An Investigation of 5-year Simultaneous X-ray and Radio Light Curves of the Dwarf Seyfert Galaxy UGC 6728

TL;DR

This study presents five-year simultaneous radio and X-ray observations of the dwarf Seyfert galaxy UGC 6728, revealing a flare in X-rays with correlated radio flux changes, interpreted as magnetic disk activity or obscuration events.

Contribution

First detailed long-term simultaneous radio and X-ray light curves of UGC 6728, providing insights into AGN variability and potential magnetic activity or obscuration mechanisms.

Findings

X-ray flare with stable spectrum and hardness ratio.

Radio flux remains constant until the end of the X-ray flare.

X-ray and radio behaviors suggest magnetic disk activity or plasma obscuration.

Abstract

We present serendipitous simultaneous radio and X-ray light curves of the dwarf Seyfert galaxy UGC 6728 spanning 5 years. The X-ray light curve exhibits a flaring period, followed by a gradual rise and decline. Throughout these events, the X-ray hardness ratio and spectrum do not change significantly. The radio flux is constant, as far as can be determined from its sparse sampling, until the end of the X-ray flare, then decreases by a factor of two by the midpoint of the gradual X-ray rise before returning to baseline at the end of the X-ray decline. We interpret this behavior in light of a similar event recently reported in NGC 2992, in which there is a temporary obscuration of the radio source by a blob of plasma ejected by a magnetic reconnection in the accretion disk. The energetics of the X-ray flare are consistent with those expected from magnetic disk activity. As in NGC 2992, the X-ray spectrum does not evolve during the obscuration event. We also discuss the possibility that the observed phenomena are due to normal AGN coronal flaring and variability, which is plausible but unlikely given the lack of spectral variation.