Search for gravitational waves from Scorpius X-1 in the first Advanced LIGO observing run with a hidden Markov model

Abstract

Results are presented from a semicoherent search for continuous gravitational waves from the brightest low-mass X-ray binary, Scorpius X-1, using data collected during the first Advanced LIGO observing run. The search combines a frequency domain matched filter (Bessel-weighted $\mathcal{F}$-statistic) with a hidden Markov model to track wandering of the neutron star spin frequency. No evidence of gravitational waves is found in the frequency range 60--650 Hz. Frequentist 95% confidence strain upper limits, ${h}_{0}^{95%}=4.0\ifmmode\times\else\texttimes\fi{}1{0}^{\ensuremath{-}25}$, $8.3\ifmmode\times\else\texttimes\fi{}1{0}^{\ensuremath{-}25}$, and $3.0\ifmmode\times\else\texttimes\fi{}1{0}^{\ensuremath{-}25}$ for electromagnetically restricted source orientation, unknown polarization, and circular polarization, respectively, are reported at 106 Hz. They are $\ensuremath{\le}10$ times higher than the theoretical torque-balance limit at 106 Hz.