Shock Breakout in Dense Mass Loss: Luminous Supernovae

We examine the case where a circumstellar medium around a supernova is sufficiently opaque that a radiation dominated shock propagates in the circum-stellar region. The initial propagation of the shock front into the circumstellar region can be approximated by a self-similar solution that determines the ra-diative energy in a shocked shell; the eventual escape of this energy gives the maximum luminosity of the supernova. If the circumstellar density is described by ρ = Dr−2 out to a radius Rw, where D is a constant, the properties of the shock breakout radiation depend on Rw and Rd ≡ κDvsh/c, where κ is the opac-ity and vsh is the shock velocity. If Rw Rd, the rise to maximum light begins at ∼ Rd/vsh; the duration of the rise is also ∼ Rd/vsh; the outer parts of the opaque medium are extended and at low velocity at the time of peak luminosity; and a dense shell forms whose continued interaction with the dense mass loss gives a characteristic flatter portion of the declining light curve. If Rw Rd, the rise to maximum light begins at Rw/vsh; the duration of the rise is R 2 w/vshRd; the outer parts of the opaque medium are not extended and are accelerated to high velocity by radiation pressure at the time of maximum luminosity; and a dense shell forms but does not affect the light curve near maximum. We argue that SN 2006gy is an example of the first kind of event, while SN 2010gx and related supernovae are examples of the second. Subject headings: circumstellar matter — shock waves — supernovae: general — supernovae: individual (SN 2006gy)