SN 2021gno: a calcium-rich transient with double-peaked light curves

We present extensive ultraviolet (UV) and optical photometric and optical spectroscopic follow-up of supernova (SN) 2021gno by the 'Precision Observations of Infant Supernova Explosions' (POISE) project, starting less than 2 d after the explosion. Given its intermediate luminosity, fast photometric evolution, and quick transition to the nebular phase with spectra dominated by [Ca II ] lines, SN 2021gno belongs to the small family of Calcium-rich transients. Moreo v er, it shows double-peaked light curves, a phenomenon shared with only four other Calcium-rich events. The projected distance from the centre of the host galaxy is not as large as other objects in this family. The initial optical light-curve peaks coincide with a very quick decline of the UV flux, indicating a fast initial cooling phase. Through hydrodynamical modelling of the bolometric light curve and line velocity evolution, we found that the observations are compatible with the explosion of a highly stripped massive star with an ejecta mass of 0.8 M-circle dot and a Ni-56 mass of 0.024 M-circle dot. The initial cooling phase (first light-curve peak) is explained by the presence of an extended circumstellar material comprising similar to 10 (-2) M-circle dot with an extension of 1100 R-circle dot. We discuss if hydrogen features are present in both maximum-light and nebular spectra, and their implications in terms of the proposed progenitor scenarios for Calcium-rich transients.

Automated summary

We present extensive follow-up observations of supernova 2021gno, including photometric and spectroscopic analysis. The supernova belongs to the Calcium-rich transients family and exhibits intermediate luminosity, fast photometric evolution, and double-peaked light curves. The observations suggest that it resulted from the explosion of a highly stripped massive star. The presence of hydrogen features in the spectra and their implications on progenitor scenarios for Calcium-rich transients are also discussed.