Flare Expansion to a Magnetic Rope Accompanied by Rare Radio Bursts

TL;DR

This study analyzes a solar flare that expanded into a magnetic rope, accompanied by rare radio bursts and unique EUV structures, revealing insights into particle beams and magnetic field configurations.

Contribution

It provides a multispectral analysis of flare expansion into a magnetic rope, highlighting rare radio burst behaviors and associated EUV structures, with interpretations of particle beam propagation.

Findings

Rare positively drifting radio bursts observed

Unique EUV structure moving along the rope

Particle beam propagation explained the S-like burst form

Abstract

We present multispectral analysis (radio, H$\alpha$, UV/EUV, and hard X-ray) of a confined flare from 2015 March 12. This flare started within the active region NOAA 12 297 and then it expanded into a large preexisting magnetic rope embedded with a cold filament. The expansion started with several brightenings located along the rope. This process was accompanied by a group of slowly positively drifting bursts in the 0.8--2 GHz range. The frequency drift of these bursts was 45 -- 100 MHz s$^{-1}$. One of the bursts had an S-like form. During the brightening of the rope we observed an unique bright EUV structure transverse to the rope axis. The structure was observed in a broad range of temperatures and it moved along the rope with the velocity of about 240 km s$^{-1}$. When the structure dissipated, we saw a plasma further following twisted threads in the rope. The observed slowly positively drifting bursts were interpreted considering particle beams and we show that one with the S-like form could be explained by the beam propagating through the helical structure of the magnetic rope. The bright structure transverse to the rope axis was interpreted considering line-of-sight effects and the dissipation-spreading process, which we found to be more likely.