Impulsive Heating of Solar Flare Ribbons Above 10 MK

TL;DR

This study provides evidence of impulsive heating above 10 MK in solar flare ribbons during a specific event, using multi-wavelength observations and spectral analysis to investigate plasma evolution and heating mechanisms.

Contribution

It demonstrates the presence of hot plasma above 10 MK in flare ribbons and evaluates the limitations of collisional beam heating as the sole mechanism.

Findings

Hot plasma above 10 MK observed at flare ribbons.

Emission measure peaks near hard X-ray peak time.

Collisional beam heating insufficient to explain observed heating.

Abstract

The chromospheric response to the input of flare energy is marked by extended extreme ultraviolet (EUV) ribbons and hard X-ray (HXR) footpoints. These are usually explained as the result of heating and bremsstrahlung emission from accelerated electrons colliding in the dense chromospheric plasma. We present evidence of impulsive heating of flare ribbons above 10 MK in a two-ribbon flare. We analyse the impulsive phase of SOL2013-11-09T06:38, a C2.6 class event using data from Atmospheric Imaging Assembly (AIA) on board of Solar Dynamics Observatory (SDO) and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) to derive the temperature, emission measure and differential emission measure of the flaring regions and investigate the evolution of the plasma in the flaring ribbons. The ribbons were visible at all SDO/AIA EUV/UV wavelengths, in particular, at 94 and 131 \AA\ filters, sensitive to temperatures of 8 MK and 12 MK. Time evolution of the emission measure of the plasma above 10 MK at the ribbons has a peak near the HXR peak time. The presence of hot plasma in the lower atmosphere is further confirmed by RHESSI imaging spectroscopy analysis, which shows resolved sources at 11-13 MK associated with at least one ribbon. We found that collisional beam heating can only marginally explain the necessary power to heat the 10 MK plasma at the ribbons.