2001/01/24 by Stefanie Komossa, S. Komossa · 2 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Galaxies: Formation, Evolution, Phenomena #astro-ph
paper · pdf · doi:10.1051/0004-6361:20010022
A&A, in press (scheduled for Feb./March issue); preprint and related papers also available at http://www.xray.mpe.mpg.de/~skomossa/
arxiv created 2001/01/24 · openalex publication_date 2001/03/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
MR 2251-178 was the first quasar initially discovered in X-rays, and the first one found to host a warm absorber. The quasar turned out to be an outstanding object in many respects. It has a high ratio of X-ray/optical luminosity, is surrounded by the largest quasar emission-line nebula known, and is located in the outskirts of a cluster of galaxies. Here, we present results from an analysis of the X-ray spectral, temporal, and spatial properties of this source and its environment based on deep ROSAT observations. Remarkably, we do not detect any excess X-ray cold absorption expected to originate from the giant gas nebula surrounding MR 2251-178. This excludes the presence of a huge HI envelope around the quasar. The X-ray spectrum of MR 2251-178 is best fit by a warm-absorbed powerlaw with an ionization parameter and a column density which, however, cannot be the same material as the giant optical emission line nebula. The mean (0.1-2.4) keV X-ray luminosity amounts to 1045 erg/s. A spatial analysis shows that the bulk of the X-ray emission from the quasar is consistent with a point source, as expected in view of the powerlaw-shaped X-ray spectrum and the rapid X-ray variability we detect. In addition, extended emission appears at weak emission levels, including a bridge between the quasar and the cD galaxy of the cluster. The X-ray emission from the intra-cluster medium is weak or absent. We derive an upper limit on the X-ray luminosity of erg/s, weaker than other clusters of comparable richness. None of the other member galaxies of the cluster to which MR 2251-178 belongs, are detected in X-rays. However, east of the quasar there is a significant excess of X-ray sources, several of them without optical counterparts on the UK Schmidt plates.