AAS 203rd Meeting, January 2004
Session 132 Gamma Ray Bursts: Processes and Phenomena
Oral, Thursday, January 8, 2004, 2:00-3:30pm, Centennial IV

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[132.01] Early Optical Afterglow from GRB 030418 and Progenitor Mass Loss

D. A. Smith, E. S. Rykoff (University of Michigan), P. A. Price (RSAA, Mt. Stromlo Observatory), C. W. Akerlof (University of Michigan), M. C. B. Ashley (UNSW), D. Bizyaev (University of Texas, El Paso), G. J. Garradd (RSAA, Mt. Stromlo Observatory), T. A. McKay (University of Michigan), R. H. McNaught (RSAA, Mt. Stromlo Observatory), A. Phillips (UNSW), R. Quimby (University of Texas, Austin), B. Schaefer (Louisiana State University), B. Schmidt (RSAA, Mt. Stromlo Observatory), W. T. Vestrand (Los Alamos National Laboratory), J. C. Wheeler (University of Texas, Austin), J. Wren (Los Alamos National Laboratory)

The ROTSE-IIIa telescope and the SSO-40 inch telescope, both located at Siding Spring Observatory, imaged the early time afterglow of GRB 030418. We detect optical emission that rises for ~600 s, slowly varies around R=17.3 mag for ~1400 s, and then fades as a power law of index \alpha=-1.36. This early afterglow behavior is qualitatively different from other afterglows such as GRB 990123 and GRB 021211, and may explain why so few early afterglows have been observed. We find that a simplified model of an absorbed afterglow embedded in a dense wind environment describes the data more accurately than the expected curve caused by a break in a cooling synchrotron spectrum passing through the optical band. If absorption does determine the behavior of this early afterglow, it provides further evidence for the connection between gamma-ray bursts and the collapse of massive stars.

The author(s) of this abstract have provided an email address for comments about the abstract: donaldas@umich.edu

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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.