The SDSS/XMM-Newton Quasar Sample. I. First Results
Abstract
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, αOX and (4) no relation between αOX 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 (NH>1022 cm-2), of which one has high luminosity (1.5×1044 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.
- Publication:
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The Astrophysical Journal
- Pub Date:
- August 2005
- DOI:
- 10.1086/444413
- arXiv:
- arXiv:astro-ph/0507434
- Bibcode:
- 2005ApJ...629L..17R
- Keywords:
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- Galaxies: Active;
- Galaxies: Nuclei;
- X-Rays: Galaxies;
- Astrophysics
- E-Print:
- 13 pages, 3 figures. Accepted for publication in ApJ Letters. Corrected typos &