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arXiv · 1712.05272

A decades-long fast-rise-exponential-decay flare in low-luminosity AGN NGC 7213

Zhen Yan·Fu-Guo Xie
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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 $\approx 4$ within 200d, and then decreased exponentially with an $e$-folding time $\approx 8116$d ($\approx 22.2$ 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 tidal disruption event (TDE) model. We find that a delayed tidal disruption of a main-sequence star is most favourable; either the thermal-viscous disk instability model or radiation pressure instability model fails to explain some key properties observed, thus we argue them unlikely.

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Zhen Yan, Fu-Guo Xie. 2018-01-02. A decades-long fast-rise-exponential-decay flare in low-luminosity AGN NGC 7213. https://doi.org/10.1093/mnras%2Fstx3259

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