Spectroscopic Observations of Magnetic Reconnection and Chromospheric Evaporation in an X-shaped Solar Flare

TL;DR

This study uses IRIS observations to analyze UV spectral signatures during an X-shaped solar flare, revealing details of magnetic reconnection and chromospheric evaporation processes.

Contribution

It provides new spectroscopic evidence of bidirectional flows at the separator and detailed plasma dynamics during an atypical X-shaped flare.

Findings

Bidirectional flows indicated by broadened Si IV line wings near the separator.

Chromospheric evaporation evidenced by blueshifted Fe XXI and redshifted cooler lines.

Spectral signatures support magnetic reconnection at the X-point.

Abstract

We present observations of distinct UV spectral properties at different locations during an atypical X-shaped flare (SOL2014-11-09T15:32) observed by the Interface Region Imaging Spectrograph (IRIS). In this flare, four chromospheric ribbons appear and converge at an X-point where a separator is anchored. Above the X-point, two sets of non-coplanar coronal loops approach laterally and reconnect at the separator. The IRIS slit was located close to the X-point, cutting across some of the flare ribbons and loops. Near the location of the separator, the Si IV 1402.77 A line exhibits significantly broadened line wings extending to 200 km/s but an unshifted line core. These spectral features suggest the presence of bidirectional flows possibly related to the separator reconnection. While at the flare ribbons, the hot Fe XXI 1354.08 A line shows blueshifts and the cool Si IV 1402.77 A, C II 1335.71 A, and Mg II 2803.52 A lines show evident redshifts up to a velocity of 80 km/s, which are consistent with the scenario of chromospheric evaporation/condensation.