A Trio of GRB-SNe

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. Additionally, we present spectroscopic observations of SN 2013ez, where undulations are seen in the optical spectrum that are reminiscent of other GRB-SNe. A blueshifted Fe II λ5169 absorption feature at v ≈4000 km s−1 at t − t0 = 16.1 d in the rest-frame, indicating that it is of type Ic, making it the first GRB-SNe to not be classified as a type Ic-BL. We have determined the brightness and shape of each accompanying SN relative to a template supernova (SN 1998bw), and in doing so we make estimates of the amount of nickel nucleosynthesized 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 typical of other GRB-SNe. For GRB 130215A, we take advantage of contemporaneous optical/NIR observations obtained by RATIR and GROND to construct an optical/NIR bolometric LC of the afterglow. We fit the bolometric LC with the millisecond magnetar model of Zhang & Mészáros (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 × 1015 G, which are similar to those found for magnetar central engines of other long-duration GRBs.