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          Institute: MPI für Kernphysik     Collection: High-Energy Astrophysics     Display Documents

ID: 281380.0, MPI für Kernphysik / High-Energy Astrophysics
Optical Light Curve and Cooling Break of GRB 050502A
Authors:Rykoff, E.S.; Aharonian, F.; Akerlof, C. W.; Alatalo, K.; Ashley, M. C. B.; Güver, T.; Horns, Dieter; Blake, C. H.; Kiziloglü, Ü.; McKay, T. A.; Özel, M.; Phillips, A.; Quimby, R. M.; Schaefer, B. E.; Smith, D. A.; Swan, H. F.; Vestrand, W. T.; Wheeler, J. C.; Wren, J.; Yost, S. A.; Gögüs, E.; Bloom, J. S.; Boettcher, M.; Falco, E. E.; Halpern, J. P.; Joshi, M.; Mirabal, N.; Rujopakarn, W.; Shields, J. C.; Skrutskie, M.; Starr, D. L.; Szentgyorgyi, A.
Research Context:gamma rays: bursts
Date of Publication (YYYY-MM-DD):2005-01-10
Title of Journal:The Astrophysical Journal
Issue / Number:2, part 1
Start Page:959
End Page:966
Copyright:The American Astronomical Society
Review Status:Peer-review
Audience:Experts Only
Abstract / Description:We present light curves of the afterglow of GRB 050502A, including very early data at t - tGRB < 60 s. The light curve is composed of unfiltered ROTSE-IIIb optical observations from 44 s to 6 hr postburst, R-band MDM observations from 1.6 to 8.4 hr postburst, and PAIRITEL JHKs observations from 0.6 to 2.6 hr postburst. The optical light curve is fit by a broken power law, where tα steepens from α = -1.13 ± 0.02 to -1.44 ± 0.02 at ±5700 s. This steepening is consistent with the evolution expected for the passage of the cooling frequency νc through the optical band. Even in our earliest observation at 44 s postburst, there is no evidence that the optical flux is brighter than a backward extrapolation of the later power law would suggest. The observed decay indices and spectral index are consistent with either an ISM or a wind fireball model, but slightly favor the ISM interpretation. The expected spectral index in the ISM interpretation is consistent within 1 σ with the observed spectral index β = -0.8 ± 0.1; the wind interpretation would imply a spectral index slightly ( ±2 σ) shallower than observed. A small amount of dust extinction at the source redshift could steepen an intrinsic spectrum sufficiently to account for the observed value of β. In this picture, the early optical decay, with the peak at or below 4.7 × 1014 Hz at 44 s, requires very small electron and magnetic energy partitions from the fireball.
Free Keywords:gamma rays: bursts
External Publication Status:published
Document Type:Article
Affiliations:MPI für Kernphysik/Group H. J. Völk/High Energy Astrophysics (F. Aharonian)
External Affiliations:University of Michigan, 2477 Randall Laboratory, 450 Church Street, Ann Arbor, MI 48104;
Astronomy Department, 601 Campbell Hall, University of California, Berkeley, CA 94720;
School of Physics, Department of Astrophysics and Optics, University of New South Wales, Sydney, NSW 2052, Australia;
Harvard College Observatory, Cambridge, MA 02138;
Ohio University, Athens, OH 45701;
Sabanci University, Orhanli-Tuzla 34956 Istanbul, Turkey;
Istanbul University Science Faculty, Department of Astronomy and Space Sciences, 34119, University-Istanbul, Turkey,
Columbia Astrophysics Lab, Columbia University, 550 West 120th Street, Mail Code 5230, New York, NY 10027-6601;
Middle East Technical University, 06531 Ankara, Turkey;
Çanakkale Onsekiz Mart Üniversitesi, Terziolu 17020, Çanakkale, Turkey;
Department of Astronomy, University of Texas, Austin, TX 78712;
Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803;
Department of Astronomy, University of Virginia, P.O. Box 3818, Charlottesville, VA 22903;
Gemini Observatory, Hilo, HI 96720;
Los Alamos National Laboratory, NIS-2 MS D436, Los Alamos, NM 87545;
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