Spitzer space telescope observations of Kepler's supernova remnant:: A detailed look at the circumstellar dust component

We present 3.6-160 mu m infrared images of Kepler's supernova remnant ( SN 1604) obtained with the IRAC and MIPS instruments on the Spitzer Space Telescope. We also present MIPS SED low-resolution spectra in the 55-95 mu m region. The observed emission in the MIPS 24 mu m band shows the entire shell. Emission in the MIPS 70 mu m and IRAC 8 mu m bands is seen only from the brightest regions of 24 mu m emission, which also correspond to the regions seen in optical H alpha images. Shorter wavelength IRAC images are increasingly dominated by stars, although faint filaments are discernible. The SED spectrum of shows a faint continuum dropping off to longer wavelengths and confirms that strong line emission does not dominate the mid-IR spectral region. The emission we see is due primarily to warm dust emission from dust heated by the primary blast wave; no excess infrared emission is observed in regions where supernova ejecta are seen in X-rays. We use models of the dust to interpret the observed 70/24 mu m ratio and constrain the allowed range of temperatures and densities. We estimate the current mass of dust in the warm dust component to be 5.4 x 10(-4) M-circle dot, and infer an original mass of about 3 x 10(-3) M-circle dot before grain sputtering. The MIPS 160 mu m band shows no emission belonging to the remnant. We place a conservative but temperature-dependent upper limit on any cold dust component roughly a factor of 10 below the cold dust mass inferred from SCUBA observations. Finally, we comment on issues relevant to the possible precursor star and the supernova type.