Imaging the Expanding Shell of SN 2011dh

Abstract

We report on third epoch VLBI observations of the radio-bright supernova SN 2011dh located in the nearby (7.8 Mpc) galaxy M51. The observations took place at $t=453$ d after the explosion and at a frequency of 8.4 GHz. We obtained a fairly well resolved image of the shell of SN 2011dh, making it one of only six recent supernovae for which resolved images of the ejecta are available. SN 2011dh has a relatively clear shell morphology, being almost circular in outline, although there may be some asymmetry in brightness around the ridge. By fitting a spherical shell model directly to the visibility measurements we determine the angular radius of SN 2011dh's radio emission to be $636\pm 29$ $\mu$as. At a distance of 7.8 Mpc, this angular radius corresponds to a linear radius of $(7.4\pm 0.3)\times 10^{16}$ cm and an average expansion velocity since the explosion of $19000_{-2400}^{+2800}$ kms${}^{-1}$. We combine our VLBI measurements of SN 2011dh's radius with values determined from the radio spectral energy distribution under the assumption of a synchrotron-self-absorbed spectrum, and find all the radii are consistent with a power-law evolution, with $R\sim t^{0.97\pm 0.01}$, implying almost free expansion over the period $t=4$ d to 453 d.

Accepted in MNRAS

References in corpus (6)

• Circumstellar Emission from Type Ib and Ic Supernovae
• Uncovering the Putative B-Star Binary Companion of the SN 1993J Progenitor
• A Blue Point Source at the Location of Supernova 2011dh
• SN 1993J VLBI (IV): A Geometric Determination of the Distance to M81 with the Expanding Shock Front Method
• Spectropolarimetry of SN 2011dh in M51: geometric insights on a Type IIb supernova progenitor and explosion
• Shell revealed in SN 1979C

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• Spectropolarimetry of SN 2011dh in M51: geometric insights on a Type IIb supernova progenitor and explosion
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• SN 2014C: VLBI Images of a Supernova Interacting with a Circumstellar Shell
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• The Late Time Optical Evolution of Twelve Core-Collapse Supernovae: Detection of Normal Stellar Winds
• SN 2014C: VLBI image shows a shell structure and decelerated expansion
• A Snapshot Survey of Nearby Supernovae with the Hubble Space Telescope
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