We present extensive observations of the Type Ib/c SN2013ge from -13 to +457 days, including spectra and Swift UV-optical photometry beginning 2-4 days post-explosion. This data set 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---and reveals 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 blue continua and show a plethora of high velocity (~15,000 km/s) but narrow (~3500 km/s) features, indicating that the line-forming region is restricted. The explosion parameters estimated for the bulk explosion are standard for Type Ib/c SN, and there is evidence for weak He features at early times. In addition, SN2013ge exploded in a low metallicity environment and we have obtained some of the deepest radio and X-ray limits for a Type Ib/c SN to date, which constrain the progenitor mass-loss rate. 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 either possessed a low-mass extended envelope or ejected a portion of its envelope in the final <1 year before core-collapse. Alternatively, if the first component is due to outwardly mixed Ni-56, then our observations are consistent with the asymmetric ejection of a distinct clump of nickel-rich material at high velocities. 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, the spectra of the first component of SN2013ge are similar to those of the rapidly-declining SN2002bj.
We present extensive multi-wavelength observations of the extremely rapidly declining Type Ic supernova, SN 2005ek. Reaching a peak magnitude of M_R = -17.3 and decaying by ~3 mag in the first 15 days post-maximum, SN 2005ek is among the fastest Type
I supernovae observed to date. The spectra of SN 2005ek closely resemble those of normal SN Ic, but with an accelerated evolution. There is evidence for the onset of nebular features at only nine days post-maximum. Spectroscopic modeling reveals an ejecta mass of ~0.3 Msun that is dominated by oxygen (~80%), while the pseudo-bolometric light curve is consistent with an explosion powered by ~0.03 Msun of radioactive Ni-56. Although previous rapidly evolving events (e.g., SN 1885A, SN 1939B, SN 2002bj, SN 2010X) were hypothesized to be produced by the detonation of a helium shell on a white dwarf, oxygen-dominated ejecta are difficult to reconcile with this proposed mechanism. We find that the properties of SN 2005ek are consistent with either the edge-lit double detonation of a low-mass white dwarf or the iron-core collapse of a massive star, stripped by binary interaction. However, if we assume that the strong spectroscopic similarity of SN 2005ek to other SN Ic is an indication of a similar progenitor channel, then a white-dwarf progenitor becomes very improbable. SN 2005ek may be one of the lowest mass stripped-envelope core-collapse explosions ever observed. We find that the rate of such rapidly declining Type I events is at least 1-3% of the normal SN Ia rate.
