Multiwavelength Imaging and Spectroscopy of Chromospheric Evaporation in an M-Class Solar Flare

Veronig, Astrid; Rybák, J.; Gömöry, P.; Berkebile-Stoiser, S.; Temmer, Manuela; Otruba, W.; Vršnak, Bojan; Pötzi, W.; Baumgartner, D.

doi:10.1088/0004-637x/719/1/655

Cited by 44 publications

(49 citation statements)

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“…Observational evidence for the proposed momentum balance during explosive evaporation was found for several events (Zarro et al 1988;Teriaca et al 2006;Milligan et al 2006a). Other observational studies, however, also revealed downflows at coronal temperatures (Milligan & Dennis 2009;Young et al 2013), suggesting that the flaring atmosphere is very dynamic and complex on small spatial scales (e.g., Veronig et al 2010). Simplified hydrodynamic simulations therefore probably fall short of adequately describing all responses of the flaring atmosphere.…”

Section: Introductionmentioning

confidence: 99%

Chromospheric evaporation flows and density changes deduced from Hinode/EIS during an M1.6 flare

Gömöry

Veronig

et al. 2016

A&A

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Aims. We study the response of the solar atmosphere during a GOES M1.6 flare using spectroscopic and imaging observations. In particular, we examine the evolution of the mass flows and electron density together with the energy input derived from hard X-ray (HXR) in the context of chromospheric evaporation.Methods. We analyzed high-cadence sit-and-stare observations acquired with the Hinode/EIS spectrometer in the Fe xiii 202.044 Å (log T = 6.2) and Fe xvi 262.980 Å (log T = 6.4) spectral lines to derive temporal variations of the line intensity, Doppler shifts, and electron density during the flare. We combined these data with HXR measurements acquired with RHESSI to derive the energy input to the lower atmosphere by flare-accelerated electrons.Results. During the flare impulsive phase, we observe no significant flows in the cooler Fe xiii line but strong upflows, up to 80-150 km s −1 , in the hotter Fe xvi line. The largest Doppler shifts observed in the Fe xvi line were co-temporal with the sharp intensity peak. The electron density obtained from a Fe xiii line pair ratio exhibited fast increase (within two minutes) from the pre-flare level of 5.01 × 10 9 cm −3 to 3.16 × 10 10 cm −3 during the flare peak. The nonthermal energy flux density deposited from the coronal acceleration site to the lower atmospheric layers during the flare peak was found to be 1.34 × 10 10 erg s −1 cm −2 for a low-energy cut-off that was estimated to be 16 keV. During the decline flare phase, we found a secondary intensity and density peak of lower amplitude that was preceded by upflows of ∼15 km s −1 that were detected in both lines. The flare was also accompanied by a filament eruption that was partly captured by the EIS observations. We derived Doppler velocities of 250-300 km s −1 for the upflowing filament material. Conclusions. The spectroscopic results for the flare peak are consistent with the scenario of explosive chromospheric evaporation, although a comparatively low value of the nonthermal energy flux density was determined for this phase of the flare. This outcome is discussed in the context of recent hydrodynamic simulations. It provides observational evidence that the response of the atmospheric plasma strongly depends on the properties of the electron beams responsible for the heating, in particular the steepness of the energy distribution. The secondary peak of line intensity and electron density detected during the decline phase is interpreted as a signature of flare loops being filled by expanding hot material that is due to chromospheric evaporation.

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Section: Introductionmentioning

confidence: 99%

Chromospheric evaporation flows and density changes deduced from Hinode/EIS during an M1.6 flare

Gömöry

Veronig

et al. 2016

A&A

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“…However, the n-distribution is a parametric distribution that describes well only the bulk of the distribution function during flares . In particular, the ndistributions do not contain the high-energy tail observed commonly during flares (e.g., Asai et al 2009;Veronig et al 2010;Zharkova et al 2010;Guo et al 2011). This high-energy tail then dominates the bremsstrahlung spectrum at the X-ray wavelengths and corresponding photon energies of tens of keV.…”

Section: Non-maxwellian Bremsstrahlung Spectrummentioning

confidence: 98%

“…In solar physics, on which we focus here, departures from the equilibrium Maxwellian distribution occur every time particles are accelerated, e.g., in flares, where high-energy tails Appendix A is available in electronic form at http://www.aanda.org are ubiquitous (Petkaki & MacKinnon 2007Zharkova & Gordovskyy 2006;Veronig et al 2010;Zharkova et al 2010Zharkova et al , 2011Fletcher et al 2011;Holman et al 2011). Apart from that, departures from Maxwellian distributions can occur at low plasma densities if there are strong gradients of temperature and density, i.e., in the transition region (e.g., Owocki & Scudder 1983;Ljepojevic & MacNiece 1988;Scudder 1992;Pinfield et al 1999;, in conditions where the mean energy can change (Collier 2004), i.e., during plasma heating.…”

