Stirring the embers: High-sensitivity VLBI observations of GRB 030329

We present high-sensitivity Very Long Baseline Interferometry (VLBI) observations 806 days after the 7-ray burst of 2003 March 29 (GRB 030329). The angular diameter of the radio afterglow is measured to be 0.347 ±0.09 mas, corresponding to 0.99 ±0.26 pc at the redshift of GRB 030329 (z = 0.1685). The evolution of the image size favors a uniform external density over an R^-2 windlike density profile (at distances of R ≳ 10 ¹⁸ cm from the source), although the latter cannot be ruled out yet. The current apparent expansion velocity of the image size is only mildly relativistic, suggesting a nonrelativistic transition time of t_NR ∼ 1 yr. A rebrightening, or at least a significant flattening in the flux decay, is expected within the next several years as the counterjet becomes visible (this has not yet been observed). An upper limit of < 1.9c is set on the proper motion of the flux centroid.