Bounding the strength of gravitational radiation from Sco-X1 C Messenger, V Re and A Vecchio on behalf of the LSC GWDAW 2004 Annecy, 15th – 18th December 2004

Scope of S2 analysis Frequentist upper-limit on GWs from Sco X-1 using a coherent frequency domain approach Using F-statistic as detection statistic (JKS 98) GWs at 2 frot (mass quadrupole, not r-modes) 2 frequency window: 464 – 484 Hz (reasonably disturbed) and 604 – 624 Hz (reasonably clean) Tobs = 6 hrs (set by computational resources) Analyse L1 and H1 in coincidence L1 6 hours, 1 filter H2 H1 L1 (whole S2) SCO X-1 GWDAW, Annecy 15th – 18th December, 2004

Analysis pipeline H1 F-Statistic L1 F-Statistic above threshold Selection of 6 Hour dataset S2 H1 data S2 L1 data Generate Orbital template Bank For L1 Generate Orbital template Bank For H1 S2 L1 data subset S2 H1 data subset H1 6 hour Template bank L1 6 hour Template bank Generate PDF’s Via MC injection Compute F statistic over bank of filters and frequency range Store results above “threshold” Compute F statistic over bank of filters and frequency range Store results above “threshold” H1 F-Statistic above threshold L1 F-Statistic above threshold Find Coincidence events Coincident Results Calculate Upper Limits per band Find loudest event per band Follow up candidates GWDAW, Annecy 15th – 18th December, 2004

Sco X-1 parameter space The latest observations of Sco X-1 were made by Steeghs and Cesares in 2001. They publish the following ephemeris for the low mass companion. The orbit is assumed circular (e<10-3) The projected orbital semi-major axis is (4.33+/-0.52) X 108 m The time of periapse passage (SSB frame) is 731163327+/-299 sec The GW frequency is not well known and the current model predicts two possible bands, (464<f0<484) and (604<f0<624) Hz. (Van Der Klis) GWDAW, Annecy 15th – 18th December, 2004

Computational Costs 2 weeks 6 hours Number of Orbital filters scales as Tobs3(Tobs<P), const(Tobs>P) Frequency filters scales as Tobs Code speed scales as Tobs The Computational time scales as Tobs5 Additional parameter space dimensions become important for Tobs>106 (inc spin up/down, period error, eccentricity) 2 weeks Using Tsunami (200 node Beowulf cluster) For 1 s errors In parameters 6 hours GWDAW, Annecy 15th – 18th December, 2004

Orbital templates Templates are laid in an approximately “flat” 2D space by choosing a sensible parameterisation. The template bank covers the uncertainty in the value of the projected semi-major axis and the time of periapse passage. The template placement is governed by the parameter space metric GWDAW, Annecy 15th – 18th December, 2004

The frequency resolution Using the projected metric to lay orbital templates takes advantage of frequency – orbital correlations. A mismatch in orbital parameters can be compensated for by a mismatch in frequency. We find 1/(5Tobs) is approximately continuous ? GWDAW, Annecy 15th – 18th December, 2004

Coincidence events The orbital template bank guarantees a >90% match with the closest filter. If a signal is detected in a detector we can therefore identify a region around an orbital filter within which the true signal is sure to lie. Now find the possible orbital filters in the second detector that could be the closest. The coincidence detection is based on geometric arguments only. Remember that the frequency could be mismatched up to +/- 15 frequency bins. ~200 possible coincident locations per event. GWDAW, Annecy 15th – 18th December, 2004

Understanding the search ARTIFICIAL DATA GWDAW, Annecy 15th – 18th December, 2004

Selecting the optimal 6hr We construct the following measure of detector sensitivity to a particular sky position GWDAW, Annecy 15th – 18th December, 2004

The current status We have analysed a 1/5 of the total parameter space S1 paper ~ 20 We have analysed a 1/5 of the total parameter space The preliminary results are consistent with statistics We are undergoing an LSC code review Getting a better understanding of the coincidence statistics Ready to set frequentist upper limits via Monte-Carlo injections into the data set. GWDAW, Annecy 15th – 18th December, 2004

Future work Short term targets Longer term targets Complete LSC code review (Organise growing number of codes + documentation) Analyse the entire search bandwidth (40 Hz) Longer term targets Implement a suitable veto strategy (Fstat shape test, Fstat time domain test, …) Follow up loudest candidate(s) and hopefully veto them out (observe for longer ?) Start applying our understanding to the incoherent stacking approach (Virginia Re, Greg Mendell) Apply the coherent approach to other LMXB’s (Dominic Kasprzyk) GWDAW, Annecy 15th – 18th December, 2004