Variable X-ray absorption in the QSO MR 2251-178.
Abstract
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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 1984
- DOI:
- 10.1086/162077
- Bibcode:
- 1984ApJ...281...90H
- Keywords:
-
- Quasars;
- X Ray Absorption;
- X Ray Sources;
- Background Radiation;
- Heao 2;
- Proportional Counters;
- X Ray Spectra;
- Astrophysics