Searching for Gravitational Waves from Binary Inspirals with LIGO Duncan Brown University of...

Searching for Gravitational Waves fromBinary Inspirals with LIGO

Duncan BrownUniversity of Wisconsin-Milwaukee

for theLIGO Scientific Collaboration

Inspiral Working Group

LIGO-G030671-00-Z

LIGO-G030671-00-Z LIGO Scientific Collaboration - Inspiral Working Group 2

S1 Binary Neutron Star Search Results

• B. Abbott et. al. “Analysis of LIGO Data for Gravitational Waves from Binary Neutron Stars” gr-qc/0308069, submitted to PRD

• Searched total of 236 hours of LIGO data» Used LHO 4k and LLO 4k single IFO and double coincident data

• Average sensitivity to an optimal 2 x 1.4 Msun binary at r = 8» LLO 4k: 176 kpc, LHO 4k: 46 kpc

• No double coincident inspiral signals were found

• Loudest event found at r = 15.9 in LLO 4k» Not an inspiral signal: due to a photodiode saturation in the interferometer

Upper Limit: R90% < 1.7 x 102

per year per MWEG


S2 Analysis Goals

• Binary Neutron Star Search» Well modeled waveforms and known population» Detection search for non-spinning binaries» In absence of detection place upper limit on rate

• Binary Black Hole Search» Waveforms not well known, no population model» Search using waveforms from non-spinning BCV detection family» See talks by Cokelaer and Messaritaki

• Binary Black Hole MACHO search» Proposed population of ~ 0.5 Msun binaries in galactic halo» Well modeled waveforms and theoretical population» Detection search and upper limit on rate


S2 Binary Search Pipeline

• LIGO interferometers recorded data from Feb 14 – Apr 14 2003 (S2)

• Apply Data Quality cuts to raw data to obtain science segments

• Only use coincident data (either double or triple)

• Perform a triggered search of the coincident data

• Apply instrumental vetoes to inspiral triggers

• Demand coincidence between triggers from different interferometers

• Use time slides to determine threshold for desired background rate (Brady)

• Measure pipeline efficiency and set upper limit if no detection is made

• Tune the pipeline on playground data and then run the search on full data set


S2 Binary Inspiral Search Sensitivity

• Average sensitivity to optimally oriented 2 x 1.4 Msun neutron star binary at r = 8 in playground data:

» LLO 4k: 1.81 Mpc» LHO 4k: 0.90 Mpc» LHO 2k: 0.60 Mpc

• Sensitive to inspirals in» Milky Way» Magellanic Clouds» Andromeda» M33, M32, M110


Data Quality Cuts

• Good IFO data flagged as science mode by operators during run

• Extra information used in deciding what data to analyze:

» Exclude photodiode saturations» Exclude data without calibration lines» Exclude data with invalid timing» Exclude times with excess noise in LHO 4k


Binary Neutron Star Templates

• Search for inspiral signals with matched filtering» Templates: 2 pN stationary phase waveforms 1.0 < (m1,m2) < 3.0 Msun

» Generate bank for each chunk with maximum 3% loss in signal-to-noise

» Apply a low frequency cutoff of 100 Hz to data

» 15 x 256 sec data segments overlapped by 128 sec

» Median power spectral estimate using 15 segments


Generation of Inspiral Triggers

• Resample data to 4096 Hz and high pass above 90 Hz

• Compute median PSD for 15 segments of length 256 sec

• Matched filter templates to obtain signal-to-noise ρ

• If SNR ρ > ρ* compute template based veto, 2

» Small values of 2 indicate that ρ was accumulated in a manner consistent with an inspiral signal: If 2 < 2

* then record trigger at maximum ρ

• Triggers are clustered within duration of each template

• Multiple templates can trigger at same time


Instrumental Vetoes

• Construct vetoes to remove spurious inspiral triggers» Some inspiral triggers are due to “obvious” instrumental glitches» Look for explanation of spurious inspiral triggers in other channels

– Glitch monitors on auxiliary interferometer channels– Physical environment monitoring channels

Gravitational Wave Channel

Beam SplitterPick off

• Tune vetoes on playground then apply to inspiral triggers» See talk by Christensen and Shawhan


Trigger Coincidence Test

• Look for coincident triggers» Present in all interferometers» Coincident to within 11 ms between sites, 1 ms at the same site» Coincident in both mass parameters

• L and H detectors are not co-aligned, so ratio of effective distance varies

• Cannot use an amplitude cut on coincident signals

• Could use arrival time of signals» Obtain information about sky position

from time delay between sites» Will not be used in S2


Threshold Selection

• Time slide the data from one interferometer and look for coincidences between shifted and un-shifted interferometer

» Slide by longer than a chirp length» Any coincidences must be due to background, not events

• Pick signal-to-noise threshold, ρ* , so only get a coincident trigger 1 in 100 times

• Look for coincidence in un-shifted data» Any event above threshold has 99% chance of being an event

• Best result of search would be a detection!

• Follow up candidate events in other interferometer channels (auxiliary interferometer, PEM, etc.)


Upper Limit on the Rate

• In absence of detection, construct an upper limit on event rate

• Simulate a population of binary neutron stars

• Inject signals from population into data from all three LIGO interferometers

» Inject in software» Validated by hardware injections (Fairhurst)

• Determine efficiency, e, for detection of simulated signals at threshold ρ*

» Efficiency e = Ndet / Ninj

• Rate ] ( e(ρ*) T )-1


Playground Results: Pipeline Efficiency

e = 0.3044

Detected Milky Way Injections

Detected Andromeda Injections

Missed Andromeda Injections

(Too far away)

Average L1 Sensitivity

Average H1 Sensitivity


Conclusions

• S1 result: R90% < 1.7 x 102 per year per MWEG

• S2 binary neutron start search is almost complete» Final results will be under internal LSC review in January

• Two other searches underway that are not yet mature:» Non-spinning binary black hole search

» Search for binary black holes MACHOs in the galactic halo

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