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

Asai, Ayumi; Kiyohara, Junko; Takasaki, Hiroyuki; Narukage, Noriyuki; Yokoyama, T.; Masuda, S.; Shimojo, Masataka; Nakajima, Hiroshi

doi:10.1088/0004-637x/763/2/87

Cited by 30 publications

(27 citation statements)

References 37 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…of 0.97/0.88 are detected between the Fe XXI 1354.09Å blue shifts and the microwave 17/34 GHz emissions, a correlation coefficient of 0.87 is observed between the Fe XXI 1354.09Å blue shifts and the HXR 25−50 keV emission, and a correlation coefficient of 0.88 is found between the Fe XXI 1354.09Å blue shifts and the SXR 1.0−8.0Å flux derivative. Such high correlation coefficients demonstrate that the electron beams which might be accelerated by magnetic reconnection (e.g., Kundu et al 1994;Brosius & Holman 2007;White et al 2003;Asai et al 2013) drive the explosive chromospheric evaporation during the flare precursor Brosius et al 2016;Li et al 2017a). Meanwhile, the microwave and HXR emissions observed by NoRH and RHESSI images exhibit a pronounced brightening source that is co-spatial with the ribbon-like transient during the flare precursor peak, which gives an additional evidence of electron-driven evaporation before the GOES flare onset (Veronig et al 2010;Zhang et al 2016b;Li et al 2017b).…”

Section: Resultsmentioning

confidence: 98%

Observations of Electron-driven Evaporation in a Flare Precursor

Liu

et al. 2018

ApJ

View full text Add to dashboard Cite

We investigate the relationship between the blue shifts of a hot emission line and the nonthermal emissions in microwave and hard X-ray (HXR) wavelengths during the precursor of a solar flare on 2014 October 27. The flare precursor is identified as a small but well-developed peak in soft X-ray and extreme-ultraviolet passbands before the GOES flare onset, which is accompanied by a pronounced burst in microwave 17 & 34 GHz and HXR 25−50 keV. The slit of Interface Region Imaging Spectrograph (IRIS) stays at one ribbon-like transient during the flare precursor, where shows visible nonthermal emissions in NoRH and RHESSI images. The IRIS spectroscopic observations show that the hot line of Fe XXI 1354.09Å (logT ∼ 7.05) displays blue shifts, while the cool line of Si IV 1402.77Å (logT ∼ 4.8) exhibits red shifts. The blue shifts and red shifts are well correlated to each other, indicative of an explosive chromospheric evaporation during the flare precursor particularly combining with a high nonthermal energy flux and a short characteristic timescale. In addition, the blue shifts of Fe XXI 1354.09Å are well correlated with the microwave and HXR emissions, implying that the explosive chromospheric evaporation during the flare precursor is driven by nonthermal electrons.

show abstract

Section: Resultsmentioning

confidence: 98%

Observations of Electron-driven Evaporation in a Flare Precursor

Liu

et al. 2018

ApJ

View full text Add to dashboard Cite

show abstract

“…Combined analysis of HXRs and microwaves reveal that the electron energy distribution inferred from the microwave spectrum is harder than that from the HXR spectrum; this result suggests an intrinsic spectral hardening for the source electron spectrum around several hundred keV (e.g., Silva et al 2000;Asai et al 2013). On the other hand, in a recent study by Kawate et al (2012), these authors concluded that electrons responsible for HXRs and microwaves have a common energy distribution and that the hardening of microwave emission is due to a more efficient trapping of electrons with higher energies.…”

Section: Introductionmentioning

confidence: 94%

A Statistical Study of the Spectral Hardening of Continuum Emission in Solar Flares

Kong

Chen

2013

ApJ

View full text Add to dashboard Cite

The observed hard X-ray and γ -ray continuum in solar flares is interpreted as Bremsstrahlung emission of accelerated non-thermal electrons. It has been noted for a long time that in many flares the energy spectra show hardening at energies around or above 300 keV. In this paper, we first conduct a survey of spectral hardening events that were previously studied in the literature. We then perform a systematic examination of 185 flares from the Solar Maximum Mission. We identify 23 electron-dominated events whose energy spectra show clear double power laws. A statistical study of these events shows that the spectral index below the break (γ 1 ) anti-correlates with the break energy (ε b ). Furthermore, γ 1 also anti-correlates with Fr, the fraction of photons above the break compared to the total photons. A hardening spectrum, as well as the correlations between (γ 1 , ε b ) and (γ 1 , Fr), provide stringent constraints on the underlying electron acceleration mechanism. Our results support a recent proposal that electrons are being accelerated diffusively at a flare termination shock with a width of the order of an ion inertial length scale.

show abstract

“…Moses et al (1989) showed that in some flares the associated energetic electrons detected in-situ presented spectral hardening at high energies. Asai et al (2013) found that the electron spectral index deduced from the microwave emission was harder than that from the HXRs of the same source (also by Silva et al 2007), and deduced that the source electrons may be intrinsically hard at high energies. These studies provide additional support to the above interpretation of the high-energy hardening of the associated energetic electrons.…”

Section: Introductionmentioning

confidence: 96%

Gyrosynchrotron Emission Generated by Nonthermal Electrons with the Energy Spectra of a Broken Power Law

Chen

Ning

et al. 2019

ApJ

View full text Add to dashboard Cite

Latest observational reports of solar flares reveal some uncommon features of microwave spectra, such as unusually hard (or even positive) spectra, and/or a super-high peak frequency. For a better understanding of these features, we conduct a parameter study to investigate the effect of brokenpower-law spectra of energetic electrons on microwave emission on the basis of gyrosynchrotron mechanism. The electron broken-power-law energy distribution is characterized by three parameters, the break energy (E B ), the power-law indices below (δ 1 ) and above (δ 2 ) the break energy. We find that with the addition of the δ 2 component of the electron spectra, the total flux density can increase by several times in the optically-thick regime, and by orders of magnitude in the optically-thin regime; the peak frequency (ν p ) also increases and can reach up to tens of GHz; and the degree of polarization (r c ) decreases in general. We also find that (1) the variation of the flux density is much larger in the optically-thin regime, and the microwave spectra around the peak frequency manifest various profiles with the softening or soft-hard pattern; (2) the parameters δ 1 and E B affect the microwave spectral index (α) and the degree of polarization (r c ) mainly in the optically-thick regime, while δ 2 mainly affects the optically-thin regime. The results are helpful in understanding the lately-reported microwave bursts with unusual spectral features and point out the demands for a more-complete spectral coverage of microwave bursts, especially, in the high-frequency regime, say, > 10 − 20 GHz.

show abstract

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

Cited by 30 publications

References 37 publications

Observations of Electron-driven Evaporation in a Flare Precursor

Observations of Electron-driven Evaporation in a Flare Precursor

A Statistical Study of the Spectral Hardening of Continuum Emission in Solar Flares

Gyrosynchrotron Emission Generated by Nonthermal Electrons with the Energy Spectra of a Broken Power Law

Contact Info

Product

Resources

About