M. I. Krauss, A. M. Soderberg, L. Chomiuk, B. A. Zauderer, A. Brunthaler, M. F. Bietenholz, R. A. Chevalier, C. Fransson, M. Rupen
We report on Expanded Very Large Array (EVLA) observations of the Type IIb
supernova 2011dh, performed over the first 100 days of its evolution and
spanning 1-40 GHz in frequency. The radio emission is well-described by the
propagation of a self-similar spherical shockwave, generated as the supernova
ejecta interact with the local circumstellar environment. Modeling this
emission with a standard synchrotron self-absorption (SSA) model gives an
average expansion velocity of v ~ 0.1c, supporting the classification of the
progenitor as a compact star (R ~ 10^11 cm). We find that the circumstellar
density is consistent with a r^-2 profile. We determine that the progenitor
shed mass at a constant rate of 4 x 10^-5 M_sun/yr, assuming a wind velocity of
1000 km/s (values appropriate for a Wolf-Rayet star), or 9 x 10^-7 M_sun/yr
assuming 20 km/s (appropriate for a yellow supergiant [YSG] star). Both values
of the mass-loss rate assume a converted fraction of kinetic to magnetic energy
density of epsilon_B = 0.1. Although the presence of a YSG is favored by
optical imaging, the observed rapid optical evolution and fast expansion argue
for a compact progenitor. Furthermore, the excellent agreement of the radio
properties of SN 2011dh with the SSA model implies that any YSG companion is
likely in a wide, non-interacting orbit, or that interaction with the companion
is mitigated by explosion/ejecta asymmetries. Finally, it is possible that the
YSG is unrelated and is only coincidentally along the same line of sight.
View original:
http://arxiv.org/abs/1201.0770
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