The nearby He-rich superluminous supernova SN 2021bnw during photospheric phases

Aims. We present and interpret the data of the nearby hydrogen-deficient but helium-rich superluminous supernova SN 2021bnw, which reached a magnitude of –20.7 at maximum luminosity in g band. Methods. We discuss the light curves and spectra of SN 2021bnw based on its spectro-photometric follow-up, exploiting different observational facilities. We reproduced the near-IR spectrum of SN 2021bnw with TARDIS to inspect the chemical composition at late photospheric phases and identify helium features. We also used a STELLA model coupling hydrodynamics and radiation transport to constrain the physical parameters of the explosion assuming a 56 Ni+CSM scenario. Results. We suggest that SN 2021bnw was mainly powered by the interaction of the ejecta with a previously lost He-rich circumstellar material, coupled with a central power source. Conclusions. This work expands the data sample of He-rich superluminous supernovae (SLSNe Ib), and for a single-progenitor scenario, it can constrain the masses and physics of their progenitors.