  A source coincident with the position of the type IIb supernova (SN) 2008ax
is identified in pre-explosion Hubble Space Telescope (HST) Wide Field
Planetary Camera 2 observations in three optical filters. We identify and
constrain two possible progenitor systems: (i) a single massive star that lost
most of its hydrogen envelope through radiatively driven mass loss processes,
prior to exploding as a helium-rich Wolf-Rayet star with a residual hydrogen
envelope, and (ii) an interacting binary in a low mass cluster producing a
stripped progenitor. Late time, high resolution observations along with
detailed modelling of the SN will be required to reveal the true nature of this
progenitor star.

Astrophysics