  We present optical and near-infrared (NIR) photometry for three gamma-ray
burst supernovae (GRB-SNe): GRB 120729A, GRB 130215A / SN 2013ez and GRB
130831A / SN 2013fu. In the case of GRB 130215A / SN 2013ez, we also present
optical spectroscopy at t-t0=16.1 d, which covers rest-frame 3000-6250
Angstroms. Based on Fe II (5169) and Si (II) (6355), our spectrum indicates an
unusually low expansion velocity of 4000-6350 km/s, the lowest ever measured
for a GRB-SN. Additionally, we determined the brightness and shape of each
accompanying SN relative to a template supernova (SN 1998bw), which were used
to estimate the amount of nickel produced via nucleosynthesis during each
explosion. We find that our derived nickel masses are typical of other GRB-SNe,
and greater than those of SNe Ibc that are not associated with GRBs. For GRB
130831A / SN 2013fu, we use our well-sampled R-band light curve (LC) to
estimate the amount of ejecta mass and the kinetic energy of the SN, finding
that these too are similar to other GRB-SNe. For GRB 130215A, we take advantage
of contemporaneous optical/NIR observations to construct an optical/NIR
bolometric LC of the afterglow. We fit the bolometric LC with the millisecond
magnetar model of Zhang & Meszaros (2001), which considers dipole radiation as
a source of energy injection to the forward shock powering the optical/NIR
afterglow. Using this model we derive an initial spin period of P=12 ms and a
magnetic field of B=1.1 x 10^15 G, which are commensurate with those found for
proposed magnetar central engines of other long-duration GRBs.
