  The progenitors of SNe Ia are not yet fully understood. The two leading
progenitor scenarios are the single-degenerate (SD) scenario and the
double-degenerate scenario. In the SD scenario, the collision of the SN Ia
ejecta with its companion star is expected to produce detectable ultraviolet
(UV) emission in the first few days after the SN explosion within certain
viewing angles. A strong UV flash has recently been detected in an SN
2002es-like peculiar SN Ia iPTF14atg by Cao et al., which is interpreted as
evidence of an early-time UV signature due to SN ejecta interacting with its
companion star, supporting the SD scenario. In this paper, we present the
expected luminosity distributions of early-time UV emission arising from SN Ia
ejecta-companion interaction by performing binary population synthesis
calculations for different progenitor systems in the SD scenario. Our
theoretical predictions will be helpful for future early-time observations of
SNe Ia to constrain their possible progenitors. Assuming the observed strong UV
pulse of iPTF14atg was indeed produced by the SN ejecta-companion interaction,
our population synthesis model suggests that the progenitor system of iPTF14atg
is most likely a red-giant donor binary system, and it is unlikely to have been
a main-sequence or helium-star donor system.
