Nonequilibrium Ionization Modeling of Petschek-type Shocks in Reconnecting Current Sheets in Solar Eruptions

Shen, Chengcai; Raymond, J. C.; Murphy, N. A.

doi:10.3847/1538-4357/aca6e7

Cited by 3 publications

(2 citation statements)

References 60 publications

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“…That result is somewhat surprising, in that one might expect strong heating and large populations of energetic electrons in reconnection current sheets, leading to elevated values of 〈Q〉 in impulsive events. High charge states in current sheets are observed in EUV images and UV spectra (Innes et al 2003;Ciaravella & Raymond 2008;Reeves & Golub 2011;Warren et al 2018) and predicted by models (Shen et al 2013(Shen et al , 2023. The heating may be less intense in jets than in flares; Joshi et al (2020) found temperatures of 1.4-1.8 MK.…”

Section: Introductionmentioning

confidence: 84%

Solar Energetic Particle Charge States and Abundances with Nonthermal Electrons

Lee,

Kahler,

Raymond

et al. 2024

ApJ

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An important aspect of solar energetic particle (SEP) events is their source populations. Elemental abundance enhancements of impulsive SEP events, originating in presumed coronal reconnection episodes, can be fitted to steep power laws of A/Q, where A and Q are the atomic mass and ionic charge. Since thermal electron energies are enhanced and nonthermal electron distributions arise in the reconnection process, we might expect that ionic charge states Q would be increased through ionization interactions with those electron populations during the acceleration process. The temperature estimated from the SEPs corresponds to the charge state during the acceleration process, while the actual charge state measured in situ may be modified as the SEPs pass through the corona. We examine whether the temperature estimation from the A/Q would differ with various κ values in a κ function representing high-energy tail deviating from a Maxwellian velocity distribution. We find that the differences in the A/Q between a Maxwellian and an extreme κ distribution are about 10%–30%. We fit power-law enhancement of element abundances as a function of their A/Q with various κ values. Then, we find that the derived source region temperature is not significantly affected by whether or not the electron velocity distribution deviates from a Maxwellian, i.e., thermal, distribution. Assuming that electrons are heated in the acceleration region, the agreement of the SEP charge state during acceleration with typical active region temperatures suggests that SEPs are accelerated and leave the acceleration region in a shorter time than the ionization timescale.

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Section: Introductionmentioning

confidence: 84%

Solar Energetic Particle Charge States and Abundances with Nonthermal Electrons

Lee,

Kahler,

Raymond

et al. 2024

ApJ

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“…The rapid heating or cooling of plasma can lead to departures from ionisation equilibrium; a state when the plasma ionic composition does not reflect its electron temperature, e.g., Refs. [57,[81][82][83][84][85][86]. This transient ionisation in turn can affect other diagnostics, e.g., Refs.…”

Section: Departures From Ionisation Equilibriummentioning

confidence: 99%

Spectral Imager of the Solar Atmosphere: The First Extreme-Ultraviolet Solar Integral Field Spectrograph Using Slicers

Calcines Rosario,

Auchère,

Corso

et al. 2024

Aerospace

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Particle acceleration, and the thermalisation of energetic particles, are fundamental processes across the universe. Whilst the Sun is an excellent object to study this phenomenon, since it is the most energetic particle accelerator in the Solar System, this phenomenon arises in many other astrophysical objects, such as active galactic nuclei, black holes, neutron stars, gamma ray bursts, solar and stellar coronae, accretion disks and planetary magnetospheres. Observations in the Extreme Ultraviolet (EUV) are essential for these studies but can only be made from space. Current spectrographs operating in the EUV use an entrance slit and cover the required field of view using a scanning mechanism. This results in a relatively slow image cadence in the order of minutes to capture inherently rapid and transient processes, and/or in the spectrograph slit ‘missing the action’. The application of image slicers for EUV integral field spectrographs is therefore revolutionary. The development of this technology will enable the observations of EUV spectra from an entire 2D field of view in seconds, over two orders of magnitude faster than what is currently possible. The Spectral Imaging of the Solar Atmosphere (SISA) instrument is the first integral field spectrograph proposed for observations at ∼180 Å combining the image slicer technology and curved diffraction gratings in a highly efficient and compact layout, while providing important spectroscopic diagnostics for the characterisation of solar coronal and flare plasmas. SISA’s characteristics, main challenges, and the on-going activities to enable the image slicer technology for EUV applications are presented in this paper.

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Nonthermal Observations of a Flare Loop-top Using IRIS Fe xxi: Implications for Turbulence and Electron Acceleration

Ashfield IV,

Polito,

et al. 2024

ApJ

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The excess broadening of high-temperature spectral lines, long observed near the tops of flare arcades, is widely considered to result from magnetohydrodynamic turbulence. According to different theories, plasma turbulence is also believed to be a candidate mechanism for particle acceleration during solar flares. However, the degree to which this broadening is connected to the acceleration of nonthermal electrons remains largely unexplored outside of recent work, and many observations have been limited by limited spatial resolution and cadence. Using the Interface Region Imaging Spectrometer, we present spatially resolved observations of loop-top (LT) broadenings using hot (≈11 MK) Fe xxi 1354.1 Å line emission at ≈9 s cadence during the 2022 March 30 X1.3 flare. We find nonthermal velocities upward of 65 km s−1 that decay linearly with time, indicating the presence and subsequent dissipation of plasma turbulence. Moreover, the initial Fe xxi signal was found to be cospatial and cotemporal with microwave emission measured by the Expanded Owens Valley Solar Array, placing a population of nonthermal electrons in the same region as the LT turbulence. Evidence of electron acceleration at this time is further supported by hard X-ray measurements from the Spectrometer/Telescope for Imaging X-rays on board Solar Orbiter. Using the decay of nonthermal broadenings as a proxy for turbulent dissipation, we found the rate of energy dissipation to be consistent with the power of nonthermal electrons deposited into the chromosphere, suggesting a possible connection between turbulence and electron acceleration.

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Nonequilibrium Ionization Modeling of Petschek-type Shocks in Reconnecting Current Sheets in Solar Eruptions

Cited by 3 publications

References 60 publications

Solar Energetic Particle Charge States and Abundances with Nonthermal Electrons

Solar Energetic Particle Charge States and Abundances with Nonthermal Electrons

Spectral Imager of the Solar Atmosphere: The First Extreme-Ultraviolet Solar Integral Field Spectrograph Using Slicers

Nonthermal Observations of a Flare Loop-top Using IRIS Fe xxi: Implications for Turbulence and Electron Acceleration

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