Gamma-ray pulsar glitches: a study of variability in Fermi-LAT data

Pulsars are generally acknowledged as very stable astrophysical rotators, and they gradually slow down by emitting radiation at the expense of their rotational energy. Occasionally, pulsars can undergo transient events called glitches, which consist in rapid changes in their rotational parameters and are often followed by a relaxation. During its first 15 years of operations, the NASA's Fermi Large Area Telescope (LAT) monitored the rotation of almost 300 gamma-ray pulsars and detected more than 100 glitches. On the other hand, radio observatories have detected almost 3300 radio pulsars and almost 600 glitches. In this thesis we analysed and compared the glitch activity among the gamma-ray and radio pulsar populations. Variability in the emission features correlated to glitches has been observed in a small family of radio pulsars and in the radio-quiet PSR J2021+4026, which is the only variable pulsar observed by the LAT. Here we present a novel analysis of the LAT gamma-ray pulsars consisting of a study of variability correlated with changes in the spin-down rate. We perform a maximum likelihood spectral analysis of the LAT data around detected glitches, aiming at measuring variations in the gamma-ray flux and spectral parameters. In order to study the variability in the shape of the pulse peaks, we fit the pulse profiles. This allows to infer information about variations at the state change, which ultimately relate to variations in the geometry of the emitting region