Gaussian fits to the Hα line profiles during the flare. Panel A: double-Gaussian fit to the first Hα difference profile (normalised flare spectrum minus the normalised reference spectrum). Yellow dots denote the observed Hα line profile, the solid red line shows the total Gaussian fit, the dashed blue line marks the blueshifted component, and the dashed green line marks the redshifted component. The reduced χ² value is indicated in the upper-left corner. The vertical dashed gray line marks the Hα rest wavelength in quiescence. Panel B: single-Gaussian fit to the second Hα difference profile.