Searching for Gravitational Waves from Binary Inspirals with LIGO - PowerPoint PPT Presentation

Searching for Gravitational Waves from Binary Inspirals with LIGO Duncan Brown University of Wisconsin-Milwaukee for the LIGO Scientific Collaboration Inspiral Working Group LIGO-G030671-00-Z

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

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-G030671-00-Z LIGO Scientific Collaboration - Inspiral Working Group 3

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 LIGO-G030671-00-Z LIGO Scientific Collaboration - Inspiral Working Group 4

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-G030671-00-Z LIGO Scientific Collaboration - Inspiral Working Group 5

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-G030671-00-Z LIGO Scientific Collaboration - Inspiral Working Group 6

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-G030671-00-Z LIGO Scientific Collaboration - Inspiral Working Group 7

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-G030671-00-Z LIGO Scientific Collaboration - Inspiral Working Group 8

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-G030671-00-Z LIGO Scientific Collaboration - Inspiral Working Group 9

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-G030671-00-Z LIGO Scientific Collaboration - Inspiral Working Group 10

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-G030671-00-Z LIGO Scientific Collaboration - Inspiral Working Group 11

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-G030671-00-Z LIGO Scientific Collaboration - Inspiral Working Group 12

Playground Results: Pipeline Efficiency Detected Andromeda Injections Average L1 Sensitivity Average H1 Sensitivity Missed Andromeda Injections Detected (Too far away) Milky Way Injections e = 0.3044 LIGO-G030671-00-Z LIGO Scientific Collaboration - Inspiral Working Group 13

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-G030671-00-Z LIGO Scientific Collaboration - Inspiral Working Group 14