Strongly decelerated expansion of SN 1979C

March 2002 • 2002A&A...384..408M

Authors • Marcaide, J. M. • Pérez-Torres, M. A. • Ros, E. • Alberdi, A. • Diamond, P. J. • Guirado, J. C. • Lara, L. • Van Dyk, S. D. • Weiler, K. W.

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 lambda 18 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 6+/-2 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 M_sw ~ 1.6 M_sun, 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 M_env ~ 0.9 M_sun. 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.

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Schuyler Van Dyk

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