The fall of CSS100217: a tidal disruption-induced low state in an apparently hostless active galactic nucleus

TL;DR

This paper presents evidence supporting the interpretation of a luminous flare in a galaxy as a tidal disruption event, leading to a long-term low luminosity state and a compact host galaxy, challenging previous AGN variability explanations.

Contribution

It provides new observational evidence favoring a tidal disruption event over AGN variability for the CSS100217 flare, including host galaxy analysis and post-flare luminosity changes.

Findings

The galaxy entered a long-term low luminosity state after the flare.

The host galaxy is compact with no extended component.

A retrograde star disruption created a cavity in the accretion disk.

Abstract

CSS100217 was a nuclear, rapid and luminous flare in a Narrow-Line Seyfert 1 galaxy, whose initial interpretation as a supernova is now debated between variability of the active galactic nucleus (AGN) or a tidal disruption event (TDE). In this paper, we present and discuss new evidence in favour of a TDE or extreme flaring episode scenario. After the decay of the flare, the galaxy entered a long-term low luminosity state, 0.4 magnitudes lower than the pre-outburst emission in the V band. We attribute this to the creation of a cavity in the accretion disk after the tidal disruption of a star in a retrograde orbit with respect to the accretion disk rotation, making a TDE our favoured interpretation of the flare. We also show how the host galaxy shows a point-like, compact profile, no evidence for an extended component and a relatively low mass, unlike what expected from an AGN host galaxy at z=0.147. A compact host galaxy may result in an increased TDE rate, strengthening our interpretation of the event.