2005/07/25 by Guido Risaliti, G. Risaliti, M. Elvis +2 · 3 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Galaxies: Formation, Evolution, Phenomena #astro-ph
paper · pdf · doi:10.1086/444413
published as Astrophys.J.629:L17-20,2005 · 13 pages, 3 figures. Accepted for publication in ApJ Letters. Corrected typos & references
arxiv created 2005/07/25 · openalex publication_date 2005/07/26 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/01
We have searched in the XMM-Newton public archive for quasars in the Sloan Digital Sky Survey First Data Release and found 55 lying in the field of an XMM-Newton observation with exposure times >20 ks (as of 2004 August). The 35 quasars that yielded good X-ray spectra span redshifts from 0.5 to 2.5. The large collecting area of XMM-Newton allows us to investigate the dependence of the X-ray spectra of quasars on luminosity, redshift, and optical colors. We find (1) no evolution of X-ray slope (Γ) with either redshift or luminosity; (2) no correlation between Γ (or absorbing column density) and the optical-to-X-ray ratio, α OX ; and (4) no relation between α OX and optical colors. The two latter results suggest that obscuration is not the dominant cause of the spread in X-ray slope or optical color. We find four unusual quasars (i.e., 10% of the sample): three are absorbed ( N H > 10 22 cm -2 ), of which one has high luminosity (1.5 × 10 44 ergs s -1 ); the fourth has Γ = 0.6 ± 0.2, which is far flatter than the typical value of 1.8-2.0, and a strong emission line (EW = 1.2 ± 0.4 keV), which, if Fe K, implies a redshift of ~1.4.