SN 2014C: VLBI Images of a Supernova Interacting with a Circumstellar Shell

Abstract

We report on VLBI measurements of supernova 2014C at several epochs between $t=384$ and 1057 days after the explosion. SN 2014C was an unusual supernova that initially had Type Ib optical spectrum, but after $t=130$ d it developed a Type IIn spectrum with prominent H$\alpha$ lines, suggesting the onset of strong circumstellar interaction. Our first VLBI observation was at $t=384$ d, and we find that the outer radius of SN 2014C was $(6.40\pm 0.26)\times 10^{16}$ cm (for a distance of 15.1 Mpc), implying an average expansion velocity of $19300\pm 790$ \kms\ up to that time. At our last epoch, SN 2014C was moderately resolved and shows an approximately circular outline but with an enhancement of the brightness on the W side. The outer radius of the radio emission at $t=1057$ d is $(14.9\pm 0.6)\times 10^{16}$ cm. We find that the expansion between $t=384$ and 1057 d is well described by a constant velocity expansion with $v=13600\pm 650$ \kms. SN 2014C had clearly been substantially decelerated by $t=384$ d. Our measurements are compatible with a scenario where the expanding shock impacted upon a shell of dense circumstellar material during the first year, as suggested by the observations at other wavelengths, but had progressed through the dense shell by the time of the VLBI observations.

9 pages, 4 figures, accepted to MNRAS. This version adds the changes made in response to the referee's comments

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• The changing-type SN 2014C may come from an 11-$M_{\odot }$ star stripped by binary interaction and violent eruption
• Supernova 2014C: ongoing interaction with extended circumstellar material with silicate dust
• Seven Years of SN 2014C: a Multi-Wavelength Synthesis of an Extraordinary Supernova
• Late-Time Evolution and Modeling of the Off-Axis Gamma-ray Burst Candidate FIRST J141918.9+394036
• The Exceptional X-ray Evolution of SN1996cr in High Resolution
• SN 2014C: VLBI image shows a shell structure and decelerated expansion
• Large Cold Dust Reservoir Revealed in Transitional SN Ib 2014C by James Webb Space Telescope Mid-Infrared Spectroscopy
• Multi-wavelength View of the Type IIn Zoo: Optical to X-ray Emission Model of Interaction-Powered Supernovae
• A Multi-epoch X-ray Study of the Spiral Galaxy NGC 7331
• Survival of the Fittest: Numerical Modeling of Supernova 2014C
• Outside the Wall: Hydrodynamics of Type I Supernovae Interacting with a Partially Swept-Up Circumstellar Medium
• Spitzer's Last Look at Extragalactic Explosions: Long-Term Evolution of Interacting Supernovae
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