Evidence for Pre-existing Dust in the Bright Type IIn SN 2010jl

SN 2010jl was an extremely bright, Type IIn supernova (SN) which showed a significant infrared (IR) excess no later than 90 days after explosion. We have obtained Spitzer 3.6 and 4.5 μm and JHK observations of SN 2010jl ~90 days post-explosion. Little to no reddening in the host galaxy indicated that the circumstellar material lost from the progenitor must lie in a torus inclined out of the plane of the sky. The likely cause of the high mid-IR flux is the reprocessing of the initial flash of the SN by pre-existing circumstellar dust. Using a three-dimensional Monte Carlo radiative-transfer code, we have estimated that between 0.03 and 0.35 M _sun of dust exists in a circumstellar torus around the SN located 6 × 10¹⁷ cm away from the SN and inclined between 60° and 80° to the plane of the sky. On day 90, we are only seeing the illumination of approximately 5% of this torus, and expect to see an elevated IR flux from this material up until day ~ 450. It is likely this dust was created in a luminous blue variable (LBV) like mass-loss event of more than 3 M _sun, which is large but consistent with other LBV progenitors such as η Carinae.