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Searching for gravitational wave bursts with the new global detector network

Searching for gravitational wave bursts with the new global detector network. Shourov K. Chatterji INFN Sezioni di Roma / Caltech LIGO Laboratory for the LIGO Scientific and Virgo Collaborations 7 th Eduardo Amaldi Conference on Gravitational Waves 2007 July 8-14 Sydney, Australia.

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Searching for gravitational wave bursts with the new global detector network

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  1. Searching for gravitational wave bursts with the new global detector network Shourov K. Chatterji INFN Sezioni di Roma / Caltech LIGO Laboratory for the LIGO Scientific and Virgo Collaborations 7th Eduardo Amaldi Conference on Gravitational Waves 2007 July 8-14 Sydney, Australia

  2. Abstract 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

  3. Overview • Benefits of joint data analysis • Agreement on joint data analysis • Previous studies based on coincidence methods • Investigations with simulated data • Current investigations with real data • Coherent methods for joint data analysis • Special case of collocated detectors • General case of multiple non-aligned detectors • Maximum likelihood statistics • Null stream consistency tests • Source reconstruction • Hierarchical search approach • Conclusions 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

  4. Benefits of a global network • Improved sky coverage • Less likely that event occurs in null of detector network • Improved duty cycle • More likely that at least one detector observes an event 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

  5. Benefits of a global network • Increased signal to noise ratio • Coherently sum signals from multiple detectors • Improved detection confidence • Multi-detector coincidence greatly reduces false rate • Coherent consistency tests can differentiate between gravitational-wave signals and instrumental glitches • Improved source reconstruction • “Inverse problem” requires three non-aligned detectors • Provides sky position and both polarizations of waveform • Permits comparison with theory • This is where the science is! • Shared best practices • Learn from each other’s approaches 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

  6. Agreement on joint data analysis • Recognizing the benefits of joint data analysis, the LIGO Scientific and Virgo collaborations have entered into an agreement to jointly analyze data from the GEO, LIGO, and Virgo detectors • Sharing of data started in May 2007 when Virgo commenced its first long science run in coordination with LIGO’s fifth science run • A joint run plan committee is coordinating detector operation and commissioning schedules to improve the prospects for detection • Joint data analysis meetings are already taking place • Joint data analysis exercises with simulated and small amounts of real data have already been performed for the inspiral, burst, and stochastic analysis 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

  7. H1 2.2 days 1.8 days 1.4 days 1.2 days 1.89 days 2.1 days 1.4 days V1 L1 Project 2b • ~72 hours of coincident data from the G1, H1, H2, L1, and V1 detectors from September 2006 (LIGO’s fifth science run and Virgo’s first weekly science run) • Data shifted in time by a secret amount • Perform “end to end” analysis using one of the methods • Produce upper limits for a variety of simulated burst signals • Study coherent methods • Identify options and issues for the upcoming joint analysis 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

  8. Coincident analysis • Applied the excess power search algorithm • Searches for statistically significant signals using a time-frequency decomposition of the data • Tests for coincident events between multiple detectors • Searched from 800 to 2000 Hz 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

  9. Pairwise coincident sensitivity • Based on previous investigations, we study the union of all pairwise coincident triggers • The detection threshold in each detector was set to maximize detection efficiency for all simulated waveforms at a false event rate of 1 uHz. • The resulting efficiencies are compared with the efficiency of using only the two 4km LIGO detectors. Preliminary results 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

  10. Preliminary sensitivities 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

  11. Coherent analysis Naturally handles arbitrary networks of detectors Coherent sum: Find linear combinations ofdetector data that maximizesignal to noise ratio data = response x signal + noise X = F h + n coherent null N-2 dimensionalnull space detector data Null sum: Linear combinations ofdetector data that cancelthe signal provide usefulconsistency tests. coherent sum 2 dimensionalsignal space 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

  12. c2 / DOF consistency with a GWB as a function of direction for a simulated supernova (~1 kpc) Interference fringes from combining signal in two detectors. • True source location: • intersection of fringes • c2 / DOF ~ 1 Coherent consistency tests • Coherent methods also off the possibility of consistency tests • Test null stream for consistency with noise over sky GWB: Dimmelmeier et al. A1B3G3 waveform, Astron. Astrophys. 393 523 (2002) , SNR = 20 Network: H1-L1-Virgo, design sensitivity 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

  13. Example consistency sky maps Simulated gravitational-wave burst Simulated coincident glitch 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

  14. Source position recovery • Given a statistically significant and consistent signal • What direction on the sky maximizes the coherent sum? • What direction on the sky minimizes the null stream? • Sky position estimates typically fall along rings of constant time delay between sites, leading to poor direction. • Other statistics or image processing techniques may be needed Null energy Enull varies slowly along rings of constant time delay with respect to any detector pair. Noise fluctuations often move minimum away from source location (pointing error) source location 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

  15. H1xL1 L1xH1xH2xV1xG1 Coherent sky position recovery example • Comparison of sky position recovery by Coherent WaveBurst algorithm for LIGO only and LIGO/GEO/Virgo networks. WILL BE REPLACED WITH SIMULATED DATA SKY POSITION RECOVERY EXAMPLE USING XPIPELINE APPROACH 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

  16. Timing based recovery of sky position 1 ms Gaussian signals recoveredwithin ~1 degree of true positionusing Gaussian matched filter andtiming based recovery of position Rings of constant time of arrivaldelay between detectors Source location Plane of detectors Mirror imagesource location 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

