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

## TL;DR

This study conducted a semi-coherent search for continuous gravitational waves from Scorpius X-1 using LIGO O1 data, employing a hidden Markov model to account for spin frequency wandering, but found no evidence of such waves.

## Contribution

It introduces a novel semi-coherent search method combining a matched filter with a hidden Markov model for detecting gravitational waves from low-mass X-ray binaries.

## Key findings

- No gravitational waves detected in the 60-650 Hz range.
- Upper limits on strain amplitude were established at 106 Hz.
- Upper limits are within an order of magnitude of the theoretical torque-balance limit.

## Abstract

Results are presented from a semi-coherent 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 (O1). 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, $h_0^{95\%} = 4.0\times10^{-25}$, $8.3\times10^{-25}$, and $3.0\times10^{-25}$ for electromagnetically restricted source orientation, unknown polarization, and circular polarization, respectively, are reported at 106 Hz. They are $\leq 10$ times higher than the theoretical torque-balance limit at 106 Hz.