A MULTIWAVELENGTH STUDY OF THE RELATIVISTIC TIDAL DISRUPTION CANDIDATE SWIFT J2058.4+0516 AT LATE TIMES

We report a multiwavelength (X-ray, ultraviolet/optical/infrared (UVOIR), radio) analysis of the relativistic tidal disruption event (TDE) candidate Sw J2058+05 from 3 months to 3 yr post-discovery in order to study its properties and compare its behavior with that of Sw J1644+57. Our main results are as follows: (1) The long-term X-ray light curve of Sw J2058+05 shows a remarkably similar trend to that of Sw J1644+57. After a prolonged power-law decay, the X-ray flux drops off rapidly by a factor of greater than or similar to 160 within a span of Delta t/t <= 0.95. Associating this sudden decline with the transition from super-Eddington to sub-Eddington accretion, we estimate the black hole mass to be in the range of 10(4-6) M-circle dot. (2) We detect rapid (less than or similar to 500 s) X-ray variability before the drop-off, suggesting that, even at late times, the X-rays originate from close to the black hole (ruling out a forward-shock origin). (3) We confirm using Hubble Space Telescope and Very Long Baseline Array astrometry that the location of the source coincides with the galaxy's center to within less than or similar to 400 pc (in projection). (4) We modeled Sw J2058+05's UVOIR spectral energy distribution with a single-temperature blackbody and find that while the radius remains more or less constant at a value of 63.4 +/- 4.5 AU (similar to 10(15) cm) at all times during the outburst, the blackbody temperature drops significantly from similar to 30,000 K at early times to a value of similar to 15,000 K at late times (before the Xray drop-off). Our results strengthen Sw J2058+05's interpretation as a TDE similar to Sw J1644+57.