Directed search for gravitational waves from Scorpius X-1 with initial LIGO data

Aasi, J. and Abbott, B. P. and Abbott, R. and Abbott, T. and Abernathy, M. R. and Acernese, F. and Ackley, K. and Adams, C. and Adams, T. and Addesso, P. and Adhikari, R. X. and Adya, V. and Affeldt, C. and Agathos, M. and Agatsuma, K. and Aggarwal, N. and Aguiar, O. D. and Ain, A. and Ajith, P. and Alemic, A. and Allen, B. and Allocca, A. and Amariutei, D. and Anderson, S. B. and Anderson, W. G. and Arai, K. and Araya, M. C. and Arceneaux, C. and Areeda, J. S. and Arnaud, N. and Bojtos, István Péter and Debreczeni, Gergely and Frei, Zsolt and Gergely, Árpád László and Gondán, László and Nagy-Egri, Máté Ferenc and Rácz, István and Raffai, Péter and Szeifert, Gábor and Tápai, Márton and Vasúth, Mátyás Zsolt (2015) Directed search for gravitational waves from Scorpius X-1 with initial LIGO data. PHYSICAL REVIEW D, 91 (6). ISSN 2470-0010

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Abstract

We present results of a search for continuously emitted gravitational radiation, directed at the brightest low-mass x-ray binary, Scorpius X-1. Our semicoherent analysis covers 10 days of LIGO S5 data ranging from 50-550 Hz, and performs an incoherent sum of coherent F-statistic power distributed amongst frequency-modulated orbital sidebands. All candidates not removed at the veto stage were found to be consistent with noise at a 1% false alarm rate. We present Bayesian 95% confidence upper limits on gravitational-wave strain amplitude using two different prior distributions: a standard one, with no a priori assumptions about the orientation of Scorpius X-1; and an angle-restricted one, using a prior derived from electromagnetic observations. Median strain upper limits of 1.3 x 10(-24) and 8 x 10(-25) are reported at 150 Hz for the standard and angle-restricted searches respectively. This proof-of-principle analysis was limited to a short observation time by unknown effects of accretion on the intrinsic spin frequency of the neutron star, but improves upon previous upper limits by factors of similar to 1.4 for the standard, and 2.3 for the angle-restricted search at the sensitive region of the detector.

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