Section: Introductionmentioning

confidence: 99%

“…There, the power-law distributions were usually assumed to be responsible for the observed emission processes, such as bremsstrahlung in the hard X-ray range (e.g., Brown 1971;Lin & Hudson 1971;Holman et al 2003;Krucker & Lin 2008;Asai et al 2009;Warmuth et al 2009;Veronig et al 2010;Kurt et al 2010;Zharkova et al 2010;Guo et al 2011;Kontar et al 2011) or gyrosynchrotron emission in the radio range (e.g., Dulk 1985;Zhou & Karlický 1994;Kuznetsov et al 2011). Yasnov & Karlický (2009) presented an inverse method to determine the characteristics of the electron power-law tail distribution in radio bursts.…”

Section: Introductionmentioning

confidence: 99%

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The non-Maxwellian continuum in the X-ray, UV, and radio range

Dudík

Kašparová

Dzifčáková

et al. 2012

A&A

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Aims. We investigate the X-ray, UV, and also the radio continuum arising from plasmas with a non-Maxwellian distribution of electron energies. The two investigated types of distributions are the κ-and n-distributions. Methods. We derived analytical expressions for the non-Maxwellian bremsstrahlung and free-bound continuum spectra. The spectra were calculated using available cross-sections. Then we compared the bremsstrahlung spectra arising from the different bremsstrahlung cross-sections that are routinely used in solar physics.Results. The behavior of the bremsstrahlung spectra for the non-Maxwellian distributions is highly dependent on the assumed type of the distribution. At flare temperatures and hard X-ray energies, the bremsstrahlung is greatly increased for κ-distributions and exhibits a strong high-energy tail. With decreasing κ, the maximum of the bremsstrahlung spectrum decreases and moves to higher wavelengths. In contrast, the maximum of the spectra for n-distributions increases with increasing n, and the spectrum then falls off very steeply with decreasing wavelength. In the millimeter radio range, the non-Maxwellian bremsstrahlung spectra are almost parallel to the thermal bremsstrahlung. Therefore, the non-Maxwellian distributions cannot be detected by off-limb observations made by the ALMA instrument. The free-bound continua are also highly dependent on the assumed type of the distribution. For n-distributions, the ionization edges disappear and a smooth continuum spectrum is formed for n 5. Opposite behavior occurs for κ-distributions where the ionization edges are in general significantly enhanced, with details depending on κ and T through the ionization equilibrium. We investigated how the non-Maxwellian κ-distributions can be determined from the observations of the continuum and conclude that one can sample the low-energy part of the distribution from the continuum.

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“…X-ray observations with, e.g., RHESSI (Lin et al 2002) show that the flare electron distribution is composed of a plasma bulk, which is usually considered to be Maxwellian, and a high-energy tail, approximated with a power-law distribution (e.g., Brown 1971;Lin & Hudson 1971;Holman et al 2003;Brown et al 2008;Krucker & Lin 2008;Asai et al 2009;Warmuth et al 2009;Veronig et al 2010;Kurt et al 2010;Zharkova et al 2010;Guo et al 2011). The ionization equilibrium and synthetic spectra for the Maxwellian electron distribution are widely known (e.g., CHIANTI, Landi et al 2006;Dere et al 2009), but there are only few papers on the influence of the high-energy tail on the ionization equilibrium and the line spectra.…”

Section: Introductionmentioning

confidence: 99%

The ionization equilibrium and flare line spectra for the electron distribution with a power-law tail

Dzifčáková

Homola

Dudík

2011

A&A

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Context. Electron energy spectra exhibiting a high-energy tail are commonly observed during solar flares. Aims. We investigate the influence of the high-energy tail and thermal or nonthermal plasma bulk on the ionization equilibrium of Si and Si flare line spectra. Methods. We construct a realistically composed distribution that reflects the fits to RHESSI observations. We describe the high-energy tail by a power-law distribution and the bulk of the electron distribution by either the Maxwellian or n-distribution. The shape of this composed distribution is described by three parameters: the ratio of the plasma bulk density to the density of the high-energy tail, the power-law index of the high-energy tail, and the parameter n, which describes the bulk of the distribution. Results. Both the plasma bulk and the high-energy tail change the ionization equilibrium. The relative ion abundances are sensitive to the shape of the plasma bulk, but are much less sensitive to the high-energy tail. The high-energy tail increases the ratio of temperaturesensitive lines Si XIV λ5.22/Si XIII λ5.68. Because this ratio can be fitted with a thermal distribution with higher temperature, the highenergy tail influences the temperature diagnostics from flare lines. The high-energy tail has only a small effect on the ratio of the satellite-to-allowed Si XIId/Si XIII lines, which are dominantly sensitive on the shape of the plasma bulk. This enables us to perform an accurate diagnostic of the parameter n describing the plasma bulk. Conclusions. The realistically composed distribution is able to explain the observed features of the RESIK X-ray flare line spectra.

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Multiwavelength Imaging and Spectroscopy of Chromospheric Evaporation in an M-Class Solar Flare

Cited by 44 publications

References 68 publications

Chromospheric evaporation flows and density changes deduced from Hinode/EIS during an M1.6 flare

Chromospheric evaporation flows and density changes deduced from Hinode/EIS during an M1.6 flare

The non-Maxwellian continuum in the X-ray, UV, and radio range

The ionization equilibrium and flare line spectra for the electron distribution with a power-law tail

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