The study of radio emission from extragalactic supernovae has resulted in
the detection of a few tens of examples of Type Ib/c and Type II SNe ofvarious sub-classes. No Type Ia supernova has ever been detected in the
radio. Approaching 200 SNe of all types and sub-types have been studiedwithout detection over the same interval.Out of this extensive study of the radio emission from supernovae, several
general observations can be made: (1) Type Ia SNe are not radio emitters tothe detection limit of the VLA; (2) Type Ib/c SNe are radio luminous with
steep spectral indices (generally, spectral index < -1) and a fastturn-on/turn-off, usually peaking at 6 cm near or before optical
maximum; (3) Type II SNe (with various optically determined sub-types) show
a range of radio luminosities with flatter spectral indices
(generally, spectral index > -1) and a relatively slow
turn-on/turn-off, usually peaking at 6 cm significantly after optical
maximum; and (4) At least some type Ib/c SNe are related to the
``soft-slow'' subclass of gamma-ray bursters (GRBs).From the radio data it is possible to classify the properties of supernovae
and to develop and test models for the radio emission which match the light
curves. Among the results of this work are estimates of the density and
structure of the circumstellar material, the density evolution of thepresupernova stellar wind, and insight into the last stages of stellar
evolution before the explosion.
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