Inferring Fundamental Properties of the Flare Current Sheet Using Flare Ribbons: Oscillations in the Reconnection Flux Rates

Abstract

Magnetic reconnection is understood to be the main physical process that facilitates the transformation of magnetic energy into heat, motion, and particle acceleration during solar eruptions. Yet, observational constraints on reconnection region properties and dynamics are limited due to a lack of high-cadence and high-spatial-resolution observations. By studying the evolution and morphology of postreconnected field-lines footpoints, or flare ribbons and vector photospheric magnetic field, we estimate the magnetic reconnection flux and its rate of change with time to study the flare reconnection process and dynamics of the current sheet above. We compare high-resolution imaging data to study the evolution of the fine structure in flare ribbons as ribbons spread away from the polarity inversion line. Using data from two illustrative events (one M- and X-class flare), we explore the relationship between the ribbon-front fine structure and the temporal development of bursts in the reconnection region. Additionally, we use the RibbonDB database to perform statistical analysis of 73 (C- to X-class) flares and identify quasiperiodic pulsation (QPP) properties using the Wavelet Transform. Our main finding is the discovery of QPP signatures in the derived magnetic reconnection rates in both example events and the large flare sample. We find that the oscillation periods range from 1 to 4 minutes. Furthermore, we find nearly cotemporal bursts in Hard X-ray (HXR) emission profiles. We discuss how dynamical processes in the current sheet involving plasmoids can explain the nearly cotemporal signatures of quasiperiodicity in the reconnection rates and HXR emission.

Localizing Quasiperiodic Pulsations in Hard X-Ray, Microwave, and Lyα Emissions of an X6.4 Flare

“…This mechanism can be used to explain those flare QPPs that are strongly associated with magnetic loops and current sheets (I. V. . The flare QPPs could be driven by the repetitive regime of magnetic reconnection, which would periodically accelerate nonthermal ions and electrons (Thurgood et al 2017;Karampelas et al 2022;Corchado Albelo et al 2024). The quasiperiodic reconnection may be spontaneous such as the self-oscillatory process (McLaughlin et al 2009) and the magnetic tuning fork model (Takasao & Shibata 2016), or might be triggered by an external wave (Kumar et al 2016;Nakariakov et al 2018;Li & Chen 2022).…”