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

Horesh, Assaf and Cenko, S. Bradley and Perley, Daniel A. and Kulkarni, S. R. and Hallinan, Gregg and Bellm, Eric (2015) The Unusual Radio Afterglow of the Ultra-Long Gamma-Ray Burst GRB 130925A. Astrophysical Journal, 812 (1). Art. No. 86. ISSN 0004-637X.

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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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Horesh, Assaf0000-0002-5936-1156
Cenko, S. Bradley0000-0003-1673-970X
Perley, Daniel A.0000-0001-8472-1996
Kulkarni, S. R.0000-0001-5390-8563
Hallinan, Gregg0000-0002-7083-4049
Bellm, Eric0000-0001-8018-5348
Additional Information:© 2015. The American Astronomical Society. Received 2015 May 26; accepted 2015 September 10; published 2015 October 9. We thank R. Barniol Duran, T. Piran, E. Nakar, R. Sari, and K. Mooley for useful discussions. We thank the VLA staff for promptly scheduling the observation of this target of opportunity. We also acknowledge the use of the Astronomical Matlab Packages by Ofek (2014). The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Research leading to these results has received funding from the EU/FP7 via ERC grant 307260; ISF, Minerva, and Weizmann-UK grants; as well as the Quantum Universe I-Core Program of the Planning and Budgeting Committee and the Israel Science Foundation. S.B.C. acknowledges funding from NASA grant NNH13ZDA001N. Support for D.A.P was provided by NASA through an award issued by JPL/Caltech, and through Hubble Fellowship grant HST-HF-51296.01-A awarded by the Space Telescope Science Institute.
Funding AgencyGrant Number
European Research Council (ERC)307260
Israel Science FoundationUNSPECIFIED
Quantum Universe I-Core Program of the Planning and Budgeting CommitteeUNSPECIFIED
NASA Hubble FellowshipHST-HF-51296.01-A
Subject Keywords:gamma-ray burst: general
Issue or Number:1
Record Number:CaltechAUTHORS:20151207-092434694
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Official Citation:Assaf Horesh et al 2015 ApJ 812 86
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:62636
Deposited By: Ruth Sustaita
Deposited On:08 Dec 2015 16:28
Last Modified:20 Nov 2019 05:37

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