Joint LIGO-Virgo data analysis Inspiral 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 HanfordLivingstonVirgo

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 } }

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 inclination 2PN chirp inspiral generation –Burst: Galactic center direction 2 core collapse simulated waveforms 2 Gaussian peaks 2 CosineGaussians Random polarization Normalization: only one event seen at SNR > 10 In 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 results Hanford-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 HLV HLVHLV 61%62%56%75% HLHVLV HL  HV  LV 42%32%30%56% MBTA efficiencies M87 (16 Mpc) NGC 6744 (10 Mpc) HLV24%48% quite high  source location often 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 same template 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 coverage Source in the direction of the Galactic center 24 hours Virgo and LIGO ITFs do not see the Galaxy center at the same time …  is there an interest of coincidence analysis? Burst SNR seen in each ITF as function of time

Burst coincidence search results performance of the HLV network HLHVLV HL  HV  LV 41%22% 60% HLV 63%60%55% Example: A2B4G1 waveform Single interferometer results: –Best efficiency among 5 filters –False alarm rate 0.1 Hz (~ FA per day) Coincidence: –Require time (and frequency) coincidence –Double coincidence: False alarm: Hz –Triple coincidence: False alarm: Hz HLV 19% Adding Virgo to LIGO increases the network efficiency by ~50% 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 pass White 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. ( χ 2 minimization and likelihood maximization). –Comparison to be done! –Talks of F. Cavalier & S. Klimenko Example: burst from GC using the χ 2 method using triple coincidence events over 24 hours (HLV eff=19%) GC: α GC = 266.4˚ δ GC = ˚ Rec: α GC = 266.4˚ +/- 0.70˚ δ GC = ˚ +/- 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 talk A. 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