Tidal disruption events as a site of an evolving relativistic spectral~line

Abstract

In nuclei of galaxies strong tidal forces can destroy stars passing within a critical distance from the central super-massive black hole (SMBH). Observational signatures of tidal disruption events (TDEs) depend on the environment around the SBMH horizon and the level of its accretion activity. Evidence for optical and UV spectral features has been reported in TDE flares; nevertheless, to test the effects of General Relativity in the immediate vicinity of SMBH, the relativistically broadened and skewed X-ray line would tell us significantly more useful information. This will require to proceed beyond inactive nuclei. To this end we consider a system where the material from a disrupted star forms a gaseous ring that circularises near the tidal radius around SMBH, it gradually spreads in radius by viscous processes, and resides embedded within a hot corona. In our test calculation the remnant trail is assumed to be fully circularized and embedded in a hot environment and illuminated by X-rays from a surrounding corona or a jet base of (mild) AGN activity. We show the expected effects on the observed profile and the centroid energy. In future the evolving spectral features can enhance the diagnostic capability and provide a novel way to reveal the parameters of TDEs in such sources; namely, the distance of the remnant gas from the SMBH, the radial extent of the gaseous trail, and the spin of the SMBH could be measured.