RXTE MEASUREMENT OF THE DIFFUSE-X-RAY EMISSION FROM THE GALACTIC RIDGE - IMPLICATIONS FOR THE ENERGETICS OF THE INTERSTELLAR-MEDIUM

The diffuse X-ray emission from the thin disk surrounding the Galactic mid-plane (the so-called Galactic ridge) was measured with RXTE PCA i n order to determine the spatial extent, spectral nature, and origin o f the emission. Spatial analysis of the emission in the central 30 deg rees of the plane in Galactic longitude reveals the presence of a thin component of width approximate to 0.degrees 2 and a broad component t hat can be approximated as a Gaussian distribution with FWHM of approx imate to 8 degrees. The spectrum can be interpreted as the superpositi on of the two spatial components with differing amount of absorption. Each spatial component can be modelled with a Raymond-Smith plasma com ponent of temperature similar to 2 keV and a power law component with photon index of similar to 2.5. Based on these findings, we argue that the temperature of the hot phase of the Interstellar Medium (ISM) is less than the previously reported values of 5 - 15 keV. We find that a supernova explosion rate of similar to 1 - 5 per century is adequate to power the thermal emission from the ridge. We discuss the origin of the emission in the hard X-ray band in terms of non-thermal bremsstra hlung of accelerated electrons and protons in supernova remnant (SNR) sites.