We present a search for continuous gravitational-wave signals from an unidentified pulsar potentially powering HESS J1427-608, a spatially unresolved TeV point source detected by the High Energy Stereoscopic System (HESS). The search uses a semicoherent algorithm, which combines the maximum likelihood $\mathcal{F}$ statistic with a hidden Markov model to efficiently detect and track quasimonochromatic signals that wander randomly in frequency. It uses data from the second observing run of the Advanced Laser Interferometer Gravitational-Wave Observatory. Multiwavelength observations of the HESS source are combined with the proprieties of the population of TeV-bright pulsar wind nebulae to constrain the search parameters. We find no evidence of gravitational-wave emission from this target. We set upper limits on the characteristic wave strain $h_0^{95\%}$ (for circularly polarized signals) at 95% confidence level in sample subbands and interpolate it to estimate the sensitivity in the full band. We find $h_0^{95\%}=1.3\times {10}^{-25}$ near 185 Hz. The implied constraints on the ellipticity and $r$-mode amplitude reach $\epsilon \le {10}^{-5}$ and $\alpha \le {10}^{-3}$ at 200 Hz, respectively.

• Received 10 July 2022
• Accepted 4 October 2022

DOI:https://doi.org/10.1103/PhysRevD.106.103018