The SXT movies show data from the earlier part of the impulsive phase, as displayed in the figure below:
where the infrequent tick marks show the times of the relevant EIT images.
The wave is quite amazingly bright, and does not appear to show a rarefaction trough:
These are brightness cuts in the northern half of the images showing the front. The earliest image, shown by the solid line, already has a much-enhanced brightness level relative to the preflare quiet-Sun images from the same location. The front therefore seems very bright, which could be a puzzle; the lack of a rarefaction might seem difficult to understand theoretically (see later) but in fact the scattered light from the flare may simply have obscured it.
Comments to: hudson@isass0.solar.isas.ac.jp