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A distorted radio shell in the young supernova SN 1986J,
M.A. Pérez-Torres, A. Alberdi, J.M. Marcaide, J.C. Guirado,
L. Lara, F. Mantovani, E. Ros, K.W. Weiler
Monthly Notices of the Royal Astronomical Society, in press (2002)
- Abstract
We report here on 5 GHz global very-long-baseline interferometry (VLBI)
observations of SN 1986J, 16 yr after its explosion.
We obtained a high-resolution image of the supernova,
which shows a distorted shell of radio emission, indicative
of a deformation of the shock front. The angular size
of the shell is ~4.7 milliarcseconds, corresponding to a linear size of
~6.8x1017cm for a distance of 9.6 Mpc to NGC891. The average
speed of the shell has decreased from ~7600 km/s in 1998.74 down
to about 6300 km/s in 1999.14, indicative of a mild
deceleration in the expansion of SN 1986J. Assuming
a standard density profile for the progenitor wind (rhocs propto
r-s, s=2), the swept-up mass by the shock front is
~2.2 solar masses. This large swept-up mass, coupled with
the mild deceleration suffered by the supernova, suggests that
the mass of the hydrogen-rich envelope ejected at explosion was larger or
simmilar to 12 solar masses. Thus, the supernova progenitor must have
kept intact most of its hydrogen-rich envelope by the time of explosion,
which favours a single, massive star progenitor scenario.
We find a flux density for SN 1986J of ~7.2 mJy at the observing
frequency of 5 GHz, which results in a radio luminosity of ~1.4x1037
ergs/s for the frequency range 107-1010 Hz
(alpha=-0.69, Snu propto nualpha). We
detect four bright knots that delineate the shell structure,
and an absolute minimum of emission, which we tentatively identify with
the centre of the supernova explosion. If this is the case, SN 1986J
has then suffered an asymmetric expansion, which could be due to an asymmetry
in the presupernova wind, or to the supernova envelope colliding with an
anisotropic, clumpy (or filamentary) medium.
Eduardo Ros
ros@mpifr-bonn.mpg.de