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Paper: Properties and Evolution of the Highly Ionized Gas in MR 2251−178
Volume: 311, AGN Physics with the Sloan Digital Sky Survey
Page: 333
Authors: Kaspi, S.; Netzer, H.; Chelouche, D.; George, I.M.; Turner, T.J.; Nandra, K.
Abstract: We present the first XMM-Newton observations of the radio-quiet quasar MR 2251-178. We model the X-ray spectrum with two power laws, one at high energies with a slope of Γ = 1.6 and the other to model the soft excess with a slope of Γ = 2.9, both absorbed by at least two warm absorbers (WAs). The high-resolution grating spectrum shows emission lines from N VI, O VII, O VIII, Ne IX, and Ne X, as well as absorption lines from the low ionization ions O III, O IV, and O V. A study of the spectral variations in MR 2251-178 over a period of 8.5 years yields that all X-ray observations can be fitted with the above model. Luminosity variations over timescales of years seem to correlate with the soft excess variations but not with the WA properties' variations. The overall picture is that of a stratified WA that enters and disappears from the line-of-sight on timescales of several months. We also present the first FUSE spectrum of MR 2251-178. The general characteristics of the UV and X-ray absorbers seem to be consistent.
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