Spatially Resolved Oscillations of a Flare Looptop X-Ray Source

Abstract The looptop region in solar flares is a crucial site to understand the physical processes of magnetic reconnection and particle acceleration. Here, we report novel details of a flare looptop X-ray source that is associated with electron acceleration. The looptop source exhibits an oscillation in height that is statistically anticorrelated with the X-ray intensity, in which the variation in intensity slightly precedes the height. Two oscillation periods are found, i.e., a period of ∼2 minutes with a large amplitude and a relatively weak period of ∼1 minute. The nonthermal electron spectral index and flux deduced from X-ray spectra, and the intensity of flare ribbons/footpoints seen in EUV/UV images all show similar oscillations. In addition, the repeated downward contracting loops/plasmoids from the reconnection current sheet are observed. These observations strongly support a physical scenario where repeated reconnection outflows impinge on the flare looptop, while concurrently accelerated electrons are also quasiperiodically injected into it. These energy inputs (bulk flow and electron beams) subsequently produce oscillations in the looptop X-ray source, and cause brightness fluctuations in the flare ribbons/footpoints in the lower atmosphere.