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I propose a scenario according to which the dense compact circumstellarmatter (CSM) that the ejecta of many core collapse supernovae (CCSNe) collidewith within several days after explosion results from a dense zone where inaddition to the stellar wind there is gas that does not reach the escapevelocity. In this effervescent zone around red supergiant (RSG) stars, thereare dense clumps that are ejected from the vicinity of the RSG surface, rise toradii of tens of astronomical units, and then fall back. I consider two simplevelocity distributions of the ejected clumps. I find that the density of thebound mass can be tens of times that of the escaping wind, and therefore canmimic a very high mass loss rate. The dense effervescent compact CSM zone can(1) explain the collision of the ejecta of many CCSNe with a dense compact CSMdays after explosion, (2) facilitate very high mass loss rate if the starexperiences powerful pre-explosion activity, (3) form dust that obscures theprogenitor in the visible band, and (4) lead to an efficient mass transfer to astellar companion at separations of tens of astronomical units, if exists. Theeffervescent zone might exist for thousands of years and more, and thereforethe effervescent CSM model removes the requirement from many type II CCSNprogenitors to experience a very strong outburst just years to months beforeexplosion.

A pre-explosion extended effervescent zone around core collapse supernova progenitors