The Cos-B GeV gamma-ray sources

COS-B has surveyed about 9 steradians of the sky along the entire Galactic plane and with some excursions at high latitudes. Using a likelihood analysis to search for point-like excesses above the diffuse gamma radiation born in the interstellar medium, 12 sources have been detected with high statistical significance to a flux level of about 10^-7 γ cm^-2 s^-1 between 300 MeV and 5 GeV. A list of 24 candidate sources has also been compiled which require confirmation at GeV or other energies. Only two sources have been clearly identified, namely the Vela and Crab pulsars. No other VHE candidate has been firmly seen by COS-B in the GeV range.

A striking analogy exists between Vela and Geminga in the 50 MeV-5 GeV range. They behave similarly, both in their variability over a time-scale of months and in their unusual hard spectrum, suggesting that Geminga be a Vela-type pulsar. Both sources are good candidates for detection by telescopes sensitive at a few hundred GeV.