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The central region of M31 observed with XMM-Newton (I. Group properties and diffuse emission)

R. Shirey·R. Soria·K. Borozdin·J. P. Osborne·A. Tiengo·M. Guainazzi·C. Hayter·N. La Palombara·K. O. Mason·S. Molendi·F. Paerels·W. Pietsch·W. Priedhorsky·A. M. Read·M. G. Watson·R. G. West
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Abstract

We present the results of a study based on an XMM-Newton Performance Verification observation of the central 30 arcmin of the nearby spiral galaxy M31. In the 34-ks European Photon Imaging Camera (EPIC) exposure, we detect 116 sources down to a limiting luminosity of 6 x 10^35 erg/s (0.3--12 keV, d = 760 kpc). The luminosity distribution of the sources detected with XMM-Newton flattens at luminosities below ~ 2.5 x 10^37 erg/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 M31 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 M31, and we illustrate its extent in a wavelet-deconvolved image.

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R. Shirey, R. Soria, K. Borozdin, J. P. Osborne, A. Tiengo, M. Guainazzi, C. Hayter, N. La Palombara, K. O. Mason, S. Molendi, F. Paerels, W. Pietsch, W. Priedhorsky, A. M. Read, M. G. Watson, R. G. West. 2000-11-13. The central region of M31 observed with XMM-Newton (I. Group properties and diffuse emission). https://doi.org/10.1051/0004-6361%3A20000243

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