Radiative Properties of Pair-instability Supernova Explosions
  We present non-LTE time-dependent radiative-transfer simulations of
pair-instability supernovae (PISNe) stemming from red-supergiant (RSG),
blue-supergiant (BSG) and Wolf-Rayet (WR) star rotation-free progenitors born
in the mass range 160-230Msun, at 10^-4 Zsun. Although subject to uncertainties
in convection and stellar mass-loss rates, our initial conditions come from
physically-consistent models that treat evolution from the main-sequence, the
onset of the pair-production instability, and the explosion phase. With our set
of input models characterized by large 56Ni and ejecta masses, and large
kinetic energies, we recover qualitatively the Type II-Plateau, II-peculiar,
and Ib/c light-curve morphologies, although they have larger peak bolometric
luminosities (~10^9 to 10^10 Lsun) and a longer duration (~200d). We discuss
the spectral properties for each model during the photospheric and nebular
phases, including Balmer lines in II-P and II-pec at early times, the dominance
of lines from intermediate-mass-elements (IMEs) near the bolometric maximum,
and the strengthening of metal line blanketing thereafter. Having similar
He-core properties, all models exhibit similar post-peak spectra that are
strongly blanketed by FeII and FeI lines, characterized by red colors, and that
arise from photospheres/ejecta with a temperature of <4000K. Combined with the
modest line widths after bolometric peak, these properties contrast with those
of known super-luminous SNe suggesting that PISNe are yet to be discovered.
Being reddish, PISNe will be difficult to observe at high redshift except when
they stem from RSG explosions, in which case they could be used as metallicity
probes and distance indicators.
