Hard X-ray and ultraviolet emission during the 2011 June 7 solar flare

摘要

The relationship between X-ray and UV emission during flares, particularly inthe context of quasi-periodic pulsations, remains unclear. To address this, westudy the impulsive X-ray and UV emission during the eruptive flare of 2011June 7 utilising X-ray imaging from RHESSI and UV 1700A imaging from SDO/AIA.This event is associated with quasi-periodic pulsations in X-ray and possiblyUV emission, as well as substantial parallel and perpendicular motion of thehard X-ray footpoints. The motion of the footpoints parallel to the flare ribbons is unusual; it isshown to reverse direction on at least two occasions. However, there is noassociated short-timescale motion of the UV bright regions. Additionally, wefind that the locations of the brightest X-ray and UV regions are different,particularly during the early portion of the flare impulsive phase, despitetheir integrated emission being strongly correlated in time. Correlationanalysis of measured flare properties, such as the footpoint separation, flareshear, photospheric magnetic field and coronal reconnection rate, reveals that- in the impulsive phase - the 25 - 50 keV hard X-ray flux is only weaklycorrelated with these properties, in contrast to previous studies. We characterise this event in terms of long-term behaviour, where the X-raynonthermal, thermal, and UV emission sources appear temporally and spatiallyconsistent, and short-term behaviour, where the emission sources areinconsistent and quasi-periodic pulsations are a dominant feature requiringexplanation. We suggest that the short timescale behaviour of hard X-rayfootpoints, and the nature of the observed quasi-periodic pulsations, isdetermined by fundamental, as-yet unobserved properties of the reconnectionregion and particle acceleration sites. This presents a challenge for currentthree-dimensional flare reconnection models.