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Published January 20, 2014 | Published + Submitted
Journal Article Open

The Afterglow of GRB 130427A from 1 to 10^(16) GHz

Abstract

We present multiwavelength observations of the afterglow of GRB 130427A, the brightest (in total fluence) gamma-ray burst (GRB) of the past 29 yr. Optical spectroscopy from Gemini-North reveals the redshift of the GRB to be z = 0.340, indicating that its unprecedented brightness is primarily the result of its relatively close proximity to Earth; the intrinsic luminosities of both the GRB and its afterglow are not extreme in comparison to other bright GRBs. We present a large suite of multiwavelength observations spanning from 300 s to 130 days after the burst and demonstrate that the afterglow shows relatively simple, smooth evolution at all frequencies, with no significant late-time flaring or rebrightening activity. The entire data set from 1 GHz to 10 GeV can be modeled as synchrotron emission from a combination of reverse and forward shocks in good agreement with the standard afterglow model, providing strong support to the applicability of the underlying theory and clarifying the nature of the GeV emission observed to last for minutes to hours following other very bright GRBs. A tenuous, wind-stratified circumburst density profile is required by the observations, suggesting a massive-star progenitor with a low mass-loss rate, perhaps due to low metallicity. GRBs similar in nature to GRB 130427A, inhabiting low-density media and exhibiting strong reverse shocks, are probably not uncommon but may have been difficult to recognize in the past owing to their relatively faint late-time radio emission; more such events should be found in abundance by the new generation of sensitive radio and millimeter instruments.

Additional Information

© 2014 American Astronomical Society. Received 2013 July 16; accepted 2013 November 18; published 2014 January 6. D.A.P. acknowledges a prescient conversation on 2013 April 18 with A. Collazzi in Nashville on the origin of the lack (at the time) of Fermi-LAT GRBs at z < 0.5, and comments from Y. Fan and A. van der Horst. We are grateful for excellent staff assistance at the various observatories where we obtained data. We thank B. Sesar for the execution of our P200 target-of opportunity observations and assistance with the data reduction. J. Carpenter and CARMA provided additional DDT time to continue observations of GRB 130427A after t = 2 days, and K. Alatalo assisted with flagging and reducing these observations. We thank S. Kulkarni for the Keck/LRIS data. We would like to thank all members of the Swift and Fermi teams, whose successful missions made this work possible. The National Radio Astronomy Observatory is a facility of the NSF operated under cooperative agreement by Associated Universities, Inc. Support for CARMA construction was derived from the states of California, Illinois, and Maryland, the James S. McDonnell Foundation, the Gordon and Betty Moore Foundation, the Kenneth T. and Eileen L. Norris Foundation, the University of Chicago, the Associates of the California Institute of Technology, and the NSF. Ongoing CARMA development and operations are supported by the NSF under a cooperative agreement, and by the CARMA partner universities. The article contains data taken with the IRAM Plateau deBure interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain). We acknowledge the support of the Spanish Ministerio de Ciencia y Tecnología through Projects AYA2009-14000-C03-01/ESP, AYA2011-29517-C03-01, and AYA2012-39727-C03-01. KAIT and its ongoing operation were made possible by donations from Sun Microsystems, Inc., the Hewlett-Packard Company, Auto-Scope Corporation, Lick Observatory, the NSF, the University of California, the Sylvia and Jim Katzman Foundation, and the TABASGO Foundation. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA; the Observatory was made possible by the generous financial support of the W. M. Keck Foundation. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester, and the NASA Extragalactic Database. Part of the funding for GROND (both hardware as well as personnel) was generously granted from the Leibniz-Prize to Prof. G. Hasinger (DFG grant HA 1850/28-1). D.A.K. acknowledges F. Ludwig and U. Laux for helping to obtain the TLS images. Support for this research was provided by NASA through Hubble Fellowship grant HST-HF-51296.01-A awarded by the Space Telescope Science Institute, which is operated for NASA by the Association of Universities for Research in Astronomy, Inc., under contract NAS 5-26555. A.V.F.'s group at UC Berkeley has received generous financial assistance from Gary and Cynthia Bengier, the Christopher R. Redlich Fund, the Richard and Rhoda Goldman Fund, the TABASGO Foundation, NSF grant AST-1211916, and NASA/Swift grants NNX10AI21G and NNX12AD73G. E.S. acknowledges assistance from the Scientific and Technological Research Council of Turkey (TÜBİTAK) through project 112T224. X.H.Z. acknowledges partial support by the NSFC (No. 11203067), Yunnan Natural Science Foundation (2011FB115), and the West Light Foundation of the CAS. J. Mao is supported by Grants-in-Aid for Foreign JSPS Fellow (No. 24.02022). J. M. Bai is supported by the NSFC (No. 11133006). A.S.P. and A.A.V. acknowledge assistance from RFFI grants 12-02-01336 and 13-01-92204. S.S. acknowledges support by the Thüringer Ministerium für Bildung, Wissenschaft und Kultur under FKZ 12010-514. S.K. acknowledges support by DFG grant Kl 766/16-1. Facilities: Swift, Fermi, PO:1.5m, UKIRT,Max Planck:2.2m, Hale, Gemini:Gillett, CARMA, VLA, Keck:I, Shane, KAIT, Nickel, IRAM: Interferometer.

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Published - 0004-637X_781_1_37.pdf

Submitted - 1307.4401v4.pdf

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Created:
August 22, 2023
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