* Astronomy

Title: SN 1986J VLBI. III. The Central Component Becomes Dominant
Author: Michael F. Bietenholz, Norbert Bartel

We present a new 5-GHz global-VLBI image of supernova 1986J, observed in 2014 at t = 31.6 yr after the explosion, and compare it to previous images to show the evolution of the supernova. Our new image has a dynamic range of ~100 and a background rms noise level of 5.9 microJy/beam. There is no significant linear polarization, with the image peak being <3% polarized. The latest image is dominated by the compact central component, whose flux density is now comparable to that of the extended supernova shell. This central component is marginally resolved with a FWHM width of 900 (-500,+100) micro-arcsec, corresponding to a radius of r_comp = 6.7 (-3.7,+0.7) * 10^{16} cm for a distance of 10 Mpc. Using VLBI observations between 2002 and 2014, we measured the proper motions of both the central component and a hot-spot to the NE in the shell relative to the quasar 3C~66A. The central component is stationary to within the uncertainty of 12 micor-arcsec/yr, corresponding to 570 km/s. Our observations argue in favour of the central component being located near the physical center of SN 1986J. The shell hot-spot had a mean velocity of 2700 ± 810 km/s to the NE, which is consistent with it taking part in the homologous expansion of the shell seen earlier. The shell emission is evolving in a non-selfsimilar fashion, with the brightest emission shifting inwards within the structure, and with only relatively faint emission being seen near the outer edge and presumed forward shock.

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Ed ~ Supernova 1986J was hosted in NGC 891