Bright common envelope formation requires jets

I compared with each other and with observations three energy sources to power intermediate luminosity optical transients (ILOTs) and conclude that only jets can power bright ILOTs with rapidly rising lightcurves. I present an expression for the power of the jets that a main sequence secondary star launches as it enters a common envelope evolution (CEE) with a primary giant star. The expression includes the Keplerian orbital period on the surface of the primary star, its total envelope mass, and the ratio of masses. I show that the shock that the secondary star excites in the envelope of the primary star cannot explain bright peaks in the lightcurves of ILOTs, and that powering by jets does much better in accounting for rapidly rising, about 10 days and less, peaks in the lightcurves of ILOTs than the recombination energy of the ejected mass. I strengthen previous claims that jets powered the Great Eruption of Eta Carinae, which was a luminous variable major eruption, and the luminous red novae (LRNe) V838 Mon and V1309 Scorpii. I therefore predict that the ejecta (nebula) of V1309 Scorpii will be observed in a decade or two to be bipolar. My main conclusion is that only jets can power a bright peak with a short rising time of ILOTs (LRNe) at CEE formation.