Late-time Observations of Calcium-Rich Transient SN 2019ehk Reveal a Pure Radioactive Decay Power Source

Understand

We present $\textit{Hubble Space Telescope}$ imaging of the Calcium-rich supernova (SN) 2019ehk at 276 - 389 days after explosion.

• These observations represent the latest photometric measurements of a Calcium-rich transient to date and allows for the first opportunity to analyze the late-time evolution of an object in this observational SN class.
• We find that the late-time bolometric light curve of SN 2019ehk can be described predominantly through the radioactive decay of ${}^{56}\textrm{Co}$ for which we derive a mass of $M({}^{56}\textrm{Co}) = (2.8 \pm 0.1) \times 10^{-2}$$\rm{M}_\odot$.
• Furthermore, the rate of decline in bolometric luminosity requires the leakage of $\gamma$-rays on timescale $t_{\gamma} = 53.9 \pm 1.30$ days, but we find no statistical evidence for incomplete positron trapping in the SN ejecta.