Early interaction signatures and an extended plateau phase in Type II SN 2020aze

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ABSTRACT We present a photometric and spectroscopic analysis of the fast-declining Type II SN 2020aze, observed in optical bands from 2.2 to 137.4 d post-explosion. The V-band light curve reaches a peak absolute magnitude of $-16.97\ \pm$ 0.20 mag by 15 d, followed by a recombination phase with a decline rate of $2.04\pm 0.13$ mag (100 d)$^{-1}$, lasting $\sim$120 d. Early spectra (<6.0 d) exhibits a transient weak narrow emission line at 4687 Å and a bump or ledge feature spanning 4400–4800 Å, attributed to narrow and broad blue-shifted He ii $\lambda$4686, indicating interaction between the rapidly expanding ejecta and dense circumstellar material (CSM). Spectral comparison with literature models suggests a red supergiant progenitor with a weak wind and a mass-loss rate of ${\sim} 10^{-3}$ M$_\odot$ yr$^{-1}$. Semi-analytical light curve modelling yields an initial radius of 1100 R$_{\odot }$, an ejecta mass of 12 M$_\odot$, a total explosion energy of 1.5$\times 10^{51}$ erg, and a progenitor mass of approximately 14 M$_\odot$. The combination of a steep luminosity decline, early interaction signatures, and an unusually extended photospheric phase highlights the complex interplay between pre-SN mass-loss, CSM interaction, and progenitor properties, positioning SN 2020aze as an important case for understanding the diversity of Type II SNe.

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