Plasma Diagnostics From Active Region and Quiet Sun Spectra Observed by Hinode/EIS: Quantifying the Departures from a Maxwellian Distribution

Abstract

We perform plasma diagnostics, including that of the non-Maxwellian $\kappa$-distributions, in several structures observed in the solar corona by the Extreme-Ultraviolet Imaging Spectrometer (EIS) onboard the Hinode spacecraft. To prevent uncertainties due to the in-flight calibration of EIS, we selected spectral atlases observed shortly after the launch of the mission. One spectral atlas contains an observation of an active region, while the other is an off-limb quiet Sun region. To minimize the uncertainties of the diagnostics, we rely only on strong lines and we average the signal over a spatial area within selected structures. Multiple plasma parameters are diagnosed, such as the electron density, differential emission measure, and the non-Maxwellian parameter $\kappa$. To do that, we use a simple, well-converging iterative scheme based on refining the initial density estimates via the DEM and $\kappa$. We find that while the quiet Sun spectra are consistent with a Maxwellian distribution, the coronal loops and moss observed within active region are strongly non-Maxwellian with $\kappa$ $⪅$ 3. These results were checked by calculating synthetic ratios using DEMs obtained as a function of $\kappa$. Ratios predicted using the DEMs assuming $\kappa$-distributions converged to the ratios observed in the quiet Sun and coronal loops. To our knowledge, this work presents a strong evidence of a presence of different electron distributions between two physically distinct parts of the solar corona.

23 pages, 8 figures, 4 tables

References in corpus (22)

• CHIANTI - an atomic database for emission lines - Paper XV: Version 9, improvements for the X-ray satellite lines
• RHESSI Microflare Statistics II. X-ray Imaging, Spectroscopy & Energy Distributions
• High precision density measurements in the solar corona: I. Analysis methods and results for Fe XII and Fe XIII
• The Formation of Kappa-Distribution Accelerated Electron Populations in Solar Flares
• Particle acceleration and transport in reconnecting twisted loops in a stratified atmosphere
• Microflare Heating of a Solar Active Region Observed with NuSTAR, Hinode/XRT, and SDO/AIA
• Non-Equilibrium Processes in the Solar Corona, Transition Region, Flares, and Solar Wind \textit{(Invited Review)}
• Kappa distribution and hard X-ray emission of solar flares
• The Temperature and Density Structure of the Solar Corona. I. Observations of the Quiet Sun with the EUV Imaging Spectrometer (EIS) on Hinode
• KAPPA: A Package for Synthesis of optically thin spectra for the non-Maxwellian kappa-distributions based on the CHIANTI database
• The Origin of Non-Maxwellian Solar Wind Electron Velocity Distribution Function: Connection to Nanoflares in the Solar Corona
• Observation and Modeling of Coronal "Moss" With the EUV Imaging Spectrometer on Hinode
• Effect of collisions and magnetic convergence on electron acceleration and transport in reconnecting twisted solar flare loops
• Diagnosing the time-dependence of active region core heating from the emission measure: II. Nanoflare trains
• Non-Gaussian Velocity Distributions in Solar Flares from Extreme Ultraviolet Lines: A Possible Diagnostic of Ion Acceleration
• Signatures of the non-Maxwellian $\kappa$-distributions in optically thin line spectra \subtitle{I. Theory and synthetic Fe IX--XIII spectra}
• Estimating the Chromospheric Absorption of Transition Region Moss Emission
• Imaging and Spectroscopic Observations of a Transient Coronal Loop: Evidence for the Non-Maxwellian $\kappa$-Distributions
• Suprathermal electron distributions in the solar transition region
• Temperature and Density Structure of a Recurring Active Region Jet
• Signatures of the non-Maxwellian $\kappa$-distributions in optically thin line spectra. II. Synthetic Fe XVII--XVIII X-ray coronal spectra and predictions for the Marshall Grazing-Incidence X-ray Spectrometer (MaGIXS)
• Synthetic IRIS spectra of the solar transition region: Effect of high-energy tails