Delayed Shock-induced Dust Formation in the Dense Circumstellar Shell
  Surrounding the Type IIn Supernova SN 2010jl
  The light curves of Type IIn supernovae are dominated by the radiative energy
released through the interaction of the supernova shockwaves with their dense
circumstellar medium (CSM). The ultraluminous Type IIn supernova SN 2010jl
exhibits an infrared emission component that is in excess of the extrapolated
UV-optical spectrum as early as a few weeks post-explosion. This emission has
been attributed by some as evidence for rapid formation of dust in the cooling
postshock CSM. We investigate the physical processes that may inhibit or
facilitate the formation of dust in the CSM. When only radiative cooling is
considered, the temperature of the dense shocked gas rapidly drops below the
dust condensation temperature. However, by accounting for the heating of the
postshock gas by the downstream radiation from the shock, we show that dust
formation is inhibited until the radiation from the shock weakens, as the shock
propagates into the less dense outer regions of the CSM. In SN 2010jl dust
formation can therefore only commence after day 380. Only the IR emission since
that epoch can be attributed to the newly formed CSM dust. Observations on day
460 and later show that the IR luminosity exceeds the UV-optical luminosity.
The post-shock dust cannot extinct the radiation emitted by the expanding SN
shock. Therefore, its IR emission must be powered by an interior source, which
we identify with the reverse shock propagating through the SN ejecta. IR
emission before day 380 must therefore be an IR echo from preexisting CSM dust.
