Tidal disruption events from a nuclear star cluster as possible origin of transient relativistic spectral lines near SMBH

TL;DR

This paper proposes that tidal disruption events near dormant supermassive black holes can produce transient relativistic iron spectral lines in X-ray signals, offering a new way to probe black hole parameters in inactive galactic nuclei.

Contribution

It introduces a model where TDEs in nuclear star clusters generate transient relativistic spectral lines, differing from standard lamp-post models in active galaxies.

Findings

TDEs can produce observable relativistic iron lines in X-ray spectra.

The model suggests a flattened nuclear star cluster geometry influences line profiles.

Transient lines can help determine SMBH and system parameters.

Abstract

We discuss a possibility that a tidal disruption event near a dormant supermassive black hole (SMBH) can give rise to spectral features of iron in 6-7 keV X-ray signal: a relativistic line profile emerges from debris illuminated and ionised by an intense flash produced from the destroyed star. This could provide a unique way to determine parameters of the system. We consider a model where the nuclear stellar population acquires an oblate shape (i.e., a flattened distribution) in the inner region near a supermassive black hole, and also the primary irradiation flare is expected to occur more likely near the equatorial plane, co-planar with the infalling material. This suggests that the reprocessing of primary X-rays results in a transient profile that should be relevant for tidal-disruption events (TDE) in otherwise under-luminous (inactive) galactic nuclei, i.e. with no prior accretion disc. Resonance mechanisms of the stellar motion can increase the orbital eccentricity for some stars in the nuclear cluster and help to bring them close to the tidal radius, where they can give rise to TDEs. The proposed scenario appears to be distinguishably different from the standard scheme of lamp-post model for the origin of the relativistic line in active galaxies, where the source is thought to be located predominantly near the symmetry axis.