An analytical density profile of dense circumstellar medium in Type II supernovae

Observations of Type II supernovae imply that a large fraction of their progenitors experience enhanced mass loss years to decades before core collapse, creating a dense circumstellar medium (CSM). Assuming that the CSM is produced by a single mass eruption event, we analytically model its density profile. We find that a double power-law profile, where the inner (outer) power-law index has a characteristic value of -1.5 (-10 to -12), gives a good fit to the CSM profile obtained using radiation hydrodynamical simulations. With our profile the CSM is well described by just two parameters, the transition radius r(*) and density at r = r. (alternatively r(*) and the total CSM mass). We encourage future studies to include this profile, if possible, when modelling emission from interaction-powered transients.