First ALMA Light Curve Constrains Refreshed Reverse Shocks and Jet Magnetization in GRB 161219B
Alexander, Kate D.
Kilpatrick, Charles D.
Milne, P. A.
Drout, Maria R.
Mundell, C. G.
Duran, Rodolfo Barniol
Menten, Karl M.
Williams, Peter K. G.
AffiliationUniv Arizona, Steward Observ
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PublisherIOP PUBLISHING LTD
CitationTanmoy Laskar et al 2018 ApJ 862 94
Rights© 2018. The American Astronomical Society. All rights reserved.
Collection InformationThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at email@example.com.
AbstractWe present detailed multiwavelength observations of GRB 161219B at z = 0.1475, spanning the radio to X-ray regimes, and the first Atacama Large Millimeter/submillimeter Array (ALMA) light curve of a gamma-ray burst (GRB) afterglow. The centimeter- and millimeter-band observations before 8.5 days require emission in excess of that produced by the afterglow forward shock (FS). These data are consistent with radiation from a refreshed reverse shock (RS) produced by the injection of energy into the FS, signatures of which are also present in the X-ray and optical light curves. We infer a constant-density circumburst environment with an extremely low density, n(0) approximate to 3 x 10(-4 )cm(-3), and show that this is a characteristic of all strong RS detections to date. The Karl G. Lansky Very Large Array (VLA) observations exhibit unexpected rapid variability on roughly minute timescales, indicative of strong interstellar scintillation. The X-ray, ALMA, and VLA observations together constrain the jet break time, t(jet) approximate to 32 days, yielding a wide jet opening angle of theta(jet) approximate to 13 degrees, implying beaming-corrected gamma-ray and kinetic energies of E-gamma approximate to 4.9 x 10(48) erg and E-K approximate to 1.3 x 10(50) erg, respectively. Comparing the RS and FS emission, we show that the ejecta are only weakly magnetized, with relative magnetization, R-B approximate to 1, compared to the FS. These direct, multifrequency measurements of a refreshed RS spanning the optical to radio bands highlight the impact of radio and millimeter data in probing the production and nature of GRB jets.
VersionFinal published version
SponsorsNSF [AST-1411763]; NASA [NNX15AE50G]; Science and Technology Facilities Council; W. M. Keck Foundation; Spanish MINECO [AyA2014-55216]; [15A-235]