Late-time supernova light curves: The effect of internal conversion and Auger electrons

TL;DR

This paper investigates how internal conversion and Auger electrons, often neglected, significantly influence supernova light curves, especially when gamma-ray transparency occurs, affecting interpretations of nucleosynthetic yields.

Contribution

It introduces the importance of Auger and internal conversion electrons as additional heat sources in supernova light curves, refining previous models.

Findings

Auger and internal conversion electrons can significantly contribute to supernova heating.

Including these electrons explains the slow-down in SN 1998bw's light curve.

For Type Ia supernovae, 55Fe electrons surpass 44Ti decay energy after explosion.

Abstract

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.