Six Years of Luminous X-Ray Emission from the Strongly Interacting Type-Ib SN2014C Captured by Chandra and NuSTAR

We present the first coordinated soft and hard 0.3–80 keV X-ray campaign of the extragalactic supernova SN2014C in the first ∼2307 days of its evolution. SN2014C initially appeared to be an ordinary type Ib explosion but evolved into a strongly-interacting hydrogen-rich SN IIn over ∼1 yr. We observed signatures of interaction with a dense medium across the X-ray spectrum, which revealed the presence of a ∼1−2M⊙ shell of material at ∼6 × 1016 cm from the progenitor. This finding challenges current understanding of hydrogen-poor core-collapse progenitor evolution. Potential scenarios to interpret these observations include (i) the ejection of the hydrogen envelope by the progenitor star in the centuries prior to the explosion; (ii) interaction of the fast Wolf-Rayet (WR) star wind with the slow, dense wind of the Red Super Giant phase, with an anomalously short WR phase.