RADIO-EMISSION FROM SUPERNOVAE .2. SN1986J - A DIFFERENT KIND OF TYPE-II

SN 1986J is the most luminous radio supernova (RSN) which has ever been discovered, being more than 3 times brighter than SN 1979C. We present extensive new radio observations for the period from 1986 May through 1988 December at the five VLA wavelengths of 90, 20, 6, 2, and 1.3 cm. All other known radio data from the literature are also collected to assemble almost 100 measurements of the source. These are analyzed and are found to be poorly described by the external, thermal absorbing screen model which has been very successful for all previously known radio supernovae. However, a slightly more complex model allowing for the possibility of mixed thermal absorbers and nonthermal emitters is found to describe the overall properties of the radio emission from SN 1986J quite well. We are also able to estimate the properties of an external absorbing medium and apparently observe small variations in the optical depth of this external medum. The implications of these new radio data in terms of the mass loss from the presupernova star, the ejected mass in the supernova explosion, and the probable main-sequence mass of the progenitor star are all discussed. In particular, we find Mdot ∼ 2.4 × 10-4 M⊙, yr-1, M(ejecta) ≥ 1.9 M⊙, and 20 M⊙ < M(progenitor) < 30 M⊙. Also, the available data at optical wavelengths are reconsidered, showing that SN 1986J could have been "normally" bright at maximum light (Mv ∼ -18 mag) and still have gone undetected. Considering all of these data, we conclude that SN 1986J represents a relatively rare subclass of Type II supernovae produced by massive progenitors. We also speculate that in SN 1986J we may be observing the birth of an object like the Crab Nebula - a plerion.