GROND coverage of the main peak of gamma-ray burst 130925A

J. Greiner, H. -F. Yu, T. Krühler, D.~D. Frederiks, A. Beloborodov, P.~N. Bhat, J. Bolmer, H. van Eerten, R.~L. Aptekar, J. Elliott, S.~V. Golenetskii, J.~F. Graham, K. Hurley, D.~A. Kann, S. Klose, A. Nicuesa Guelbenzu, A. Rau, P. Schady, S. Schmidl, V. SudilovskyD.~S. Svinkin, M. Tanga, M.~V. Ulanov, K. Varela, A. von Kienlin, X. -L. Zhang

Research output: Contribution to journalArticlepeer-review


Aims.Prompt or early optical emission in gamma-ray bursts (GRBs) is notoriously difficult to measure, and observations of the dozen cases show a large variety of properties. Yet, such early emission promises to help us achieve a better understanding of the GRB emission process(es).
Methods. We performed dedicated observations of the ultra-long duration (T90 about 7000 s) Swift GRB 130925A in the optical/near-infrared with the 7-channel Gamma-Ray burst Optical and Near-infrared Detector (GROND) at the 2.2 m MPG/ESO telescope.
Results. We detect an optical/near-infrared flare with an amplitude of nearly 2 mag which is delayed with respect to the keV−MeV prompt emission by about 300−400 s. The decay time of this flare is shorter than the duration of the flare (500 s) or its delay.
Conclusions. While we cannot offer a straightforward explanation, we discuss the implications of the flare properties and suggest ways toward understanding it.
Original languageEnglish
Article numberA75
Pages (from-to)1-9
Number of pages9
JournalAstronomy & Astrophysics
Publication statusPublished - 20 Aug 2014


  • gamma rays
  • stars
  • radiation mechanisms
  • non-thermal


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