The Awakening Beast in the Seyfert 1 Galaxy KUG 1141+371 I

TL;DR

This paper investigates the decade-long multi-wavelength luminosity increase in Seyfert galaxy KUG 1141+371, analyzing X-ray spectral variability and accretion changes, and exploring its relation to black hole transients.

Contribution

It provides a detailed multi-epoch X-ray spectral analysis and SED modeling revealing accretion rate increase and disc evolution in KUG 1141+371, linking galaxy activity to black hole transients.

Findings

Significant increase in optical, UV, and X-ray flux over a decade.

Evidence of rising accretion rate from 0.6% to 3.2% of Eddington limit.

Disc temperature increases while inner radius decreases with accretion.

Abstract

KUG 1141+371 is a Seyfert 1 galaxy that shows a simultaneous flux increase in the optical and UV bands in the past decade. For instance, the latest Swift observation in 2019 shows that the UVW2 flux of the AGN in KUG 1141+371 has increased by over one order of magnitude since 2009. Meanwhile, the soft X-ray flux of KUG 1141+371 also shows a steady increase by one order of magnitude since 2007. The significant multi-wavelength luminosity change is likely due to a boost of mass accretion rate from approximately 0.6% of the Eddington limit to 3.2%, assuming a black hole mass of $10^{8}M_{\odot}$. In this work, we conduct detailed multi-epoch X-ray spectral analysis focusing on the variability of the X-ray continuum emission and the puzzling soft excess emission. In addition, our SED models also suggest a simultaneous increase of disc temperature and a decreasing inner disc radius along with the increasing accretion rate. Finally, we discuss possible connection between KUG 1141+371 and black hole transients in outburst.