ASASSN-15lh: a TDE about a maximally rotating $10^9 M_{\odot}$ black hole

Abstract

We model the light curves of the novel and extremely luminous transient ASASSN-15lh at nine different frequencies, from infrared to ultra-violet photon energies, as an evolving relativistic disc produced in the aftermath of a tidal disruption event. Good fits to all nine light curves are simultaneously obtained when $M_{\rm acc} \simeq 0.07 M_{\odot}$ is accreted onto a black hole of mass $M \simeq 10^9 M_{\odot}$, and near maximal rotation $a/r_g = 0.99$. The best fit black hole mass is consistent with a number of existing estimates from galactic scaling relationships. If confirmed, our results represent the detection of one of the most massive rapidly spinning black holes to date, and are strong evidence for a TDE origin for ASASSN-15lh. This would be the first TDE to be observed in the disc dominated state at optical and infrared frequencies.