Astronomy and Astrophysics – Astrophysics – Cosmology and Extragalactic Astrophysics
Scientific paper
2011-03-09
Astronomy and Astrophysics
Astrophysics
Cosmology and Extragalactic Astrophysics
Accepted for publication in Proceedings of Science
Scientific paper
We present the most recent VLBI images of SN 1993J, taken at 1.7 GHz on 2010 March 5-6, along with a discussion of its evolution with time. The new image is the latest in a sequence covering almost the entire lifetime of the supernova. For these latest observations we used an "in beam calibrator" technique, and obtained a background rms brightness of 3.7 micro-Jy/beam. The supernova shell remains quite circular in outline. Modulations in brightness are seen around the rim which evolve relatively slowly, having remained generally similar over the last several years of observation. We determine the outer radius of the supernova using visibility-plane model-fitting. The supernova has slowed down to around 30% of its original expansion velocity, and continues to expand with radius approximately proportional to t^0.8, however, deviations from a strict power-law evolution are seen. We do not find any clear-cut evidence for systematically frequency-dependent evolution, suggesting that the radii as determined from visibility-plane model-fitting continue to provide reasonable estimates of the physical outer shock-front radius.
Bartel Norbert
Beasley Anthony J.
Bietenholz Michael F.
Cannon Wayne
Conway Jessica
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