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

TL;DR

This study investigates the relationship between X-ray and UV emissions in the galaxy IRAS 13224-3809, finding no direct correlation despite strong X-ray variability, suggesting complex or indirect interactions between the corona and the disc.

Contribution

It provides the first detailed multi-wavelength monitoring of IRAS 13224-3809, exploring the connection between X-ray and UV emissions in a highly variable AGN.

Findings

No correlation between X-ray and UV flux over 40 days

UV variability consistent with disc irradiation

X-ray variability does not directly translate to UV changes

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 day 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.