Faint X‐Ray Sources Resolved in the ASCA Galactic Plane Survey and Their Contribution to the Galactic Ridge X‐Ray Emission

The X-ray emission from the central region of the Galactic plane, |l|<45 degand |b|<0.4 deg, was studied in the 0.7-10 keV energy band with a spatialresolution of ~3' with the ASCA observatory. We developed a new analysis methodfor the ASCA data to resolve discrete sources from the extended Galactic ridgeX-ray emission (GRXE). We resolved 163 discrete sources with a flux down to10^-12.5 ergs cm^-2 s^-1 and determined the intensity variations of the GRXE asa function of the Galactic longitude with a spatial resolution of ~1 deg. Thelongitudinal variation of the GRXE in the energy band above 4 keV shows a largeenhancement within |l|<30 deg. This suggests a strong enhancement of X-rayemissivity inside the 4-kpc arms. Searches for identifications of the resolvedsources with cataloged X-ray sources and optical stars show that the 66% areunidentified. Spectral analysis of each source shows that a large number of theunidentified sources have hard X-ray spectra. We classified the sources intoseveral groups according to the spectra and analyzed the spectra summed withineach group. Possible X-ray origins of these sources are discussed based on thegrouping analysis. Also, we derived the LogN-LogS relations of the resolvedsources in the energy bands below and above 2 keV. The obtained LogN-LogSrelation of the Galactic X-ray sources above 2 keV is represented by apower-law with an index of -0.79+/-0.07. This flat LogN-LogS relation suggeststhat the spatial distribution of the sources should have an arm-like structurein which the Solar system is included. The integrated surface brightness of theresolved sources is about 10% of the total GRXE in both energy bands. Theapproximately 90% of the emission remaining is still unresolved.Comment: 54 pages, 12 figures, accepted for publication in ApJ Supplements Serie