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Publication Details
AFRICAN RESEARCH NEXUS
SHINING A SPOTLIGHT ON AFRICAN RESEARCH
earth and planetary sciences
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
Astrophysical Journal, Volume 748, No. 1, Article 36, Year 2012
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Description
We present continued radio observations of the tidal disruption event SwiftJ164449.3+573451 extending to δt 216days 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 δt 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 ρr -3/2 (0.1-1.2 pc) with a significant flattening at r 0.4-0.6 pc. The increase in energy cannot be explained with continuous injection from an Lt -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(> Γj)Γ-2.5j. The similar ratios of duration to dynamical timescale for Sw1644+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 0.5 pc in good agreement with the Bondi radius for a few × 106 M ⊙ black hole. The density at 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 (δt 216days) we find that the jet energy is E j, iso 5 × 1053 erg (Ej 2.4 × 1051 erg for θj = 0.1), the radius is r 1.2 pc, the Lorentz factor is Γj 2.2, the ambient density is n 0.2 cm -3, and the projected angular size is r proj 25 μas, below the resolution of the VLBA+Effelsberg. Assuming no future changes in the observed evolution and a final integrated total energy of Ej 10 52 erg, we predict that the radio emission from Sw1644+57 should be detectable with the EVLA for several decades and will be resolvable with very long baseline interferometry in a few years. © 2012 The American Astronomical Society. All rights reserved.
Authors & Co-Authors
Berger, Edo
United States, Cambridge
Harvard-smithsonian Center for Astrophysics
Zauderer, A.
United States, Cambridge
Harvard-smithsonian Center for Astrophysics
Pooley, Guy G.
United Kingdom, Cambridge
Department of Physics
Soderberg, Alicia M.
United States, Cambridge
Harvard-smithsonian Center for Astrophysics
Sari, Re'Em
United States, Cambridge
Harvard-smithsonian Center for Astrophysics
Israel, Jerusalem
Hebrew University of Jerusalem
Brunthaler, Andreas
Germany, Bonn
Max Planck Institute for Radio Astronomy
United States, Socorro
National Radio Astronomy Observatory Socorro
Bietenholz, Michael F.
Canada, Toronto
York University
South Africa, Krugersdorp
Hartebeesthoek Radio Astronomy Observatory
Statistics
Citations: 107
Authors: 7
Affiliations: 7
Identifiers
Doi:
10.1088/0004-637X/748/1/36
ISSN:
0004637X
e-ISSN:
15384357
Research Areas
Environmental