Swift J2058.4+0516 ( Sw J2058+05 , hereafter ) has been suggested as the second member ( after Sw J1644+57 ) of the rare class of tidal disruption events accompanied by relativistic ejecta .
Here we report a multiwavelength ( X-ray , ultraviolet/optical/infrared , radio ) analysis of 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 \gtrsim 160 within a span of \Delta t / t \leq 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 _ { \odot } .
( 2 ) We detect rapid ( \lesssim 500 s ) X-ray variability before the dropoff , 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 HST and VLBA astrometry that the location of the source coincides with the galaxy ’ s center to within \lesssim 400 pc ( in projection ) .
( 4 ) We modeled Sw J2058+05 ’ s ultraviolet/optical/infrared 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 \pm 4.5 AU ( \sim 10 ^ { 15 } cm ) at all times during the outburst , the blackbody temperature drops significantly from \sim 30,000 K at early times to a value of \sim 15,000 K at late times ( before the X-ray dropoff ) .
Our results strengthen Sw J2058+05 ’ s interpretation as a tidal disruption event similar to Sw J1644+57 .
For such systems , we suggest the rapid X-ray dropoff as a diagnostic for black hole mass .