SIMBAD references

We present the results of a study based on an XMM-Newton Performance Verification observation of the central 30' of the nearby spiral galaxy M 31. In the 34-ks European Photon Imaging Camera (EPIC) exposure, we detect 116 sources down to a limiting luminosity of 6x10³⁵erg/s (0.3-12keV, d=760kpc). The luminosity distribution of the sources detected with XMM-Newton flattens at luminosities below ∼2.5x10³⁷erg/s. We make use of hardness ratios for the detected sources in order to distinguish between classes of objects such as super-soft sources and intrinsically hard or highly absorbed sources. We demonstrate that the spectrum of the unresolved emission in the bulge of M 31 contains a soft excess which can be fitted with a ∼0.35-keV optically-thin thermal-plasma component clearly distinct from the composite point-source spectrum. We suggest that this may represent diffuse gas in the centre of M 31, and we illustrate its extent in a wavelet-deconvolved image.