Searching for Gravitational Waves from Binary Inspirals with LIGO

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1 Searching for Gravitational Waves from Binary Inspirals with LIGO Duncan Brown University of Wisconsin-Milwaukee for the LIGO Scientific Collaboration Inspiral Working Group LIGO-G Z

2 S1 Binary Neutron Star Search Results B. Abbott et. al. Analysis of LIGO Data for Gravitational Waves from Binary Neutron Stars gr-qc/ , 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 M sun 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: R 90% < 1.7 x 10 2 per year per MWEG LIGO-G Z LIGO Scientific Collaboration - Inspiral Working Group 2

3 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 M sun binaries in galactic halo» Well modeled waveforms and theoretical population» Detection search and upper limit on rate LIGO-G Z LIGO Scientific Collaboration - Inspiral Working Group 3

4 S2 Binary Search Pipeline LIGO interferometers recorded data from Feb 14 Apr (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 LIGO-G Z LIGO Scientific Collaboration - Inspiral Working Group 4

5 S2 Binary Inspiral Search Sensitivity Average sensitivity to optimally oriented 2 x 1.4 M sun 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 LIGO-G Z LIGO Scientific Collaboration - Inspiral Working Group 5

6 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 LIGO-G Z LIGO Scientific Collaboration - Inspiral Working Group 6

7 Binary Neutron Star Templates Search for inspiral signals with matched filtering» Templates: 2 pn stationary phase waveforms 1.0 < (m 1,m 2 ) < 3.0 M sun» 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 LIGO-G Z LIGO Scientific Collaboration - Inspiral Working Group 7

8 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, χ 2» Small values of χ 2 indicate that ρ was accumulated in a manner consistent with an inspiral signal: If χ 2 < χ 2 * then record trigger at maximum ρ Triggers are clustered within duration of each template Multiple templates can trigger at same time LIGO-G Z LIGO Scientific Collaboration - Inspiral Working Group 8

9 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 Splitter Pick off Tune vetoes on playground then apply to inspiral triggers» See talk by Christensen and Shawhan LIGO-G Z LIGO Scientific Collaboration - Inspiral Working Group 9

10 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 LIGO-G Z LIGO Scientific Collaboration - Inspiral Working Group 10

11 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.) LIGO-G Z LIGO Scientific Collaboration - Inspiral Working Group 11

12 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 = N det / N inj Rate ] ( e(ρ * ) T ) -1 LIGO-G Z LIGO Scientific Collaboration - Inspiral Working Group 12

13 Playground Results: Pipeline Efficiency Detected Andromeda Injections Average L1 Sensitivity Detected Milky Way Injections Missed Andromeda Injections (Too far away) e = Average H1 Sensitivity LIGO-G Z LIGO Scientific Collaboration - Inspiral Working Group 13

14 Conclusions S1 result: R 90% < 1.7 x 10 2 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 LIGO-G Z LIGO Scientific Collaboration - Inspiral Working Group 14