  The Type IIb supernova (SN) 1993J is one of only a few stripped-envelope
supernovae with a progenitor star identified in pre-explosion images. SN IIb
models typically invoke H envelope stripping by mass transfer in a binary
system. For the case of SN 1993J, the models suggest that the companion grew to
22 M_solar and became a source of ultraviolet (UV) excess. Located in M81, at a
distance of only 3.6 Mpc, SN 1993J offers one of the best opportunities to
detect the putative companion and test the progenitor model. Previously
published near-UV spectra in 2004 showed evidence for absorption lines
consistent with a hot (B2 Ia) star, but the field was crowded and dominated by
flux from the SN. Here we present Hubble Space Telescope (HST) Cosmic Origins
Spectrograph (COS) and Wide-Field Camera 3 (WFC3) observations of SN 1993J from
2012, at which point the flux from the SN had faded sufficiently to potentially
measure the UV continuum properties from the putative companion. The resulting
UV spectrum is consistent with contributions from both a hot B star and the SN,
although we cannot rule out line-of-sight coincidences.
