What mechanism powers the extended, long-lasting glow after a Type II supernova reaches its peak brightness?

Answer

Radioactive decay of newly synthesized heavy elements

The protracted light curve, which fades over years, is powered not by the initial mechanical shock but by the radioactive decay chain starting with Nickel-56.

What mechanism powers the extended, long-lasting glow after a Type II supernova reaches its peak brightness?
physicsastronomystarssupernovacore collapse