  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 56Ni mass. We investigate the
contemporaneous photometric and spectroscopic properties of a sequence of
delayed-detonation models, characterized by 56Ni masses between 0.18 and 0.81
Msun. Starting at 1d after explosion, we perform the full non-LTE,
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-UV to 1 micron, for standard as well as
low-luminosity 91bg-like SNe Ia. Our models predict an increase in rise time to
peak with increasing 56Ni mass, from ~15 to ~21d, yield peak bolometric
luminosities that match Arnett's rule to within 10%, and reproduce the much
smaller scatter in near-IR magnitudes compared to the optical. We reproduce the
morphology of individual spectral features, the stiff dependence of the R(Si)
spectroscopic ratio on 56Ni mass, and the onset of blanketing from TiII/ScII in
low-luminosity SNe Ia with a 56Ni mass <0.3 Msun. We find that ionization
effects, which often dominate over abundance variations, can produce
high-velocity features in CaII 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.
