Late‐Time Observations of the Afterglow and Environment of GRB 030329

Abstract

We present Very Long Baseline Interferometry (VLBI) observations 217 days after the gamma-ray burst of 2003 March 29. These observations provide further measurements of the size and position of GRB 030329 that are used to constrain the expansion rate and proper motion of this nearby GRB. The expansion rate appears to be slowing down with time, favoring expansion into a constant density interstellar medium, rather than a circumstellar wind with an r -2 density profile. We also present late time Arecibo observations of the redshifted HI and OH absorption spectra towards GRB 030329. No absorption (or emission) is seen allowing us to place limits on the atomic neutral hydrogen of NH < 8.5 x 10 20 cm -2, and molecular hydrogen of NH2 < 1.4 x 10 22 cm -2. Finally, we present VLA limits on the radio polarization from the afterglow of <2% at late times.