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1.3 PHYSICAL SCIENCES
Astrophysics and Astronomy
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.
Watson, D. et al., 2004. XMM-Newton observations of the BL Lac MS 0205.7+3509: A dense, low-metallicity absorber. Astronomy & Astrophysics, 418(2), pp.459–463. Available at: http://dx.doi.org/10.1051/0004-6361:20034524.