Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21531102y&link_type=abstract
American Astronomical Society, AAS Meeting #215, #311.02; Bulletin of the American Astronomical Society, Vol. 42, p.311
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. The large sample size enables 1) deeper investigation of interesting sub-populations, and 2) large, statistical studies.
(1) We first present the rare sub-population of intrinsically red quasars. We find that 7 out of 17 of the reddest SDSS quasars can be classified as probable "intrinsically red" objects. Low accretion rates, rather than absorption may explain their steep optical continua.
(2) We then use the full sample to investigate the relation between optical and X-ray emission, parameterized as the correlation between the optical-to-X-ray slope (alphaox, defined at 2 keV and 2500A), and the UV luminosity. Optical and X-ray spectra enable a new look at this well-studied relation by defining alphaox at different frequencies than those traditionally used. We find that while the choice of optical wavelength does not strongly influence the alphaox-luminosity relation, the slope of the relation does depend on the choice of X-ray energy. By combining the alphaox-luminosity 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 luminosity, and 2) the lack of a relation between X-ray slope and optical luminosity. The consistency of the optical/X-ray correlations establishes a more complete framework for understanding the relation between quasar emission mechanisms.
Elvis Martin
Marscher Alan
Risaliti Guido
Young Monica
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