SN 2021lwz: Another exotic, luminous, and fast-evolving optical stripped-envelope supernova?

Context. Current large-scale, high-cadence surveys, such as the Zwicky Transient Facility (ZTF), provide detections of new and rare types of transients and supernovae (SNe) whose physical origins are not well understood. Aims. We aim to investigate the nature of SN 2021lwz at a redshift z = 0.065, an over-luminous SN with an absolute magnitude of M g ∼ −20.1 AB that falls in the lower range of superluminous supernovae (SLSNe) luminosities and was discovered in a faint dwarf galaxy with an absolute magnitude of M g ≃ −14.5 AB. Methods. We studied SN 2021lwz using optical spectroscopy and photometry and by imaging linear polarimetry obtained during several follow-up campaigns. All the data were used to analyse and model the evolution of the explosion. Comparisons with other SNe of well-known or rarer types were investigated. Results. SN 2021lwz belongs to the rare class of rapidly evolving transients. The bolometric light curve rises in about seven days to a peak luminosity of about 5 × 10 43 erg/s, at a rate of 0.2 mag day −1 close to the peak. Spectroscopy modelling reveals more similarities with a normal Type Ic-like SN than with an SLSN before peak, showing slightly broadened lines after peak. Light curve modelling shows that the Arnett model of the bolometric light curve using a radioactive source ( 56 Ni) is not able to reasonably explain the light curve evolution. A magnetar model seems more appropriate, suggesting that the explosion of low ejecta mass ( M ej ∼ 0.24 M ⊙ ) took place in a low-mass ( M ∼ 10 6.66 M ⊙ ) dwarf galaxy of specific star formation rate about ten times larger than typical star-forming galaxies. Conclusions. SN 2021lwz is an uncommon transient showing many similarities with several classes of transients, including rare transients. It may be an interesting example of how differences in ejecta mass and engine parameters could produce a wide range of engine-driven stripped-envelope SNe.