The anti-glitching gamma-ray pulsar PSR J1522–5735

Context. A small number of pulsar glitches have been identified as anti-glitches or spin-down glitches, where the overall contribution to the pulsar’s rotation frequency is negative. A notable example of a spin-down glitch was observed in the rotation-powered pulsar PSR J1522–5735, a radio-quiet gamma-ray pulsar discovered by blind searches in the three-year data from the Fermi Large Area Telescope (LAT). Aims. This work aims to search for PSR J1522–5735’s glitches using Fermi-LAT data from over 15 years of observations. Methods. The weighted H-test statistic was applied to identify glitches and evaluate the related changes in pulsar’s spin parameters. The timing solution based on these results was further refined by maximisation of the unbinned likelihood. The Bayesian information criterion was used to set an appropriate number of parameters in the timing solution to avoid overfitting. Results. The analysis revealed eight glitch events: a regular spin-up glitch, a spin-up glitch over-recovered to a spin-down, and six anti-glitches. These events were radiatively quiet, exhibiting no significant variations in the shape of the pulse profile or energy flux. Conclusions. The results may suggest that an internal mechanism is responsible for spin-down glitch phenomena.