# Flux rope, hyperbolic flux tube, and late EUV phases in a non-eruptive circular-ribbon flare

## TL;DR

This study analyzes the magnetic topology and EUV emissions of a confined circular flare, revealing the roles of flux ropes, hyperbolic flux tubes, and reconnection phases in flare dynamics and late EUV emissions.

## Contribution

It provides the first detailed analysis of magnetic reconnection at a hyperbolic flux tube in a confined flare, linking topology to EUV late phases.

## Key findings

- Reconnection initially occurs at the HFT below the flux rope.
- Magnetic topology includes a null point, flux rope, and HFT.
- EUV late phases are caused by cooling loops reconnecting at the null.

## Abstract

We present a detailed study of a confined circular flare dynamics associated with 3 UV late phases in order to understand more precisely which topological elements are present and how they constrain the dynamics of the flare. We perform a non-linear force free field extrapolation of the confined flare observed with the HMI and AIA instruments onboard SDO. From the 3D magnetic field we compute the squashing factor and we analyse its distribution. Conjointly, we analyse the AIA EUV light curves and images in order to identify the post-flare loops, their temporal and thermal evolution. By combining both analysis we are able to propose a detailed scenario that explains the dynamics of the flare. Our topological analysis shows that in addition to a null-point topology with the fan separatrix, the spine lines and its surrounding Quasi-Separatix Layers halo (typical for a circular flare), a flux rope and its hyperbolic flux tube (HFT) are enclosed below the null. By comparing the magnetic field topology and the EUV post-flare loops we obtain an almost perfect match 1) between the footpoints of the separatrices and the EUV 1600~\AA{} ribbons and 2) between the HFT's field line footpoints and bright spots observed inside the circular ribbons. We showed, for the first time in a confined flare, that magnetic reconnection occured initially at the HFT, below the flux rope. Reconnection at the null point between the flux rope and the overlying field is only initiated in a second phase. In addition, we showed that the EUV late phase observed after the main flare episode are caused by the cooling loops of different length which have all reconnected at the null point during the impulsive phase.