Dust Destruction in Type Ia Supernova Remnants in the Large Magellanic Cloud

Abstract

We present first results from an extensive survey of Magellanic Cloud supernova remnants (SNRs) with the Spitzer Space Telescope. We describe IRAC and MIPS imaging observations at 3.6, 4.5, 5.8, 8, 24, and 70 mum of four Balmer-dominated Type Ia SNRs in the Large Magellanic Cloud (LMC): DEM L71 (0505-67.9), 0509-67.5, 0519-69.0, and 0548-70.4. None was detected in the four short-wavelength IRAC bands, but all four were clearly imaged at 24 mum, and two at 70 mum. A comparison of these images with Chandra broadband X-ray images shows a clear association with the blast wave, and not with internal X-ray emission associated with ejecta. Our observations are well described by one-dimensional shock models of collisionally heated dust emission, including grain size distributions appropriate for the LMC, grain heating by collisions with both ions and electrons, and sputtering of small grains. Model parameters are constrained by X-ray, optical, and far-ultraviolet observations. Our models can reproduce observed 70/24 mum flux ratios only by including sputtering, destroying most grains smaller than 0.03-0.04 mum in radius. We infer total dust masses swept up by the SNR blast waves, before sputtering, on the order of 10-2 Msolar, several times less than those implied by a dust-to-gas mass ratio of 0.3% as often assumed for the LMC. Substantial dust destruction has implications for gas-phase abundances.