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

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

Corresponding author: D. Watson, darach@astro.ku.dk

Received: 20 June 2003
Accepted: 26 January 2004

Abstract

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 and  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 () or an absorber with redshift above one (best-fit for an absorber with solar abundances). In either case the absorbing column density must be  cm^-2. A new optical spectrum is presented, with a absorption doublet detected at , 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 and associated with the galaxy that has been shown to be within ´´ of the BL Lac.