  We investigate iPTF13bvn, a core-collapse (CC) supernova (SN) in the nearby
spiral galaxy NGC 5806. This object was discovered by the intermediate Palomar
Transient Factory very soon after the explosion and was classified as a
stripped-envelope CC SN, likely of Type Ib. A possible progenitor detection in
pre-explosion Hubble Space Telescope (HST) images was reported, making this the
only SN Ib with such an identification. Based on photometry of the progenitor
candidate and on early-time SN data, it was argued that the progenitor
candidate is consistent with a single, massive Wolf-Rayet (WR) star.
  In this work we present follow-up multi-band light-curves and optical spectra
of iPTF13bvn. We perform spectral line analysis to track the evolution of the
SN ejecta, construct a bolometric light curve and perform hydrodynamical
calculations to model this light curve to constrain the synthesized radioactive
nickel mass and the total ejecta mass of the SN. Late-time photometry is
analyzed to constrain the amount of oxygen. Furthermore, image registration of
pre- and post-explosion HST images is performed.
  Our HST astrometry confirms the location of the progenitor candidate, and
follow-up spectra securely classify iPTF13bvn as a SN Ib. Our hydrodynamical
model indicates an ejecta mass of 1.9 solar masses and radioactive nickel mass
of 0.05 solar masses. The model fit requires the nickel to be highly mixed out
in the ejecta. The late-time nebular r'-band luminosity is not consistent with
predictions based on the expected oxygen nucleosynthesis in very massive stars.
  Our bolometric light curve of iPTF13bvn is not consistent with the previously
proposed single massive WR-star progenitor scenario. The ejecta mass and the
late-time oxygen emission are both significantly lower than what would be
expected from a single WR progenitor with a main-sequence mass of at least 30
solar masses.
