Simultaneous IRIS and Hinode/EIS observations and modelling of the 27 October 2014 X 2.0 class flare

TL;DR

This study combines high-resolution IRIS and Hinode/EIS observations with hydrodynamic modeling to analyze a major solar flare, revealing plasma upflows, temperature evolution, and supporting an electron beam heating mechanism.

Contribution

It provides the first detailed comparison of simultaneous IRIS and EIS observations with hydrodynamic simulations for a major flare, confirming electron beam heating as the primary energy transport.

Findings

IRIS observes fully blue-shifted x i line profiles up to 200 km/s.

Hot emission initially concentrates at footpoints before filling loops.

Simulated plasma parameters closely match observational data, supporting electron beam heating.

Abstract

We present the study of the X2-class flare which occurred on the 27 October 2014 and was observed with the Interface Region Imaging Spectrograph (IRIS) and the EUV Imaging Spectrometer (EIS) on board the Hinode satellite. Thanks to the high cadence and spatial resolution of the IRIS and EIS instruments, we are able to compare simultaneous observations of the \xxi~1354.08~\AA~and \xxiii~263.77~\AA~high temperature emission ($\gtrsim$ 10~MK) in the flare ribbon during the chromospheric evaporation phase. We find that IRIS observes completely blue-shifted \xxi~line profiles, up to 200 km s$^{-1}$ during the rise phase of the flare, indicating that the site of the plasma upflows is resolved by IRIS. In contrast, the \xxiii~line is often asymmetric, which we interpret as being due to the lower spatial resolution of EIS. Temperature estimates from SDO/AIA and Hinode/XRT show that hot emission (log($T$)[K] $>$ 7.2) is first concentrated at the footpoints before filling the loops. Density sensitive lines from IRIS and EIS give electron number density estimates of $\gtrsim$~10$^{12}$~cm$^{-3}$ in the transition region lines and 10$^{10}$~cm$^{-3}$ in the coronal lines during the impulsive phase. In order to compare the observational results against theoretical predictions, we have run a simulation of a flare loop undergoing heating using the HYDRAD 1D hydro code. We find that the simulated plasma parameters are close to the observed values which are obtained with IRIS, Hinode and AIA. These results support an electron beam heating model rather than a purely thermal conduction model as the driving mechanism for this flare.