Comparative Analysis of Nonthermal Emissions and Electron Transport in a Solar Flare

Minoshima, Takashi; Yokoyama, T.; Mitani, Natsuko

doi:10.1086/523884

Cited by 37 publications

(25 citation statements)

References 36 publications

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“…This is also consistent with results of previous studies (Yoshimori et al 1985;Dennis 1988;Matsumoto et al 2005). Minoshima et al (2008) numerically calculated the spectral indices of microwave and HXR emissions from the trapped and precipitating electrons, and showed that a softer HXR spectrum and a hard microwave spectrum can be generated. The difference of the spectral indices ∆δ ∼1.5, is consistent with our result.…”

Section: Discussionmentioning

confidence: 99%

Temporal and Spatial Analyses of Spectral Indices of Nonthermal Emissions Derived From Hard X-Rays and Microwaves

Asai

Kiyohara

Takasaki

et al. 2013

ApJ

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We studied electron spectral indices of nonthermal emissions seen in hard X-rays (HXRs) and in microwaves. We analyzed 12 flares observed by the Hard X-ray Telescope aboard Yohkoh, Nobeyama Radio Polarimeters (NoRP), and the Nobeyama Radioheliograph (NoRH), and compared the spectral indices derived from total fluxes of hard X-rays and microwaves. Except for four events, which have very soft HXR spectra suffering from the thermal component, these flares show a gap ∆δ between the electron spectral indices derived from hard X-rays δ X and those from microwaves δ µ (∆δ = δ X −δ µ ) of about 1.6. Furthermore, from the start to the peak times of the HXR bursts, the time profiles of the HXR spectral index δ X evolve synchronously with those of the microwave spectral index δ µ , keeping the constant gap. We also examined the spatially resolved distribution of the microwave spectral index by using NoRH data. The microwave spectral -2index δ µ tends to be larger, which means a softer spectrum, at HXR footpoint sources with stronger magnetic field than that at the loop tops. These results suggest that the electron spectra are bent at around several hundreds of keV, and become harder at the higher energy range that contributes the microwave gyrosynchrotron emission.

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Section: Discussionmentioning

confidence: 99%

Temporal and Spatial Analyses of Spectral Indices of Nonthermal Emissions Derived From Hard X-Rays and Microwaves

Asai

Kiyohara

Takasaki

et al. 2013

ApJ

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“…Even so, it seems to be a common phenomenon which takes place together with the filament/plasma eruption. In fact, hot thermal plasma generated by energy-release process has long cooling time-scale, around several minutes at least, while nonthermal plasma has short lifetime, within 1 seconds for HXR (Kiplinger 1995) and 1∼100 seconds for microwaves (Minoshima et al 2008). Thus, nonthermal emission of microwave and hard X-rays is essential to detect and trace the energy-release site than thermal emission of soft X-rays and EUV.…”

Section: Summary and Discussionmentioning

confidence: 99%

Systematic Microwave Source Motions along a Flare-Arcade Observed by Nobeyama Radioheliograph and AIA/SDO

Kim¹,

Masuda²,

Shibasaki³

et al. 2013

Publications of the Astronomical Society of Japan

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We found systematic microwave source motions along a flare-arcade using Nobeyama Radioheliograph (NoRH) 17 GHz images. The motions were associated with a X-class disk flare which occurred on 15th February 2011. For this study, we also used EUV images from Atmospheric Imaging Assembly (AIA) and magnetograms from Helioseismic and Magnetic Imager (HMI) onboard Solar Dynamics Observatory, and multi-channel microwave data from Nobeyama Radiopolarimeters (NoRP) and Korean Solar Radio Burst Locator (KSRBL). We traced centroids of the microwave source observed by NoRH 17 GHz during the flare and found two episodes of the motion with several facts: 1) The microwave source moved systematically along the flare-arcade, which was observed by the AIA 94Å in a direction parallel to the neutral line.2) The period of each episode was 5 min and 14 min, respectively. 3) Estimated parallel speed was 34 km s −1 for the first episode and 22 km s −1 for the second episode. The spectral slope of microwave flux above 10 GHz obtained by NoRP and KSRBL was negative for both episodes, and for the last phase of the second episodes, it was flat with the flux of 150 sfu. The negative spectrum and the flat with high flux 1 indicate that the gyrosynchrotron emission from accelerated electrons was dominant during the source motions. The sequential images from the AIA 304Å and 94Å channels revealed that there were successive plasma eruptions and each eruption was initiated just before the start time of the microwave sources motion. Based on the results, we suggest that the microwave source motion manifests the displacement of the particle acceleration site caused by plasma eruptions.

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“…Petrosian & Donaghy (1999) investigate the conditions for formation of loop-top sources and compare predicted time-profiles of the X-ray emission with time-profiles observed by Yohkoh. Minoshima et al (2008) use a trap-plus-precipitation model to explain RHESSI observations. While those studies all focused on spectra, Fletcher (1996) investigated the height of X-ray sources obtained from numerical simulations and compared them with Yohkoh observations, finding that they are consistent with partial electron trapping in a magnetic trap.…”

Section: Introductionmentioning

confidence: 99%

Numerical Simulations of Chromospheric Hard X-Ray Source Sizes in Solar Flares

Battaglia

Kontar

Fletcher

et al. 2012

ApJ

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X-ray observations are a powerful diagnostic tool for transport, acceleration, and heating of electrons in solar flares. Height and size measurements of Xray footpoints sources can be used to determine the chromospheric density and constrain the parameters of magnetic field convergence and electron pitch-angle evolution. We investigate the influence of the chromospheric density, magnetic mirroring and collisional pitch-angle scattering on the size of X-ray sources. The time-independent Fokker-Planck equation for electron transport is solved numerically and analytically to find the electron distribution as a function of height above the photosphere. From this distribution, the expected X-ray flux as a function of height, its peak height and full width at half maximum are calculated and compared with RHESSI observations. A purely instrumental explanation for the observed source size was ruled out by using simulated RHESSI images. We find that magnetic mirroring and collisional pitch-angle scattering tend to change the electron flux such that electrons are stopped higher in the atmosphere compared with the simple case with collisional energy loss only. However, the resulting X-ray flux is dominated by the density structure in the chromosphere and only marginal increases in source width are found. Very high loop densities (> 10 11 cm −3 ) could explain the observed sizes at higher energies, but are unrealistic and would result in no footpoint emission below about 40 keV, contrary to observations. We conclude that within a monolithic density model the vertical sizes are given mostly by the density scale-height and are predicted smaller than the RHESSI results show.

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Comparative Analysis of Nonthermal Emissions and Electron Transport in a Solar Flare

Cited by 37 publications

References 36 publications

Temporal and Spatial Analyses of Spectral Indices of Nonthermal Emissions Derived From Hard X-Rays and Microwaves

Temporal and Spatial Analyses of Spectral Indices of Nonthermal Emissions Derived From Hard X-Rays and Microwaves

Systematic Microwave Source Motions along a Flare-Arcade Observed by Nobeyama Radioheliograph and AIA/SDO

Numerical Simulations of Chromospheric Hard X-Ray Source Sizes in Solar Flares

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