EDP Sciences
Free access
Volume 376, Number 2, September II 2001
Page(s) 413 - 421
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20011025

A&A 376, 413-421 (2001)
DOI: 10.1051/0004-6361:20011025

BeppoSAX spectroscopy of MR 2251-178: A test for ionized reflection in radio quiet QSOs

A. Orr1, 2, P. Barr1, M. Guainazzi3, A. N. Parmar1 and A. J. Young4

1  Astrophysics Division, Space Science Department of ESA, ESTEC, Postbus 299, 2200 AG Noordwijk, The Netherlands
2  Institut für Astronomie und Astrophysik Tübingen, Waldhäuser Str. 64, 72076 Tübingen, Germany
3  XMM SOC, VILSPA, Villafranca del Castillo, Spain
4  Department of Astronomy, University of Maryland, College Park, MD 20742, USA

(Received 20 March 2000 / Accepted 9 July 2001)

We present the 0.1-200 keV BeppoSAX spectrum of MR 2251-178 observed at two epochs in 1998 separated by 5 months. Both epochs show identical spectral shape and X-ray flux. Analysis of the combined spectra allow us to confirm the presence of the ionized Fe K$\alpha$ line detected by ASCA and to test the presence of reflection from ionized material. The best self-consistent spectral fit is obtained when including a contribution from a mildly ionized reflector ( $\xi_{0.01-100} \sim 1625 $ erg cm s-1, i.e. $U_{0.1-10} \sim 0.14$) with a reflection fraction $R_{\rm ion} \sim 0.11$. An exponential cut-off to the direct power-law continuum is then required at ${E} \sim 100$ keV. The low energy spectrum is absorbed by ionized matter with a column density $N_{\rm W} = (8.1_{-1.2}^{+2.1})
\times 10^{21}$ cm-2 and an X-ray ionization parameter $U_{0.1-10}= 0.06 \pm 0.01$. The warm absorber column is slightly lower than that measured with ASCA. This change could be caused by bulk motion. The BeppoSAX absorber ionization parameter globally agrees with the "U versus Flux" correlation found for MR 2251-178 with EXOSAT, Ginga and ASCA. This suggests that the absorber is in a state of instantaneous ionization equilibrium.

Key words: galaxies: active -- galaxies: quasars: individual -- X-rays: galaxies

Offprint request: A. Orr, aorr@astro.estec.esa.nl

SIMBAD Objects in preparation

© ESO 2001