We present mid-infrared (MIR) spectroscopy of a Type II-plateau
supernova, SN 2004dj, obtained with the Spitzer Space Telescope,
spanning 106--1393d after explosion. MIR photometry plus
optical/near-IR observations are also reported. An early-time MIR
excess is attributed to emission from non-silicate dust formed within
a cool dense shell (CDS). Most of the CDS dust condensed between 50d and 165d, reaching a mass of $0.3x^(-5)Msun. Throughout the observations much of the longer wavelength (>10microns) part of the continuum is explained as an IR echo from interstellar dust. The MIR excess strengthened at later times. We show that this was due to thermal emission from warm, non-silicate dust formed in the ejecta. Using optical/near-IR line-profiles and the MIR continua, we show that the dust was distributed as a disk whose radius appeared to be slowly shrinking. The disk radius may correspond to a grain destruction zone caused by a reverse shock which also heated the dust. The dust-disk lay nearly face-on, had high opacities in the optical/near-IR regions, but remained optically thin in the MIR over much of the period studied. Assuming a uniform dust density, the ejecta dust mass by 996d was 0.5+/-0.1 x 10^(-4)Msun, and exceeded
10^(-4)Msun by 1393d. For a dust density rising toward the center the limit is higher. Nevertheless, this study suggests that the amount of freshly-synthesized dust in the SN 2004dj ejecta is consistent with that found from previous studies, and adds further weight to the claim that such events could not have been major contributors to the cosmic dust budget.
Financial support for this research was provided by NASA through an award issued by JPL/Caltech (specifically grant number 1322321 in the case of A.V.F.). A.V.F. gratefully acknowledges additional support from NSF grant AST-0908886 and the TABASGO Foundation. P.A.H. was supported by NSF grants AST-1008962 and 0708855. S.M. acknowledges support from the Academy of Finland (project 8120503). J.S. is a Royal Swedish Academy of Sciences Research Fellow supported by a grant from the Knut and Alice Wallenberg Foundation. J.C.W gratefully acknowledges support from NSF grant AST-0707769. The Dark Cosmology Centre is funded by the Danish National Research Foundation.
- Space and Planetary Science
- Astronomy and Astrophysics