Variability and the X-ray-UV ratio of Active Galactic Nuclei - Astrophysics > Cosmology and Nongalactic AstrophysicsReport as inadecuate

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Abstract: The observed relation between the X-ray radiation from AGNs, originating inthe corona, and the optical-UV radiation from the disk is usually described bythe anticorrelation between the UV to X-ray slope alpha ox and the UVluminosity. Many factors can affect this relation, including: enhanced X-rayemission associated with the jets of radio-loud AGNs; X-ray absorptionassociated with the UV Broad Absorption Line BAL outflows; other X-rayabsorption not associated with BALs; intrinsic X-ray weakness; UV and X-rayvariability, and non-simultaneity of UV and X-ray observations. The separationof these effects provides information about the intrinsic alpha ox-L UVrelation and its dispersion, constraining models of disk-corona coupling. Weextract simultaneous data from the second XMM-Newton serendipitous sourcecatalogue and the XMM-Newton Optical Monitor Serendipitous UV Source SurveyCatalog, and derive the single-epoch alpha ox indices. We use ensemblestructure functions to analyse multi-epoch data. We confirm the anticorrelationof alpha ox with L UV, and do not find any evidence of a dependence of alpha oxon z. The dispersion in our simultaneous data 0.12 is not significantlysmaller than in previous non-simultaneous studies, suggesting that -artificialalpha ox variability- introduced by non-simultaneity is not the main cause ofdispersion. -Intrinsic alpha ox variability-, i.e., the true variability of theX-ray to optical ratio, is instead important, and accounts for ~30% of thetotal variance, or more. -Inter-source dispersion-, due to intrinsicdifferences in the average alpha ox values from source to source, is alsoimportant. The dispersion introduced by variability is mostly caused by thelong timescale variations, which are expected to be driven by the opticalvariations.

Author: F. Vagnetti, S. Turriziani, D. Trevese, M. Antonucci


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