Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010head...11.0701y&link_type=abstract
American Astronomical Society, HEAD meeting #11, #7.01; Bulletin of the American Astronomical Society, Vol. 41, p.659
Astronomy and Astrophysics
Astronomy
Scientific paper
We have cross-correlated the DR5 Sloan Digital Sky Survey (SDSS) quasars with the XMM-Newton archive to obtain the largest survey with both optical and X-ray spectra of quasars: 800 X-ray observations ( 500 X-ray spectra) of optically selected quasars. We investigate the relation between optical and X-ray emission, parameterized as the correlation between the optical-to-X-ray slope (alpha_ox, defined at 2 keV and 2500A), and the UV luminosity. Optical and X-ray spectra enable a new approach to this well-studied relation by allowing alpha_ox to be defined at different frequencies than those traditionally used. We find that while the choice of optical wavelength does not strongly influence the alpha_ox-luminosity relation, the slope of the relation does depend on the choice of X-ray energy. We find that the slope of the relation steepens at low energies ( 1 keV), while becoming marginally flatter at high energies ( 7-10 keV). By combining the alpha_ox-l_opt relation with the relation between X-ray photon index and Eddington ratio, we can naturally explain two results: 1) the existence of a relation between X-ray slope and X-ray luminosity, and 2) the lack of a relation between X-ray slope and optical luminosity. We apply Comptonization theory to translate these results into a physical understanding of the disk-corona structure.
Elvis Martin
Marscher Alan
Risaliti Guido
Young Monica
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