  Energy release from radioactive decays contributes significantly to supernova
light curves. Previous works, which considered the energy deposited by
gamma-rays and positrons produced by 56Ni, 56Co, 57Ni, 57Co, 44Ti and 44Sc,
have been quite successful in explaining the light curves of both core collapse
and thermonuclear supernovae. We point out that Auger and internal conversion
electrons together with the associated X-ray cascade, constitute an additional
heat source. When a supernova is transparent to gamma-rays, these electrons can
contribute significantly to light curves for reasonable nucleosynthetic yields.
In particular, the electrons emitted in the decay of 57Co, which are largely
due to internal conversion from a fortuitously low-lying 3/2- state in the
daughter 57Fe, constitute an additional significant energy deposition channel.
We show that when the heating by these electrons is accounted for, a slow-down
in the lightcurve of SN 1998bw is naturally obtained for typical hypernova
nucleosynthetic yields. Additionally, we show that for generic Type Ia
supernova yields, the Auger electrons emitted in the ground-state to
ground-state electron capture decay of 55Fe exceed the energy released by the
44Ti decay chain for many years after the explosion.
