Multiple tidal disruption flares in the active galaxy IC 3599

TL;DR

This paper reports on repeated tidal stripping flares in galaxy IC 3599, caused by a star on a highly eccentric orbit near a black hole, with a recurrence time of 9.5 years, suggesting non-disruptive stellar interactions.

Contribution

It presents the first observational evidence of multiple tidal stripping flares in IC 3599, modeling the events as recurring non-disruptive stellar interactions with a black hole.

Findings

Recurrence time of 9.5 years for flares

Flares explained by non-disruptive tidal stripping

Potential feeding mechanism for the galaxy's active nucleus

Abstract

Tidal disruption events occur when a star passes too close to a massive black hole and it is totally ripped apart by tidal forces. It may also happen that the star is not close enough to the black hole to be totally disrupted and a less dramatic event might happen. If the stellar orbit is bound and highly eccentric, just like some stars in the centre of our own Galaxy, repeated flares should occur. When the star approaches the black hole tidal radius at periastron, matter might be stripped resulting in lower intensity outbursts recurring once every orbital period. We report on Swift observations of a recent bright flare from the galaxy IC 3599 hosting a middle-weight black hole, where a possible tidal disruption event was observed in the early 1990s. By light curve modelling and spectral fitting we can consistently account for the events as the non-disruptive tidal stripping of a star into a highly eccentric orbit. The recurrence time is 9.5 yr. IC 3599 is also known to host a low-luminosity active galactic nucleus. Tidal stripping from this star over several orbital passages might be able to spoon-feed also this activity.