A. Gomboc, Faculty of Mathematics and Physics, University of Ljubljan & Astrophysics Research Institute, Liverpool John Moores University
S. Kobayashi, Astrophysics Research Institute, Liverpool John Moores University
C. Guidorzi, Astrophysics Research Institute, Liverpool John Moores University & INAFYOsservatorio Astronomico di Brera
A. Melandri, Astrophysics Research Institute, Liverpool John Moores University
V. Mangano, INAF-Instituto di Astrofisica Spaziale e Fisica Cosmica di Palermo
B. Sbarufatti, INAF-Instituto di Astrofisica Spaziale e Fisica Cosmica di Palermo
C. G. Mundell, Astrophysics Research Institute, Liverpool John Moores University
P. Schady, The UCL Mullard Space Science Laboratory
R. J. Smith, Astrophysics Research Institute, Liverpool John Moores University
A C. Updike, Clemson University
D A. Kann, Thüringer Landessternwarte Tautenburg
K Misra, Aryabhatta Research Institute of Observational Sciences
E Rol, University of Leicester
A Pozanenko, Space Research Institute (IKI)
A J. Castro-Tirado, Instituto de Astrofísica de Andalucía (CSIC)
G C. Anupama, Indian Institute of Astrophysics
D Bersier, Liverpool John Moores University
M F. Bode, Liverpool John Moores University
D Carter, Liverpool John Moores University
P Curran, University of Amsterdam
A Fruchter, Space Telescope Science Institute
J Graham, Space Telescope Science Institute
Dieter H. Hartmann, Clemson UniversityFollow
M Ibrahimov, Ulugh Beg Astronomical Institute
A Levan, University of Warwick
A Monfardini, Liverpool John Moores University
C J. Mottram, Liverpool John Moores University
P T. O'Brien, University of Leicester
P Prema, University of Cambridge
D K. Sahu, Center for Research and Education in Science and Technology
I A. Steele, Liverpool John Moores University
N R. Tanvir, University of Leicester
K Wiersema, University of Leicester

Document Type

Article

Publication Date

Fall 11-1-2008

Publication Title

The Astrophysical Journal

Volume

687

Issue

1

Publisher

The American Astronomical Society

Abstract

We present a detailed study of the prompt and afterglow emission from Swift GRB 061126 using BAT, XRT, UVOT data and multicolor optical imaging from 10 ground-based telescopes. GRB 061126 was a long burst (T90 ¼191 s) with four overlapping peaks in its -ray light curve. The X-ray afterglow, observed from 26 minutes to 20 days after the burst, shows a simple power-law decay with X ¼1:290 Æ0:008. Optical observations presented here cover the time range from 258 s (Faulkes Telescope North) to 15 days (Gemini North) after the burst; the decay rate of the optical afterglow shows a steep-to-shallow transition (from 1 ¼1:48 Æ0:06 to 2 ¼0:88 Æ0:03) ap-proximately 13 minutes after the burst. We suggest the early, steep component is due to a reverse shock and show that the magnetic energy density in the ejecta, expressed as a fraction of the equipartition value, is a few 10 times larger than in the forward shock in the early afterglow phase. The ejecta might be endowed with primordial magnetic fields at the central engine.The optical light curve implies a late time break at about 1.5 days after the burst, while the reisno evidence of the simultaneous break in the X-ray light curve. We model the broadband emission and show that some afterglow characteristics (the steeper decay in X-ray and the shallow spectral index from optical to X-ray) are difficult to explain in the framework of the standard fireball model. This might imply that the X-ray afterglow is due to an additional emission process, such as late-time central engine activity rather than blast-wave shock emission. The possible chromatic break at 1.5 days after the burst would give support to the additional emission scenario.

Comments

This manuscript has been published in the Astrophysical Journal. Please find the published version here (note that a subscription is necessary to access this version):

http://iopscience.iop.org/0004-637X/687/1/443

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