envelope expansion is favorable to a photon diffusion, decreasing the characteristic diffusion time. The photon diffusion eventually dominates, stops this reduction at day 0.8802, and then, along with the envelope expansion, blows the photospheric radius outward.

When a velocity at the stellar surface exceeds the escape velocity, the outside layers of the star begin to cool rapidly, the color temperature begins to decrease from its maximum value, and both the effective temperature and the luminosity decrease somewhat later. A narrow peak in the bolometric luminosity forms as a result (Fig. \[fig:swbrck\]a). The peak has a width of about $0.02$ days at a half level of the luminosity maximum. Most of its radiation is emitted in an ultraviolet flash. The total number of ionizing photons above 13.598 eV for the whole outburst is $2.768 \times 10^{58}$. During the first 1.234 days the number of ionizing photons is $90\%$ of the total number, and the radiated energy adds up to $1.59 \times 10^{48}$ ergs. We conditionally define the transition time between the shock breakout and the adiabatic cooling phase, $t_1$, as the time at which the bolometric luminosity drops by one dex from its maximum value, with the understanding that the adiabatic 