  17. Recovered signal (blue) is a noisy, band-passed version of simulated GWB signal (red) Network: H1-L1-GEO GWB: Zwerger-Muller A4B1G4, SNR=40 [Astron. Astrophys. 320 209 (1997)] Injected GWB signal has hx = 0. Recovered hx (green) is just noise. Waveform recovery • Given a statistically significant and consistent signaland a best guess sky position • Solve the matrix equation x = Fh + n for the waveforms h • Find the psuedo-inverse R such that RF = I 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

  18. Summary • Coincident and coherent analysis tools are now available to take advantage of data from networks of detectors • The union of pairwise coincident triggers from the LIGO/Virgo network provides an improvement in detection efficiency and coverage over the LIGO only network • Coherent methods naturally handle arbitrary networks of detectors and provide increased detection confidence, consistency tests, and parameter estimation. • Coincident and coherent analysis methods complement eachother and can be used as part of a hierarchical search • We are ready to start analyzing joint GEO, LIGO, and Virgo data 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

  19. Outlook • Current sensitivity of the LIGO and Virgo detectors 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

  20. End

  21. Initial joint working group • Need to plan for joint analysis as soon as possible • First meeting held in June 2004 • Investigations using simulated detector noise • Develop common language to describe searches • Learn from and gain confidence in search algorithms • Demonstrate ability to analyze each other’s data • Confront different sample frequencies, file formats, etc. • Quantify the benefit of the LIGO/Virgo network • Investigations using real detector noise • Investigations using real detector noise • Learn to handle data quality and veto information • Confront non-ideal behavior of real detectors • Identify options for future joint analysis 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

  22. Project 1A • 3 hours of simulated H1 and V1 detector noise • A variety of simulated waveforms: • Binary neutron star inspirals • Unmodeled Bursts: • Core-collapse supernovae • Gaussians • Sinusoidal Gaussians • Applied a variety of LSC and Virgo search algorithms • Characterized and compared search algorithm performance • Burst and inspiral results presented at GWDAW 9 and published in corresponding conference proceedings • Burst: Class. Quant. Grav. 22, S1293 (2005) • Inspiral: Class. Quant. Grav. 22, S1149 (2005) 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

  23. Project 1A burst results 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

  24. Project 1B • 24 hours of simulated triple coincident (H1, L1, and V1) data • Injection populations of simulated waveforms • Binary neutron star inspirals from M87 and NGC 6744 • Supernovae in the direction of the galactic center • Demonstrated benefit of union of two detector networks • Demonstrated sky position reconstruction and astrophysical parameter estimation • Joint burst and inspiral results presented at Amaldi 6 and published in corresponding conference proceedings • J. Phys. Conf. Ser. 32, 212 (2006) 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

  25. Project 1b results • For coincident searches, union of double coincident detector networks provides improved performance • Burst results for simulated supernovae in the direction of the galactic center at a 1 mHz false rate: • Inspiral results for simulated signals from M87 and NGC 6744 at an SNR threshold of 6: 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

  26. Timing based recovery of sky position 1 ms Gaussian signals recoveredwithin ~1 degree of true positionusing Gaussian matched filter andtiming based recovery of position Rings of constant time of arrivaldelay between detectors Source location Plane of detectors Mirror imagesource location 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

  27. Project 1 results • Comprehensive papers describing work on simulated data • Expand on previous work incorporating lessons learned • Burst: arXiV:gr-qc/0701026 • Investigate robustness over large signal space • Investigate intersection and union of algorithms • Inspiral: arXiV:gr-qc/0701027 • Detailed comparison of analyses pipelines • Bayesian estimation of source parameters 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

  28. Project 2a • First exchange of real data occurred on 2006 June 15 • ~3 hours of non-coincident G1, H1, and V1 data including: • Periods of lock loss • Periods of good and bad data quality • Hardware injections of burst and inspiral waveforms • Data quality and veto segment information also exchanged • Applied LSC and Virgo search algorithms • Results shared at a working group meeting on 2006 June 23-24 in Orsay, France 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

  29. Project 2b • ~72 hours of coincident data from the G1, H1, H2, L1, and V1 detectors from September 2006 (LIGO’s fifth science run and Virgo’s first weekly science run) • Data shifted in time by a secret amount • Perform “end to end” analysis using one of the methods • Produce upper limits for a variety of simulated burst signals • Study coherent methods • Identify options and issues for the upcoming joint analysis • Results to be presented at Amaldi7 in Sydney, Australia 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

  30. Coincident and coherent analysis • Coincident methods • Test for time and/or frequency coincidence between detectors • Performance constrained by least sensitive detector • Difficult to select detector dependent significant thresholdsfor optimal performance • Coherent methods • Test linear combinations of detector data based on: • Frequency dependent sensitivity of each detector • Expected response of each detector to gravitational waves from a particular direction on the sky • Naturally handles arbitrary numbers of detectors • Naturally handles detectors with different sensitivities • Three different applications of coherent methods: • Event detection • Consistency testing • Source reconstruction 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

  31. General case of non-aligned detectors • Y. Gursel & M. Tinto PRD 40 3884 (1989) • “Near Optimal Solution to the Inverse Problem for GWBs”. • Full solution requires at least three non-aligned detectors • First solution of the problem for the three detector case • Procedure: • Use a linear combination of time shifted signals from two detectors to predict the signal in the third detector • For each direction on the sky, compute the prediction error • Find the direction on the sky where the prediction error is minimized • Yields best fit sky position • Also yields both polarizations of gravitational waveforms • This is equivalent to the maximum likelihood approach 7th Amaldi Conference, Sydney, Australia, 2007 July 8-14

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