XMM-Newton Observations of the M31 Northern Disk: Properties of Selected X-Ray Sources and Unresolved Emission

We present the results of an XMM-Newton survey of the northern part of M31 disk. The X-ray properties of the 37 brightest sources are studied in detail. Combining the results of X-ray analysis with available data at other wavelengths, we were able to identify 19 out of 37 sources. Two sources in our sample were previously unknown: the hard X-ray source XMMU J004415.8+413057 and a transient supersoft source XMMU J004414.1+412206. We report on the discovery of X-ray pulsations from the source XMMU J004415.8+413057 with a period of 197 s. Three X-ray sources were identified with optical and radio SNR candidates. Five bright X-ray sources coincide with Galactic foreground stars. The properties of the remaining 18 bright X-ray sources detected in the survey are consistent with an AGN in the background of M31 and X-ray binaries belonging to M31. We report on the first unambiguous detection of the soft unresolved X-ray emission from the disk of M31. It follows the pattern of the spiral arms and can be traced up to the distance of ~10 kpc from the center of the galaxy. The spectrum of the unresolved emission shows dominant soft thermal component, which can be fit with a ~0.37 keV optically thin thermal plasma emission model or a combination of two thermal plasma models with temperatures of ~0.1 and ~0.7 keV. We suggest that significant part of the unresolved X-ray emission may represent hot diffuse gas and late-type stars in the disk of M31.