The Unprecedented Metamorphosis of Supernova 2014C: New Insights from New Observations by HST and Gemini

Recent observations of major eruptions preluding supernova explosions within one year of core collapse have challenged long held notions of stellar evolution. These eruptions are not easily explained by our current understanding of the physical mechanisms that drive mass loss in evolved massive stars, and may have significant ramifications for fields of research that depend on the predictions of stellar evolution models. Our group recently discovered a remarkable event — SN 2014C — in the nearby spiral galaxy NGC 7331 (D ∼ 15.8 Mpc) whose classification underwent a metamorphosis from a hydrogen-poor type Ib explosion to a hydrogen-rich type IIn. The transformation was the result of a rarely observed delayed interaction between a stripped-envelope supernova and a massive shell of circumstellar material located ∼5x10¹⁶ cm from the explosion site. Here we present new observations of SN 2014C obtained with the Hubble Space Telescope and the Gemini-N telescope that are part of a larger multi-wavelength Chandra/NuSTAR/VLA/SMA monitoring campaign. Our late-time ultraviolet/optical/near-infrared spectroscopy probes the composition, density, temperature, and speed of the emitting gas, and our high-resolution ultraviolet/optical images map out the nearby stellar environment. We find that the mass loss experienced by the progenitor system was strongly asymmetric, and that it was potentially driven by interaction between the progenitor star and a close binary companion. Our work supports the view that delays of ∼1000 yr between eruptive mass loss and core collapse are possible in massive stars that have been stripped of their hydrogen envelopes.