  Supernova (SN) iPTF13bvn in NGC 5806 was the first Type Ib SN to have been
tentatively associated with a progenitor candidate in pre-explosion images. We
performed deep ultraviolet (UV) and optical Hubble Space Telescope (HST)
observations of the SN site 740 days after explosion. We detect an object in
the optical bands that is fainter than the pre-explosion object. This dimming
is likely not produced by dust absorption in the ejecta; thus, our finding
confirms the connection of the progenitor candidate with the SN. The object in
our data is likely dominated by the fading SN, which implies that the pre-SN
flux is mostly due to the progenitor. We compare our revised pre-SN photometry
with previously proposed progenitor models. Although binary progenitors are
favored, models need to be refined. In particular, to comply with our deep UV
detection limit, any companion star must be less luminous than a late-O star or
substantially obscured by newly formed dust. A definitive progenitor
characterization will require further observations to disentangle the
contribution of a much fainter SN and its environment.
