Study of the gamma-ray state changes of PSR J2021+4026 with Fermi-LAT

The peculiar radio-quiet PSR J2021+4026, in the Gamma Cygni supernova remnant, is one of the brightest of the over 250 pulsars detected by Fermi-LAT. It is unique in being the only known isolated gamma-ray pulsar to undergo abrupt flux changes, which are also simultaneous with spin-down variations. The first change was observed by Fermi-LAT in October 2011, and it was followed by a recovery over a timescale of 100 days around December 2014. A second change occurred in February 2018. In the last few years, PSR J2021+4026 has been widely studied at different wavelengths. We report our latest results on this source, based on a Fermi-LAT analysis of its gamma-ray variability. In particular, we have studied the changes in the spectral and timing parameters on different timescales. Our results are essential to relate the observed events to changes in the geometry of the particle acceleration regions in the pulsar magnetosphere. Therefore, this study will allow us to enhance our knowledge of this source and its behavior.