Strongly decelerated expansion of SN 1979C

¹ Departamento de Astronomía, Universitat de València, 46100 Burjassot, Spain
² Istituto di Radioastronomia/CNR, via P. Gobetti 101, 40129 Bologna, Italy
³ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁴ Instituto de Astrofísica de Andalucía, CSIC, Apdo. Correos 3004, 18080 Granada, Spain
⁵ MERLIN/VLBI National Facility, Jodrell Bank Observatory, Macclesfield, Cheshire SK11 9DL, UK
⁶ Infrared Processing and Analysis Center, California Institute of Technology, Mail Code 100-22, Pasadena, CA 91125, USA
⁷ Remote Sensing Division, Naval Research Laboratory, Code 7213, Washington, DC 20375-5320, USA

Corresponding author: J. M. Marcaide, J.M.Marcaide@uv.es

Received: 20 July 2001
Accepted: 11 December 2001

Abstract

We observed SN 1979C in M100 on 4 June 1999, about twenty years after explosion, with a very sensitive four-antenna VLBI array at the wavelength of λ18 cm. The distance to M100 and the expansion velocities are such that the supernova cannot be fully resolved by our Earth-wide array. Model-dependent sizes for the source have been determined and compared with previous results. We conclude that the supernova shock was initially in free expansion for yrs and then experienced a very strong deceleration. The onset of deceleration took place a few years before the abrupt trend change in the integrated radio flux density curves. We estimate the shocked swept-up mass to be , assuming a standard density profile for the CSM. Such a swept-up mass for SN 1979C suggests a mass of the hydrogen-rich envelope ejected at explosion no larger than . If SN 1979C originated in a binary star, the low value of M_env suggests that the companion of the progenitor star stripped off most of the hydrogen-rich envelope mass of the presupernova star prior to the explosion.