf
Дата изменения: Tue Mar 29 23:22:03 2005
Дата индексирования: Tue Oct 2 11:21:48 2012
Кодировка:

Searching for GRB-GWB coincidence during LIGO science runs

Isabel Leonor University of Oregon

LIGO-G050216-00-Z

Motivation
almost 40 years since GRBs were discovered past 15 years has been time of important "clues" isotropic and inhomogeneous distribution (BATSE); first optical, x-ray, radio counterparts; redshift measurements; association with core-collapse supernovae yet important questions remain as to origin, engine detection of coincident gravitational-waves would provide important information
March 23, 2005 Livingston, LA LSC Meeting I. Leonor

The first GRB detected (Klebesadel, Strong, Olson)

2

Motivation
take advantage of readily-available and readilyaccessible GRB triggers
some GRBs with measured redshifts z ~ 1, but most GRBs don't have measured redshifts reduces trials of search

use definite GRBs as triggers triggers are from Swift, HETE, INTEGRAL, others search optimized for short-duration GW bursts
~1 to ~10 ms, e.g. supernova core-collapse models, late stage of inspiral mergers

March 23, 2005 Livingston, LA

LSC Meeting I. Leonor

3

Motivation
Swift is up and running "catching GRBs on the fly"
"first GRB light" on December 17, 2004 has detected 23 GRBs since then expected average rate of >100 GRBs per year

prepare for S5 run
one year of coincident S5 run => ~100 GRB triggers more triggers means nearby GRB triggers more likely

March 23, 2005 Livingston, LA

LSC Meeting I. Leonor

4

Sequence of events for search (new for S4)
receive GCN (Global Coordinates Network)
RA, Dec, UT time

calculate GPS time and IFO-IFO time delay

submit condor jobs

search on-source segment for signal

search off-source segments (estimate probability)
March 23, 2005 Livingston, LA LSC Meeting I. Leonor 5

Search method -- crosscorrelation
each search segment is 180-seconds long, centered on GRB trigger time (less ~1.5 seconds at ends of segment) each 180-second segment conditioned (whitened and calibrated) use crosscorrelation windows of length 25 ms each, windows overlapping by half a window length calculate normalized crosscorrelation for each 25-ms second find largest crosscorrelation within each 180-second search segment, for H1-H2; find largest abs(cc) for H1L1 and H2-L1 due to unknown polarization
March 23, 2005 Livingston, LA LSC Meeting I. Leonor 6

sample GRB lightcurve (BATSE) trigger time

H1

H2

7

Time-of-flight delay change during on-source search

March 23, 2005 Livingston, LA

LSC Meeting I. Leonor

8

Data conditioning whitening and phase correction
DFT1 condition this segment DFT2

data conditioning done in frequency domain data DFTed using 1-second Tukey windows adjacent 1-sec segments DFTed to determine factor for whitening in frequency domain whitening factor(f) = max(DFT1(f),DFT2(f)) use phase calibration to correct signal phase

March 23, 2005 Livingston, LA

LSC Meeting I. Leonor

9

False alarm probability vs. integration length for short duration signals (~1 ~10 ms)
probability for getting median of simulated on-source distribution, given off-source distribution probability takes into account trials in search probability is function of length of crosscorrelation window small window: 1/sqrt(N); more trials large window: more noise integrated
March 23, 2005 Livingston, LA LSC Meeting I. Leonor 10

The S4/S3/S2 GRB Samples
S4: 6 GRBs with at least double coincidence (2 with redshift)
4 for H1-H2 3 for H1-L1 3 for H2-L1

S3: 11 GRBs with at least double coincidence (0 with redshift)
11 for H1-H2 1 for H1-L1 1 for H2-L1

S2: 29 GRBs with at least double coincidence (3 with redshift)
23 for H1-H2 7 for H1-L1 7 for H2-L1

only well-localized GRBs considered for H1-L1, H2-L1 search
March 23, 2005 Livingston, LA LSC Meeting I. Leonor 11

GRB Local Map for S4
F
2 +

=

Fв2

March 23, 2005 Livingston, LA

LSC Meeting I. Leonor

12

After-trials probability distribution
http://www.uoregon.edu/~ileonor/ligo/s4/grb/online/s4grbs_online.html

local off-source distribution determined for each IFO pair for each GRB trigger distribution determined from searches within science segments occurring within a few hours of GRB trigger largest crosscorrelation found in each on-source search indicated by black arrow probability is estimated using this distribution

March 23, 2005 Livingston, LA

LSC Meeting I. Leonor

13

S2 off-source distribution examples H1-H2

March 23, 2005 Livingston, LA

LSC Meeting I. Leonor

14

Hardware injections search (H1-H2)
looked at hardware injections using 10-second search duration (spacing of injections) instead of 180 seconds significant fraction had cc above after-trials distribution detection times consistent with injection times

March 23, 2005 Livingston, LA

LSC Meeting I. Leonor

15

Hardware injections search (H1-L1, H2-L1)

H1-L1 better "detection" rate than H1-H2 or H2-L1, as expected

H2-L1

March 23, 2005 Livingston, LA

LSC Meeting I. Leonor

16

What are the odds? Current S4 results
calculate after-trials probability using off-source distribution test sample distribution using K-S test (Kolmogorov-Smirnov) probability that measured statistic will be larger under null hypothesis: p = 0.70 consistent with null hypothesis
March 23, 2005 Livingston, LA LSC Meeting I. Leonor 17

What are the odds? Combined S2 and S3 probabilities

p = 0.81

March 23, 2005 Livingston, LA

LSC Meeting I. Leonor

18

Summary
developed scheme for searching for GRB-GWB coincidence in near real time looking forward to S5 run with ~100 GRB triggers in one year of coincident run performed search for short-duration GW bursts coincident with S4, S3, and S2 GRBs using crosscorrelation method sample probability distribution consistent with null hypothesis

March 23, 2005 Livingston, LA

LSC Meeting I. Leonor

19