Hidden Markov model tracking of continuous gravitational waves from a neutron star with wandering spin

S. Suvorova, L. Sun, A. Melatos, W. Moran, and R. J. Evans
Phys. Rev. D 93, 123009 – Published 17 June 2016

Abstract

Gravitational wave searches for continuous-wave signals from neutron stars are especially challenging when the star’s spin frequency is unknown a priori from electromagnetic observations and wanders stochastically under the action of internal (e.g., superfluid or magnetospheric) or external (e.g., accretion) torques. It is shown that frequency tracking by hidden Markov model (HMM) methods can be combined with existing maximum likelihood coherent matched filters like the F-statistic to surmount some of the challenges raised by spin wandering. Specifically, it is found that, for an isolated, biaxial rotor whose spin frequency walks randomly, HMM tracking of the F-statistic output from coherent segments with duration Tdrift=10d over a total observation time of Tobs=1yr can detect signals with wave strains h0>2×1026 at a noise level characteristic of the Advanced Laser Interferometer Gravitational Wave Observatory (Advanced LIGO). For a biaxial rotor with randomly walking spin in a binary orbit, whose orbital period and semimajor axis are known approximately from electromagnetic observations, HMM tracking of the Bessel-weighted F-statistic output can detect signals with h0>8×1026. An efficient, recursive, HMM solver based on the Viterbi algorithm is demonstrated, which requires 103 CPU hours for a typical, broadband (0.5-kHz) search for the low-mass x-ray binary Scorpius X-1, including generation of the relevant F-statistic input. In a “realistic” observational scenario, Viterbi tracking successfully detects 41 out of 50 synthetic signals without spin wandering in stage I of the Scorpius X-1 Mock Data Challenge convened by the LIGO Scientific Collaboration down to a wave strain of h0=1.1×1025, recovering the frequency with a root-mean-square accuracy of 4.3×103Hz.

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  • Received 7 April 2016

DOI:https://doi.org/10.1103/PhysRevD.93.123009

© 2016 American Physical Society

Physics Subject Headings (PhySH)

  1. Research Areas
  1. Physical Systems
Gravitation, Cosmology & Astrophysics

Authors & Affiliations

S. Suvorova1,2, L. Sun2,*, A. Melatos2,†, W. Moran1, and R. J. Evans3

  • 1School of Electrical and Computer Engineering, RMIT University, Melbourne, Victoria 3000, Australia
  • 2School of Physics, University of Melbourne, Parkville, Victoria 3010, Australia
  • 3Department of Electrical and Electronic Engineering, University of Melbourne, Parkville, Victoria 3010, Australia

  • *lings2@student.unimelb.edu.au
  • amelatos@unimelb.edu.au

See Also

Hidden Markov model tracking of continuous gravitational waves from a binary neutron star with wandering spin. II. Binary orbital phase tracking

S. Suvorova, P. Clearwater, A. Melatos, L. Sun, W. Moran, and R. J. Evans
Phys. Rev. D 96, 102006 (2017)

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Vol. 93, Iss. 12 — 15 June 2016

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