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 dwith 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 ~0.09M⊙ of 56Ni was synthesized in the explosion. The earliest spectrum (-13 d) shows the presence of He I 5876Å 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 5169Å 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.