  It is well known that massive stars (M > 8 M_sun) evolve up to the collapse
of the stellar core, resulting in most cases as a supernova (SN) explosion.
Their heterogeneity is related mainly to different configurations of the
progenitor star at the moment of the explosion, and to their immediate
environments. We present photometry and spectroscopy of SN 2010bt, which was
classified as a Type IIn SN from a spectrum obtained soon after discovery and
was observed extensively for about two months. After the seasonal interruption
owing to its proximity to the Sun, the SN was below the detection threshold,
indicative of a rapid luminosity decline. We can identify the likely progenitor
with a very luminous star (log L/L_sun ~ 7) through comparison of Hubble Space
Telescope images of the host galaxy prior to explosion with those of the SN
obtained after maximum light. Such a luminosity is not expected for a quiescent
star, but rather for a massive star in an active phase. This progenitor
candidate was later confirmed via images taken in 2015 (~ 5 yr post-discovery),
in which no bright point source was detected at the SN position. Given these
results and the SN behavior, we conclude that SN 2010bt was likely a Type IIn
SN and that its progenitor was a massive star that experienced an outburst
shortly before the final explosion, leading to a dense H-rich circumstellar
environment around the SN progenitor.
