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

Ertini, K. and Folatelli, G. and Martinez, L. and Bersten, M. C. and Anderson, J. P. and Ashall, C. and Baron, E. and Bose, S. and Brown, P. J. and Burns, C. and DerKacy, J. M. and Ferrari, L. and Galbany, L. and Hsiao, E. and Kumar, S. and Lu, J. and Mazzali, P. and Morrell, N. and Orellana, M. and Pessi, P. J. and Phillips, M. M. and Piro, A. L. and Polin, A. and Shahbandeh, M. and Shappee, B. J. and Stritzinger, M. and Suntzeff, N. B. and Tucker, M. and Elias-Rosa, N. and Kuncarayakti, H. and Székely, Péter and Szalai, Tamás and Barna, Barnabás and Könyves-Tóth, Réka and Csányi, István and Kriskovics, Levente and Pál, András and Szakáts, Róbert and Vida, Krisztián and Vinkó, József (2023) SN 2021gno: a calcium-rich transient with double-peaked light curves. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 526 (1). pp. 279-298. ISSN 0035-8711

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Abstract

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. Moreover, 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 $0.8\\, M_\\odot$ and a 56Ni mass of 0.024 M⊙. The initial cooling phase (first light-curve peak) is explained by the presence of an extended circumstellar material comprising ~$10^{-2}\\, {\\rm M}_{\\odot }$ with an extension of $1100\\, R_{\\odot }$. 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.

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