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Volume 365, Number 1, January I 2001
First Results from XMM-Newton
Page(s) L195 - L201
DOI http://dx.doi.org/10.1051/0004-6361:20000243

A&A 365, L195-L201 (2001)
DOI: 10.1051/0004-6361:20000243

The central region of M 31 observed with XMM-Newton

I. Group properties and diffuse emission
R. Shirey1, R. Soria2, K. Borozdin3, J. P. Osborne4, A. Tiengo5, M. Guainazzi5, C. Hayter4, N. La Palombara6, K. Mason2, S. Molendi6, F. Paerels7, W. Pietsch8, W. Priedhorsky3, A. M. Read8, M. G. Watson4 and R. G. West4.

1  Department of Physics, University of California, Santa Barbara, Santa Barbara, CA 93106, USA
2  Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking RH5 6NT, UK
3  NIS-2, Space and Remote Sensing Sciences, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
4  Department of Physics & Astronomy, University of Leicester, Leicester LE1 7RH, UK
5  XMM-Newton SOC, VILSPA-ESA, Apartado 50727, 28080 Madrid, Spain
6  Istituto di Fisica Cosmica "G. Occhialini", Via Bassini 15, 20133 Milano, Italy
7  Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027, USA
8  Max Planck Institut für Extraterrestrische Physik, Giessenbachstraße, 85741 Garching bei München, Germany

(Received 7 October 2000 / Accepted 13 November 2000)

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 #1 10#2 erg s-1 (0.3-12 keV, d=760 kpc). The luminosity distribution of the sources detected with XMM-Newton flattens at luminosities below $\sim$ 2.5 1037 erg s-1 . 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 $\sim$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.

Key words: galaxies: individual: M 31 -galaxies: spiral -galaxies: general -galaxies: ISM -X-rays: galaxies

Offprint request: R. E. Shirey, shirey@xmmom.physics.ucsb.edu

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