The IBIS/ISGRI Survey of the Galactic Plane - Global Characteristics of the Gamma-Ray Sources

INTEGRAL is the first gamma-ray astronomy mission with a sufficient sensitivity and angular resolution combination appropriate to the detection and identification of considerable numbers of gamma-ray emitting sources. The large field of view enables INTEGRAL to survey the Galactic Plane on a regular (∼weekly) basis as part of the core programme. The first source catalogue, based on the 1st year of core programme data (∼5 Msec) has been completed and published (Bird et al. 2004). It contained 123 γ-ray sources (24 HMXB, 54 LMXB, 28 “unknown”, plus 17 others) - sufficient numbers for a reasonable statistical analysis of their global properties. The detection of previously unknown γ-ray emitting sources generally exhibiting high intrinsic absorption, which do not have readily identifiable counterparts at other wavelengths, is intriguing. The substantial fraction of unclassified γ-ray sources suggests they must constitute a significant family of objects. In this paper we review the global characteristics of the known galactic sources as well as the unclassified objects.