Constraining the energy budget of GRB 080721

Rhaana L C Starling, Evert Rol, Alexander J van der Horst, Sung-Chul Yoon, Valentin D Pal'Shin, Cedric Ledoux, Kim L Page, Johan Peter Uldall Fynbo, Klass Wiersema, Nial R Tanvir, Pall Jakobsson, Cristiano Guidorzi, Peter A Curran, Andrew J Levan, Paul T O'Brien, Julian P Osborne, Dmitry S Svinkin, Antonio de Ugarte Postigo, Tim Oosting, Ian D Howarth

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We follow the bright, highly energetic afterglow of Swift-discovered GRB 080721 at z = 2.591 out to 36 d or 3 x 106 s since the trigger in the optical and X-ray bands. We do not detect a break in the late-time light curve inferring a limit on the opening angle of and setting tight constraints on the total energy budget of the burst of E luminance greater than or equal to 9.9 x 1051 erg within the fireball model. To obey the fireball model closure relations, the gamma-ray burst (GRB) jet must be expanding into a homogeneous surrounding medium and likely lies behind a significant column of dust. The energy constraint we derive can be used as an observational input for models of the progenitors of long GRBs: we discuss how such high collimation-corrected energies could be accommodated with certain parameters of the standard massive star core-collapse models. We can, however, most probably rule out a magnetar progenitor for this GRB which would require 100 per cent efficiency to reach the observed total energy.
Original languageEnglish
Pages (from-to)90 - 99
Number of pages10
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Publication statusPublished - 2009
Externally publishedYes

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