INTERACTION OF TYPE IA SUPERNOVAE WITH THEIR SURROUNDINGS

Type Ia supernovae (SNe) are presumed to arise from white dwarf progen itors, which may not appreciably modify their ambient medium. We study the interaction of the resulting supernova remnants with a constant d ensity interstellar medium. Density profiles obtained from detailed ex plosion models of Type Ia SN explosions can be complex, but an exponen tial profile gives the best approximate representation of a set of pro files, and we emphasize this case. We describe the time evolution of d ynamical quantities (such as radius, velocity, and expansion parameter ) as a result of the interaction in terms of dimensionless variables a nd present the profiles of physical quantities. We compare our results to the power-law and constant ejecta density cases; a characteristic feature of the exponential case is that the shocked ejecta have a rela tively constant temperature. The effect of a possible circumstellar wi nd region dose to the supernova is to create a dense, cool shell near the contact discontinuity between the shocked ejecta and the surroundi ng medium. The complex density structure found in some supernova model s persists in the shocked layer, giving rise to density and temperatur e variations. We apply our results to the two likely historical Type I a SNe, SN 1006 and Tycho. The observed angular sizes and expansion rat es are consistent with a distance of 1.95 +/- 0.4 kpc and an ambient H density of 0.05-0.1 cm(-3) for SN 1006. For Tycho's SNR, the results are not conclusive but indicate a distance around 2.3 kpc for an ambie nt density of 0.6-1.1 cm(-3). In both cases, the low expansion rate li mits the extent of a possible circumstellar wind region. The evidence for temperature variations in the ejecta of Tycho's remnant suggests t hat the supernova profile was more complex than an exponential profile and contained density inhomogeneities, or that there was early intera ction with a circumstellar wind.