ASpitzer Space TelescopeStudy of SN 2002hh: An Infrared Echo from a Type IIP Supernova

We present late-time (590-994 d) mid-IR photometry of the normal, buthighly-reddened Type IIP supernova SN 2002hh. Bright, cool, slowly-fadingemission is detected from the direction of the supernova. Most of this fluxappears not to be driven by the supernova event but instead probably originatesin a cool, obscured star-formation region or molecular cloud along theline-of-sight. We also show, however, that the declining component of the fluxis consistent with an SN-powered IR echo from a dusty progenitor CSM. Mid-IRemission could also be coming from newly-condensed dust and/or an ejecta/CSMimpact but their contributions are likely to be small. For the case of a CSM-IRecho, we infer a dust mass of as little as 0.036 M(solar) with a correspondingCSM mass of 3.6(0.01/r(dg))M(solar) where r(dg) is the dust-to-gas mass ratio.Such a CSM would have resulted from episodic mass loss whose rate declinedsignificantly about 28,000 years ago. Alternatively, an IR echo from asurrounding, dense, dusty molecular cloud might also have been responsible forthe fading component. Either way, this is the first time that an IR echo hasbeen clearly identified in a Type IIP supernova. We find no evidence for oragainst the proposal that Type IIP supernovae produce large amounts of dust viagrain condensation in the ejecta. However, within the CSM-IR echo scenario, themass of dust derived implies that the progenitors of the most common ofcore-collapse supernovae may make an important contribution to the universaldust content.Comment: 41 pages, 11 figures, 4 tables, accepted for publication in Astrophysical Journal (References corrected