Searching for Gravitational-Wave Bursts

Isabel LeonorUniversity of Oregon

for the LIGO Scientific Collaboration (LSC)LIGO-G060528-01-Z

October 23, 2006 NSF Annual Review LIGO-G060528-01-Z 2

Gravitational-Wave Bursts: Sources and Searches

possible sources are core-collapse supernovae, coalescing compact binaries, gamma-ray burst (GRB) engines, soft gamma repeaters, ???

waveforms of gravitational-wave burst signals from these sources are unknown

untriggered search: perform an all-sky search using entire data set

triggered search: analyze data which are contemporaneous with astrophysical events observed by other experiments, e.g. GRBs found by satellite experiments

credit: Laura Whitlock,GSFC, NASA

SNR E0102-72NASA, Chandra, SAO, Hubble

ATNF, ATCF

Astrophysical sources:

Search methods:

GRB

October 23, 2006 NSF Annual Review LIGO-G060528-01-Z 3

Untriggered Search

October 23, 2006 NSF Annual Review LIGO-G060528-01-Z 4

Overview of the Most Mature Search Pipeline

measures signal power in time-frequency plane

signal time scale < 1 second frequency range of 64-1600

Hz for each interferometer,

WaveBurst searches for signals with power in excess of baseline noise

be seen in all three

interferometers with a combined, overall significance above a pre-determined WaveBurst threshold

be “coincident” in time at the three interferometers; have consistent amplitudes at H1 and H2; have consistent waveforms at the three interferometers

time-frequency plane

We require a candidate GW signal to:

WaveBurst algorithm:

We estimate the background rate by: shifting the LLO data stream relative to the LHO data streams, and then identifying events which pass the selection requirements

We analyze many auxiliary channels to decide on data quality cuts and vetoes

October 23, 2006 NSF Annual Review LIGO-G060528-01-Z 5

S4 Search Sensitivity for Sine-gaussian Waveforms sensitivity of search is measured by injecting burst-like waveforms, e.g. sine-gaussians, into data and performing search

hrss: root-sum-square strain amplitude of injected waveform

efficiency curves give a measure of the sensitivity of the search at different frequencies

e.g. at 153 Hz, 50% efficiency at hrss = 1.2e-21 strain/Hz1/2

h h t dt2

rss ( )

We also use other types of waveforms.Similar sensitivities expected for differentwaveforms with similar overall properties.

preliminary

October 23, 2006 NSF Annual Review LIGO-G060528-01-Z 6

S4 Search Results

set upper limit on rate of gravitational-wave bursts (90% C.L.):

No event candidates pass all cuts

paper in

preparation

90 0.15 events per dayR

WaveBurst significance cut

waveform consistency cut

preliminary

October 23, 2006 NSF Annual Review LIGO-G060528-01-Z 7

S4 rate upper limit:

S2 rate upper limit:

S1 rate upper limit:

Comparison of S4 Run Results to Published Results from Previous Runs

Rate exclusion curves forQ=8.9 sine-gaussian waveforms

90 0.15 events per dayR

90 0.26 events per dayR

90 1.6 events per dayR

published

published

paper in

prepara

tion

(S3 sensitivity: ~10e-20 strain/Hz1/2)publis

hed

preliminary

October 23, 2006 NSF Annual Review LIGO-G060528-01-Z 8

S5 Run Preliminary Burst Search Results

using a high threshold for WaveBurst search, no candidate GW events were found in S5 data up to October 8, 2006

low-threshold search will also be performed

S5 burst search sensitivity for low-threshold search is about a factor of 2 better than S4 sensitivity

e.g. at 153 Hz,50% efficiency of hrss = 5.8e-22 strain/Hz1/2

effi

cien

cy

Efficiency curves forQ=8.9 sine-gaussian waveforms

Still being tuned.

under internal review

October 23, 2006 NSF Annual Review LIGO-G060528-01-Z 9

Triggered Searches

October 23, 2006 NSF Annual Review LIGO-G060528-01-Z 10

Triggered Searches

analyze segments of data which coincide with astrophysical events observed by other experiments to look for associated gravitational-wave bursts

one can think of this as “pointing” the detectors at the target astrophysical source for short time intervals –-- this decreases the amount of background noise significantly

cosmic gamma-ray bursts (GRB) detected by satellite experiments

hyperflares from soft gamma repeaters (SGR) or magnetars detected by satellite experiments

crosscorrelate interferometer data streams in pair-wise manner to search for correlated signals

search for excess power in data spectrum

We currently use the following astrophysical events as triggers:

