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Early-Time VLA Observations and Broadband Afterglow Analysis of the FERMI/LAT Detected GRB 130907A

Veres, P, Corsi, A, Frail, DA, Cenko, SB and Perley, DA (2015) Early-Time VLA Observations and Broadband Afterglow Analysis of the FERMI/LAT Detected GRB 130907A. The Astrophysical Journal, 810 (1). ISSN 1538-4357

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We present multi-wavelength observations of the hyper-energetic gamma-ray burst (GRB) 130907A, a Swift-discovered burst with early radio observations starting at ≈4 hr after the γ-ray trigger. GRB 130907A was also detected by the Fermi/LAT instrument and at late times showed a strong spectral evolution in X-rays. We focus on the early-time radio observations, especially at >10 GHz, to attempt to identify reverse shock signatures. While our radio follow-up of GRB 130907A ranks among the earliest observations of a GRB with the Karl G. Jansky Very Large Array, we did not see an unambiguous signature of a reverse shock. While a model with both reverse and forward shock can correctly describe the observations, the data is not constraining enough to decide upon the presence of the reverse-shock component. We model the broadband data using a simple forward-shock synchrotron scenario with a transition from a wind environment to a constant density interstellar medium (ISM) in order to account for the observed features. Within the confines of this model, we also derive the underlying physical parameters of the fireball, which are within typical ranges except for the wind density parameter (A∗), which is higher than those for bursts with wind-ISM transition, but typical for the general population of bursts. We note the importance of early-time radio observations of the afterglow (and of well-sampled light curves) for unambiguously identifying the potential contribution of the reverse shock. © 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
Divisions: Astrophysics Research Institute
Publisher: American Astronomical Society
Date Deposited: 21 Feb 2017 12:10
Last Modified: 04 Sep 2021 11:53
DOI or ID number: 10.1088/0004-637X/810/1/31
URI: https://researchonline.ljmu.ac.uk/id/eprint/5687
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