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XMM-Newton observations of the BL Lac MS0205.7+3509: a dense, low-metallicity absorber

D. Watson·B. McBreen·L. Hanlon·J. N. Reeves·N. Smith·E. Perlman·J. Stocke·T. A. Rector
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Abstract

The high-frequency-peaked BL Lac, MS0205.7+3509 was observed twice with XMM-Newton. Both X-ray spectra are synchrotron-dominated, with mean 0.2--10keV fluxes of 2.80+/-0.01 and 3.34+/-0.02 E-12 erg/cm^2/s. 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 ~9E21 cm^-2. A new optical spectrum is presented, with a MgII 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. MS0205.7+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 ~2" of the BL Lac.

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D. Watson, B. McBreen, L. Hanlon, J. N. Reeves, N. Smith, E. Perlman, J. Stocke, T. A. Rector. 2004-02-04. XMM-Newton observations of the BL Lac MS0205.7+3509: a dense, low-metallicity absorber. https://doi.org/10.1051/0004-6361%3A20034524

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