16922

Supernova (SN) 2021gno in NGC 4165 (D=30.5 Mpc) is the second closest known Calcium-rich (Ca-rich) transient and only the second object in this class with an X-ray detection. Prompt comma high-cadence follow-up of this transient across the EM spectrum has indicated that the progenitor star was likely low mass (e.g. comma white dwarf or <10 Msun) and surrounded by dense circumstellar material (CSM) whose geometry-density was capable of producing luminous X-ray emission as well as a double-peaked light curve. The close proximity of SN 2021gno provides only the second opportunity to track the photometric evolution of a Ca-rich transient at late phases (>300 days) when the SN luminosity is governed by radioactive decay and-or additional power sources e.g. comma CSM comma and is too faint for ground-based observatories. These objects typically decrease in magnitude rapidly and thus their late-time decline rate and power source remains ambiguous. Here we propose multi-color imaging of SN 2021gno in order to understand its late-time bolometric behavior and to constrain the total masses of radioactive decay isotopes Ni-56 and Ni-57 synthesized in the explosion. This will allow us to test whether SN 2021gno is powered solely by radioactive decay or by additional CSM at large distances from the progenitor system.