Search for continuous gravitational waves from PSR J0437$-$4715 with a hidden Markov model in O3 LIGO data

Results are presented for a semi-coherent search for continuous gravitational waves from the millisecond pulsar PSR J0437$-$4715, using a hidden Markov model to track spin wandering, in LIGO data from the third LIGO-Virgo observing run. This is the first search for PSR J0437$-$4715 to cover a wide frequency range from $60$ Hz to $500$ Hz and simultanously accommodate random spin deviations from the secular radio ephemeris. Two searches are performed with plausible coherence times of $10$ days and $30$ days, as the frequency wandering time-scale of the gravitational-wave-emitting quadrupole is unknown. The former analysis yields no surviving candidates, while the latter yields five candidates after the veto procedure. The detection statistic of each of the five survivors is mapped as a function of sky position, in preparation for follow-up analyses in the future, e.g. during LIGO-Virgo-KAGRA fourth observing run.