The unprecedented metamorphosis of SN2014C: from a H-stripped explosion to a strongly interacting SN

Mass loss in evolved massive stars is one of the least understood yet fundamental aspects of stellar evolution. HOW and WHEN do massive stars lose their H-envelopes? This central question motivates this proposal. We request NuSTAR observations to map the unique situation of the interaction of a H-stripped SN2014C with a H-rich shell ejected by its progenitor star, as part of our radio-to-gamma-ray follow-up. Our goal is to constrain the density and proximity of the ejected material, and hence the mass-loss history of the progenitor star. Unlike all the other H-stripped SNe, the radio and X-ray emission of SN14C is still increasing at t>300 days, giving us the unprecedented opportunity to map the density profile of the ejected material and constrain the epoch of its ejection in fine detail.