Is there a UV/X-ray connection in IRAS 13224−3809?

Abstract

We present results from the optical, ultraviolet, and X-ray monitoring of the NLS1 galaxy IRAS 13224−3809 taken with Swift and XMM–Newton during 2016. IRAS 13224−3809 is the most variable bright AGN in the X-ray sky and shows strong X-ray reflection, implying that the X-rays strongly illuminate the inner disc. Therefore, it is a good candidate to study the relationship between coronal X-ray and disc UV emission. However, we find no correlation between the X-ray and UV flux over the available ∼40 d monitoring, despite the presence of strong X-ray variability and the variable part of the UV spectrum being consistent with irradiation of a standard thin disc. This means either that the X-ray flux which irradiates the UV emitting outer disc does not correlate with the X-ray flux in our line of sight and/or that another process drives the majority of the UV variability. The former case may be due to changes in coronal geometry, absorption or scattering between the corona and the disc.

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