Unidentified EGRET sources in the Galaxy

Identifying gamma-ray sources in the Galaxy is hampered by their poor localization, source confusion, and the large variety of potential emitters. Neutron stars and their environment offer various ways to power gamma-ray sources: pulsed emission from the open magnetosphere and unpulsed gamma rays from the wind nebula and from the cosmic rays accelerated in the supernova remnant. While the latter still awaits confirmation, new candidate associations bring forward the importance of 10-kyr old pulsars as GeV sources, with a diversity that will help constrain the acceleration mechanisms near the pulsar and in the wind. Theoretical interest in the gamma-ray activity of X-ray binaries and micro-quasars has also been revived by the emergence of a subset of variable sources in the inner Galaxy and another one in the halo.