Investigation of a confined C-class flare in an arch filament system close to a regular sunspot

TL;DR

This study analyzes a confined C1.1 class solar flare near a sunspot, revealing how flux cancellation and magnetic field dynamics trigger and confine the flare within an arch filament system.

Contribution

It provides detailed observational evidence linking flux cancellation and magnetic twist increase to flare initiation and confinement in an arch filament system.

Findings

Flux cancellation at the neutral line triggers the flare.

The arch filament unwinds but remains confined by overlying magnetic fields.

Small-scale magnetic flux movements facilitate flare development.

Abstract

A moderate C1.1 class confined flare is investigated here, which occurred on 2013 September 24 at 22:56~UT, in an arch filament system close to a regular, unipolar sunspot. Spectro-polarimetric observations from the Tenerife Infrared Polarimeter at the 70 cm German Vacuum Tower Telescope were combined with data from the Helioseismic Magnetic Imager and the Atmospheric Imaging Assembly to identify the processes that triggered the flare. The legs of this arch filament were anchored in the leading sunspot and the network flux region of opposite polarity. The flare was driven by small-scale, flux cancellation at the weak neutral line underlying the arch filament which resulted in two small flaring events within an hour of the C1.1 flare. Flux cancellation was facilitated by the moat flow from the leading sunspot wherein small-scale magnetic fragments stream towards patches of pre-existing flux. The cancellation of flux led to the destabilization of the arch filament which was seen as an increase in the twist along the arch filament. The horizontal fields across the weak neutral line decay faster which cannot prevent the filament from rising that results in a two-ribbon flare at the neutral line. The arch filament unwinds as it rises, but is confined by the higher, overlying fields between the two polarities of the active region that decay much more slowly.