We study the electron energy spectra of two powerful solar flares SOL2003-10-28T 11:06:16 (GOES class X17.2) and SOL2002-07-23T00:18:16 (X4.8) on the basis of HXR and gamma-ray spectra obtained from RHESSI data. Electron-electron (e-e) bremsstrahlung makes a significant contribution to the X-ray flux at energies above 500 keV. In X-ray flux calculations different electron pitch-angle distributions were considered: quasi-transverse and quasi-longitudinal. It was shown that breaks in hard X-ray spectra occur on energies $ε\approx100$ keV with photon spectral-index difference $Δγ\ge 1$ in the case of quasi-longitudinal anisotropy and hard power-law electron energy spectra. We deduce the parameters of non-thermal electrons energy spectra from RHESSI data for the extreme solar flares of 2003 October 28 and 2002 July 23. After including e-e bremsstrahlung, the non-thermal electrons energy spectra obtained in the thick-target model can be fitted using power-law with spectral index $δ\approx 5$. For the 2002 July 23 flare, there is a pronounced asymmetry towards the southern footpoint, starting from energies above 100 keV. The separation of HXR sources at energies above 100 keV may be related to a feature of relativistic electron transport in flaring loops.
The aim of this study is to generate maps of the hard X-ray emission produced by energetic electrons in a solar flare and compare them with observations. The ultimate goal is to test the viability of the combined MHD/test-particle approach for data-driven modelling of active events in the solar corona and their impact on the heliosphere. Based on an MHD model of X-class solar flare observed on the 8th of September 2017, we calculate trajectories of a large number of electrons and protons using the relativistic guiding-centre approach. Using the obtained particle trajectories, we deduce the spa…
We report hard X-ray and gamma-ray observations of the impulsive phase of the SOL2017-09-06T11:55 X9.3 solar flare. We focus on a high-energy part of the spectrum, >100 keV, and perform time resolved spectral analysis for a portion of the impulsive phase, recorded by the Konus-Wind experiment, that displayed prominent gamma-ray emission. Given a variety of possible emission components contributing to the gamma-ray emission, we employ a Bayesian inference to build the most probable fitting model. The analysis confidently revealed contributions from nuclear deexcitation lines, electron-positron …
Calculations of the emission spectrum of a homogeneous plane layer of pure hydrogen plasma taking into account nonlinear effects (the influence of bremsstrahlung and recombination radiation of the layer itself on its Menzel factors) [Morchenko et al., Ap&SS, Vol. 357, article id. 119 (2015)] show that the blue component of the optical continuum during the impulsive phase of large flares on dMe stars originates from the near-photospheric layers [Grinin and Sobolev, Afz, Vol. 13, 587 (1977)]. The gas behind the front of a stationary radiative shock wave propagating in the red dwarf chromosphere …
We describe a new approach for modeling the transport of high energy particles accelerated during flares from the acceleration region in the solar corona until their eventual thermalization in the flare footpoint. Our technique numerically solves the Fokker-Planck equation and includes forces corresponding to Coulomb collisions in a flux loop with nonuniform ionization, synchrotron emission reaction, magnetic mirroring and a return current electric field. Our solution to the Fokker-Planck equation includes second-order pitch angle and momentum diffusion. It is applicable to particles of arbitr…
Derivation of Stochastic Acceleration Model Characteristics for Solar Flares From RHESSI Hard X-Ray Observations
湍流对粒子的随机加速模型已成功地解释了太阳耀斑的许多观测特征。本文提出了一种利用RHESSI（RavenRamaty High Energy Solar Spectroscopic Imager）提供的高分辨率硬X射线观测数据获得加速电子能谱和重要加速模型参数的新方法。在我们的模型中，电子加速或非常接近环顶部产生薄的目标韧致辐射，然后向下逃逸产生厚的目标发射在循环的足点。基于RHESSI计数粒子的正则化反演得到的电子通量谱图像，我们导出了加速模型的几个重要参数。我们将此方法应用于2003年11月03日的太阳耀斑，它显示了一个环顶源高达100- 150千电子伏的硬X射线与一个相对平坦的频谱，除了两个脚点源。结果表明，存在强散射和湍流能量的高密度与陡峭的频谱中的加速区域。
Brown & Mallik 2008 and the Brown et al. 2010 corrigendum of it presented expressions for non-thermal recombination (NTR) in the collisionally thin- and thick-target regimes, claiming that the process could account for a substantial part of hard X-ray continuum in solar flares usually attributed entirely to thermal and non-thermal bremsstrahlung (NTB). However, we have found the thick-target expression to become unphysical for low cut-offs in the injected electron energy spectrum. We trace this to an error in the derivation, derive a corrected version which is real-valued and continuous for al…
