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Laskar, T and Alexander, KD and Berger, E and Fong, WF and Margutti, R and Shivvers, I and Williams, PKG and Kopač, D and Kobayashi, S and Mundell, C and Gomboc, A and Zheng, W and Menten, KM and Graham, ML and Filippenko, AV (2016) A REVERSE SHOCK in GRB 160509A. Astrophysical Journal, 833 (1). ISSN 0004-637X

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We present the second multi-frequency radio detection of a reverse shock in a γ-ray burst. By combining our extensive radio observations of the Fermi-Large Area Telescope γ-ray burst 160509A at z = 1.17 up to 20 days after the burst with Swift X-ray observations and ground-based optical and near-infrared data, we show that the afterglow emission comprises distinct reverse shock and forward shock contributions: the reverse shock emission dominates in the radio band at ≲10 days, while the forward shock emission dominates in the X-ray, optical, and near-infrared bands. Through multi-wavelength modeling, we determine a circumburst density of , supporting our previous suggestion that a low-density circumburst environment is conducive to the production of long-lasting reverse shock radiation in the radio band. We infer the presence of a large excess X-ray absorption column, N H ≈ 1.5 ×1022 , and a high rest-frame optical extinction, A V ≈ 3.4 mag. We identify a jet break in the X-ray light curve at , and thus derive a jet opening angle of , yielding a beaming-corrected kinetic energy and radiated γ-ray energy of erg and erg (1-104 keV, rest frame), respectively. Consistency arguments connecting the forward shocks and reverse shocks suggest a deceleration time of s ≈ T 90, a Lorentz factor of , and a reverse-shock-to-forward-shock fractional magnetic energy density ratio of . Our study highlights the power of rapid-response radio observations in the study of the properties and dynamics of γ-ray burst ejecta. © 2016. The American Astronomical Society. All rights reserved.

Item Type: Article
Uncontrolled Keywords: 0201 Astronomical And Space Sciences, 0305 Organic Chemistry, 0306 Physical Chemistry (Incl. Structural)
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Q Science > QD Chemistry
Divisions: Astrophysics Research Institute
Publisher: American Astronomical Society
Date Deposited: 09 Jan 2017 12:10
Last Modified: 06 Sep 2017 14:11
DOI or Identification number: 10.3847/1538-4357/833/1/88
URI: http://researchonline.ljmu.ac.uk/id/eprint/5204

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