SN 2014C: Shell structure and deceleration reveal details of ejecta colliding… with a dense circumstellar medium

The unusual supernova 2014C, in the nearby galaxy NGC 7331, was initially of the H-poor Type Ib. Over the course of ~1 yr, however, it developed bright H-alpha lines, implying strong interaction with H-rich circumstellar medium (CSM). The expanding shock-front collided with a dense, H-rich shell of CSM at age of ~1 yr. Since then, the shock has emerged from the dense shell, and is now expanding into the lower density CSM beyond. I report on new VLBI measurements of SN 2014C made with the European VLBI Network ~5 yr after the explosion, as well as VLA and Chandra-NuSTAR X-ray observations. The VLBI observations, at 8.4 GHz, reveal a shell structure and continued expansion, with deceleration that appears to get stronger at the latest times. Since the first year after explosion, SN 2014C has shown an unusual, almost constant flux density as well as a relatively flat powerlaw spectrum. X-ray observations support the implications of the ejecta colliding with a dense CSM