Oral Presentation
An Intrinsic Link Between UV/Optical Variations and X-ray Loudness in Quasars
Presenter: Wenyong Kang (USTC)
Observations have shown that UV/optical variation amplitude of quasars depend on several physical parameters including luminosity, Eddington ratio, and likely also black hole mass. Identifying new factors which correlate with the variation is essential to probe the underlying physical processes. Combining ∼ ten years long quasar light curves from SDSS stripe 82 and X-ray data from Stripe 82X, we build a sample of X-ray detected quasars to investigate the relation between UV/optical variation and X-ray loudness. We find that quasars with more intense X-ray radiation (compared to bolometric luminosity) are more variable in UV/optical. Such correlation remains highly significant after excluding the effect of other parameters including luminosity, black hole mass, Eddington ratio, redshift, rest-frame wavelength (i.e., through partial correlation analyses). It apparently appears consistent with the X-ray processing paradigm in which UV/optical variation is produced by a variable central X-ray emission illuminating the accretion disk. However, as the reprocessing paradigm faces many severe observational challenges, it is unlikely the dominant cause of UV/optical variations in quasars. Attributing the UV/optical variation to disk turbulence, our discovery strikingly provides a direct support to the scheme that the X-ray corona heating is also closely associated with magnetic turbulence.
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