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Paper: Correlated X-ray to UV Variability in MCG—6-30-15
Volume: 360, AGN Variability from X-Rays to Radio Waves
Page: 127
Authors: Arevalo, P.; Papadakis, I.; Kuhlbrodt, B.; Brinkmann, W.
Abstract: We used a ~ 300 ks long XMM-Newton observation of MCG—6-30-15 to study the correlation between the 0.2–10 keV X-ray and the 3000–4000 Å U bands. The light curves are well correlated with a time lag of τmax ~ 160 ks where the U-band variations lead the variations in the X-ray band. This result gives evidence for Comptonisation scenarios where the X-rays are produced through Compton up-scattering of hard UV seed photons, as this process naturally predicts the observed soft U-band variations will precede similar flux variations in the X-rays. The length of the time lag favours models where the observed U band and seed photon emitting regions are connected by perturbations of the accretion flow traveling inwards through the disc affecting first the observed U-band emitting radii and then the innermost region where the bulk of the seed photons are expected to be produced. Finally, the absence of a positive correlation, where X-ray flux variations precede the U-band variations, indicates that the observed U band photons are not mainly produced through reprocessing of X-rays in this source.
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