Swift J164449.3+573451 and Swift J2058.4+0516: Black hole mass estimates for tidal disruption event sources

TL;DR

This study estimates black hole masses in tidal disruption event sources Swift J1644+57 and Swift J2058+05 by analyzing their X-ray spectra and spectral saturation features, confirming the presence of massive black holes.

Contribution

The paper introduces a spectral analysis method using the Bulk Motion Comptonization model and scaling techniques to estimate black hole masses in TDE sources, providing new mass constraints.

Findings

Gamma saturation indicates black hole presence.

Estimated black hole mass in Swift J1644+57 exceeds 7 million solar masses.

Estimated black hole mass in Swift J2058+05 exceeds 20 million solar masses.

Abstract

A tidal disruption event (TDE) is an astronomical phenomenon in which a previously dormant black hole (BH) destroys a star passing too close to its central part. We analyzed the flaring episode detected from the TDE sources, Swift~J1644+57 and Swift J2058+05 using RXTE, Swift and Suzaku data. The spectra are well fitted by the so called Bulk Motion Comptonization model for which the best-fit photon index Gamma varies from 1.1 to 1.8. We have firmly established the saturation of Gamma versus mass accretion rate at Gamma_{sat} about 1.7 -- 1.8. The saturation of Gamma is usually identified as a signature of a BH now established in Swift~J1644+57 and Swift J2058+05. In Swift~J1644+57 we found the relatively low Gamma_{sat} values which indicate a high electron (plasma) temperature, kT_e ~ 30 -- 40 keV. This is also consistent with high cutoff energies, E_{cut} ~ 60 -- 80 keV found using best fits of the RXTE spectra. Swift~J2058+05 shows a lower electron temperature, kT_e ~ 4-10 keV than that for Swift~J1644+57. For the BH mass estimate we used the scaling technique taking the Galactic BHs, GRO J1655--40, GX~339--4, Cyg~X--1 and 4U~1543--47 as reference sources and found that the BH mass in Swift~J1644+57 is M_{BH}> 7x10^6 solar masses assuming the distance to this of 1.5 Gpc. For Swift J2058+05 we obtain M_{BH}> 2x 10^7 solar masses assuming the distance to this source of 3.7 Gpc.