Article

GRB 081008: FROM BURST TO AFTERGLOW AND THE TRANSITION PHASE IN BETWEEN

F. YuanPhysics Department, University of Michigan, Ann Arbor, MI 48109, USAP. SchadyJ. L. RacusinDepartment of Astronomy & Astrophysics, The Pennsylvania State University, 525 Davey Lab, University Park, PA 16802, USAR. WillingaleDepartment of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UKT. KrühlerMax-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, GermanyP. T. O'BrienDepartment of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UKJ. GreinerMax-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, GermanyS. R. OatesE. S. RykoffPhysics Department, University of California at Santa Barbara, 2233B Broida Hall, Santa Barbara, CA 93106, USAF. AharonianMax-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, GermanyC. W. AkerlofPhysics Department, University of Michigan, Ann Arbor, MI 48109, USAM. C. B. AshleySchool of Physics, University of New South Wales, Sydney, NSW 2052, AustraliaS. D. BarthelmyNASA Goddard, Greenbelt, MD 20771, USAR. FilgasMax-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, GermanyH. A. FlewellingInstitute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USAN. GehrelsNASA Goddard, Greenbelt, MD 20771, USAE. GöğüşFaculty of Engineering & Natural Sciences, Sabancı University, Orhanlı, Tuzla 34956, İstanbul, TurkeyT. GüverDepartment of Astronomy and Steward Observatory, University of Arizona, Tucson, AZ 85721, USAD. HornsMax-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, GermanyÜ. KızıloǧluDepartment of Physics, Middle East Technical University, 06531 Ankara, TurkeyH. A. KrimmNASA Goddard, Greenbelt, MD 20771, USAT. A. McKayPhysics Department, University of Michigan, Ann Arbor, MI 48109, USAM. E. ÖzelDepartment of Mathematics, Cag University, Tarsus 33800, TurkeyA. PhillipsSchool of Physics, University of New South Wales, Sydney, NSW 2052, AustraliaR. M. QuimbyAstronomy Department, California Institute of Technology, 105-24, Pasadena, CA 91125, USAG. RowellMax-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, GermanyW. RujopakarnDepartment of Astronomy and Steward Observatory, University of Arizona, Tucson, AZ 85721, USAB. E. SchaeferDepartment of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803, USAW. T. VestrandLos Alamos National Laboratory, NIS-2 MS D436, Los Alamos, NM 87545, USAJ. C. WheelerDepartment of Astronomy, University of Texas, Austin, TX 78712, USAJ. WrenLos Alamos National Laboratory, NIS-2 MS D436, Los Alamos, NM 87545, USA

2010en

ABI

Abstract

We present a multi-wavelength study of GRB 081008, at redshift 1.967, by Swift, ROTSE-III, and Gamma-Ray Burst Optical/NearInfrared Detector. Compared to other Swift GRBs, GRB 081008 has a typical gamma-ray isotropic equivalent energy output (~1053 erg) during the prompt phase, and displayed two temporally separated clusters of pulses. The early X-ray emission seen by the Swift X-Ray Telescope was dominated by the softening tail of the prompt emission, producing multiple flares during and after the Swift Burst Alert Telescope detections. Optical observations that started shortly after the first active phase of gamma-ray emission showed two consecutive peaks. We interpret the first optical peak as the onset of the afterglow associated with the early burst activities. A second optical peak, coincident with the later gamma-ray pulses, imposes a small modification to the otherwise smooth light curve and thus suggests a minimal contribution from a probable internal component. We suggest the early optical variability may be from continuous energy injection into the forward shock front by later shells producing the second epoch of burst activities. These early observations thus provide a potential probe for the transition from the prompt phase to the afterglow phase. The later light curve of GRB 081008 displays a smooth steepening in all optical bands and X-ray. The temporal break is consistent with being achromatic at the observed wavelengths. Our broad energy coverage shortly after the break constrains a spectral break within optical. However, the evolution of the break frequency is not observed. We discuss the plausible interpretations of this behavior.

Identifiers

DOI: 10.1088/0004-637x/711/2/870

Citations and references

Cited by 20 references

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