SUPERNOVA 2001em IN UGC 11794
      C. J. Stockdale and B. Kaster, Marquette University; L. O. Sjouwerman
and M. P. Rupen, National Radio Astronomy Observatory; I. Marti-Vidal and J.
M. Marcaide, University of Valencia; S. D. Van Dyk, Spitzer Science Center,
California Institute of Technology; K. W. Weiler, Naval Research Laboratory;
B. Paczynski, Princeton University; and N. Panagia, European Space Agency
and Space Telescope Science Institute, report a test of the proposal by
Paczynski (2001, Acta Astron. 51, 1) and by Granot and Loeb (2003, Ap.J.
593, L81) that type-Ib/c supernovae may produce late-time radio jet
emission.  A Very Long Baseline Array measurement on 2004 July 1 of the
oldest known radio-emitting type-Ib/c supernova, SN 2001em, at age about
1020 days after explosion, shows no extended radio emission to a 3-sigma
limit of 0.3 mJy/beam.  The detected radio emission at 8.4 GHz of 1.8 +/-
0.2 mJy from SN 2001em appears unresolved at a resolution of 0".0019 x
0".0008, corresponding to a radius of < 0.4 +/- 0.2 pc at a distance of 90
Mpc or an average expansion speed for any detectable radio emitting material
of < 150000 km/s (< 0.5c).