Disk-corona Connection In Quasars: The α_{ox}-l_{uv} Correlation
Abstract
The controversial anti-correlation between the optical-to-X-ray spectral index (α_{ox}) and the optical luminosity in quasars has been discussed for over 30 years. No physical basis for the relation has yet been proposed, and the relation itself provides little guidance. In part, this is because previous studies have largely used the traditional, observationally convenient, but physically arbitrary, endpoints of 2500 Angstroms and 2 keV. They also assume an X-ray photon index to obtain the X-ray flux at 2 keV. A systematic study with measured optical and X-ray spectra has enabled an investigation of the relation at different frequencies than those traditionally used, hopefully revealing clues about the relation's physical underpinnings.
By cross-correlating the DR5 Sloan Digital Sky Survey (SDSS) quasar selection with the XMM-Newton archive, we obtain the largest known sample of quasars with both optical and X-ray spectra. We present preliminary results with respect to the slope, the significance, and the dispersion of the correlation. The slope and statistical significance of the correlation decrease significantly with optical wavelength and X-ray energy, even as the correlation tightens. The relation nearly disappears when defined at 5000 Angstroms and 10 keV. We will also investigate the dependence of α_{ox} on more fundamental parameters, such as accretion rate and black hole mass. This work is funded by NASA grants NNX07AI22G and G06-7102X.- Publication:
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American Astronomical Society Meeting Abstracts #213
- Pub Date:
- January 2009
- Bibcode:
- 2009AAS...21348406Y