Article

Multiwavelength Analysis of the Intriguing GRB 061126: The Reverse Shock Scenario and Magnetization

A. GombocAstrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Birkenhead, CH41 1LD, UKS. KobayashiAstrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Birkenhead, CH41 1LD, UKC. GuidorziAstrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Birkenhead, CH41 1LD, UKA. MelandriAstrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Birkenhead, CH41 1LD, UKV. ManganoINAF-Instituto di Astrofisica Spaziale e Fisica Cosmica di Palermo, via Ugo La Malfa 153, 90146 Palermo, ItalyB. SbarufattiINAF-Instituto di Astrofisica Spaziale e Fisica Cosmica di Palermo, via Ugo La Malfa 153, 90146 Palermo, ItalyC. G. MundellAstrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Birkenhead, CH41 1LD, UKP. SchadyR. J. SmithAstrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Birkenhead, CH41 1LD, UKA. C. UpdikeDepartment of Physics and Astronomy, Clemson University, Clemson, SC 29634Д. А. КаннThüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, GermanyKuntal MisraAryabhatta Research Institute of Observational Sciences, Manora Peak, Nainital 263 129, IndiaE. RolDepartment of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH, UKA. PozanenkoSpace Research Institute (IKI), 84/32 Profsoyuznaya Street, Moscow 117997, RussiaA. J. Castro‐TiradoInstituto de Astrofísica de Andalucía (CSIC), P.O. Box 03004, E-18080 Granada, SpainG. C. AnupamaIndian Institute of Astrophysics, Bangalore, 560 034, IndiaD. BersierAstrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Birkenhead, CH41 1LD, UKM. F. BodeAstrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Birkenhead, CH41 1LD, UKD. CarterAstrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Birkenhead, CH41 1LD, UKP. A. CurranAstronomical Institute Anton Pannekoek, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, NetherlandsA. S. FruchterSpace Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218J. F. GrahamSpace Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218D. H. HartmannDepartment of Physics and Astronomy, Clemson University, Clemson, SC 29634M. IbrahimovUlugh Beg Astronomical Institute, Tashkent 700052, UzbekistanA. J. LevanDepartment of Physics, University of Warwick, Coventry CV4 7AL, UKA. MonfardiniAstrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Birkenhead, CH41 1LD, UKC. J. MottramAstrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Birkenhead, CH41 1LD, UKP. T. O’BrienDepartment of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH, UKP. PremaInstitute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UKD. K. SahuCenter for Research and Education in Science and Technology, Hosakote, Bangalore, 562 114, IndiaI. A. SteeleAstrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Birkenhead, CH41 1LD, UKN. R. TanvirDepartment of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH, UKK. WiersemaDepartment of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH, UK

The Astrophysical Journaljournal2008en

ABI

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=191 s) with four overlapping peaks in its γ-ray light curve. The X-ray afterglow, observed from 26 minutes to 20 days after the burst, shows a simple power-law decay with αX=1.290+/-0.008. 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 α1=1.48+/-0.06 to α2=0.88+/-0.03) approximately 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 there is no 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.

Topics

Gamma-ray bursts and supernovae Stellar, planetary, and galactic studies Astrophysical Phenomena and Observations

Identifiers

DOI: 10.1086/592062

Citations and references

Cited by 5 70 references

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