Late-time evolution of the interacting stripped-envelope supernova 2017dio

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 H α 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 ∼0.2 M ⊙ yr −1 and that the typical value over most epochs is ∼0.06 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 × 10 15 cm. The IR excess identified in the light curves is consistent with the radiation from dust with a mass increasing from ∼0.001 to ∼0.005 M ⊙ in the case of carbon dust or ∼0.005 to ∼0.02 M ⊙ in the case of silicate dust. From IR echo modelling, we estimate an upper limit on the dust mass of 4 × 10 −5 M ⊙ , which implies an SN progenitor mass-loss rate of 2.4 × 10 −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 ∼170 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.