The diffuse X-ray emission from the thin disk surrounding the Galactic mid-plane ( the so-called Galactic ridge ) was measured with RXTE PCA in order to determine the spatial extent , spectral nature , and origin of the emission .
Spatial examination of the diffuse emission in the central 30 ^ { \circ } of the plane in Galactic longitude reveals the presence of two components : a thin disk of full width \lesssim 0 ^ { \circ } .5 centered roughly on the Galactic mid-plane , and a broad component which can be approximated as a Gaussian distribution with FWHM of about 4 ^ { \circ } .
Assuming an average distance of 16 kpc to the edge of the galaxy , a scale height of about 70 pc and 500 pc is derived for the thin and broad disk components , respectively .
Spectral examination of the emission clearly reveals the presence of a hard power law tail above 10 keV and an emission line from He-like iron , indicating both thermal and possibly non-thermal origins for the diffuse emission .
The averaged spectrum from the ridge in the 3 - 35 keV band can be modelled with a Raymond-Smith plasma component of temperature \sim 2 - 3 keV and a power law component of photon index \sim 1.8 .
Based on this finding , 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 .

Motivated by the similarities between the characteristics of the thermal component of the Galactic ridge emission in our model and the thermal emission from supernova remnants ( SNRs ) , we discuss the origin of the thermal emission in terms of a population of SNRs residing in the Galactic disk .
We find that a SN explosion rate of less than 5 per century is adequate to power the thermal emission from the ridge .
The origin of the emission in the hard X-ray band modelled by a power law remains uncertain .
Possible contributions from non-thermal bremsstrahlung of cosmic ray electrons and protons , inverse Compton scattering of energetic electrons from ambient microwave , infrared , and optical photons , non-thermal emission from SNRs , and emission from discrete X-ray sources are discussed .
We speculate that bremsstrahlung of accelerated electrons and protons in SNR sites can play a significant role in producing the hard tail of the spectrum .
Moreover , their collisional losses can play a major role in the ionization of the ISM .