The observed feature of the light curve of SN 1993J, which has two maxima, are shown to be well reproduced by the explosion of red supergiant if its H/He envelope mass has been decreased below ∼0.9 M⊙. The first maximum of the light curve is due to shock heating of the thin envelope, while the second maximum is due to the radioactive decay of 56Co. From the date of the second maximum, the progenitor's main-sequence mass is estimated to be ∼12-15 M⊙. The thin envelope is likely to be the result of a close binary evolution. The mass of 56Ni synthesized in SN 1993J is ∼0.08 M⊙. The light curve properties, in particular, the date of the minimum and the decline rate of the tail suggest that substantial 56Ni was mixed into helium layers as has been predicted for Type Ib/Ic supernovae. We also calculate the light curves of line γ-rays as well as the spectral evolution of hard X-rays resulting from the 56Ni-56Co decays and discuss the possibility of observing hard radiation with the Compton Gamma-Ray Observatory. We show that hard X-rays from the pulsar can be observed with ASCA in ∼ 3 years if the pulsar luminosity is as high as the Crab Nebula.
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