A Multiwavelength Study of the Relativistic Tidal Disruption Candidate Swift J2058.4+0516 at Late Times
Fruchter, Andrew S.; Filippenko, Alexei V.; Cenko, S. Bradley; O'Brien, Paul T.; Bower, Geoffrey C.; Page, Kim L.; Pasham, Dheeraj R.; Greiner, Jochen; Tanvir, Nial R.; Horesh, Assaf; Rau, Arne; Levan, Andrew J.; Brown, Gregory C.; Dolan, Stephen; Wiersema, Klaas
United States, United Kingdom, Israel, Germany
Abstract
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 ≳160 within a span of Δt/t≤slant 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 104-6 M⊙ . (2) We detect rapid (≲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 ≲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 (∼ {{10}15} cm) at all times during the outburst, the blackbody temperature drops significantly from ∼30,000 K at early times to a value of ∼15,000 K at late times (before the X-ray drop-off). Our results strengthen Sw J2058+05's interpretation as a TDE similar to Sw J1644+57.