X-ray/Radio Quasi-periodic Pulsations Associated with Plasmoids in Solar Flare Current Sheets

TL;DR

This study presents direct imaging of multiple plasmoids in solar flare current sheets and their association with quasi-periodic pulsations in X-ray and radio wavelengths, revealing insights into particle acceleration mechanisms.

Contribution

It provides the first direct imaging evidence of multiple plasmoid formation and ejection in flare current sheets linked with QPPs, supported by multi-wavelength observations and MHD simulations.

Findings

Multiple plasmoids propagate bidirectionally along the current sheet.

QPPs with periods of approximately 10 and 100 seconds are associated with plasmoid ejection.

Energetic electrons are accelerated during plasmoid ejection and coalescence.

Abstract

Plasmoids (or magnetic islands) are believed to play an important role in the onset of fast magnetic reconnection and particle acceleration during solar flares and eruptions. Direct imaging of flare current sheets and formation/ejection of multiple plasmoids in extreme ultraviolet (EUV) images, along with simultaneous X-ray and radio observations, offers significant insights into the mechanisms driving particle acceleration in solar flares. Here we present direct imaging of the formation and ejection of multiple plasmoids in flare plasma/current sheets and associated quasi-periodic pulsations (QPPs) observed in X-ray and radio wavelengths, using observations from SDO/AIA, RHESSI, and Fermi GBM. These plasmoids propagate bidirectionally upward and downward along the flare current sheet beneath the erupting flux rope during two successive flares associated with confined/failed eruptions. The flux rope exhibits evidence of helical kink instability with formation and ejection of multiple plasmoids in the flare current sheet, as predicted in an MHD simulation of a kink-unstable flux rope. RHESSI X-ray images show double coronal sources (``loop-top" and higher coronal sources) located at both ends of the flare current/plasma sheet. Moreover, we detected an additional transient faint X-ray source (6-12 keV) located between the double coronal sources, which was co-spatial with multiple plasmoids in the flare current sheet. X-ray (soft and hard) and radio (decimetric) observations unveil QPPs (periods$\approx$10-s and 100-s) associated with the ejection and coalescence of plasmoids. These observations suggest that energetic electrons are accelerated during the ejection and coalescence of multiple plasmoids in the flare current sheet.