One-dimensional delayed-detonation models of Type Ia supernovae: confrontation to observations at bolometric maximum

The delayed-detonation explosion mechanism applied to a Chandrasekhar-mass white dwarf offers a very attractive model to explain the inferred characteristics of Type Ia supernovae (SNe Ia). The resulting ejecta are chemically stratified, have the same mass and roughly the same asymptotic kinetic energy, but exhibit a range in Ni-56 mass. We investigate the contemporaneous photometric and spectroscopic properties of a sequence of delayed-detonation models, characterized by Ni-56 masses between 0.18 and 0.81 M-circle dot. Starting at 1 d after explosion, we perform the full non-local thermodynamic equilibrium, time-dependent radiative transfer with the code CMFGEN, with an accurate treatment of line blanketing, and compare our results to SNe Ia at bolometric maximum. Despite the 1D treatment, our approach delivers an excellent agreement to observations. We recover the range of SN Ia luminosities, colours and spectral characteristics from the near-ultraviolet to 1 mu m, for standard as well as low-luminosity 91bg-like SNe Ia. Our models predict an increase in rise time to peak with increasing Ni-56 mass, from similar to 15 to similar to 21 d, yield peak bolometric luminosities that match Arnett's rule to within 10 per cent and reproduce the much smaller scatter in near-infrared magnitudes compared to the optical. We reproduce the morphology of individual spectral features, the stiff dependence of the R(Si) spectroscopic ratio on Ni-56 mass and the onset of blanketing from Ti II/Sc II in low-luminosity SNe Ia with a Ni-56 mass less than or similar to 0.3 M-circle dot. We find that ionization effects, which often dominate over abundance variations, can produce high-velocity features in Ca II lines, even in 1D. Distinguishing between different SN Ia explosion mechanisms is a considerable challenge but the results presented here provide additional support to the viability of the delayed-detonation model.