Fermi view of the EGRET pulsars

Abstract

The six EGRET gamma ray pulsars are among the most interesting objects in the sky observed by Fermi: they are bright galactic gamma ray sources and they have good and updated timing solutions. EGRET has studied these pulsars up to an energy of 10 GeV, and at least for the brightest three it has analyzed the evolution of the emission with phase. The Large Area Telescope (LAT) on Fermi, thanks to its excellent sensitivity, has collected, in only one year, more photons then EGRET in its entire lifetime. The increased photon statistic and the outstanding timing capability, has allowed us to build detailed pulse profiles of all these six pulsars and to deeply study the changes of the emission spectrum with phase. Moreover we have obtained an excellent timing solution for Geminga using only gamma rays, and for all these pulsars we have observed that the emission spectrum is consistent with a power law with simple exponential cut-off. The study of the six EGRET pulsars with Fermi is therefore very important to improve our understanding of the pulsed gamma ray emission from neutron stars and, thanks to the very rich details of the analysis, it is a good test bench for different emission models.