Extreme-ultraviolet Late Phase Caused by Magnetic Reconnection over Quadrupolar Magnetic Configuration in a Solar Flare
A second emission enhancement in warm coronal extreme-ultraviolet (EUV) lines (about 2-7 MK) during some solar flares is known as the EUV late phase. Imaging observations confirm that the late-phase emission originates from a set of longer or higher loops than the main flare loops. Nevertheless, some questions remain controversial: What is the relationship between these two loop systems? What is the heating source of late-phase emission? Does heating accompany the main-phase heating or does it occur quite later? In this paper, we present clear evidence for a heating source in a late-phase solar flare: magnetic reconnection of the overlying field in a quadrupolar magnetic configuration. The event is triggered by an erupted core structure that eventually leads to a coronal mass ejection. A cusp feature and its shrinkage motion high in the late-phase emission region are manifestations of the later phase reconnection following the main flare reconnection. Using the enthalpy-based thermal evolution of loops model, we reasonably reproduce the late-phase emissions in some EUV lines. We suggest that continuous additional heating is responsible for the appearance of the elongated EUV late phase.