Thermal X-Ray Emission with Intense 6.7-keV Iron Line from the Galactic Ridge

Abstract

Abstract An intense emission feature attributed to iron has been discovered in the unresolved excess emission along the galactic ridge. The mean line energy is 6.71 ±0.04 keV, which indicates emission from iron of helium-like ions. The observed spectra are in good agreement with that predicted from a model of thermal bremsstrahlung from an optically thin plasma. The temperature is found to vary from region to region in the range of KT=5–10 keV. The observed intensity distribution is consistent with a disk-shaped emission region with a scale height of 100–300 pc and a radius of 10 kpc. The average luminosity per unit surface area is estimated to be (2.4–2.8)× 1029 erg s−1 pc−2, giving a total luminosity of roughly 1038 erg s−1 for the whole disk. This excess emission is considered to be of discrete origin. Within the constraints imposed by the observational results, possible classes of sources are discussed, including white dwarf binaries, RS CVn’s, emission nebulae as well as unidentified supernova remnants .