Narrowband Searches for Continuous and Long-duration Transient Gravitational Waves from Known Pulsars in the LIGO-Virgo Third Observing Run

Isolated neutron stars that are asymmetric with respect to their spin axis are possible sources of detectablecontinuous gravitational waves. This paper presents a fully coherent search for such signals from eighteen pulsarsin data from LIGO and Virgo's third observing run (O3). For known pulsars, efficient and sensitive matched-filtersearches can be carried out if one assumes the gravitational radiation is phase-locked to the electromagneticemission. In the search presented here, we relax this assumption and allow both the frequency and the timederivative of the frequency of the gravitational waves to vary in a small range around those inferred fromelectromagnetic observations. We find no evidence for continuous gravitational waves, and set upper limits on thestrain amplitude for each target. These limits are more constraining for seven of the targets than the spin-down limitdefined by ascribing all rotational energy loss to gravitational radiation. In an additional search, we look in O3 datafor long-duration (hours-months) transient gravitational waves in the aftermath of pulsar glitches for six targetswith a total of nine glitches. We report two marginal outliers from this search, but find no clear evidence for suchemission either. The resulting duration-dependent strain upper limits do not surpass indirect energy constraints forany of these targets.