Interaction of Type Ia Supernovae with Their Surroundings

Type Ia supernovae (SNe) are presumed to arise from white dwarf progenitors, which may not appreciably modify their ambient medium. We study the interaction of the resulting supernova remnants with a constant density interstellar medium. Density profiles obtained from detailed explosion models of Type Ia SN explosions can be complex, but an exponential profile gives the best approximate representation of a set of profiles, and we emphasize this case. We describe the time evolution of dynamical quantities (such as radius, velocity, and expansion parameter) as a result of the interaction in terms of dimensionless variables and 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 relatively constant temperature. The effect of a possible circumstellar wind region close to the supernova is to create a dense, cool shell near the contact discontinuity between the shocked ejecta and the surrounding medium. The complex density structure found in some supernova models persists in the shocked layer, giving rise to density and temperature variations. We apply our results to the two likely historical Type Ia SNe, SN 1006 and Tycho. The observed angular sizes and expansion rates 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 ambient density of 0.6-1.1 cm -3 . In both cases, the low expansion rate limits the extent of a possible circumstellar wind region. The evidence for temperature variations in the ejecta of Tycho's remnant suggests that the supernova profile was more complex than an exponential profile and contained density inhomogeneities, or that there was early interaction with a circumstellar wind.