Rykoff, E. S. and Aharonian, F. and Akerlof, C. W. and Ashley, M. C. B. and Barthelmy, S. D. and Flewelling, H. A. and Gehrels, N. and Göǧüş, E. and Kiziloǧlu, Ü. and Krimm, H. A. and McKay, T. A. and Özel, M. and Phillips, A. and Quimby, R. M. and Rowell, G. and Rujopakarn, W. and Schaefer, B. E. and Smith, D. A. and Vestrand, W. T. and Wheeler, J. C. and Wren, J. and Yuan, F. and Yost, S. A. (2009) Looking Into the Fireball: ROTSE-III and Swift Observations of Early Gamma-ray Burst Afterglows. Astrophysical Journal, 702 (1). pp. 489-505. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20090914-131650146
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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 γ-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 ≲ Γ_0 ≲ 1000, consistent with expectations.
|Additional Information:||© 20009 American Astronomical Society. Print publication: Issue 1 (2009 September 1); received 2009 March 27; accepted for publication 2009 June 8; published 2009 August 13. E.S.R. thanks the TABASGO foundation. This work has been supported by NASA grant NNG-04WC41G, NSF grants AST- 0407061 and PHY-0801007, the Australian Research Council’s Discovery Projects funding scheme, the University of New South Wales, the University of Texas, and the University of Michigan. H.A.F. has been supported by NSF grant AST 03- 35588 and by the Michigan Space Grant Consortium. F.Y. has been supported under NASA Swift Guest Investigator grants NNG-06GI90G and NNX-07AF02G. J.C.W. is supported in part by NSF grant AST-0707769. Special thanks to David Doss at McDonald Observatory, Toni Hanke at the H.E.S.S. site, and Tuncay O¨ zıs¸ık at TUG.|
|Subject Keywords:||gamma rays: bursts|
|Official Citation:||Looking Into the Fireball: ROTSE-III and Swift Observations of Early Gamma-ray Burst Afterglows E. S. Rykoff, F. Aharonian, C. W. Akerlof, M. C. B. Ashley, S. D. Barthelmy, H. A. Flewelling, N. Gehrels, E. Göǧüş, T. Güver, Ü. Kiziloǧlu, H. A. Krimm, T. A. McKay, M. Özel, A. Phillips, R. M. Quimby, G. Rowell, W. Rujopakarn, B. E. Schaefer, D. A. Smith, W. T. Vestrand, J. C. Wheeler, J. Wren, F. Yuan, and S. A. Yost 2009 ApJ 702 489-505 doi: 10.1088/0004-637X/702/1/489|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||15 Sep 2009 17:16|
|Last Modified:||26 Dec 2012 11:22|
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