AAS 201st Meeting, January, 2003
Session 84. Gamma Ray Observations
Poster, Wednesday, January 8, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[84.01] Optical Observations of the GRB 021004 Afterglow

N. Mirabal (Columbia U.), R. Chornock, A.V. Filippenko (U.C. Berkeley), J.P. Halpern (Columbia U.), D. Terndrup (OSU)

The rapid localization of GRB 021004 by the HETE-2\/ satellite allowed nearly continuous monitoring of its early optical afterglow decay, as well as high-quality optical spectra that determined a redshift of 2.328 for its host, an active starburst galaxy with strong Lyman \alpha emission and several absorption lines. We report the detection of statistically significant fluctuations about the mean power-law optical decay. In particular, an equal number of well-sampled, high S/N images in B, V, R, and I filters were obtained during the period 15--24 hours after the burst, which finely sampled one of the largest such deviations. Fluctuations must be present at some level due to inhomogeneities in the circumburst medium and/or if the afterglow is ``refreshed'' by collisions among separate shells of ejecta. We will discuss the observational properties of these multicolor light curves, and possible explanations of the small-scale fluctuations. Interpretations of complex spectral absorption features in the Si~IV and C~IV lines that are blueshifted by up to ~ 3,200 km~s-1 from the redshift of the host galaxy will also be discussed.

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