Tracking continuous gravitational waves from a neutron star at once and twice the spin frequency with a hidden Markov model

Abstract

Searches for continuous gravitational waves from rapidly spinning neutron stars normally assume that the star rotates about one of its principal axes of moment of inertia, and hence the gravitational radiation emits only at twice the spin frequency of the star, $2f_{\ast }$. The superfluid interior of a star pinned to the crust along an axis nonaligned with any of its principal axes allows the star to emit gravitational waves at both $f_{\ast }$ and $2f_{\ast }$, even without free precession, a phenomenon not clearly observed in known pulsars. The dual-harmonic emission mechanism motivates searches combining the two frequency components of a signal to improve signal-to-noise ratio. We describe an economical, semicoherent, dual-harmonic search method, combined with a maximum likelihood coherent matched filter, F-statistic, and improved from an existing hidden Markov model (HMM) tracking scheme to track two frequency components simultaneously. We validate the method and demonstrate its performance through Monte Carlo simulations. We find that for sources emitting gravitational waves at both $f_{\ast }$ and $2f_{\ast }$, the rate of correctly recovering synthetic signals (i.e., detection efficiency), at a given false alarm probability, can be improved by $\sim 10$%-70% by tracking two frequencies simultaneously compared to tracking a single component only. For sources emitting at $2f_{\ast }$ only, dual-harmonic tracking only leads to minor sensitivity loss, producing $\lesssim 10\%$ lower detection efficiency than tracking a single component. In directed continuous-wave searches where $f_{\ast }$ is unknown and hence the full frequency band is searched, the computationally efficient HMM tracking algorithm provides an option of conducting both the dual-harmonic search and the conventional single frequency tracking to obtain optimal sensitivity, with a typical run time of $\sim 10^3$ core-hr for one year's observation.

References in corpus (8)

• Advanced Virgo: a 2nd generation interferometric gravitational wave detector
• Advanced LIGO
• Recent searches for continuous gravitational waves
• Spinning down newborn neutron stars: nonlinear development of the r-mode instability
• Hidden Markov model tracking of continuous gravitational waves from a binary neutron star with wandering spin. II. Binary orbital phase tracking
• Cross-correlation search for continuous gravitational waves from a compact object in SNR 1987A in LIGO Science Run 5
• On the free-precession candidate PSR B1828-11: Evidence for increasing deformation
• Does the accreting millisecond pulsar XTE J1814-338 precess?

Cited by in corpus (6)

• Searches for Continuous-Wave Gravitational Radiation
• Search methods for continuous gravitational-wave signals from unknown sources in the advanced-detector era
• Status and perspectives of Continuous Gravitational Wave searches
• Applications of machine learning in gravitational wave research with current interferometric detectors
• Searches for Continuous Gravitational Waves from Supernova Remnants in the first part of the LIGO-Virgo-KAGRA Fourth Observing run
• Constraints on gravitational waves from the 2024 Vela pulsar glitch