EDP Sciences
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Volume 420, Number 1, June II 2004
Page(s) 79 - 88
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20040061

A&A 420, 79-88 (2004)
DOI: 10.1051/0004-6361:20040061

The XMM-Newton and BeppoSAX view of the Ultra Luminous Infrared Galaxy MKN 231

V. Braito1, 2, R. Della Ceca1, E. Piconcelli3, 4, P. Severgnini1, L. Bassani3, M. Cappi3, A. Franceschini2, K. Iwasawa5, G. Malaguti3, P. Marziani6, G. G. C. Palumbo7, M. Persic8, G. Risaliti9, 10 and M. Salvati9

1  INAF - Osservatorio Astronomico di Brera, Milano, Italy
2  Dipartimento di Astronomia, Università di Padova, Italy
3  IASF - CNR, Bologna, Italy
4  XMM-SOC (VILSPA), ESA, Madrid, Spain
5  Institute of Astronomy, University of Cambridge, Madingley Road Cambridge CB3 OHA, UK
6  INAF - Osservatorio Astronomico di Padova, Italy
7  Dipartimento di Astronomia, Università di Bologna, Italy
8  INAF - Osservatorio Astronomico di Trieste, Italy
9  INAF - Osservatorio Astrofisico di Arcetri, Firenze, Italy
10  Harvard-Smithsonian Center for Astrophysics, Cambridge, USA

(Received 28 May 2003 / Accepted 15 January 2004)

We discuss XMM-Newton and BeppoSAX observations of MKN 231, the lowest-redshift Broad Absorption Line (BAL) QSO known so far and one of the best-studied Ultra Luminous Infrared Galaxies. By combining the XMM-Newton spectral resolution and the high-energy bandpass of BeppoSAX we have been able to study in more detail than previously possible its 0.2-50 keV spectral properties. The BeppoSAX PDS data unveiled, for the first time, a highly absorbed ( $N_{\rm H}\sim 2\times
10^{24}$  cm -2) power-law component. We find that: a) below 10 keV we are seeing only reprocessed radiation through reflection and/or scattering; b) the intrinsic 2-10 keV luminosity of MKN 231 is  $ 1^{+1.0}_{-0.5} \times
10^{44}$  erg s -1, i.e. more than an order of magnitude greater than previous measurements; c) the starburst activity significantly contributes to the soft ( E<2 keV) X-ray emission.

Key words: X-rays: galaxies -- galaxies: individual: Markarian 231

Offprint request: V. Braito, braito@brera.mi.astro.it

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