  We report on two epochs of very-long-baseline interferometry (VLBI)
observations of the Type Ib/c supernova SN 2008D, which was associated with the
X-ray outburst XRF 080109. At our first epoch, at t = 30 days after the
explosion, we observed at 22 and 8.4 GHz, and at our second, at t = 133 days,
at 8.4 and 5.0 GHz. The VLBI observations allow us to accurately measure the
source's size and position at each epoch, and thus constrain its expansion
velocity and proper motion. We find the source at best marginally resolved at
both epochs, allowing us to place a 3sigma upper limit of ~0.75c on the
expansion velocity of a circular source. For an elongated source, our
measurements are compatible with mildly relativistic expansion. However, our
3sigma upper limit on the proper motion is 4 micro-arcsec/day, corresponding to
an apparent velocity of <0.6c, and is consistent with a stationary flux
centroid. This limit rules out a relativistic jet such as an gamma-ray burst
jet away from the line of sight, which would be expected to show apparent
proper motion of >c. Taken together, our measurements argue against the
presence of any long-lived relativistic outflow in SN 2008D. On the other hand,
our measurements are consistent with the nonrelativistic expansion velocities
of <30,000 km/s and small proper motions (<500 km/s) seen in typical
supernovae.
