C. Humina

The discovery of stripped-envelope core-collapse supernovae (SNe) interacting with dense circumstellar medium (CSM) challenges our current understanding of massive star evolution. We present late-time observations of the interacting Type Ic SN 2017dio and investigate its mass-loss mechanism and progenitor channel. We analysed late-time spectra and light curves that are dominated by a strong ejecta–CSM interaction and reveal a slow photometric evolution primarily powered by this interaction. We examined the CSM and the source of the infrared (IR) excess by modelling the radiation produced by the ejecta–CSM interaction and the IR echo from circumstellar dust. In addition, we studied the temporal evolution of spectral features, with a particular emphasis on the Hα emission line. From the combined analysis of the light curves and spectral properties, we infer that the peak mass-loss rate for the CSM reaches sim0.2 mathrm M_⊙ yr^ -1 and that the typical value over most epochs is sim0.06 mathrm M_⊙ yr^ -1 . The nearby CSM was formed over a period of 4 to 65 years before the explosion. The CSM radius begins at ∼ 1.3 cm. The IR excess identified in the light curves is consistent with the radiation from dust with a mass increasing from sim0.001 to sim0.005 in the case of carbon dust or sim0.005 to sim0.02 in the case of silicate dust. 15 M_⊙ M_⊙ From IR echo modelling, we estimate an upper limit on the dust mass of 4 -5 M_⊙ , which implies an SN progenitor mass-loss rate of 2.4 -5 M_⊙ yr^ -1 at the dust evaporation radius determined by the SN peak luminosity (0.017 pc for carbon dust, corresponding to mass loss sim170 years before the explosion). This implies a very rapid increase in the mass-loss rate ahead of the explosion. Although the progenitor of SN 2017dio has lost its helium envelope, it interacted with a hydrogen-rich CSM formed shortly before the explosion, strongly suggesting that this material originated from a companion star rather than the progenitor itself.

Observations of core-collapse supernovae (CCSNe) suggest that some massive stars undergo intense mass loss shortly before explosion, but the underlying mechanisms remain unknown. Here, we report evidence of giant outbursts of clumpy material from a massive star in the final decades before explosion. Photometric, spectroscopic, and polarimetric data of SN 2024qiw reveal a bumpy light curve, a broad H α profile, and variable polarization, all consistent with interactions taking place between SN ejecta and clumpy circumstellar material, implying a mass-loss rate of ≳10 ⁻² M _⊙ yr ⁻¹ . Taken together, the most likely explanation is multiple major eruptions, similar to those of luminous blue variables (LBVs), but occurring shortly before explosion. This challenges standard stellar evolution theory by requiring either that LBVs explode terminally or that other evolutionary phases produce eruptive episodes. In spite of very high pre-SN mass loss, the resulting SN is classed as Type II, rather than Type IIn, highlighting diverse and previously unrecognized late-stage mass-loss processes.