The Double-Peaked SN 2013ge: A Type Ib/c Sn with an Asymmetric Mass Ejection or an Extended Progenitor Envelope

We present extensive multiwavelength (radio to X-ray) observations of the Type Ib/c SN2013ge from −13 to +457 days relative to maximum light, including a series of optical spectra and Swift UV-optical photometry beginning 2 − 4 days post explosion. This makes SN2013ge one of the best observed normal Type Ib/c SN at early times, when the light curve is particularly sensitive to the progenitor configuration and mixing of radioactive elements. These early observations reveal two distinct light curve components in the UV bands. The first component rises over 4 − 5 days and is visible for the first week post-explosion. Spectra of the first component have a blue continuum and show a plethora of high velocity (~ 14,000 km s^(−1)) but narrow (~ 3500 km s^(−1)) spectroscopic features, indicating that the line forming region is restricted. The explosion parameters estimated for the bulk explosion (M_(ej) ~ 2 − 3 M_⊙; EK ~ 1 − 2 × 10^(51) ergs) are standard for Type Ib/c SN, while detailed analysis of optical and NIR spectra identify weak He features at early times (in an object which would have otherwise been classified as Type Ic), and nebular spectra show evidence for mixing and asymmetry in the bulk ejecta. In addition, SN2013ge exploded in a low metallicity environment (~ 0.5 Z_⊙) and we have obtained some of the deepest radio and X-ray limits for a Type Ib/c SN to date that constrain the progenitor mass-loss rate to be M < 4 × 10^(−6) M_⊙ yr^(−1). We are left with two distinct progenitor scenarios for SN2013ge depending on our interpretation of the early emission. If the first component is cooling envelope emission, then the progenitor of SN2013ge possessed a low-mass extended (≳ 30 R_⊙) envelope. Alternatively, if the first component is due to outwardly mixed 56Ni then our observations are consistent with the asymmetric ejection of a small amount of mass (~ 0.05 M_⊙) ahead of the bulk explosion. Current models for the collision of a SN shock with a binary companion cannot reproduce both the timescale and luminosity of the early emission in SN2013ge. Finally, we find that the spectra of the first component of SN2013ge are similar to those of the rapidly-declining SN2002bj.