Continuous and transient gravitational waves from neutron stars in the LIGO-Virgo Collaboration observing run O3

Gravitational-wave strain data recorded LIGO, Virgo, and Kagra may carry the imprint of galactic neutron stars as well as extragalactic merger transients. For example, isolated neutron stars that are asymmetric with respect to their spin axis are sources of continuous gravitational waves. Efficient and sensitive matched-filter searches can be carried out for known pulsars if one assumes the frequency and frequency time-derivative of gravitational radiation lie in a small range around those inferred from electromagnetic observations. We present searches for gravitational wave emission from known pulsars in data from LIGO and Virgo’s third observing run (O3). We find no evidence for continuous gravitational waves, but upper limits are more constraining for seven of the targets than the spin-down limit defined by ascribing all rotational energy loss to gravitational radiation.

In the aftermath of pulsar glitches, long-duration (hours–months) transient gravitational waves may be emitted due to r-mode oscillations excited by the glitch. We also search for gravitational wave emission due to r-modes in the epochs between glitches of PSR J0537-6910, a young energetic X-ray pulsar, making use of timing ephemeris obtained from NICER data. Our upper limits place stringent constraints on theoretical models for an r-mode driven spin-down in PSR J0537-6910, especially for high frequencies at which our results probe below the spin-down limit.