We characterize and provide a catalog of thirty >100 MeV sustained gamma-ray emission (SGRE) events observed by Fermi LAT. These events are temporally and spectrally distinct from the associated solar flares. Their spectra are consistent with decay of pions produced by >300 MeV protons and are not consistent with electron bremsstrahlung. SGRE start times range from CME onset to two hours later. Their durations range from about four minutes to twenty hours and appear to be correlated with durations of >100 MeV SEP proton events. The >300 MeV protons producing SGRE have spectra that can be fit w…
Hard X-ray (HXR) sources are frequently observed near the top of solar flare loops, and the emission is widely ascribed to bremsstrahlung. We here revisit an alternative scenario which stresses the importance of inverse Compton processes and the Kelvin- Helmholtz instability (KHI) proposed by Fang et al. (2016). This scenario adds a novel ingredient to the standard flare model, where evaporation flows from flare-impacted chromospheric foot-points interact with each other near the loop top and produce turbulence via KHI. The turbulence can act as a trapping region and as an efficient accelerato…
Determination of the Acceleration Region Size in a Loop-structured Solar Flare
为了研究太阳耀斑中产生韧致辐射的电子的加速和传播，我们分析了不同时刻耀斑环大小随能量的演化。利用\textit{Ramaty High Energy Solar Spectroscopic Imager}（\textit{RHESSI}）观测资料，对2002年4月14日23：55左右开始的GOES M3.7环结构耀斑进行了详细研究。我们构建光子和平均电子通量地图在2 keV的能量箱通过处理观测推导的光子和电子vibrium，分别通过几种图像处理方法：基于可扩展性的前向拟合（FWD）算法，最大熵（MEM）的程序和UV平滑（UVS）的方法。我们估计细长耀斑的大小（即，张开环的长度和宽度）。采用扩展的加速区域的碰撞模型，我们适合的环长度作为能量的函数在光子和电子域。由此得到的拟合参数允许我们估计在$\sim 13 \rm{arcsec}$和$\sim 19 \rm{arcsec}$之间的加速度区域的范围。前向拟合和uv平滑算法的结果基本相似，但在电子域的拟合效果更好，这两种方法的一致性为模型能够可靠地确定加速区的几何参数提供了强有力的支持。加速区域估计是一个相当大的分数（$\sim 1/2$）的循环范围，表明这种密集的耀斑循环结合了加速和运输的电子，与并发厚目标韧致辐射发射。
Context. We present an analysis of a GOES M1.8 flare with excellent observational coverage in UV, EUV, and X-ray, including observations from the instruments IRIS, SDO with AIA, Hinode/EIS, Hinode/XRT, and Solar Orbiter with the Spectrometer/Telescope for Imaging X-rays (STIX). Hard X-ray emission is often observed at the footpoints of flare loops and is occasionally observed in the corona. In this flare, four nonthermal hard X-ray sources are seen. Aim. Our aim is to understand why we can observe four individual nonthermal sources in this flare and how we can characterize the physical propert…
Sudden jets of collimated plasma arise from many locations on the Sun, including active regions. The magnetic field along which a jet emerges is often open to interplanetary space, offering a clear "escape route" for any flare-accelerated electrons and making jets lucrative targets for studying particle acceleration and the solar sources of transient heliospheric events. Bremsstrahlung hard X-rays (HXRs) could, in principle, trace the accelerated electrons that escape along the paths of the jets, but measurements of the escaping electron beams are customarily difficult due to the low densities…
Appreciable hard X-ray (HXR) and gamma-ray emissions in the 0.04 to 150 MeV energy range associated with the 2003 October 29 solar flare (X10/3B) were observed at 20:38 to 20:58 UT by the SONG instrument onboard the CORONAS-F mission. To restore flare gamma-ray spectra we fitted the SONG energy loss spectra with a three-component model of the incident spectrum: (1) a power law in energy, assumed to be due to electron bremsstrahlung; (2) a broad continuum produced by prompt nuclear de-excitation gamma-lines; and (3) a broad gamma-line generated from pion decay. We also restored spectra from the…
The sub-THz event observed on the 4 July 2012 with the Bauman Moscow State Technical University Radio Telescope RT-7.5 at 93 and 140~GHz as well as Kislovodsk and Metsähovi radio telescopes, Radio Solar Telescope Network (RSTN), GOES, RHESSI, and SDO orbital stations is analyzed. The spectral flux between 93 and 140 GHz has been observed increasing with frequency. On the basis of the SDO/AIA data the differential emission measure has been calculated. It is shown that the thermal coronal plasma with the temperature above 0.5~MK cannot be responsible for the observed sub-THz flare emission. The …
