We present the analysis of ASCA archival data from the Galactic source W51. The ASCA spectra show that the soft (kT less than or similar to 2.5 keV) X-rays are of thermal origin and are compatible with W51C being a single isothermal (kT similar or equal to 0.3 keV) supernova remnant at the far side of the Sagittarius arm. The ASCA images reveal hard (kT greater than or similar to 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. References: 29
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