University of Hertfordshire

From the same journal

From the same journal

The Early-Time Optical Properties of Gamma-Ray Burst Afterglows

Research output: Contribution to journalArticle

  • A. Melandri
  • C.G. Mundell
  • S. Kobayashi
  • C. Guidorzi
  • A. Gomboc
  • I.A. Steele
  • R.J. Smith
  • D. Bersier
  • C.J. Mottram
  • D. Carter
  • M.F. Bode
  • P.T. O'Brien
  • N. Tanvir
  • E. Rol
  • R. Chapman
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Original languageEnglish
Pages (from-to)1209-1230
JournalThe Astrophysical Journal
Publication statusPublished - 2008


We present a multiwavelength analysis of 63 gamma-ray bursts observed with the world's three largest robotic optical telescopes, the Liverpool and Faulkes Telescopes (North and South). Optical emission was detected for 24 GRBs with brightnesses ranging from R = 10 to 22 mag in the first 10 minutes after the burst. By comparing optical and X-ray light curves from t = 100 to ~106 seconds, we introduce four main classes, defined by the presence or absence of temporal breaks at optical and/or X-ray wavelengths. While 14/24 GRBs can be modeled with the forward-shock model, explaining the remaining 10 is very challenging in the standard framework even with the introduction of energy injection or an ambient density gradient. Early X-ray afterglows, even segments of light curves described by a power law, may be due to additional emission from the central engine. Thirty-nine GRBs in our sample were not detected and have deep upper limits (R < 22 mag) at early time. Of these, only 10 were identified by other facilities, primarily at near infrared wavelengths, resulting in a dark burst fraction of ~50%. Additional emission in the early-time X-ray afterglow due to late-time central engine activity may also explain some dark bursts by making the bursts brighter than expected in the X-ray band compared to the optical band.


Original article can be found at: Copyright American Astronomical Society DOI: 10.1086/591243 [Full text of this article is not available in the UHRA]

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