LIGO Document P2100405-v11

Search for gravitational waves from Scorpius X-1 with a hidden Markov model in O3 LIGO data

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P - Publications
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Results are presented for a semi-coherent search for continuous gravitational waves from the low-mass X-ray binary Scorpius X-1, using a hidden Markov model (HMM) to allow for spin wandering. This search improves on previous HMM-based searches of Laser Interferometer Gravitational-wave Observatory (LIGO) data by including the orbital period in the search template grid, and by analyzing data from the latest (third) observing run (O3). In the frequency range searched, from 60 to 500 Hz, we find no evidence of gravitational radiation. This is the most sensitive search for Scorpius X-1 using a HMM to date. For the most sensitive sub-band, starting at \( 256.06\,\rm{Hz} \), we report an upper limit on gravitational wave strain (at 95% confidence) of \( h_0^{95\%} = 6.16 \times 10^{-26} \), assuming the orbital inclination angle takes its electromagnetically restricted value of \( \iota = 44^\circ \). The upper limits on gravitational wave strain reported here are on average a factor of 0.33 lower than in the O2 HMM search. This is the first Scorpius X-1 HMM search with upper limits that reach below the indirect torque-balance limit for certain sub-bands, assuming \( \iota = 44^\circ \).
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CW search
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minor figure tweak.

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