We investigate the sequence of events leading to the solar X1 flare SOL2014-03-29T17:48 .
Because of the unprecedented joint observations of an X-flare with the ground-based Dunn Solar Telescope and the spacecraft IRIS , Hinode , RHESSI , STEREO , and SDO , we can sample many solar layers from the photosphere to the corona .
A filament eruption was observed above a region of previous flux emergence , which possibly led to a change in magnetic field configuration , causing the X-flare .
This was concluded from the timing and location of the hard X-ray emission , which started to increase slightly less than a minute after the filament accelerated .
The filament showed Doppler velocities of \sim 2–5 km s ^ { -1 } at chromospheric temperatures for at least one hour before the flare occurred , mostly blueshifts , but also redshifts near its footpoints .
15 minutes before the flare , its chromospheric Doppler shifts increased to \sim 6–10 km s ^ { -1 } and plasma heating could be observed , before it lifted off with at least 600 km s ^ { -1 } , as seen in IRIS data .
Compared to previous studies , this acceleration ( \sim 3–5 km s ^ { -2 } ) is very fast , while the velocities are in the common range for coronal mass ejections .
An interesting feature was a low-lying twisted second filament near the erupting filament , which did not seem to participate in the eruption .
After the flare ribbons started on each of the second filament ’ s sides , it seems to have untangled and vanished during the flare .
These observations are some of the highest resolution data of an X-class flare to date and reveal some small-scale features yet to be explained .