Optical observations of the fast declining Type Ib supernova iPTF13bvn

Abstract

We present optical UBVRI photometry and medium resolution spectroscopy of the Type Ib supernova iPTF13bvn, spanning a phase of ∼−13 d to +71 d with respect to B-band maximum. The post-maximum decline rates indicate a fast decline with Δm15(B) = 1.82. Correcting for a Galactic extinction E(B − V)MW = 0.045 and host galaxy extinction of E(B − V)host = 0.17, the absolute V-band magnitude peaks at MV = −17.23 ± 0.20. The bolometric light curve indicates that ∼0.09 M⊙ of 56Ni was synthesized in the explosion. The earliest spectrum (−13 d) shows the presence of He i 5876 Å feature at a velocity of ∼15 000 km s−1, which falls rapidly by the time the SN approaches the epoch of B-band maximum. The photospheric velocity near maximum light, as indicated by the Fe ii 5169 Å feature, is ∼9000 km s−1. The estimate for the 56Ni mass, together with the estimates for the ejected mass (Mej) and kinetic energy of the explosion (Ek) indicate that iPTF13bvn is a low-luminosity Type Ib supernova, with a lower than average ejected mass and kinetic energy. Our results suggest that the progenitor of iPTF13bvn is inconsistent with a single Wolf–Rayet star.