SN 2014C: VLBI image shows a shell structure and decelerated expansion

TL;DR

VLBI imaging of supernova 2014C reveals a shell structure and decelerated expansion, indicating interaction with circumstellar material and providing insights into supernova evolution.

Contribution

First VLBI imaging of SN 2014C showing shell structure and deceleration, highlighting the supernova's interaction with circumstellar medium over time.

Findings

Shell structure observed in VLBI images.

Supernova expansion shows increasing deceleration.

Radio luminosity remains steady since 1 year post-explosion.

Abstract

We report on new Very Long Baseline Interferometry radio measurements of supernova 2014C in the spiral galaxy NGC 7331, made with the European VLBI Network ~5 yr after the explosion, as well as on flux density measurements made with the Jansky Very Large Array (VLA). SN 2014C was an unusual supernova, initially of Type Ib, but over the course of ~1 yr it developed strong H$\alpha$ lines, implying the onset of strong interaction with some H-rich circumstellar medium (CSM). The expanding shock-front interacted with a dense shell of circumstellar material during the first year, but has now emerged from the dense shell and is expanding into the lower density CSM beyond. Our new VLBI observations show a relatively clear shell structure and continued expansion with some deceleration, with a suggestion that the deceleration is increasing at the latest times. Our multi-frequency VLA observations show a relatively flat powerlaw spectrum with $S_\nu \propto \nu^{-0.56 \pm 0.03}$, and show no decline in the radio luminosity since $t\sim1$ yr.