M.-A. Bizouard, F. Cavalier. GWDAW 8 Milwaukee 19/12/03

Transcription

1 Coincidence and coherent analyses for burst search using interferometers M.-A. Bizouard, F. Cavalier on behalf of the Virgo-Orsay group Network model Results of coincidence analysis: loose and tight coincidence Results of coherent analysis Comparison of all scenarios GWDAW 8 Milwaukee 19/12/03

2 Network of detectors For burst events a single detector can t claim for a GW discovery Need several ITF output to reject transient Coincidence with other kind of detectors (optical, ν, ) can help ITF Network: hypotheses of this study ITFs: Identical ITF sensitivity curves ITF Beam pattern and orientation Time delays between ITFs Up to 6 ITFs: Virgo, LIGO Hanford, LIGO Livingston, GEO, TAMA and AIGO Sources = Gaussian peak (width=1ms) and uniformly distributed in the sky Noise = Gaussian and white noise Filtering method: match filtering Monte Carlo simulations to estimate the efficiency versus false alarm rate curves (ROC)

3 h( t) F h ( t) + F h ( t) = + + Fx and F+ depend on detector location Source position Polarisation angle Ψ Network beam patterns x x Sky map = Ψ averaged beam pattern functions 2 2 F = F+ + F x LIGO maps similar by design Virgo and GEO more or less similar due to geometrical proximity Virgo and LIGO maps are orthogonal

4 Single ITF performance (Virgo) Beam Pattern Effect Selected Events Beam pattern effect on the GW SNR Virgo detection efficiency vs the source sky location

5 Coincidence Definition of a time window depending on time delay between detectors ij j i i j n. D D t = t t = c The source location is not known: loose coincidence ij ij t < t max +. η t ij RMS ( t ij max ~ 10ms...42ms) The source position is known: tight coincidence residual ij t <. η t ij RMS ij t RMS t ij RMS has been determined on simulation (SNR dependence): (<0.3 ms for SNR>5) ω 10 ~ 0.15ms 1ms SNR for SNR>6

6 Virgo-LIGO coincidence (loose) Request on 1/3 Twofold coincidence Good sky global coverage: average efficiency of 67% No more blind regions Coincidence less likely: ~ 20% for the 2 LIGO ~ 30% by adding Virgo Large regions almost blind

7 Loose coincidence in LIGO-Virgo network SNR opt =10 Best strategy: twofold coincidences (at least 2 among 3) Twofold coincidence is dominated by the 2 LIGO network (beam pattern matching) Single detector less efficient than coincidences Threefold coincidences are rare

8 Full network loose coincidence SNR opt =10 Twofold coincidence quite likely even at small false alarm rate Threefold coincidences also possible Larger coincidences much rarer

9 Full network tight coincidence Loose vs tight coincidence: - only few % of improvement in the region 1 false alarm per hour - 20% at very low false alarm rate For the Virgo-LIGO network very small improvement SNR opt =10

10 Coherent analysis Coherent statistics derived from a likelihood ratio (Pai, Bose & Dhurandhar (2001) method for coalescing binaries) General case: the source location is not known bank of N templates to cover the full sky for a Gaussian peak signal N goes 1/w 2 for w=1ms and MM=0.97 N ~ 5000 whatever the configuration (up to 6 ITFs)

11 Virgo-LIGO coherent analysis results Significant improvement in detection efficiency with respect to the coincidence case Efficiency remains above 60% for SNR opt = 10 even at a false alarm rate of 1 per week (35% for a twofold coincidence) Still no real hope to detect a weak signal (SNR opt = 5) in the 3 interferometer Virgo-LIGO network

12 Full network coherent analysis Clear enhancement of detection efficiencies by going from 3 to 6 ITFs Almost certain detection for SNR opt = 10 Still more than 80% SNR opt = 7.5 Efficiency remains SNR opt = 5 and below

13 Comparison Coherent/Coincident SNR = 10, False Alarm Rate = Single detector 39% OR strategy in Virgo-LIGO 69% OR strategy in full network 97% Twofold coincidence in Virgo-LIGO 52% Twofold coincidence in full network (loose) 90% Twofold coincidence in full network (tight) 93% Threefold coincidence in Virgo-LIGO 23% Threefold coincidence in full network (loose) 73% Threefold coincidence in full network (tight) 78% Coherent in Virgo-LIGO 78% Coherent in full network 99%

14 Coincident: This study has shown: No large increase of the efficiency when using tight coincidence Virgo-LIGO network: significant enhancement of the twofold efficiency when adding Virgo! One definitely gains more with a 6 ITFs network Increase of the network size is mandatory The sensitivity of the ITF in the network is also a fundamental parameter Virgo+LH4km+LL4km LH2km+LH4km+LL4km : Increase the false alarm rate by 2 orders of magnitude at equal efficiency! Coherent vs coincident: Coherent analysis is much more powerful than coincidence (even tight one) but is heavier to set up Future work: Improvement of the coincident analysis by introducing criteria about the main characteristics of the signal events?