Reducing False Alarms in Searches for Gravitational Reducing False Alarms in Searches for Gravitational Waves from Coalescing Binary SystemsWaves from Coalescing Binary Systems

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Andrés C. RodríguezLouisiana State University

M.S. Thesis Defense Thesis Advisor: Professor Gabriela González

6.20.07LIGO-G070394-00-Z

• LIGO

• Sources of Gravitational Waves

• Data Analysis for Coalescing Binary Systems

• Methods to Reduce False Alarms - 2 Veto, r2 Test

• LIGO S3 Primordial Black Hole Search

• Conclusions

OutlineOutline

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Laser Interferometer Gravitational Wave Observatory (LIGO)Laser Interferometer Gravitational Wave Observatory (LIGO)

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s(t) = [Lx - Ly]/L

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LIGO SitesLIGO Siteslsc.orglsc.org

Hanford: two interferometers in same vacuum envelope - 4km (H1), 2km(H2)

Livingston: 4km (L1)

Generated with Google EarthTM6.20.07 04

Improved Sensitivity, Improved Sensitivity, LIGO Science RunsLIGO Science Runs

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• S1 Aug ‘02 - Sept ‘02

• S2 Feb ‘03 - April ‘03

• S3 Oct ‘03 - Jan ‘04

• S4 Feb ‘05 - March ’05

• S5 Nov ‘05 - current

7/9/2003 `LIGO Scientific Collaboration - Amaldi 2003

Sources of Gravitational WavesSources of Gravitational Waves

• periodic signals: pulsars

• burst signals: supernovae, gamma ray bursts

• stochastic background: early universe, unresolved sources

• compact binary coalescing (CBC) systems: neutron stars, black holes

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Crab pulsar (NASA, Chandra Observatory)

NASA, WMAP

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• General Relativity predicts the decay of the binary orbit due to the emission of gravitational radiation.

• Waveforms can be well approximated by 2nd order post-Newtonian expansion.

Non -spinning waveforms parameterized by: » masses: m1,m2, total mass M, or reduced mass » orbital phase & orientation » position in the sky: ,

Coalescing Binary SystemsCoalescing Binary Systems

• Effective Distance:

• Chirp Mass:

• Symmetric Mass ratio :

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Coalescing Binary Systems IICoalescing Binary Systems II

Matched Filtering Matched Filtering

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*

• Data stream searched using matched filtering between data & template waveform:

Effective Distance:

• Matched Filter:

• Characteristic Amplitude:

• Signal to Noise Ratio (SNR):

• Inspiral Trigger: &

• Data Collection

• Template Bank Generation: h(f)

• Matched Filter I: z(t), (t), ask > *

• 1st Coincidence (time, , Mc )

• Matched Filter 2: 2, r2 Test

• 2nd Coincidence (time, , Mc)

• Follow Up

Inspiral Inspiral Coincidence Coincidence

PipelinePipeline

*

,

Inspiral Trigger:

&

Methods to Reduce False Alarms I:Methods to Reduce False Alarms I:22 Veto Veto

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*2

Simulated Waveform vs False AlarmSimulated Waveform vs False Alarm

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Methods to Reduce False Alarms II:Methods to Reduce False Alarms II:rr22 Test Test

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• Use the r2 time series (2/p) as a method to search for excess noise.• Impose a higher r2 threshold (r*2) than the search employs.

» Count the number of time samples (t) above r*2 in a time interval (t*) before inferred coalescence

t = 0.9 sec

t*

r*2

*2

Methods to Reduce False Alarms IIMethods to Reduce False Alarms IIrr2 2 Test Result: S4 BNS SearchTest Result: S4 BNS Search

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Simulated Waveforms: 0% falsely dismissedFalse Alarms: 35%, 36% vetoed

rd r

t = 0.26 sec

rr22 Test Results: Test Results: Searches performed by CBC Group in the LSCSearches performed by CBC Group in the LSC

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• r2 test is included in current LIGO searches: S5 Low Mass (M < 35MSOL) 1 year

• Black hole composed with mass < 1.0 MSOL is believed to be a primordial black hole (PBH).

• They are compact objects may have formed in the early, highly compressed stages of the universe immediately following the big bang.

• Speculated to be part of the galactic halo or constituent of dark matter (small fraction).

• Binary system composed of two PBH’s will emit gravitational waves that may be detectable by LIGO.

• A PBH binary composed of 2 x 0.35 MSOL objects would have a coalescence frequency of 2023Hz and would spend about 22 seconds in LIGO’s sensitive band.

S3 Primordial Black Hole (PBH) Search IS3 Primordial Black Hole (PBH) Search I

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• Target Sources:

S3: October 3 - January 09: 2004

* Numbers in () represent time left after data used for tuning search.

S3 PBH Search IIS3 PBH Search II

• Coincidence Windows

• H1H2 Effective Distance Cut

, = 0.45

• Parameters Selected:

S3 PBH Search III - TuningS3 PBH Search III - Tuning

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• Effective SNR:

• Combined SNR:

S3 PBH Search IV - TuningS3 PBH Search IV - Tuning

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S3 PBH Search V: ResultS3 PBH Search V: Result

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• No triple coincident foreground candidate events or background events were found.• Number of double coincidences found ( ) consistent with measured background (+).

c2

• r2 test greatly reduces rate of false alarms in LIGO CBC searches.

• The r2 test be incorporated into future LIGO searches: S5 Low Mass (M < 35MSOL) 1 year.

• A search for primordial black hole binary systems (M < 1MSOL) in LIGO’s S3 run was performed with results consistent with measured background.

ConclusionsConclusions

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Prof. Gabriela González

Thesis Committee: Prof. James Matthews, Prof. David Young, Prof. Jorge Pullin

LSU-LIGO Group: Chad, Ravi, Rupal, Prof. Warren Johnson, Jake, Dr. Myungkee Sung, Prof. Joseph Giaime, Shyang, Andy W., Jeff, Dr. Romain Gouaty

CBC Group: Dr. Duncan Brown, Dr. Stephen Fairhurst, Dr. Eirini Messaritaki, Prof. Patrick Brady, Dr. Alexander Dietz, Drew Keppel

LSC: Prof. Peter Shawhan, Prof. Alan Weinstein, Prof. Laura Cadonati, Dr. John Whelan, Prof. Vicky Kalogera, Dr. Bill Kells

LSC and CBC Group for access to LIGO data

LSU Dept. of Physics & Astronomy, NSF, Alfred P. Sloan Foundation

This research has been supported by National Science Foundation grants: PHY-0135389, PHY-0355289.

Thank You!Thank You!

Extra SlidesExtra Slides

BNS WaveformBNS Waveform

PBH WaveformPBH Waveform

BBH WaveformBBH Waveform

SNRSNR

\xi^2\xi^2

InjectionInjection

Injection vs TriggerInjection vs Trigger

r^2 testr^2 test

r^2 exampler^2 example

r^2 - S3 BNSr^2 - S3 BNS

r^2 - S3 PBHr^2 - S3 PBH

r^2 - S4 BNSr^2 - S4 BNS

r^2 - S4 PBHr^2 - S4 PBH

r^2 - S5 BBH epoch 1r^2 - S5 BBH epoch 1

PipelinePipeline

S3 PBH - Effective Distance CutS3 PBH - Effective Distance Cut

Effective SNR - S3 PBHEffective SNR - S3 PBH

Tuning - S3PBHTuning - S3PBH