An XMM-Newton view of M101 - II. Global X-ray source properties

Abstract

We present the global X-ray properties of the point source population in the grand-design spiral galaxy M101, as seen with XMM-Newton. 108 X-ray sources are detected within the D25 ellipse of M101, of which ~24 are estimated to be background sources. Multiwavelength cross-correlations show that 20 sources are coincident with HII regions and/or supernova remnants (SNRs), 7 have identified/candidate background galaxy counterparts, 6 are coincident with foreground stars and one has a radio counterpart. We apply an X-ray colour classification scheme to split the source population into different types. Approximately 60 per cent of the population can be classified as X-ray binaries (XRBs), although there is source contamination from background AGN in this category as they have similar spectral shapes in the X-ray regime. Fifteen sources have X-ray colours consistent with supernova remnants (SNRs), three of which correlate with known SNR/HII radio sources. We also detect 14 candidate supersoft sources, with significant detections in the softest X-ray band (0.3-1 keV) only. Sixteen sources display short-term variability during the XMM-Newton observation, twelve of which fall into the XRB category, giving additional evidence of their accreting nature. Using archival Chandra & ROSAT HRI data, we find that ~40 per cent of the XMM sources show long-term variability over a baseline of up to ~10 years, and eight sources display potential transient behaviour between observations. Sources with significant flux variations between the XMM and Chandra observations show a mixture of softening and hardening with increasing luminosity. The spectral and timing properties of the sources coincident with M101 confirm that its X-ray source population is dominated by accreting XRBs (abridged).