SN 1986J VLBI. III. The Central Component Becomes Dominant

Abstract

Abstract We present a new 5 GHz global very-long-baseline interferometry (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 μJy beam−1. There is no significant linear polarization, with the image peak <3% polarized. The latest image is dominated by a compact central component, whose flux density is now comparable to that of the extended supernova shell. This central component is marginally resolved with an FWHM of , corresponding to a radius of 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 μas yr−1, corresponding to 570 km s−1. Our observations argue that the central component is located near the physical center of SN 1986J. The shell hot spot had a mean velocity of 2810 ± 750 km s−1 to the NE, which is consistent with its taking part in the homologous expansion of the shell seen earlier. The shell emission is evolving in a non-self-similar fashion, with the brightest emission shifting inward within the structure and with only relatively faint emission seen near the outer edge and the presumed forward shock. An animation of the explosion is available.