High-Resolution Radio Observations of Supernova SN1986J

Abstract

We present high-resolution observations of the supernova SN1986J in the galaxy NGC891 at the frequency of 5 GHz, more than 15 years after its explosion. The image shows a highly distorted shell of radio emission, suggesting that the shock front has been strongly deformed. The brightness distribution within the shell is also highly asymmetric, and we propose that such asymmetry could be due to the collision of the supernova ejecta with an anisotropic, clumpy medium. The average speed of the shell has decreased from about 7400 km s−1 in 1988.74 down to ~ 6300 km s−1 in 1999.14, pointing to a mild deceleration in the expansion of SN 1986J. Assuming a standard density profile for the progenitor wind, we infer a swept-up mass by the shock front of ≈ 2.2 M⊙. Since the supernova has not yet suffered a strong deceleration, momentum conservation arguments point to a mass of the hydrogen-rich envelope ejected at explosion as large as ~ 12 M⊙.