Resolving Two Distinct Thermal X-Ray Components in a Compound Solar Flare

X-ray emission provides the most direct diagnostics of the energy release process in solar flares. Occasionally, a superhot X-ray source is found to be above hot flare loops of similar to 10 MK temperature. While the origin of the superhot plasma is still elusive, it has conjured up an intriguing image of in situ plasma heating near the reconnection site high above the flare loops, in contrast to the conventional picture of chromospheric evaporation. Here we investigate an extremely long duration solar flare, in which EUV images show two distinct flare loop systems that appear successively along a Gamma-shaped polarity inversion line (PIL). When both flare loop systems are present, the hard X-ray spectrum is found to be well fitted by combining a hot component (T (e) similar to 12 MK) and a superhot component (T-e similar to 30 MK). Associated with a fast coronal mass ejection (CME), the superhot X-ray source is located at the top of the flare arcade that appears earlier, straddling and extending along the long "arm" of the Gamma-shaped PIL. Associated with a slow CME, the hot X-ray source is located at the top of the flare arcade that appears later and sits astride the short "arm" of the Gamma-shaped PIL. Aided by observations from a different viewing angle, we are able to verify that the superhot X-ray source is above the hot one in projection, but the two sources belong to different flare loop systems. Thus, this case study provides a stereoscopic observation explaining the coexistence of superhot and hot X-ray-emitting plasmas in solar flares.