PKS 0438-436: A High-Redshift Quasar with Strong X-Ray Absorption
Abstract
We report the first X-ray spectrum of a high-redshift (z = 2.85) quasar. The ROSAT PSPC spectrum of PKS 0438-436, covering 0.3-9 keV in the quasar's rest frame, reveals unexpected absorption of ~1 x 10^22^ cm^-2^ assuming it occurs at the source. Only one other high-luminosity quasar (of >~ 50 observed by Einstein) shows significant absorption in its X-ray spectrum. Of the common line-of-sight absorbers, only highly ionized Lyα forest clouds may be able to explain this amount of absorption. Candidates for an intrinsic absorber are discussed. Absorption at ~1 keV (rest frame) is due primarily to heavy elements (O, Ne, Mg, Si, S) raising the possibility of measuring early universe abundances via X-ray absorption in this and like quasars. PKS 0438-436 may be a high-redshift member of a population of quasars which can contribute to the X-ray background above 2 keV, without being detectable by previous imaging missions.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 1992
- DOI:
- 10.1086/186436
- Bibcode:
- 1992ApJ...393L...1W
- Keywords:
-
- Quasars;
- Red Shift;
- X Ray Absorption;
- Absorption Spectra;
- Lyman Alpha Radiation;
- Rosat Mission;
- X Ray Spectra;
- Astrophysics