High-resolution Observations of the X-flare on 2014-03-29

Abstract:

We investigate the sequence of events leading to the 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. We find that a filament eruption, which was possibly caused by a thermal instability, was the cause of this X-flare. The filament was rising in the chromosphere for at least one hour before the flare occurred with a velocity of $\sim$2--5 km/s. 15 minutes before the flare, its chromospheric rise velocity increased to $\sim$6--10 km/s, before it lifted off with at least 600 km/s, as seen by IRIS in the transition region. Doppler velocities from H-alpha images reveal intriguing small scale flows along the filament and enable us to derive its probable shape. An unusual feature was a low-lying twisted flux rope near the filament, which did not participate in the filament eruption. After the flare ribbons started on each of its sides, the flux rope seems to have untangled and vanished during the flare. We present a comprehensive overview of the flare, including polarimetric and spectroscopic data at subarcsecond resolution.