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Bietenholz et al. present broadband radio flux-density measurements of the
supernova (SN) 1996cr, made with MeerKAT, ATCA and ALMA, and images
made from Very Long Baseline Interferometry (VLBI) observations with
the Southern Hemisphere Long Baseline Array.
SN 1996cr was observed using the Southern Hemisphere Long Baseline
Array, (LBA), at 2.3 GHz on 2020 Feb. 17 and at 4.8 GHz on 2020 March
3 using telescopes in Australia, South Africa, and New Zealand. The
VLBI image shows an approximately circular structure, with a central
minimum reminiscent of an optically-thin spherical shell of emission.
The image above shows SN 1996cr made by combining the data at 4.8 GHz
and the amplitude-scaled data at 2.3 GHz. The restoring beam,
indicated at lower left, was 4 x 3 mas at a position angle of −15
degrees. Both the colourscale, labelled in mJy/beam, and the contours
show brightness. The contours are drawn at −16, 16, 30, 50
(emphasized), 70 and 90% of the peak brightness, which was 1.26
mJy/beam.
For a distance of 3.7 Mpc, SN 1996cr has been expanding with a
velocity of 4650 ± 1060 km/s between t = 4307 and 8859 d. It must
have undergone considerable deceleration before t = 4307 d.
Deviations from a circular shell structure in the image suggest a
range of velocities up to ∼7000 km/s, and hint at the presence of a
ring- or equatorial-belt-like structure rather than a complete
spherical shell.
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