F. J. Virgili, Astrophysics Research Institute, Liverpool John Moores University
C. G. Mundell, Astrophysics Research Institute, Liverpool John Moores University
V. Pal'shin, Ioffe Physical Technical Institute, St. Petersburg
C. Guidorzi, Department of Physics and Earth Sciences, University of Ferrara
R. Margutti, Harvard-Smithsonian Center for Astrophysic
A. Melandri, INAF/Brera Astronomical Observatory
R. Harrison, Astrophysics Research Institute, Liverpool John Moores University
S. Kobayashi, Astrophysics Research Institute, Liverpool John Moores University
R. Chornock, Harvard-Smithsonian Center for Astrophysic
A Henden, AAVSO
A C. Updike, Roger Williams University
S B. Cenko, University of California - Berkeley
N R. Tanvir, University of Leicester
I A. Steele, Liverpool John Moores University
A Cucchiara, University of California - Santa Cruz
A Gomboc, University of Ljubljana
A Levan, University of Warwick
Z Cano, University of Iceland
C J. Mottram, Liverpool John Moores University
N R. Clay, Liverpool John Moores University
D Bersier, Liverpool John Moores University
D Kopac, University of Ljubljana
J Japelj, University of Ljubljana
A V. Filippenko, University of California - Berkeley
W Li, University of California - Berkeley
D Svinkin, Ioffe Physico-Technical Institute
S Golenetskii, Ioffe Physico-Technical Institute
Dieter H. Hartmann, Clemson UniversityFollow
P A. Milne, University of Arizona
G Williams, University of Arizona
P T. O'Brien, University of Leicester
D B. Fox, Pennsylvania State University
E Berger, Harvard-Smithsonian Center for Astrophysics

Document Type


Publication Date

Fall 11-20-2013

Publication Title

The Astrophysical Journal






The American Astronomical Society


We present a broadband study of gamma-ray burst (GRB) 091024A within the context of other ultra-long-duration GRBs. An unusually long burst detected by Konus–Wind (KW), Swift, and Fermi, GRB 091024A has prompt emission episodes covering ∼1300 s, accompanied by bright and highly structured optical emission captured by various rapid-response facilities, including the 2 m autonomous robotic Faulkes North and Liverpool Telescopes, KAIT, S-LOTIS, and the Sonoita Research Observatory. We also observed the burst with 8 and 10 m class telescopes and determine the redshift to be z = 1.0924 ± 0.0004. We find no correlation between the optical and γ-ray peaks and interpret the optical light curve as being of external origin, caused by the reverse and forward shock of a highly magnetized jet (RB ≈ 100–200). Low-level emission is detected throughout the near-background quiescent period between the first two emission episodes of the KW data, suggesting continued central-engine activity; we discuss the implications of this ongoing emission and its impact on the afterglow evolution and predictions. We summarize the varied sample of historical GRBs with exceptionally long durations in gamma-rays ( 1000 s) and discuss the likelihood of these events being from a separate population; we suggest ultra-long GRBs represent the tail of the duration distribution of the long GRB population.


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