A decades-long fast-rise-exponential-decay flare in low-luminosity AGN NGC 7213. Issue 1 (20th December 2017)

• Record Type: Journal Article
• Authors: Yan, Zhen; Xie, Fu-Guo
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 475:Issue 1(2018)
• Page Start: 1190
• Page End: 1197
• Publication Date: 2017-12-20
• Subjects: accretion, accretion discs -- black hole physics -- galaxies: individual: NGC 7213 -- galaxies: nuclei; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stx3259
• Languages: English
• ISSNs: 0035-8711

Abstract

Abstract: We analysed the four-decades-long X-ray light curve of the low-luminosity active galactic nucleus (LLAGN) NGC 7213 and discovered a fast-rise-exponential-decay (FRED) pattern, i.e. the X-ray luminosity increased by a factor of ≈4 within 200 d, and then decreased exponentially with an e -folding time ≈8116 d (≈22.2 yr). For the theoretical understanding of the observations, we examined three variability models proposed in the literature: the thermal-viscous disc instability model, the radiation pressure instability model, and the TDE model. We find that a delayed tidal disruption of a main-sequence star is most favourable; either the thermal-viscous disc instability model or radiation pressure instability model fails to explain some key properties observed, thus we argue them unlikely.