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

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

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

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 5

S2 Binary Inspiral Search Sensitivity

• Average sensitivity to
• ptimally 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

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

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

LIGO-G030671-00-Z LIGO Scientific Collaboration - Inspiral Working Group 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, χ2

» Small values of χ2 indicate that ρ was accumulated in a manner consistent with an inspiral signal: If χ2 < χ2

* 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 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-G030671-00-Z LIGO Scientific Collaboration - Inspiral Working Group 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-G030671-00-Z LIGO Scientific Collaboration - Inspiral Working Group 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-G030671-00-Z LIGO Scientific Collaboration - Inspiral Working Group 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 = Ndet / Ninj

• Rate ] ( e(ρ*) T )-1

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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

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

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