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The Unusual Radio Afterglow of the Ultra-Long Gamma-Ray Burst GRB 130925A

Horesh, A, Cenko, SB, Perley, DA, Kulkarni, SR, Hallinan, G and Bellm, E (2015) The Unusual Radio Afterglow of the Ultra-Long Gamma-Ray Burst GRB 130925A. The Astrophysical Journal, 812 (1). ISSN 1538-4357

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GRB 130925A is one of the recent additions to the growing family of ultra-long gamma-ray bursts (GRBs; T90 ≳1000 s). While the X-ray emission of ultra-long GRBs have been studied extensively in the past, no comprehensive radio data set has been obtained so far. We report here the early discovery of an unusual radio afterglow associated with the ultra-long GRB 130925A. The radio emission peaks at low-frequencies (∼7 GHz) at early times, only 2.2 days after the burst occurred. More notably, the radio spectrum at frequencies above 10 GHz exhibits a rather steep cut-off, compared to other long GRB radio afterglows. This cut-off can be explained if the emitting electrons are either mono-energetic or originate from a rather steep, dN/dE ∝ E-4, power-law energy distribution. An alternative electron acceleration mechanism may be required to produce such an electron energy distribution. Furthermore, the radio spectrum exhibits a secondary underlying and slowly varying component. This may hint that the radio emission we observed is comprised of emission from both a reverse and a forward shock. We discuss our results in comparison with previous works that studied the unusual X-ray spectrum of this event and discuss the implications of our findings on progenitor scenarios.
© 2015. 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: 21 Feb 2017 09:54
Last Modified: 04 Sep 2021 11:54
DOI or ID number: 10.1088/0004-637X/812/1/86
URI: https://researchonline.ljmu.ac.uk/id/eprint/5617
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