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Although both electron-ion and electron-electron bremsstrahlung contribute to the hard X-ray emission from solar flares, the latter is normally ignored. Such an omission is not justified at electron (and photon) energies above $\sim 300$…

The optical and near-ultraviolet (NUV) continuum radiation in M dwarf flares is thought to be the impulsive response of the lower stellar atmosphere to magnetic energy release and electron acceleration at coronal altitudes. This radiation…

Solar and Stellar Astrophysics · Physics 2023-02-07 Adam F. Kowalski

The acceleration and transport of energetic electrons during solar flares is one of the outstanding topics in solar physics. Recent X-ray and radio imaging and spectroscopy observations have provided diagnostics of the distribution of…

Solar and Stellar Astrophysics · Physics 2022-12-21 Xiangliang Kong , Bin Chen , Fan Guo , Chengcai Shen , Xiaocan Li , Jing Ye , Lulu Zhao , Zelong Jiang , Sijie Yu , Yao Chen , Joe Giacalone

Acceleration and transport of high-energy particles and fluid dynamics of atmospheric plasma are interrelated aspects of solar flares. We present here self-consistently combined Fokker-Planck modeling of particles and hydrodynamic…

Solar and Stellar Astrophysics · Physics 2009-09-28 Wei Liu , Vahe Petrosian , John T. Mariska

We present observations of electron energization in magnetic reconnection outflows during the pre-impulsive phase of solar flare SOL2012-07-19T05:58. During a time-interval of about 20 minutes, starting 40 minutes before the onset of the…

Solar and Stellar Astrophysics · Physics 2019-03-06 Marina Battaglia , Eduard P. Kontar , Galina Motorina

As it was shown by many authors, a slow decrease in X-rays observed during the decay phase of long duration flares (LDE) can be explained only by a magnetic reconnection and energy release ceaselessly ongoing in the coronal part of a flare.…

Solar and Stellar Astrophysics · Physics 2011-04-08 Sylwester Kolomanski , Zbigniew Koltun , Tomasz Mrozek , Urszula Bak-Steslicka

In the solar corona and solar wind, electron heat conduction is an important process that transports energy over large distances and helps determine the spatial variation of temperature. High-density regions undergoing rapid…

Solar and Stellar Astrophysics · Physics 2021-11-03 Steven R. Cranmer , Avery J. Schiff

Simultaneous solar flare observations with SDO and RHESSI provide spatially resolved information about hot plasma and energetic particles in flares. RHESSI allows the properties of both hot (> 8 MK) thermal plasma and nonthermal electron…

Solar and Stellar Astrophysics · Physics 2015-06-17 Marina Battaglia , Eduard P. Kontar

Spatially-resolved X-ray observations are the key to understanding electron acceleration in solar flares. Currently, the underlying processes that efficiently energize solar flare particles are poorly constrained. Abundant flare…

Solar and Stellar Astrophysics · Physics 2026-03-09 Morgan Stores , Natasha Jeffrey , Ewan Dickson , James McLaughlin , Eduard Kontar

The aim of this paper is to demonstrate the effect of turbulent background density fluctuations on flare-accelerated electron transport in the solar corona. Using the quasi-linear approximation, we numerically simulated the propagation of a…

Solar and Stellar Astrophysics · Physics 2015-06-12 I. G. Hannah , E. P. Kontar , H. A. S. Reid

We investigate accelerated electron energy spectra for different sources in a large flare using simultaneous observations obtained with two instruments, the Nobeyama Radio Heliograph (NoRH) at 17 and 34 GHz, and the Reuven Ramaty High…

Solar and Stellar Astrophysics · Physics 2015-05-13 M. R. Kundu , V. V. Grechnev , S. M. White , E. J. Schmahl , N. S. Meshalkina , L. K. Kashapova

RHESSI measurements relevant to the fundamental processes of energy release and particle acceleration in flares are summarized. RHESSI's precise measurements of hard X-ray continuum spectra enable model-independent deconvolution to obtain…

Solar and Stellar Astrophysics · Physics 2011-10-11 R. P. Lin

The detailed knowledge of plasma heating and acceleration region properties presents a major observational challenge in solar flare physics. Using the Ramaty High Energy Solar Spectroscopic Imager (RHESSI), the high temperature differential…

Solar and Stellar Astrophysics · Physics 2015-12-02 Natasha Jeffrey , Eduard Kontar , Brian Dennis

Nonthermal electrons accelerated in solar flares produce electromagnetic emission in two distinct, highly complementary domains - hard X-rays (HXRs) and microwaves (MWs). This paper reports MW imaging spectroscopy observations from the…

Solar and Stellar Astrophysics · Physics 2020-04-29 Natsuha Kuroda , Gregory D. Fleishman , Dale E. Gary , Gelu M. Nita , Bin Chen , Sijie Yu

A major open issue concerning the active Sun is the effectiveness with which magnetic reconnection accelerates electrons in flares. A paper published by {\em{Nature}} in 2022 used microwave observations to conclude that the Sun is an almost…

Solar and Stellar Astrophysics · Physics 2025-02-10 Anna Volpara , Paolo Massa , Michele Piana , Anna Maria Massone , A Gordon Emslie

Solar flares are powerful particle accelerators, and in the accepted standard flare model most of the flare energy is transported from a coronal energy-release region by accelerated electrons which stop collisionally in the chromosphere,…

Solar and Stellar Astrophysics · Physics 2024-06-18 Paulo J. A. Simões , Lyndsay Fletcher , Hugh S. Hudson , Graham S. Kerr , Matt Penn , Karla F. Lopez

Solar flare electron acceleration is an extremely efficient process, but the method of acceleration is not well constrained. Two of the essential diagnostics: electron anisotropy (velocity angle to the guiding magnetic field) and the high…

Solar and Stellar Astrophysics · Physics 2020-12-21 Natasha L. S. Jeffrey , Pascal Saint-Hilaire , Eduard P. Kontar

The energy input into the lower solar corona by flare evaporation events has been modeled according to the available observations for quiet regions. The question is addressed whether such heating events can provide the observed average…

Astrophysics · Physics 2008-11-26 U. Mitra-Kraev , A. O. Benz

A considerable fraction of the energy in a solar flare is released as suprathermal electrons; such electrons play a major role in energy deposition in the ambient atmosphere and hence the atmospheric response to flare heating. Historically…

Solar and Stellar Astrophysics · Physics 2018-08-08 A. G. Emslie , N. H. Bian , E. P. Kontar

The transport of the energy contained in suprathermal electrons in solar flares plays a key role in our understanding of many aspects of flare physics, from the spatial distributions of hard X-ray emission and energy deposition in the…

Solar and Stellar Astrophysics · Physics 2017-02-08 Nicolas H. Bian , A. Gordon Emslie , Eduard P. Kontar