Abstract
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 active galactic nucleus 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 multiwavelength luminosity change is likely due to a boost of mass accretion rate from approximately $0.6{{\ \rm per\ cent}}$ of the Eddington limit to $3.2{{\ \rm per\ cent}}$, assuming a black hole mass of 108 M⊙. 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.
Highlights
The nuclei in Seyfert galaxies (Sys; Seyfert 1943) are very strong and variable emitters
It is important to note that KUG 1141 does not seem to change ‘look’, e.g. Sy2 to Sy1, along with the boost of accretion rate: the XMM–Newton observation taken in 2009 when the source was in a low-λEdd state was able to rule out a Compton-thick scenario that is commonly seen in Sy2 active galactic nucleus (AGN) (Risaliti, Maiolino & Salvati 1999); during the high-λEdd state, e.g. obs 12 in 2019, the X-ray spectra of KUG 1141 still remained unobscured
We present multi-epoch X-ray spectral analysis and SED modelling of an Sy1 called KUG 1141
Summary
The nuclei in Seyfert galaxies (Sys; Seyfert 1943) are very strong and variable emitters. Two scenarios have been proposed to explain these rapidly changing Sys: a variable line-of-sight column density due to the clumpiness of the torus and a sudden change in the mass accretion rate. The ‘hide-and-seek’ of the broad emission lines can be explained by such variable obscuration In the latter case, a sudden change of the mass accretion rate in the disc may form or disrupt the broad line region. Multiwavelength variability of KUG 1141+371 917 lines in the polarized optical spectra of many Sy2s suggest the existence of a broad line region in Sy2s as in Sy1s X-ray spectra analysis will enable us to identify any variable line-of-sight obscuration (e.g. Ricci et al 2016) or any changes in the intrinsic AGN spectrum due to a varying accretion rate (e.g. soft excess; Noda & Done 2018). In Appendix C, short-term light curves of KUG 1141 obtained by XMM–Newton and NuSTAR are presented
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