Efficiently Jet-powered Radiation in Intermediate-luminosity Optical Transients

I show that a flow structure where wide jets hit a slower expanding shell might be very efficient in channeling the kinetic energy of the jets to radiation, therefore accounting for, at least a fraction of, intermediate-luminosity optical transients (ILOTs) where the total radiation energy is much larger than what recombination energy of the outflow can supply. This type of flow might occur in the frame of the high-accretion-powered ILOT (HAPI) model, where there is a high mass accretion rate as a result of stellar merger or mass transfer in a binary system. I derive the condition on the jets half opening angle for the jets not to penetrate through the slow shell, as well as the ratio of the photon diffusion time to expansion time. This ratio cannot be too large if a large fraction of the thermal energy is channeled to radiation. I apply the jet-powered radiation model to the Great Eruption of Eta Carinae, to V838.Mon, and to V4332.Sgr, and find a plausible set of parameters for these ILOTs. I expect the jet-powered radiation model to be more efficient in converting kinetic energy to radiation than ILOT models that are based on equatorial mass concentration. In many cases, though, I expect both jets and equatorial mass concentration to occur in the same system.