X-ray and Radio Constraints on the Mass of the Black Hole in Swift J164449.3+573451

Abstract

Swift J164449.3+573451 is an exciting transient event, likely powered by the tidal disruption of a star by a massive black hole. The distance to the source, its transient nature, and high internal column density serve to complicate several means of estimating the mass of the black hole. Utilizing newly-refined relationships between black hole mass, radio luminosity, and X-ray luminosity, and de-beaming the source flux, a weak constraint on the black hole mass is obtained: log(M/Msun) = 5.5 +/- 1.1 (1 sigma confidence). The confidence interval is determined from the current intrinsic scatter in the relation, which includes effects from X-ray variability and accretion modes. This mass range is broad, but it includes low values that are consistent with some variability arguments, and it safely excludes high mass values where it becomes impossible for black holes to disrupt stars. Future refinements in relationships between black hole mass, radio luminosity, and X-ray luminosity will be able to reduce the uncertainty in related mass estimates by a factor of two, making this technique comparable to estimates based on the M-sigma relationship. Possible difficulties in placing such events on the fundamental plane, a potential future test of their suitability, and uncertainties in mass stemming from variable X-ray emission are discussed. As near and longer-term survey efforts such as Pan-STARRS, LSST, LOFAR, the Square Kilometer Array, and eROSITA begin to detect many tidal disruption events, black hole mass estimates from combined X-ray and radio observations may prove to be very pragmatic.