Disk origin of broad optical emission lines of the TDE candidate PTF09djl

TL;DR

This study models the broad optical emission lines of the TDE candidate PTF09djl as originating from a relativistic elliptical accretion disk, explaining complex line profiles and their diversity through disk inclination effects.

Contribution

It provides the first detailed relativistic disk model for the broad emission lines in PTF09djl, linking line profiles and ratios to disk geometry and orientation.

Findings

Double-peaked Halpha line explained by a relativistic elliptical disk.

Peculiar line substructures due to orbital motion within the disk.

Disk inclination affects emission line strength and ratios.

Abstract

An otherwise dormant supermassive black hole (SMBH) in a galactic nucleus flares up when it tidally disrupts a star passing by. Most of the tidal disruption events (TDEs) and candidates discovered in the optical/UV have broad optical emission lines with complex and diverse profiles of puzzling origin. In this Letter, we show that the double-peaked broad Halpha line of the TDE candidate PTF09djl can be well modelled with a relativistic elliptical accretion disk and the peculiar substructures with one peak at the line rest wavelength and the other redshifted to about 3.5x10^4 km/s are mainly due to the orbital motion of the emitting matter within the disk plane of large inclination 88\degr and pericenter orientation nearly vertical to the observer. The accretion disk has an extreme eccentricity 0.966 and semimajor axis of 340 BH Schwarzschild radii. The viewing angle effects of large disk inclination lead to significant attenuation of He emission lines originally produced at large electron scattering optical depth and to the absence/weakness of He emission lines in the spectra of PTF09djl. Our results suggest that the diversities of line intensity ratios among the line species in optical TDEs are probably due to the differences of disk inclinations.