Evolution of a flare in selected chromospheric optical lines. The y axis is the flux measured at Earth, x axis is time in days. The center of the x axis (time = 0 days) corresponds to the middle of the transit (T₀ [HJD,UTC] = 2 456 109.26164). Red crosses are the measured flux value. Full black lines represent a best fit of the flare decay phase. Dashed black vertical lines mark a beginning and peak of the flare for each line individually. Horizontal dashed black lines indicate a quiescent zero level. The shaded pink area labels the duration of an exoplanetary transit. The 1σ error for the displayed data points is within the 3−6% range.