Answer:
The light variation from the supernova changed due to the influence of radioactive elements decaying. This included the decay of nickel-56 and cobalt-56. As these elements decayed, their gamma rays interacted with the material from the explosion, causing the energy output to change. Since these elements decay very quickly, they must have been created by the supernova explosion itself, they would not have survived if they had been created during earlier stages of the star's life.
Neutrinos were also observed from the supernova on the day before the light from the supernova was observed. If enough neutrinos were created so that a good number reached Earth, 160000 light-years away, and a few could interact with our detectors, this shows that a lot of neutrinos must have been made by the events connected with the supernova. This confirms our idea that in the formation of the neutron star, before the explosion, a large number of neutrinos were created in the process of joining electrons and protons to make neutrons.