This study entails the third part of a global flare energetics project, in which Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) data of 191 M and X-class flare events from the first 3.5 yrs of the Solar Dynamics Observatory (SDO) mission are analyzed. We fit a thermal and a nonthermal component to RHESSI spectra, yielding the temperature of the differential emission measure (DEM) tail, the nonthermal power law slope and flux, and the thermal/nonthermal cross-over energy $e_{\mathrm{co}}$. From these parameters we calculate the total nonthermal energy $E_{\mathrm{nt}}$ in electrons with…
Flare-associated quasiperiodic pulsations (QPPs) in radio and X-ray wavelengths, particularly those related to nonthermal electrons, contain important information about the energy release and transport processes during flares. However, the paucity of spatially resolved observations of such QPPs with a fast time cadence has been an obstacle for us to further understand their physical nature. Here, we report observations of such a QPP event that occurred during the impulsive phase of a C1.8-class eruptive solar flare using radio imaging spectroscopy data from the Karl G. Jansky Very Large Array …
On April 23, 2014, the Swift satellite responded to a hard X-ray transient detected by its Burst Alert Telescope, which turned out to be a stellar flare from a nearby, young M dwarf binary DG~CVn. We utilize observations at X-ray, UV, optical, and radio wavelengths to infer the properties of two large flares. The X-ray spectrum of the primary outburst can be described over the 0.3-100 keV bandpass by either a single very high temperature plasma or a nonthermal thick-target bremsstrahlung model, and we rule out the nonthermal model based on energetic grounds. The temperatures were the highest s…
We present a novel X-ray assembly of functionally related instrument blocks intended to measure solar flare and active region (AR) spectra from within the Russian instrument complex KORTES, to be mounted aboard the International Space Station (ISS). SolpeX consists of three blocks: fast-rotating multiple flat crystal Bragg spectrometer, pin-hole X-ray spectral imager and Bragg polarimeter. This combination of measuring blocks will offer an opportunity to detect/measure possible X-ray polarization in soft X-ray emission lines/continuum and record spectra of solar flares, in particular during th…
High energy X-ray and ultraviolet (UV) radiation from young stars impacts planetary atmospheric chemistry and mass loss. The active $\sim 22$ Myr M dwarf AU Mic hosts two exoplanets orbiting interior to its debris disk. Therefore, this system provides a unique opportunity to quantify the effects of stellar XUV irradiation on planetary atmospheres as a function of both age and orbital separation. In this paper we present over 5 hours of Far-UV (FUV) observations of AU Mic taken with the Cosmic Origins Spectrograph (COS; 1070-1360 Angstrom) on the Hubble Space Telescope (HST). We provide an item…
ZIMPOL detects scattering polarization in He I D$_3$ during a solar flare
Istituto ricerche solari Aldo e Cele Daccò (IRSOL), Faculty of Informatics, Università della Svizzera italiana (USI)（瑞士意大利大学信息学院阿尔多和切莱·达科太阳研究所）；Euler Institute, Università della Svizzera italiana (USI)（瑞士意大利大学欧拉研究所）；Astronomical Institute of the Academy of Sciences, Ondřejov, Czech Republic（捷克科学院天文台奥恩杰约夫研究所）
研究首次在日耀斑中检测到 He I D₃ 线的线偏振，通过 ZIMPOL 极化仪分析偏振变化与等离子体速度演变，发现散射偏振可能由各向异性辐射泵浦引起。
Solar flare X-ray spectra are typically dominated by thermal bremsstrahlung emission in the soft X-ray ($\lesssim$10 keV) energy range; for hard X-ray energies ($\gtrsim$30 keV), emission is typically non-thermal from beams of electrons. The low-energy extent of non-thermal emission has only been loosely quantified. It has been difficult to obtain a lower limit for a possible non-thermal cutoff energy due to the significantly dominant thermal emission. Here we use solar flare data from the EUV Variability Experiment (EVE) on-board the Solar Dynamics Observatory (SDO) and X-ray data from the Re…
We report on the Fermi-LAT detection of high-energy emission from the behind-the-limb (BTL) solar flares that occurred on 2013 October 11, and 2014 January 6 and September 1. The Fermi-LAT observations are associated with flares from active regions originating behind both the eastern and western limbs, as determined by STEREO. All three flares are associated with very fast coronal mass ejections (CMEs) and strong solar energetic particle events. We present updated localizations of the >100 MeV photon emission, hard X-ray (HXR)and EUV images, and broadband spectra from 10 keV to 10 GeV, as well…
