The Metamorphosis of SN 2014C: A Strongly Interacting Supernova

We present an analysis of five years of coordinated CXO and NuSTAR observations showing a strongly interacting and peculiar supernova, SN 2014C. This is the first broad-band X-ray monitoring of an extragalactic SN over six years of evolution in both the hard and soft X-rays. Our analysis of the bright thermal bremsstrahlung radiation reveals that SN 2014C, initially a Type Ib SN, metamorphosed into a Type IIn as a result of interaction with a hydrogen-rich circumstellar medium (CSM) consisting of 2-3 M_⊙, located 5.5×10¹⁶ cm from the explosion site. This H-rich CSM shell of material has a density profile that goes as between R^-2.5 and R^-4.3 , which clearly deviates from wind-like density profiles (R^-2) that are expected around massive stars. These findings require updates to our understanding of mass loss in massive stars that are approaching core-collapse.