Joint LIGO-Virgo data analysisInspiral and Burst

Summary of the first project results

Overview of the future activities

M.-A. Bizouard (LAL-Orsay)

on behalf of the LSC-Virgo working group

Hanford Livingston Virgo

Goals - introduction• Benefits of using multiple detectors

– Decrease false alarm– Increase sky coverage – Source location reconstruction with at least 3 detectors– Confirm or eventually kill a “golden” candidate

• Before real data joint analysis: many issues– Different search pipelines comparison– Different sampling rate and sensitivities– What are the expected benefits and performance of the network?– How well can we estimate signal parameters/source location

• Goal of the working group:– Address all the potential issues– Coincidence and coherent analysis– Define a strategy for a burst/inspiral discovery?

SIMULATED DATA!

Project Ia

Project Ib

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Coincidence search – simulated data set

• Noise: 24 hours of Virgo, Hanford and Livingston noise at nominal sensitivities

• Signals:– Inspiral: [1-3] M from 2 Galaxies

• NGC 6744 at 10 Mpc• M87 at 16 Mpc (Virgo cluster)Random polarization & orbital plane inclination2PN chirp inspiral generation

– Burst: Galactic center direction• 2 core collapse simulated waveforms• 2 Gaussian peaks• 2 CosineGaussiansRandom polarizationNormalization: only one event seen at SNR > 10In the 3 ITFs over 24 hours

.

Inspiral search

• Pipelines– Virgo: MultiBandTemplateAnalysis (MBTA) & flat search (Merlino)– LIGO: flat search

• Cross-check that all pipelines are working well and have similar performance running on Virgo and LIGO data.

• Solve few signal generation discrepancies: – G value must be the same– Chirps length must be computed in the same way at 2PN– inspiral end frequency definition: LSO or ISCO

Inspiral coincidence analysis resultsHanford-Livingston-Virgo network performance

• Single interferometer results:– SNR threshold at 6– False alarm rate 0.1 Hz

• Coincidence:– Require time and mass

coincidence

– Triple coincidence• False alarm in 24 hours: 0

– Double coincidence:• False alarm in 24 hours: 1• Adding Virgo gives ~25%

increase in efficiency for M87

H L V HLV

61% 62% 56% 75%

HL HV LV HLHVLV

42% 32% 30% 56%

MBTA efficiencies

M87(16 Mpc)

NGC 6744(10 Mpc)

HLV 24% 48%

quite high source locationoften possible!

M87

Inspiral source reconstruction

• Timing accuracy and binary parameters dependence issue• Improvement obtained by requesting a mass correlation between

the 3 ITFs template triggers (pseudo coherent follow up)

Without asking any mass correlation in The 3 ITFs triggers

Fitted direction using the sametemplate for the 3 ITFs

M87

NGC

Inspiral search – open issues

• Timing estimation bias observed in LIGO / Virgo pipelines– Signal: time domain generation both for Virgo and

LIGO data sets– Template: LIGO: stationary phase approximation

(frequency domain)Virgo: Fourier transform of time domain templates

• MBTA / LIGO SNR ratio

Burst search - pipelines

• Time frequency– Power Filter (PF), Q Transform (QT), Kleine Welle (KW)

• Time domain– Mean Filter (MF), Alternative Linear Fit Filter (ALF)

• Correlators– Gaussian templates (PC), Complex Exponential Gaussian templates (EGC)

A battery of filters used to cover a large variety of possible waveforms.

– Performance comparison: different efficiencies according to the waveform“robustness” tests

– Can we gain by combining the different filters? AND/OR analysis?

Burst LIGO-Virgo network sky coverageSource in the direction of the Galactic center

24 hours

Virgo and LIGO ITFs do not see the Galaxy centerat the same time …

is there an interest of coincidence analysis?

Burst SNR seen in each ITF as function of time

Burst coincidence search resultsperformance of the HLV network

HL HV LV HLHVLV

41% 22% 22% 60%

H L V63% 60% 55%

• Example: A2B4G1 waveform• Single interferometer results:

– Best efficiency among 5 filters– False alarm rate 0.1 Hz

(~10 000 FA per day)

• Coincidence:– Require time (and frequency)

coincidence– Double coincidence:

• False alarm: 10-6 Hz

– Triple coincidence:• False alarm: 10-6 Hz HLV

19%

Adding Virgo to LIGO increases the network efficiency by ~50%

efficiency

efficiency

efficiency

Burst AND/OR analysis (on-going work)

OR: can we “recover” events by combining several algorithm triggers?

PRELIMINARY!

At high FAR (0.1Hz) :small efficiency increase

At low FAR: no gain …

Filter “robustness” tests Goal: assess filters performance over a class of signals spanning the

duration, central frequency and frequency band parameters

Band passWhite noise + SineGaussian

• Some signal location depends on the parameter’s definition …• A filter can have different efficiency response depending on the waveform …

shows that the 3 parameters do not fully describe a signal and/or the response of a filter …

Example: PF signal SNR=10

DFM

Burst source location

• 2 “classical” methods using arrival time and SNR information of triple coincidence triggers. (χ2 minimization and likelihood maximization).– Comparison to be done!– Talks of F. Cavalier & S. Klimenko

Example: burst from GC using the χ2 method using triple coincidence events over 24 hours (HLV eff=19%)

GC: α GC = 266.4˚ δGC = -28.98˚

Rec: α GC = 266.4˚ +/- 0.70˚ δGC = -28.98˚ +/- 0.97˚

angular error ~ 1˚

Present activities

• 2 papers in preparation containing all results obtained so far

• Coherent analysis: under test and/or development

Burst: – 2 LIGO pipelines (Likelihood and NULL streams methods)– 1 Virgo pipeline (J. Sylvestre PRD 68 (2003))

Inspiral: – 1 LIGO pipeline – 1 Virgo pipeline – LIGO: coherent inspiral parameter estimation (Markov chains)

S. Klimenko talkA. Searle talk

S. Bose, S. Dhurandhar & A. Pai Int. J. Mod Phys D9, 25 (2000)}

The next project: real data exchange

• Project 1 demonstrates the benefits and the feasibility of a joint data analysis

• Pipelines are ready both in LIGO and Virgo

Project 2: real data analysis! – 2a : exchange of 3 hours of data for technical validation (S4 and C7 f.i.)– 2b: exchange of 24 hours of coincident real data

coincidence and coherent burst and inspiral searches face real noise issues!

However, many issues still open:– which data? (similar sensitivity? or at least above few hundreds of Hz)

when? wait for Virgo is back this spring!– joint data analysis coordination: the LSC-Virgo data analysis group– publication policy?– detector knowledge spreading enhancement?

Conclusions

• Inspiral and burst pipelines succesfully tested (up to source location reconstruction)!• Coincidence analysis shows clear benefits to add Virgo to LIGO network.• Coherent analysis in progress …

Work scientifically sound!

Consensus for real data exchange in the next years !

Political agreements to be signed

Good prospect for joint data set and analysis in 2006