The radio remnant of SN1993J: an instrumental explanation for the evolving complex structure - AstrophysicsReport as inadecuate

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Abstract: We present simulated images of Supernova 1993J at 8.4 GHz using Very LongBaseline Interferometry VLBI techniques. A spherically symmetric source modelis convolved with realistic uv-plane distributions, together with standardimaging procedures, to assess the extent of instrumental effects on therecovered brightness distribution. In order to facilitate direct comparisonsbetween the simulations and published VLBI images of SN1993J, the observeduv-coverage is determined from actual VLBI observations made in the yearsfollowing its discovery.The underlying source model only exhibits radial variation in its densityprofile, with no azimuthal dependence and, even though this model ismorphologically simple, the simulated VLBI observations qualitatively reproducemany of the azimuthal features of the reported VLBI observations, such asappearance and evolution of complex azimuthal structure and apparent rotationof the shell. We demonstrate that such features are inexorably coupled to theuv-plane sampling.The brightness contrast between the peaks and the surrounding shell materialare not as prominent in the simulations which of course assume no antenna- orbaseline-based amplitude or phase errors, meaning no self-calibrationprocedures will have incorporated any such features in models. It isconclusive that incomplete uv-plane sampling has a drastic effect on the finalimages for observations of this nature. Difference imaging reveals residualemission up to the 8 sigma level. Extreme care should be taken when usinginterferometric observations to directly infer the structure of objects such assupernovae.

Author: Ian Heywood, Katherine M. Blundell, Hans-Rainer Kloeckner, Anthony J. Beasley


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