Analysis methods:

October 23, 2006 NSF Annual Review LIGO-G060528-01-Z 11

Gamma-ray Burst 030329 / SN2003dh (S2 Run)

Emergence of supernova spectrumHjorth, et al. 2003, Nature, 423, 847

HETE light curve for GRB 030329

bright and “nearby” GRB z = 0.1685, DL = 800 Mpc

510GW sunE Mpublished

Search of S2 LIGO data showed no GW burstsignal associated with this GRB. The measuredhrss upper limits correspond to an energy emitted in GW waves of:

GW c rss

cE D f h

G

32 2 2

We expect to improve on this!

October 23, 2006 NSF Annual Review LIGO-G060528-01-Z 12

39 GRB Triggers used to Search for GW Bursts in S2, S3, S4 Runs

S4 best hrss upper limit (150 Hz, linear polarization):

3.6 x 10-21 strain/Hz1/2

S3 best hrss upper limit(250 Hz, linear polarization):

2.5 x 10-20 strain/Hz1/2

S2 best hrss upper limit(250 Hz, linear polarization):

2.7 x 10-20 strain/Hz1/2paper in

preparation

We found no evidence for gravitational-waveburst signals associated with this GRB sample

preliminary

October 23, 2006 NSF Annual Review LIGO-G060528-01-Z 13

GRB Triggers for S5 Run

Swift satellite experiment was launched November 2004, started detecting GRBs

10 GRB triggers per month 117 GRB triggers for S5 as

of October 7, 2006 no evidence for GW bursts

associated with the GRB sample up to Aug. 1, 2006(unreviewed)

best S5 hrss limit so far (250 Hz, linear polarization):

1.7 x 10-21 strain/Hz1/2

unreviewed

using data up to Aug. 1, 2006

For a short-duration GRB at 100 Mpc, we might expect(for circular polarization):

2 32 2 24

5GW c rss

cE D f h

G

1GW sunE M

under internal review

October 23, 2006 NSF Annual Review LIGO-G060528-01-Z 14

coun

ts/s

ec

92.5 Hz

92.7 Hz (RHESSI)

92.5 Hz (RXTE)

Search for GW Signal Associated with December 2004 Hyperflare from SGR 1806-20

searched LIGO data for GW signal associated with quasi-periodic oscillations at different frequencies; no GW signal found the best hrss limit of 2.75 x 10-22 strain/Hz1/2 at f = 92.5 Hz corresponds to an isotropic energy release in gravitational waves of:

searches were also made at other frequencies: 150.3 Hz, 626.5 Hz, 1837.0 Hz

galactic neutron star with huge magnetic field at a distance of 7.5-15 kpc source of record gamma-ray flare on December 27, 2004 flares thought to be caused by “starquakes” – magnetic stresses cause crust to break and release energy had pulsating tail lasting 6 minutes – quasi-periodic oscillations found

25-100 keV (Watts and Strohmayer, 2006, ApJL, 637, L117)

81.6 10GW sunE M

under internal review

October 23, 2006 NSF Annual Review LIGO-G060528-01-Z 15

Other Ongoing Projects Related to Burst Searches

Joint analyses with GEO and Virgo Network analysis methods Q Pipeline KleineWelle Excess Power AstroBurst GRB population study

supernovae neutrinos other hyperflare events from soft gamma repeaters

In our zeal to dig out gravitational-wave signals from the data, we have developed several analysis projects and search algorithms, in various stages of maturity, among them:

For triggered searches, we plan to expand the astrophysical sourcesused as triggers, e.g.,

October 23, 2006 NSF Annual Review LIGO-G060528-01-Z 16

Summary

We have gained considerable experience in searching LIGO data for gravitational-wave bursts several published papers, more in the works

We perform both an all-sky, untriggered search, and searches triggered by astrophysical events detected by other experiments

There was about an order of magnitude improvement in sensitivity from the S2 to the S4 run

There is about a factor of 2 improvement in sensitivity from the S4 to the S5 run

The burst group is abuzz with activity as we continue to improve our search algorithms and develop methods to search for gravitational-wave bursts!