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

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 J164449.3+573451 and Swift J2058.4+0516 (hereafter Swift J1644+57 and Swift J2058+05, respectively) 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 varies from 1.1 to 1.8. We have firmly established the saturation of the photon index versus mass accretion rate at sat about 1.71.8. The saturation of 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 sat values which indicate a high electron (plasma) temperature, kTe3040 keV. This is also consistent with high cuto energies, Ecut6080 keV found using best fits of the RXTE spectra. Swift J2058+05 shows a lower electron temperature, kTe 410 keV than that for Swift J1644+57. For the BH mass estimate we used the scaling technique taking the Galactic BHs, GRO J165540, GX 3394, Cyg X1 and 4U 154347 as reference sources and found that the BH mass in Swift J1644+57 is MBH7106 M assuming the distance to this source of 1.5 Gpc. For Swift J2058+05 we obtain MBH2 107 Massuming the distance to this source of 3.7 Gpc. We have also found that the seed (disk) photon temperatures are quite low, of order of 100400 eV, in both of the sources, which are consistent with the estimated BH masses.