An [ITAL]ASCA[/ITAL] Study of the W51 Complex

Abstract

We present the analysis of ASCA archival data from the Galactic source W51. The ASCA spectra show that the soft (kT ≲ 2.5 keV) X-rays are of thermal origin and are compatible with W51C being a single isothermal (kT ≃ 0.3 keV) supernova remnant at the far side of the Sagittarius arm. The ASCA images reveal hard (kT ≳ 2.5 keV) X-ray sources that were not seen in previous X-ray observations. Some of these sources are coincident with massive star-forming regions, and the spectra are used to derive X-ray parameters. By comparing the X-ray-absorbing column density with atomic hydrogen column density, we infer the location of star-forming regions relative to molecular clouds. There are unidentified hard X-ray sources superposed on the supernova remnant, and we discuss the possibility of their association.