Type Ia Supernovae


    Interaction of Type Ia Supernovae with their Surroundings

                         Vikram V. Dwarkadas & Roger A. Chevalier, 1998, ApJ, 497, 807

Abstract: 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.

Interaction of Type Ia Supernovae with the Surroundings II: The Exponential Profile in 2 Dimensions

                                                         V. V. Dwarkadas, 2000, ApJ, 541, 418

Abstract: The evolution of Type Ia supernovae in the surrounding medium is studied using two-dimensional numerical hydrodynamic simulations. The ejecta are assumed to be described by an exponential density profile, following the work of Dwarkadas & Chevalier. The case of a circumstellar region formed by mass loss from the progenitor or a companion star is also considered. The decelerating contact discontinuity is found to be Rayleigh-Taylor (R-T) unstable, as expected, and the nature of the instability is studied in detail for two cases: (1) a constant density ambient medium, and (2) a circumstellar medium whose density scales as r-2. The nature of the instability is found to be different in each case. In the case of a circumstellar medium the instability is much better resolved, and a fractal-like structure is seen. In the case of a constant density medium the extent of growth is less, and the R-T fingers are found to be limited by the presence of Kelvin-Helmholtz mushroom caps at the tips of the fingers. The unstable region is far enough away from the reverse shock that the latter is not affected by the mixing taking place in the interaction region. In contrast, the reverse shock in the case of a circumstellar medium is found to be rippled due to the formation of instabilities. In neither case is the outer shock front affected. These results are consistent with similar studies of power-law ejecta profiles conducted by Chevalier, Blondin, & Emmering. Our results are then applied to Tycho's supernova remnant. We conclude that it is unlikely that the instabilities seen in recent radio images of the remnant are similar to those studied herein, although we do not discount the possibility of initial conditions different from those studied herein leading to a much larger growth than we see in our simulations. We suggest that such instabilities may be better observed at X-ray wavelengths which probe the high-density shocked ejecta region.

Simulations: Here's a nice simulation showing the formation of Rayleigh-Taylor instabilities (16MB). (Please be patient, it does take a while for the instabilities to form.).

A Study of the Type Ia/IIn Supernova 2005gj from X-ray to the Infrared: Paper I

  1. J.Prieto, P Garnavich...................V. V. Dwarkadas............. et al, submitted

We present extensive ugrizYHJK photometry and optical spectroscopy of SN 2005gj obtained by the SDSS-II and CSP Supernova Projects, which give excellent coverage during the first 150 days after the time of explosion. These data show that SN 2005gj is the second clear case, after SN 2002ic, of a thermonuclear explosion in a dense circumstellar environment. Both the presence of singly and doubly ionized iron-peak elements (FeIII and weak SII, SiII) near maximum light as well as the spectral evolution show that SN 2002ic-like events are Type Ia explosions. Independent evidence comes from the exponential decay in luminosity of SN 2005gj, pointing to an exponential density distribution of the ejecta. The interaction of the supernova ejecta with the dense circumstellar medium is stronger than in SN 2002ic: (1) the supernova lines are weaker; (2) the Balmer emission lines are more luminous; and (3) the bolometric luminosity is higher close to maximum light. The velocity evolution of the Halpha components suggest that the CSM around SN 2005gj is clumpy and it has a flatter density distribution compared with the steady wind solution, in agreement with SN 2002ic. An early X-ray observation with Chandra gives an upper-limit on the mass loss rate from the companion of < 2x10^{-4} Msun/yr.