GRB 091024A and the nature of ultra-long gamma-ray bursts

F. J. Virgili, C. G. Mundell, V. Pal'Shin, C. Guidorzi, R. Margutti, A. Melandri, R. Harrison, S. Kobayashi, R. Chornock, A. Henden, A. C. Updike, S. B. Cenko, N. R. Tanvir, I. A. Steele, A. Cucchiara, A. Gomboc, A. Levan, Z. Cano, C. J. Mottram, N. R. ClayD. Bersier, D. Kopač, J. Japelj, A. V. Filippenko, W. Li, D. Svinkin, S. Golenetskii, D. H. Hartmann, P. A. Milne, G. Williams, P. T. O'Brien, D. B. Fox, E. Berger

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Abstract

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.

Original languageEnglish
Article number54
JournalAstrophysical Journal
Volume778
Issue number1
DOIs
Publication statusPublished - 20 Nov 2013

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Virgili, F. J., Mundell, C. G., Pal'Shin, V., Guidorzi, C., Margutti, R., Melandri, A., Harrison, R., Kobayashi, S., Chornock, R., Henden, A., Updike, A. C., Cenko, S. B., Tanvir, N. R., Steele, I. A., Cucchiara, A., Gomboc, A., Levan, A., Cano, Z., Mottram, C. J., ... Berger, E. (2013). GRB 091024A and the nature of ultra-long gamma-ray bursts. Astrophysical Journal, 778(1), [54]. https://doi.org/10.1088/0004-637X/778/1/54