Article

LOOKING INTO THE FIREBALL: ROTSE-III AND<i>SWIFT</i>OBSERVATIONS OF EARLY GAMMA-RAY BURST AFTERGLOWS

E. S. RykoffPhysics Department, University of California at Santa Barbara, 2233B Broida Hall, Santa Barbara, CA 93106, USAF. AharonianDivision Prof. Dr. Werner Hofmann, MPI for Nuclear Physics, Max Planck SocietyC. AkerlofDepartment of Physics, University of Michigan - Ann Arbor, MI-48109, USAM. C. B. AshleySchool of Physics, Department of Astrophysics and Optics, University of New South Wales, Sydney, NSW 2052 (Australia)A. P. BeardmoreNASA Goddard Space Flight Center, Laboratory for High-Energy Astrophysics, Greenbelt, MD 20771, USAH. FlewellingDepartment of Physics, University of Michigan - Ann Arbor, MI-48109, USAN. GehrelsNASA Goddard Space Flight Center, Laboratory for High-Energy Astrophysics, Greenbelt, MD 20771, USAErsin GöğüşFaculty of Engineering and Sciences, Sabanci University, Orhanli-Tuzla, 34956 Istanbul (Turkey)Tolga GüverDepartment of Astronomy,University of Arizona,Tucson,AZ 85721,USAÜ. KızıloǧluMiddle East Technical University, 06531 Ankara, TurkeyH. A. KrimmUniversities Space Research Association, 10227 Wincopin Circle, Suite 212, Columbia, MD 21044, USATimothy A. McKayDepartment of Physics, University of Michigan - Ann Arbor, MI-48109, USAM. E. ÖzelÇağ Üniversitesi, Faculty of Arts and Sciences, Yenice-Tarsus/Mersin, TurkeyA. PhillipsSchool of Physics, Department of Astrophysics and Optics, University of New South Wales, Sydney, NSW 2052 (Australia)R. M. QuimbyDivision of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena, CA 91125, USAGavin RowellDivision Prof. Dr. Werner Hofmann, MPI for Nuclear Physics, Max Planck SocietyW. RujopakarnSteward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ, 85721 USABradley E. SchaeferDepartment of Physics & Astronomy, Louisiana State University, Baton Rouge, LA 70803, USAD. A. SmithGuilford College, Greensboro, NC 27410, USAW. T. VestrandLos Alamos National Laboratory, NIS-2 MS D436, Los Alamos, NM 87545, USAJ. Craig WheelerDepartment of Astronomy, University of Texas, Austin, TX, 78712, USAJ. WrenLos Alamos National Laboratory, NIS-2 MS D436, Los Alamos, NM 87545, USAF. YuanDepartment of Physics, University of Michigan - Ann Arbor, MI-48109, USAS. A. YostDepartment of Physics, College of St. Benedict/St. John's University, Collegeville, MN 56321, USA

2009en

ABI

Abstract

We report on a complete set of early optical afterglows of gamma-ray bursts (GRBs) obtained with the Robotic Optical Transient Search Experiment (ROTSE-III) telescope network from 2005 March through 2007 June. This set is comprised of 12 afterglows with early optical and Swift/X-Ray Telescope observations, with a median ROTSE-III response time of 45 s after the start of gamma-ray emission (8 s after the GCN notice time). These afterglows span 4 orders of magnitude in optical luminosity, and the contemporaneous X-ray detections allow multi-wavelength spectral analysis. Excluding X-ray flares, the broadband synchrotron spectra show that the optical and X-ray emission originate in a common region, consistent with predictions of the external forward shock in the fireball model. However, the fireball model is inadequate to predict the temporal decay indices of the early afterglows, even after accounting for possible long-duration continuous energy injection. We find that the optical afterglow is a clean tracer of the forward shock, and we use the peak time of the forward shock to estimate the initial bulk Lorentz factor of the GRB outflow, and find 100 less than or similar to Gamma(0) less than or similar to 1000, consistent with expectations.

Identifiers

DOI: 10.1088/0004-637x/702/1/489

Citations and references

Cited by 20 references

Metrics — AkademScholar