Variable X-ray absorption in the QSO MR 2251 - 178

Details Variable X-ray absorption in the QSO MR 2251 - 178 Variable X-ray absorption in the QSO MR 2251 - 178

Jun 1984

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984apj...281...90h&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 281, June 1, 1984, p. 90-94.

Astronomy and Astrophysics

Astrophysics

191

Quasars, X Ray Absorption, X Ray Sources, Background Radiation, Heao 2, Proportional Counters, X Ray Spectra

Scientific paper

The monitoring proportional counter of the Einstein Observatory has been used to observe the QSO MR 2251 - 178 on two occasions, approximately 1 year apart, in the 2-10 keV range. Evidence is found for an increase in the absorbing column density by a large factor over the 1 year interval. Simultaneous measurements with the high resolution imager are used to further constrain the soft X-ray flux and to show that the highly absorbed spectrum must have excess emission below 1 keV. A model is presented in which photoionization by the X-ray continuum ionizes a cloud or shell of material, so that the emergent spectrum is transparent below the K-edge of O VII at 739 eV, but is highly absorbed above this energy.

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