Observations of a Two-stage Solar Eruptive Event (SEE): Evidence for Secondary Heating

Abstract

We present RHESSI, SDO/AIA, SOHO/LASCO, STEREO, and GOES observations of a partially occulted solar eruptive event that occurred at the southwest limb on 2011 March 8. The GOES X-ray light curve shows two peaks separated by almost 2 hr that we interpret as two stages of a single event associated with the delayed eruption of a coronal mass ejection (CME). A hot flux rope formed during the first stage and continued expanding and rising throughout the event. The speed of the flux rope decreased from ~120 to 14 km s^-1 during the decay phase of the first stage and increased again during the second stage to become the CME with a speed of ~516 km s^-1. RHESSI and GOES data analyses show that the plasma temperature reached over 20 MK in the first stage, then decreased to ~10 MK and increased to 15 MK in the second stage. This event provides clear evidence for a secondary heating phase. The enhanced EUV and X-ray emission came from the high corona (~60 arcsec above the limb) in the second stage, ~40 arcsec higher than the site of the initial flare emission. STEREO-A on-disk observations indicate that the post-flare loops during this stage were of larger scale sizes and spatially distinct from those in the first stage.