Journal Article

The radio remnant of SN 1993J: an instrumental explanation for the evolving complex structure

Ian Heywood, Katherine M. Blundell, Hans-Rainer Klöckner and Anthony J. Beasley

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 392, issue 2, pages 855-867
Published in print January 2009 | ISSN: 0035-8711
Published online December 2008 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.14102.x
The radio remnant of SN 1993J: an instrumental explanation for the evolving complex structure

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We present simulated images of Supernova 1993J at 8.4 GHz using Very Long Baseline Interferometry (VLBI) techniques. A spherically symmetric source model is convolved with realistic uv-plane distributions, together with standard imaging procedures, to assess the extent of instrumental effects on the recovered brightness distribution. In order to facilitate direct comparisons between the simulations and published VLBI images of SN 1993J, the observed uv-coverage is determined from actual VLBI observations made in the years following its discovery.

The underlying source model only exhibits radial variation in its density profile, with no azimuthal dependence and, even though this model is morphologically simple, the simulated VLBI observations qualitatively reproduce many of the azimuthal features of the reported VLBI observations, such as appearance and evolution of complex azimuthal structure and apparent rotation of the shell. We demonstrate that such features are inexorably coupled to the uv-plane sampling.

The brightness contrast between the peaks and the surrounding shell material are not as prominent in the simulations (which of course assume no antenna- or baseline-based amplitude or phase errors, meaning no self-calibration procedures will have incorporated any such features in models). It is conclusive that incomplete uv-plane sampling has a drastic effect on the final images for observations of this nature. Difference imaging reveals residual emission up to the 8σ level. Extreme care should be taken when using interferometric observations to directly infer the structure of objects such as supernovae.

Keywords: techniques: interferometric; supernovae: individual: SN 1993J; radio continuum: stars

Journal Article.  4391 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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