AAS 201st Meeting, January, 2003
Session 69. Gamma Ray Observations
Oral, Tuesday, January 7, 2003, 2:00-3:30pm, 616-617

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[69.02] Optical Spectropolarimetry of the GRB 020813 Afterglow

A.J. Barth, R. Sari, M.H. Cohen, D.W. Fox, P.A. Price, S.R. Kulkarni (Caltech), R.W. Goodrich (Keck Observatory), J.S. Bloom (Harvard-Smithsonian CfA)

The optical afterglow of GRB 020813 was observed for 3 hours with the LRIS spectropolarimeter at the Keck-I telescope, beginning 4.7 hours after the burst was detected by HETE. This is the first spectropolarimetry data ever obtained for a GRB afterglow. The spectrum reveals numerous metal absorption lines that we identify with two systems at z=1.223 and z=1.254, constraining the GRB itself to lie at z \geq 1.254. We also detect an [O II] \lambda3727 emission line at the same redshift as the more distant absorption system, and we identify the galaxy at z=1.254 as the likely host of the GRB. Over the wavelength range 3500-8800 Å, the afterglow emission has a linear polarization of 2.4-3.1%. After correcting for Galactic interstellar polarization, we find p = 1.9-2.4% at a position angle of 150-160 degrees, with some evidence for wavelength-dependent polarization variability during the 3 hours of observation. We will discuss how this dataset can constrain models for GRB afterglow emission and polarization.

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Bulletin of the American Astronomical Society, 34, #4
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