Dramatic rebrightening of the type-changing stripped-envelope supernova SN 2023aew

TL;DR

SN 2023aew exhibited a rare, dramatic rebrightening with spectral transformation from Type IIb to a stripped-envelope supernova, revealing complex ejecta structure and challenging existing supernova classification models.

Contribution

This study presents detailed observations of SN 2023aew's unusual light curve and spectral evolution, highlighting a rare type-changing event in supernovae.

Findings

SN 2023aew's second peak was broader and more luminous than typical SESNe.

Spectral lines indicated a transition from hydrogen-rich to hydrogen-poor ejecta.

Double-peaked nebular lines suggest clumpy or non-spherical ejecta structure.

Abstract

Multi-peaked supernovae with precursors, dramatic light-curve rebrightenings, and spectral transformation are rare, but are being discovered in increasing numbers by modern night-sky transient surveys like the Zwicky Transient Facility (ZTF). Here, we present the observations and analysis of SN 2023aew, which showed a dramatic increase in brightness following an initial luminous (-17.4 mag) and long (~100 days) unusual first peak (possibly precursor). SN 2023aew was classified as a Type IIb supernova during the first peak but changed its type to resemble a stripped-envelope supernova (SESN) after the marked rebrightening. We present comparisons of SN 2023aew's spectral evolution with SESN subtypes and argue that it is similar to SNe Ibc during its main peak. P-Cygni Balmer lines are present during the first peak, but vanish during the second peak's photospheric phase, before H$\alpha$ resurfaces again during the nebular phase. The nebular lines ([O I], [Ca II], Mg I], H$\alpha$) exhibit a double-peaked structure which hints towards a clumpy or non-spherical ejecta. We analyze the second peak in the light curve of SN 2023aew and find it to be broader than normal SESNe as well as requiring a very high $^{56}$Ni mass to power the peak luminosity. We discuss the possible origins of SN 2023aew including an eruption scenario where a part of the envelope is ejected during the first peak which also powers the second peak of the light curve through SN-CSM interaction.