An Echo of Supernova 2008bk
  I have discovered a prominent light echo around the low-luminosity Type
II-Plateau Supernova (SN) 2008bk in NGC 7793, seen in archival images obtained
with the Wide Field Channel of the Advanced Camera for Surveys on-board the
Hubble Space Telescope (HST). The echo is a partial ring, brighter to the north
and east than to the south and west. The analysis of the echo I present
suggests that it is due to the SN light pulse scattered by a sheet, or sheets,
of dust located ~15 pc from the SN. The composition of the dust is assumed to
be of standard Galactic diffuse interstellar grains. The visual extinction of
the dust responsible for the echo is A_V ~ 0.05 mag, in addition to the
extinction due to the Galactic foreground toward the host galaxy. That the SN
experienced much less overall extinction implies that it is seen through a less
dense portion of the interstellar medium in its environment. The late-time HST
photometry of SN 2008bk also clearly demonstrates that the progenitor star has
vanished.
