Search for gravitational waves from Scorpius X-1 in the second Advanced LIGO observing run with an improved hidden Markov model


B. P. Abbott, California Institute of Technology
R. Abbott, California Institute of Technology
T. D. Abbott, Louisiana State University
S. Abraham, Inter-University Centre for Astronomy and Astrophysics India
F. Acernese, Università degli Studi di Salerno
K. Ackley, Monash University
C. Adams, LIGO Livingston
R. X. Adhikari, California Institute of Technology
V. B. Adya, Max Planck Institute for Gravitational Physics (Albert Einstein Institute)
C. Affeldt, Max Planck Institute for Gravitational Physics (Albert Einstein Institute)
M. Agathos, University of Cambridge
K. Agatsuma, University of Birmingham
N. Aggarwal, LIGO, Massachusetts Institute of Technology
O. D. Aguiar, Instituto Nacional de Pesquisas Espaciais
L. Aiello, Gran Sasso Science Institute
A. Ain, Inter-University Centre for Astronomy and Astrophysics India
P. Ajith, Tata Institute of Fundamental Research, Mumbai
G. Allen, University of Illinois Urbana-Champaign
A. Allocca, Università di Pisa
M. A. Aloy, Universitat de València
P. A. Altin, The Australian National University
A. Amato, IN2P3 Institut National de Physique Nucleaire et de Physique des Particules
A. Ananyeva, California Institute of Technology
S. B. Anderson, California Institute of Technology
W. G. Anderson, University of Wisconsin-Milwaukee
S. V. Angelova, University of Strathclyde
S. Antier, Laboratoire de l'Accélérateur Linéaire
S. Appert, California Institute of Technology
K. Arai, California Institute of Technology
M. C. Araya, California Institute of Technology
J. S. Areeda, California State University, Fullerton
M. Arène, APC - AstroParticule et Cosmologie
N. Arnaud, Laboratoire de l'Accélérateur Linéaire

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We present results from a semicoherent search for continuous gravitational waves from the low-mass x-ray binary Scorpius X-1, using a hidden Markov model (HMM) to track spin wandering. This search improves on previous HMM-based searches of LIGO data by using an improved frequency domain matched filter, the J-statistic, and by analyzing data from Advanced LIGO's second observing run. In the frequency range searched, from 60 to 650 Hz, we find no evidence of gravitational radiation. At 194.6 Hz, the most sensitive search frequency, we report an upper limit on gravitational wave strain (at 95% confidence) of h095%=3.47×10-25 when marginalizing over source inclination angle. This is the most sensitive search for Scorpius X-1, to date, that is specifically designed to be robust in the presence of spin wandering.

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Physical Review D

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