Spectroscopic Study of Heating Distributions and Mechanisms Using Hinode/EIS

Abstract

Heating distributions along coronal loops are obtained from spectroscopic data with the Hinode/EUV Imaging Spectrometer. The loop half-lengths L _half are in the range of 24–107 Mm for our analysis of 18 loops. By using the analytical approximations to 1D hydrostatic numerical calculations of electron temperature T _e (s) and density distributions n _e (s) along a loop, the heating distribution that decreases with a heating scale height s _H toward the loop top with a heating rate E ₀ at the height of the transition region is estimated by applying a Bayesian analysis to the observed T _e (s) and n _e (s) derived by emission line ratios. We obtain s _H = 10 ± 4 Mm increasing with L _half, E ₀ = 10^‑2.0±0.5 erg cm^‑3 s^‑1 decreasing with L _half, and the heating flux F _H = 10^7.0±0.4 erg cm^‑2 s^‑1. These loops show s _H /L _half = 0.21 ± 0.07, suggesting the concentration of the heating near the lower part. Compared to the previous study using imaging data, s _H is comparable, while E ₀ and F _H are about an order of magnitude larger. We find that using the imaging data leads to the underestimation of the electron density and consequently the underestimation of E ₀ and F _H . We examine heating mechanisms using the power-law relation for F _H , the field strength B _base and L _half: FH∝BbaseβLhalfλ . We find β=1.04‑0.36+0.18 and λ=‑0.99‑0.05+0.04 , which show that the reconnection heating model is the most plausible.