The explosion energy of the type IIP supernova SN 2013fs with a confined dense circumstellar shell

The recent study of SN 2013fs flash spectrum suggests enormous for SN IIP explosion energy, far beyond possibilities of the neutrino mechanism. The issue of the explosion energy of SN 2013fs is revisited making use of effects of the early supernova interaction with the dense circumstellar shell. The velocity of the cold dense shell between reverse and forward shocks is inferred from the analysis of the broad heii,4686,AA on day 2.4. This velocity alongside with other observables provide us with an alternative energy estimate of $sim1.8times10^{51}$,erg for the preferred mass of $sim10$msun. The inferred value is within the range of the neutrino driven explosion.