EDP Sciences
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Volume 418, Number 2, May I 2004
Page(s) 459 - 463
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20034524

A&A 418, 459-463 (2004)
DOI: 10.1051/0004-6361:20034524

XMM-Newton observations of the BL Lac MS 0205.7+3509: A dense, low-metallicity absorber

D. Watson1, 2, B. McBreen3, L. Hanlon3, J. N. Reeves4, 5, N. Smith6, E. Perlman7, 8, J. Stocke9 and T. A. Rector10, 11

1  Niels Bohr Institute, Astronomical Observatory, University of Copenhagen, Juliane-Maries Vej 30, 2100 Copenhagen Ø, Denmark
2  X-Ray Astronomy Group, Department of Physics and Astronomy, Leicester University, Leicester LE1 7RH, UK
3  Dept. of Experimental Physics, University College Dublin, Dublin 4, Ireland
4  Laboratory for High Energy Astrophysics, Code 662, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
5  Universities Space Research Association
6  Dept. of Applied Physics and Instrumentation, Cork Institute of Technology, Cork, Ireland
7  Joint Center for Astrophysics, University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA
8  Johns Hopkins University, Baltimore, MD 21218, USA
9  Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, CO 80309-0389, USA
10  National Optical Astronomy Observatory, 950 N. Cherry Ave., Tucson, AZ 85719, USA
11  University of Alaska, 3211 Providence Dr., BMB 212, Anchorage, AK 99508, USA

(Received 20 June 2003 / Accepted 26 January 2004 )

The high-frequency-peaked BL Lac, MS 0205.7+3509 was observed twice with XMM-Newton. Both X-ray spectra are synchrotron-dominated, with mean 0.2-10 keV fluxes of $2.80\pm0.01$ and $3.34\pm0.02\times10^{-12}$ erg cm -2 s -1. The X-ray spectra are well fit by a power-law with absorption above the Galactic value, however no absorption edges are detected, implying a low metallicity absorber ( $Z_{\sun} =
0.04^{+0.03}_{-0.01}$ ) or an absorber with redshift above one (best-fit z=2.1 for an absorber with solar abundances). In either case the absorbing column density must be ${\sim}9\times10^{21}$ cm -2. A new optical spectrum is presented, with a $\ion{Mg}{ii}$ absorption doublet detected at z=0.351, but no other significant features. The optical spectrum shows little reddening, implying a low dust to gas ratio in the absorber. MS 0205.7+3509 must therefore be viewed through a high column density, low-metallicity gas cloud, probably at z=0.351 and associated with the galaxy that has been shown to be within ${\sim}2$´´ of the BL Lac.

Key words: galaxies: BL Lacertae objects: individual: MS 0205.7+3509 -- galaxies: active -- X-rays: galaxies

Offprint request: D. Watson, darach@astro.ku.dk

SIMBAD Objects

© ESO 2004