TDE fallback cut-off due to a pre-existing accretion disc

Abstract

Numerous tidal disruption event (TDE) candidates originating from galactic centres have been detected (e.g., by $Swift$ and ASASSN). Some of their host galaxies show typical characteristics of a weak active galactic nucleus (AGN), indicative of a pre-existing accretion disc around the supermassive black hole (SMBH). In this work, we develop an analytic model to study how a pre-existing accretion disc affects a TDE. We assume the density of the disc $\rho \propto R^{-\lambda }$, $R$ being the radial distance from the SMBH and $\lambda$ varying between $0.5$ and $1.5$. Interactions between the pre-existing accretion disc and the stream of the tidally disrupted star can stall the stream far from the SMBH, causing a sudden drop in the rate of fallback of gas into the SMBH. These interactions could explain the steep cut-off observed in the light curve of some TDE candidates (e.g., $Swift$ J1644 and $Swift$ J2058). With our model, it is possible to use the time of this cut-off to constrain some properties pertaining to the pre-existing accretion disc, such as $\lambda$ and the disc viscosity parameter $\alpha$. We demonstrate this by applying our theory to the TDE candidates $Swift$ J1644, $Swift$ J2058 and ASASSN-14li. Our analysis favours a disc profile with $\lambda \sim 1$ for viscosity parameters $\alpha \sim 0.01-0.1$.

10 pages, 7 figures

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Cited by in corpus (11)

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• First light from tidal disruption events
• A Tidal Disruption Event Candidate Discovered in the Active Galactic Nucleus SDSS J022700.77-042020.6
• Capture of stars into gaseous discs around massive black holes: Alignment, circularization and growth
• Radio Emission from Outflow-Cloud Interaction and Its Constraint on TDE Outflow
• Light curves of tidal disruption events in active galactic nuclei
• The jet structure and the intrinsic luminosity function of short gamma-ray bursts
• A decades-long fast-rise-exponential-decay flare in low-luminosity AGN NGC 7213
• Effective two-body scatterings around a massive object
• AT 2021hdr: A candidate tidal disruption of a gas cloud by a binary super massive black hole system