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Stochastic Background Search with VIRGO and GEO

4th ILIAS-GW Annual General Meeting Tuebingen , 8th and 9th October, 2007. Stochastic Background Search with VIRGO and GEO. G. Cella – INFN Pisa & VIRGO. Introduction. LSC and Virgo entered a data-sharing arrangement in Spring, 2007. Virgo VSR1 is just ended (October 1 st ).

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Stochastic Background Search with VIRGO and GEO

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  1. 4th ILIAS-GW Annual General MeetingTuebingen, 8th and 9th October, 2007 Stochastic Background Search with VIRGO and GEO G. Cella – INFN Pisa & VIRGO

  2. Introduction LSC and Virgo entered a data-sharing arrangement in Spring, 2007. Virgo VSR1 is just ended (October 1st ). • review of projected sensitivities to an isotropic stochastic background (with Virgo at design sensitivity) which have been reported in conjunction with a joint analysis of simulated data. • analysis that can be performed using the current data, taken in coincidence during LIGO’s 5th and Virgo’s 1st Science Run. • few considerations about targeted search Credits: C.N. Colacino, E. Cuoco, A. Di Virgilio, S. Mitra, T. Regimbau,E.L. Robinson, B.F. Whiting and J.T. Whelan

  3. Stochastic background search in a slide A stochastic background can be defined by the correlation it generates between two detectors: Overlap reduction function: the coherence between the detectors: SNR can be parametrized in the following way: In terms of a sensitivity integrand:

  4. Overlap reduction functions for the LSC/Virgo network The “envelope factor”: • LLO-LHO are 3× closer than LLO-Virgo and LHO Virgo pair • In spite of that projection effects make LIGO-Virgo pairs more favorable at higher frequencies.

  5. Stochastic sensitivity integrand at design H means here H1+H2 Pair H1-H2 not considered L-V and H-V pairs enhance network above 200 Hz. G-H and G-L don’t help as much because GEO is less sensitive But G-V adds to full network.

  6. Software injections: results Error bars = 1 Magnetar spectrum scaled up so detectable in 24 hr Signal recovered at a reasonable level in all pairs GWDAW proc arXiv:0704.2983 accepted by CQG Injection of a simulated magnetar spectrum.

  7. Sensitivity integrand: S5/VSR1 Including Virgo-LIGO pairs in the analysis now (S5/VSR1) can make a significant impact at high frequencies. the short-term benefit is modest (a slight improvement on the limit set with S4 LLO-ALLEGRO measurements) it will give us practical experience to be applied when Virgo achieves design sensitivity and lower frequencies [200 Hz,400 Hz] become accessible.

  8. Point source: RMS overlap reduction function The RMS amplitude is frequency independent Average over the sidereal time Depends on the declination LHO-LLO most sensitive except near poles Coherent network analysis should be investigated, but no qualitatively different results expected.  Δt 3000km Idea: use interference to “point” the network to a target. Basic observable:

  9. Conclusions • Despite their geographical separation, projection effects make LLO-Virgo and LHO-Virgo pairs more favorable for higher-frequency stochastic GW correlations than LLO-LHO. • Once Virgo achieves its design sensitivity, it will add significantly to the sensitivity of the global network to an isotropic stochastic background with support above 200 Hz. • Analysis of simulated data has illustrated the practical application of this method. • The Virgo-GEO pair can likewise play a significant role at these frequencies. • In the current run (S5 for LIGO; VSR1 for Virgo), the frequencies at which Virgo is closest to its design sensitivity are higher that those targeted in the simulation. • LIGO-Virgo pairs can make an immediate impact above 800 Hz, and the LSC & Virgo plan to perform a joint cross-correlation analysis to improve limits at these frequencies. • The experience gained will also be of use in subsequent observations at the frequencies which will become available with future improvements in Virgo sensitivity. [1] G. C. Cella et al, accepted by CQG; arXiv:0704.2983 [2] A. Lazzarini & R. Weiss, LIGO-T950018-02-E. S5 Sens LIGO-G070366-00-E. http://www.ligo.caltech.edu/jzweizig/distribution/LSC Data/ [3]M Punturo, VIR-NOT-PER-1390-51, Issue 10 (2004). http://www.virgo.infn.it/senscurve/ [4] GEO-600 theor noise budget, v4.0 w/250 Hz detuning. GEO-600 typical S5 Night & Weekend sensitivity. http://www.geo600.uni-hannover.de/geocurves/ [5] Virgo Calibration & Reconstruction Webpage, http://wwwcascina.virgo.infn.it/DataAnalysis/Calibration/ [6] B. Abbott et al (LSC), to appear in PRD; gr-qc/0703068

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