Constraining the energy budget of GRB 080721
Abstract
We follow the bright, highly energetic afterglow of Swift-discovered GRB 080721 at z=2.591 out to 36 days or 3e6 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 theta_j >= 7.3 deg and setting tight constraints on the total energy budget of the burst of E_gamma >= 9.9e51 erg within the fireball model. To obey the fireball model closure relations the 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 observational input for models of the progenitors of long gamma-ray bursts: 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% efficiency to reach the observed total energy.
Cite
@article{arxiv.0812.2490,
title = {Constraining the energy budget of GRB 080721},
author = {R. L. C. Starling and E. Rol and A. J. van der Horst and S. -C. Yoon and V. Pal'shin and C. Ledoux and K. L. Page and J. P. U. Fynbo and K. Wiersema and N. R. Tanvir and P. Jakobsson and C. Guidorzi and P. A. Curran and A. J. Levan and P. T. O'Brien and J. P. Osborne and D. Svinkin and A. de Ugarte Postigo and T. Oosting and I. D. Howarth},
journal= {arXiv preprint arXiv:0812.2490},
year = {2009}
}
Comments
11 pages, 6 figures (3 colour), accepted for publication in MNRAS following minor revision of Sections 4.2 and 5