ar X iv : a st ro - p h / 05 06 54 2 v 1 2 2 Ju n 20 05 Detection of a massive dust shell around the Type II supernova SN 2002

Dust emission from the Type II supernova SN 2002hh in NGC 6946 has been detected at mid-infrared wavelengths by the Spitzer Space Telescope from 590 to 758 days after outburst and confirmed by higher angular resolution Gemini-N mid-IR observations. The day-600 5.8 − 24-μm emission can be fit by a 290-K blackbody having a luminosity of 1.6×10 L⊙. The minimum emitting radius of 1.1×10 cm is too large for the emitting dust to have been formed in the supernova ejecta. Using radiative transfer models and realistic dust grain parameters, fits to the observed flux distribution could be obtained with an optically thick dust shell having a mass of 0.10-0.15 M⊙, corresponding to a total dust+gas mass in excess of 10 M⊙, suggesting a massive M supergiant or luminous blue variable precursor to this self-obscured object. Subject headings: dust, extinction — supernovae: general — supernovae: individual(SN 2002hh) — galaxies: individual(NGC 6946) Dept. of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT, UK Space Telescope Science Institute, 3700 San Martin Drive Baltimore, MD 21218 Gemini Observatory, Northern Operations Center, 670 North A’ohoku Place, Hilo, HI 96720 Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803 Radio Astronomy Laboratory, University of California at Berkeley, Berkeley, CA 94720 Department of Physics, Astronomy & Maths, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK Steward Observatory, University of Arizona, Tucson, Arizona 85721 Kapteyn Astronomical Institute, P.O. Box 800, 9700 AV Groningen, The Netherlands School of Physics & Astronomy, University of Manchester, PO Box 88, Manchester M60 1QD