The kinetic effects of electron beam precipitation and resulting hard X-ray intensity in solar flares
The kinetic effects of electron beam precipitation and resulting hard X-ray intensity in solar flares
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太阳耀斑中电子束沉淀的动力学效应和由此产生的硬 X 射线强度
DOI：
10.1051/0004-6361:20041102
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发表时间：
2005
影响因子：
6.5
通讯作者：
M. Gordovskyy
中科院分区：
文献类型：
--
作者：
V. Zharkova;M. Gordovskyy
本文给出了快电子从日冕射入耀斑大气，并以能量和俯仰角扩散的方式沉淀到会聚磁场环中的含时动力学Fokker-Planck方程的数值解。假设电子在与部分电离的环境等离子体的粒子的库仑碰撞中失去能量，并且由于沉淀束引起的电场而欧姆加热。发现由沉淀电子束引起的电场引起返回电流束，该返回电流束以宽的俯仰角分布回到电晕中的源。返回电流被假定为来自周围的等离子体和从束电子散射成负俯仰角。给出了不同大气深度下沉淀和返回电流电子束的能量分布和俯仰角分布，沿着给出了能谱指数为3，5，7，初始能流为108，1010，1 0 12 erg cm-2 s-1。返回电流的能量分布覆盖能量低于60 keV的较弱的软束和增加到65 keV的中等软束，或70-75 keV的更强和硬束。最大值是在30千电子伏的较弱的软光束，并向更高的能量，高达50千电子伏，更硬，更强的光束。结果表明，从耀斑大气中发射的硬X射线的光子谱具有一个打破幂律（肘型）的形状，其高能部分保持与电子束初始折射率相关的谱指数δhigh，并随束流参数略有变化。然而，对于更强或更硬的光束，X射线光子谱的较低能量部分显示出其谱指数δlow的小得多的增加或甚至显著减小。这些模拟打破幂律光子谱产生的沉淀电子束与一个单一的光谱指数同意相当不错的光子能量谱从2002年7月20日和23日的耀斑观测的RHESSI有效载荷。
The numerical solutions of the time-dependent kinetic Fokker-Planck equation are presented for fast electrons in- jected from the solar corona into a flaring atmosphere and precipitating with energy and pitch-angle diffusion into a loop with a converging magnetic field. The electrons are assumed to lose their energy in Coulomb collisions with particles of the partially ionised ambient plasma and Ohmic heating owing to the electric field induced by the precipitating beam. The electric field induced by a precipitating electron beam is found to cause a return current beam, which comes back to the source in the corona with a wide pitch angle distribution. The return current is assumed to arise from the ambient plasma and from beam electrons scattered into negative pitch-angles. Energy and pitch-angle distributions of precipitating and return current electron beams at various atmospheric depths are presented along with the precipitating beam abundances, energy fluxes and resulting hard X-ray bremsstrahlung (photon) spectra for electron beams with power law energy spectra with spectral indices of 3, 5, 7 and initial energy fluxes of 10 8 ,1 0 10 ,1 0 12 erg cm −2 s −1 . Energy distributions of the return current cover energies lower than 60 keV for weaker soft beams and increase to 65 keV for moderate soft beams, or to 70-75 keV for more intense and hard beams. The maxima are at 30 keV for weaker soft beams and are shifted towards higher energies, up to 50 keV, for harder and more intense beams. As a result, the photon spectra of hard X-ray emission emitted from a flaring atmosphere are found to have a broken power-law (elbow-type) shape with a higher energy part retaining the spectral index δhigh associated with the electron beam's initial index and varying slightly with the beam parameters. However, the lower energy part of the X-ray photon spectra shows a much smaller increase or even a substantial decrease of its spectral index δlow for more intense or harder beams. These simulated broken power-law photon spectra produced by precipitating electron beams with a single spectral index agree reasonably well with the photon energy spectra from the flares of 20 and 23 July, 2002 observed by the RHESSI payload.