Discovery, Progenitor and Early Evolution of A Stripped Envelope Supernova iPTF13bvn

The intermediate Palomar Transient Factory reports our discovery of a young supernova, iPTF13bvn, in the nearby galaxy, NGC 5806 (22.5 Mpc). Our spectral sequence in the optical and infrared suggests a Type Ib classification. We identify a blue progenitor candidate in deep pre-explosion imaging within a 2 sigma error circle of 80 mas (8.7 pc). The candidate has an M-B luminosity of -5.52 +/- 0.39 mag and a B-I color of 0.25 +/- 0.25 mag. If confirmed by future observations, this would be the first direct detection for a progenitor of a Type Ib. Fitting a power law to the early light curve, we find an extrapolated explosion date around 0.6 days before our first detection. We see no evidence of shock cooling. The pre-explosion detection limits constrain the radius of the progenitor to be smaller than a few solar radii. iPTF13bvn is also detected in centimeter and millimeter wavelengths. Fitting a synchrotron self-absorption model to our radio data, we find a mass-loading parameter of 1.3x10(12) g cm(-1). Assuming a wind velocity of 10(3) km s(-1), we derive a progenitor mass-loss rate of 3 x 10(-5) M-circle dot yr(-1). Our observations, taken as a whole, are consistent with a Wolf-Rayet progenitor of the supernova iPTF13bvn.