RADIO MONITORING OF THE TIDAL DISRUPTION EVENT SWIFT J164449.3+573451. I. JET ENERGETICS AND THE PRISTINE PARSEC-SCALE ENVIRONMENT OF A SUPERMASSIVE BLACK HOLE
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
- Mullard Radio Observatory, Cavendish Laboratory, Cambridge CB3 0HE (United Kingdom)
- Max-Planck-Institut fuer Radioastronomie, Auf dem Huegel 69, 53121 Bonn (Germany)
- Department of Physics and Astronomy, York University, Toronto, Ontario (Canada)
We present continued radio observations of the tidal disruption event Swift J164449.3+573451 extending to {delta}t Almost-Equal-To 216 days after discovery. The data were obtained with the EVLA, AMI Large Array, CARMA, the SMA, and the VLBA+Effelsberg as part of a long-term program to monitor the expansion and energy scale of the relativistic outflow, and to trace the parsec-scale environment around a previously dormant supermassive black hole (SMBH). The new observations reveal a significant change in the radio evolution starting at {delta}t Almost-Equal-To 1 month, with a brightening at all frequencies that requires an increase in the energy by about an order of magnitude, and an overall density profile around the SMBH of {rho}{proportional_to}r{sup -3/2} (0.1-1.2 pc) with a significant flattening at r Almost-Equal-To 0.4-0.6 pc. The increase in energy cannot be explained with continuous injection from an L{proportional_to}t{sup -5/3} tail, which is observed in the X-rays. Instead, we conclude that the relativistic jet was launched with a wide range of Lorentz factors, obeying E(> {Gamma}{sub j}){proportional_to}{Gamma}{sup -2.5}{sub j}. The similar ratios of duration to dynamical timescale for Sw 1644+57 and gamma-ray bursts (GRBs) suggest that this result may be applicable to GRB jets as well. The radial density profile may be indicative of Bondi accretion, with the inferred flattening at r {approx} 0.5 pc in good agreement with the Bondi radius for a {approx}few Multiplication-Sign 10{sup 6} M{sub Sun} black hole. The density at {approx}0.5 pc is about a factor of 30 times lower than inferred for the Milky Way Galactic Center, potentially due to a smaller number of mass-shedding massive stars. From our latest observations ({delta}t Almost-Equal-To 216 days) we find that the jet energy is E{sub j,iso} Almost-Equal-To 5 Multiplication-Sign 10{sup 53} erg (E{sub j} Almost-Equal-To 2.4 Multiplication-Sign 10{sup 51} erg for {theta}{sub j} = 0.1), the radius is r Almost-Equal-To 1.2 pc, the Lorentz factor is {Gamma}{sub j} Almost-Equal-To 2.2, the ambient density is n Almost-Equal-To 0.2 cm{sup -3}, and the projected angular size is r{sub proj} Almost-Equal-To 25 {mu}as, below the resolution of the VLBA+Effelsberg. Assuming no future changes in the observed evolution and a final integrated total energy of E{sub j} Almost-Equal-To 10{sup 52} erg, we predict that the radio emission from Sw 1644+57 should be detectable with the EVLA for several decades and will be resolvable with very long baseline interferometry in a few years.
- OSTI ID:
- 22016176
- Journal Information:
- Astrophysical Journal, Vol. 748, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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