Observations of a Twin Pair of Atypical Solar Flares and a Magnetic-reconnection Scenario

TL;DR

This paper presents detailed observations and a magnetic-reconnection model explaining a pair of atypical solar flares with unique ribbon evolution, highlighting slipping reconnection within specific magnetic structures.

Contribution

It introduces a novel scenario for atypical solar flares involving slipping reconnection in quasi-separatrix layers, supported by multi-instrument observations and magnetic field modeling.

Findings

Atypical flares show non-spreading, sequential brightening ribbons.

Magnetic modeling reveals quasi-separatrix layers linked to flare ribbons.

Multiple reconnection events within QSLs explain the flare pair.

Abstract

We present observations and a magnetic-reconnection scenario of a twin pair of "atypical flares" that occurred on 2022 April 22 in a quadrupolar magnetic configuration formed by two active regions. The spatio-temporal evolution of the two flares is examined using images from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO), and from the ground-based Multi-Application Solar Telescope (MAST) in Udaipur, India. Characteristic of atypical flares and indicative of slipping reconnection, the ribbons of each flare (1) do not spread apart and (2) grow longer by sequential brightening of new flare kernels. The two atypical flares are homologous and plausibly have homologous triggers. There are four additional pairs of flare ribbons, each from a different flaring event that releases much less energy than the atypical flares. Two of these four pairs are produced by precursors, each possibly triggering one of the two atypical flares. The remaining two pairs accompany a filament activation, occurring twice within the span of the two atypical flares. Using a nonlinear force-free field (NLFFF) extrapolation model, we approximate the coronal magnetic field and find two quasi-separatrix layers (QSLs) that are nearly rooted in the flare ribbons. The observations and the extrapolated field together suggest a scenario in which the nearly simultaneous occurrence of many reconnections between magnetic field lines crossing at small angles (slipping reconnection) within each of the two QSLs produces the observed pair of atypical flares.