Three-dimensional simulations of gravitationally confined detonations compared to observations of SN 1991T

Abstract

The gravitationally confined detonation (GCD) model has been proposed as a possible explosion mechanism for Type Ia supernovae in the single-degenerate evolution channel. It starts with ignition of a deflagration in a single off-centre bubble in a near-Chandrasekharmass white dwarf. Driven by buoyancy, the deflagration flame rises in a narrow cone towards the surface. For the most part, the main component of the flow of the expanding ashes remains radial, but upon reaching the outer, low-pressure layers of the white dwarf, an additional lateral component develops. This causes the deflagration ashes to converge again at the opposite side, where the compression heats fuel and a detonation may be launched. We first performed five three-dimensional hydrodynamic simulations of the deflagration phase in 1.4 M carbon/oxygen white dwarfs at intermediate-resolution (256 3 computational zones). We confirm that the closer the initial deflagration is ignited to the centre, the slower the buoyant rise and the longer the deflagration ashes takes to break out and close in on the opposite pole to collide. To test the GCD explosion model, we then performed a high-resolution (512 3 computational zones) simulation for a model with an ignition spot offset near the upper limit of what is still justifiable, 200 km. This high-resolution simulation met our deliberately optimistic detonation criteria, and we initiated a detonation. The detonation burned through the white dwarf and led to its complete disruption. For this model, we determined detailed nucleosynthetic yields by post-processing 10 6 tracer particles with a 384 nuclide reaction network, and we present multi-band light curves and time-dependent optical spectra. We find that our synthetic observables show a prominent viewing-angle sensitivity in ultraviolet and blue wavelength bands, which contradicts observed SNe Ia. The strong dependence on the viewing angle is caused by the asymmetric distribution of the deflagration ashes in the outer ejecta layers. Finally, we compared our model to SN 1991T. The overall flux level of the model is slightly too low, and the model predicts pre-maximum light spectral features due to Ca, S, and Si that are too strong. Furthermore, the model chemical abundance stratification qualitatively disagrees with recent abundance tomography results in two key areas: our model lacks low-velocity stable Fe and instead has copious amounts of high-velocity 56 Ni and stable Fe. We therefore do not find good agreement of the model with SN 1991T.

Determining the 56Ni distribution of type Ia supernovae from observations within days of explosion

“…56 Ni distributions are also shown for the DDT explosion models of Seitenzahl et al (2013), with similar 56 Ni masses, as dashed lines. The GCD model of Seitenzahl et al (2016) is shown as a dash-dot line. Light curves for our model and SN 2012fr are shown in the LSQ band, while the DDT model is shown in the V-band, which our modelling shows is extremely similar to LSQ.…”

“…Indeed, the twodimensional explosion simulations of Meakin et al (2009) consistently produce ∼1.1 M of 56 Ni. Seitenzahl et al (2016) obtain the lower 56 Ni mass of 0.74 M for GCD200 by assuming the initial deflagration is ignited far from the centre of the white dwarf. Larger offsets could potentially produce lower 56 Ni masses, however this may be unrealistic (e.g.…”

The C12(α,γ)O16deBoer1, Görres2, Wiescher3 et al. 2017Rev. Mod. Phys.19081431View full textAdd to dashboardCite

“…The carbon mass fraction impacts the overall energy release, expansion velocity, silicon-group and irongroup ejecta profiles (Calder et al, 2007;Höflich et al, 1998;Miles et al, 2016;Raskin et al, 2012;Röpke et al, 2006;Seitenzahl et al, 2016) in progenitor systems involving either one white dwarf (single degenerate channel) or two white dwarfs (double degenerate channel).…”

Nucleosynthesis in Thermonuclear Supernovae

“…For this type of explosion model, detailed nucleosynthesis calculations that go beyond a basic 13 isotope α-network have been presented for 2D simulations by Meakin et al (2009) and for 3D simulations by Seitenzahl et al (2016). A key signature of GCD models is that although it is technically a near-M ch explosion model, very little mass is burned in the deflagration.…”