SN 2024bch light curves and spectra

Its early spectra are characterised by narrow high-ionisation emission lines, often interpreted as signatures of ongoing interaction between rapidly expanding ejecta and a confined dense circumstellar medium. However, we provide a model for the bolometric light curve of the transient that does not require sources of energy different than radioactive decays and H recombination.

Our model can reproduce the bolometric light curve of SN 2024bch adopting an ejected mass of M_bulk_~+5M_{sun}_ surrounded by an extended envelope of only 0.2M_{sun}_ with an outer radius R_env_=7.0x10^13^cm. An accurate modelling focused on the radioactive part of the light curve, which accounts for incomplete gamma-ray trapping, gives a ^56^Ni mass of 0.048M_{sun}_. We propose narrow lines to be powered by Bowen fluorescence induced by scattering of HeII Ly-alpha photons, resulting in the emission of high-ionisation resonance lines.