Multiwavelength Diagnostics of Quasar Accretion Power
Abstract
We present the results of our attempts to identify a robust accretion-rate indicator for quasars based on a unique quasar sample. We selected 48 quasars from the Chandra X-ray Observatory archive that are radio quiet, do not have broad absorption lines, and have high-quality data in the C IV and Hβ spectral bands. Among the various spectral properties that we investigated, our results show that the equivalent width (EW) of C IV is the strongest indicator of the Hβ-based Eddington ratio. We do not find evidence for broad-band optical-X-ray emission (i.e., αox) improving predictions of the latter parameter. Since about half of our sources have optical-band monochromatic luminosities above 1045.5 erg/s, a potential explanation of this result could be that a strong correlation between EW(C IV) and αox is only observed above a certain luminosity threshold above which strong quasar winds may form. Shallow Chandra observations of a well-defined sample of luminous sources may allow us to mitigate the biases inherent in our archival sample and test this hypothesis. Furthermore, deeper X-ray observations of our sources may provide accurate measurements of the hard-X-ray power-law photon index (Γ), which is considered an unbiased Eddington-ratio indicator. Correlations between EW(C IV) and αox with the Γ-based Eddington ratio may yield a more robust prediction of a quasar normalized accretion rate. This work is supported by a Chandra X-ray Observatory Archival Research Grant AR8-19014X.
- Publication:
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American Astronomical Society Meeting Abstracts #235
- Pub Date:
- January 2020
- Bibcode:
- 2020AAS...23530418M