Distances and Absolute Luminosities of Galactic X-Ray Sources

Abstract

Data from two soft X-ray surveys are combined to propose a distance scale for 20 X-ray sources. These are the bright sources that lie close to the galactic plane. A relationship between measured absorption and distance is derived by using supernova remnants with known distances for nearby objects and by requiring a rough symmetry about the galactic center for the distant sources. Based on this distance scale, the calculated absolute luminosities of the sources range from 10 ' to 10 ' ergs 5-'. The sources that have not been identified with supernova remnants tend to fall into two groups. One group has luminosities in excess of 10 ' ergs 5 -`, about the same strength as the sources found in the Magellanic Clouds. These strong sources lie in a loose cluster about the galactic center. A second group of sources have luminosities that average approximately 10 ergs s '. These weaker sources were detectable by our experiment out to a distance of only about 5 kpc from the Sun. The X-ray absorption data require that the relative amount of medium-weight elements in interstellar material be greater than that of the accepted cosmic abundances, or alternatively that the density of these elements increase in the region of the galactic center.