Successive Decimetric Bursts Associated with Breakout Magnetic Reconnection during the Decay Phase of an M-Class Flare

Abstract

Radio imaging spectroscopy diagnoses coronal electron acceleration and propagation by tracking energetic electron beams and locating energy-release sites. Using MUSER (0.4-2 GHz) and SDO data, we investigate decimetric radio emission during an eruption with an M1.1 flare on 17 December 2014. The eruption involves a twisted coronal structure evolving through three stages: a violent internal eruption, a rise-and-expansion phase, and a breakout eruption. The flare peaks at 01:50 UT during the internal eruption, while the cluster of successive type III-like decimetric bursts occurs in the decay phase, linked to the breakout eruption. The radio source coincides with a high-squashing-factor Q region from nonlinear force-free field (NLFFF) extrapolations, indicating a quasi-separatrix layer (QSL). We interpret the radio emission as consistent with plasma emission driven by nonthermal electrons accelerated by breakout reconnection at this QSL, between the outer envelope of the erupting structure and the surrounding corona. The successive bursts occur in the decay phase because breakout reconnection involves a larger, more energetic twisted structure at higher altitude, where an extended high-Q region, favorable acceleration geometry, and repeated sub-eruptions sustain efficient electron acceleration. Missing soft X-ray enhancement suggests most accelerated electrons escape upward or lose energy before reaching the chromosphere. The concentrated source positions of the successive radio bursts suggest pseudostreamers may act as particle accelerators, trapping electrons and directing them along a narrow layer. These results establish decimetric radio imaging as a powerful diagnostic of breakout reconnection and particle acceleration in the solar corona, with implications for energy release in pseudostreamer environments.