An X-ray Luminosity-dependent "Changing-look" Phenomenon in UGC 3223

TL;DR

This study reports on the X-ray luminosity-dependent changing-look phenomenon in the AGN UGC 3223, showing spectral type transitions over 30 years linked to X-ray flux changes, supporting the disk-wind broad-line region model.

Contribution

First detailed X-ray and UV follow-up of UGC 3223, a repeat changing-look AGN, linking spectral transitions to X-ray flux and supporting the disk-wind model.

Findings

X-ray flux closely follows optical spectral changes.

X-ray spectral shape remains constant during transitions.

Low Eddington ratio supports disk-wind broad-line region model.

Abstract

The nature of the rare "Changing-look" (CL) phenomenon in active galactic nuclei (AGNs) is still under debate at current stage. We here present \it Swift/\rm XRT and UVOT follow-up observations of UGC\,3223, a newly discovered repeat CL-AGN with type transitions of $\mathrm{S1.5\rightarrow S2 \rightarrow S1.8}$ occurring in a period of about 30 years. By comparing the values previously reported in the \it ROSAT \rm All-sky Survey and in the second Swift-XRT Point Source catalog, we clearly find that the X-ray flux tightly follows the optical spectral transition, in which a spectral type closer to a Seyfert 1 type is associated with a higher X-ray flux. An invariable X-ray spectral shape is, however, found in the CL phenomenon of the object. An extremely low Eddington ratio of $\sim2\times10^{-4}$ can be obtained from the X-ray luminosity for its Seyfert 2 state, which suggests a favor of the disk-wind broad-line region model in explaining the CL phenomenon. A variation of the total UV emission is not revealed when compared to the previous \it GALEX \rm NUV observation, since the UVOT images indicate that $\sim90$\% UV emission comes from the intensive star formation in the host galaxy.