A Cold, Tenuous Solar Flare: Acceleration Without Heating

Fleishman, G. D.; Kontar, Eduard P.; Nita, Gelu M.; Gary, Dale E.

doi:10.1088/2041-8205/731/1/l19

Cited by 57 publications

(103 citation statements)

References 36 publications

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“…uncertainty (see, e.g., Kuznetsov et al 2011). Accordingly, in some of such cases the spectral index mismatches disappeared, when a more accurate treatment was used (Fleishman & Kuznetsov 2010;Fleishman et al 2011). In contrast, our modeling for the first time proves that the entire spectrum of the nonthermal electrons, at the same spatial location, has a double power-law form with a precisely constrained break energy, as well as low-and high-energy spectral indices.…”

Section: Discussionmentioning

confidence: 62%

“…It is well established that considering the X-ray and microwave data together can often improve the flare diagnostics greatly (see, e.g., Bastian et al 2007;Fleishman et al 2011White et al 2011). To perform a joint study of the X-ray and microwave data on the coronal thick-target sources requires a combination of reasonably complementary data sets, which would allow quantitative modeling of both X-ray and microwave emissions and their quantitative comparison with observations.…”

Section: Introductionmentioning

confidence: 99%

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Validation of the Coronal Thick Target Source Model

Fleishman

Nita

et al. 2016

ApJ

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We present detailed 3D modeling of a dense, coronal thick-target X-ray flare using the GX Simulator tool, photospheric magnetic measurements, and microwave imaging and spectroscopy data. The developed model offers a remarkable agreement between the synthesized and observed spectra and images in both X-ray and microwave domains, which validates the entire model. The flaring loop parameters are chosen to reproduce the emission measure, temperature, and the nonthermal electron distribution at low energies derived from the X-ray spectral fit, while the remaining parameters, unconstrained by the X-ray data, are selected such as to match the microwave images and total power spectra. The modeling suggests that the accelerated electrons are trapped in the coronal part of the flaring loop, but away from where the magnetic field is minimal, and, thus, demonstrates that the data are clearly inconsistent with electron magnetic trapping in the weak diffusion regime mediated by the Coulomb collisions. Thus, the modeling supports the interpretation of the coronal thick-target sources as sites of electron acceleration in flares and supplies us with a realistic 3D model with physical parameters of the acceleration region and flaring loop.

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Section: Discussionmentioning

confidence: 62%

Section: Introductionmentioning

confidence: 99%

Validation of the Coronal Thick Target Source Model

Fleishman

Nita

et al. 2016

ApJ

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“…Further, unlike footpointdominated solar flares (e.g., Antonucci et al 1982;Duijveman et al 1982;Takakura et al 1995;Sakao et al 1996;Petrosian & Donaghy 1999;Emslie et al 2003;Mrozek & Tomczak 2004;Tomczak & Ciborski 2007;Battaglia & Kontar 2011;Fleishman et al 2011;Chen & Petrosian 2013), the HXR spectra of such "coronal thick-target sources" tends to be softer than, and the sources higher than, chromospheric sources, which generally reduces the albedo contribution to X-ray images (Kontar & Jeffrey 2010), making the interpretation of the spectro-spatial structure of such sources more straightforward.…”

Section: Introductionmentioning

confidence: 99%

On the Variation of Solar Flare Coronal X-Ray Source Sizes With Energy

Jeffrey

Kontar

Bian

et al. 2014

ApJ

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Observations with RHESSI have enabled the detailed study of the structure of dense hard X-ray coronal sources in solar flares. The variation of source extent with electron energy has been discussed in the context of streaming of nonthermal particles in a one-dimensional cold-target model, and the results used to constrain both the physical extent of, and density within, the electron acceleration region. Here we extend this investigation to a more physically realistic model of electron transport that takes into account the finite temperature of the ambient plasma, the initial pitch-angle distribution of the accelerated electrons, and the effects of collisional pitch-angle scattering. The finite temperature results in the thermal diffusion of electrons, that leads to the observationally-inferred value of the acceleration region volume being an overestimate of its true value.The different directions of the electron trajectories, a consequence of both the non-zero injection pitch-angle and scattering within the target, cause the projected propagation distance parallel to the guiding magnetic field to be reduced, so that a one-dimensional interpretation can overestimate the actual density by a factor of up to ∼ 6. The implications of these results for the determination of acceleration region properties (specific acceleration rate, filling factor, etc.) are discussed.

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“…Once the two parallel 2D data cubes (unfolded and folded) are available, we step through the 2D field of view pixel by pixel and apply forward fitting of a homogeneous source to the spectra via the downhill simplex minimization algorithm (Press, Flannery, and Teukolsky, 1986), with some modifications detailed in Fleishman, Nita, and Gary (2009) to avoid local minima. The method is to choose a set of N par parameters to fit, make an initial guess for parameter values, calculate the emission for that set of parameters using the fast codes, compare the fit with the data using a standard reduced-chi-squared (χ 2 ν ) metric, adjust the parameters via the simplex method and repeat until some specified criterion for stopping has been met.…”

Section: Fitting Frameworkmentioning

confidence: 99%

Magnetography of Solar Flaring Loops with Microwave Imaging Spectropolarimetry

Gary¹,

Fleishman²,

Nita³

2013

Coronal Magnetometry

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We have developed a general framework for modeling gyrosynchrotron and free-free emission from solar flaring loops and used it to test the premise that 2D maps of source parameters, particularly magnetic field, can be deduced from spatially resolved microwave spectropolarimetry data. In this paper we show quantitative results for a flaring loop with a realistic magnetic geometry, derived from a magnetic field extrapolation, and containing an electron distribution with typical thermal and nonthermal parameters, after folding through the instrumental profile of a realistic interferometric array. We compare the parameters generated from forward fitting a homogeneous source model to each line of sight through the folded image data cube with both the original parameters used in the model and with parameters generated from forward fitting a homogeneous source model to the original (unfolded) image data cube. We find excellent agreement in general, but with systematic effects that can be understood as due to finite resolution in the folded images and the variation of parameters along the line of sight, which are ignored in the homogeneous source model. We discuss the use of such 2D parameter maps within a larger framework of 3D modeling, and the prospects for applying these methods to data from a new generation of multifrequency radio arrays now or soon to be available.

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A Cold, Tenuous Solar Flare: Acceleration Without Heating

Cited by 57 publications

References 36 publications

Validation of the Coronal Thick Target Source Model

Validation of the Coronal Thick Target Source Model

On the Variation of Solar Flare Coronal X-Ray Source Sizes With Energy

Magnetography of Solar Flaring Loops with Microwave Imaging Spectropolarimetry

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