HYDRO2GEN: Non-thermal hydrogen Balmer and Paschen emission in solar flares generated by electron beams
HYDRO2GEN: Non-thermal hydrogen Balmer and Paschen emission in solar flares generated by electron beams
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DOI：
10.1051/0004-6361/201731053
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发表时间：
2018-02
影响因子：
6.5
通讯作者：
M. Druett;V. Zharkova
中科院分区：
文献类型：
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作者：
M. Druett;V. Zharkova
的目标。中国太阳望远镜（STT）和瑞典太阳望远镜（SST）经常在耀斑开始时观测到硬x射线（HXR）发射的急剧上升，并伴随着从中心波长到4 Å的强红移的H α线轮廓，现有的辐射模型不能完全解释。此外，使用界面区成像光谱仪（IRISH）对白光（WL）和Balmer连续发射的观测显示出强烈的共时增强，并且通常与HXR发射几乎共空间。这些效应表明与HXR发射相关的燃烧大气中氢原子的快速有效激发和电离源。本文研究了电子束作为引起观测到的氢谱线和连续辐射的因素。方法。燃烧大气被认为是由电子束注入的一维流体动力学响应产生的，定义了它们的动力学温度、密度和宏观速度。我们使用完全非局部热力学平衡（NLTE）方法对5能级加连续体氢原子模型模拟了这些大气中的辐射响应，考虑了自发、外部和内部扩散辐射以及与热电子和束流电子的非弹性碰撞的激发和电离。对所有光学厚跃迁（Lyman和Balmer系列）的同时稳态和积分辐射传递方程进行迭代求解，以确定它们的源函数，相对精度为10−5。利用L2近似求出了辐射传递方程的解。计算了Balmer系列和Paschen系列的氢谱线和连续辐射强度。结果。我们发现与束电子的非弹性碰撞强烈地增加了氢原子从色球球到光球球的激发和电离。这导致莱曼连续辐射的增加，它具有很高的光学厚度，并且在光束关闭后，它控制氢电离并导致Balmer和Paschen连续辐射中持续数量级的发射增强。巴尔默头强度与其他连续体头强度的比值与光束的初始通量有关。Paschen连续体发射贡献函数的高度分布表明，其高度与报道的近翼耀斑WL和HXR发射高度密切相关。这一过程还导致Balmer线和Paschen线中翼发射（Stark翼）的强烈增加，这与水动力冲击向下运动导致的H α -H γ线发射的大红移增强叠加在一起。模拟的谱线与各种燃烧事件的观测结果吻合得很好。
Aim. Sharp rises of hard X-ray (HXR) emission accompanied by H α line profiles with strong red-shifts up to 4 Å from the central wavelength, often observed at the onset of flares with the Specola Solare Ticinese Telescope (STT) and the Swedish Solar Telescope (SST), are not fully explained by existing radiative models. Moreover, observations of white light (WL) and Balmer continuum emission with the Interface Region Imaging Spectrograph (IRISH) reveal strong co-temporal enhancements and are often nearly co-spatial with HXR emission. These effects indicate a fast effective source of excitation and ionisation of hydrogen atoms in flaring atmospheres associated with HXR emission. In this paper, we investigate electron beams as the agents accounting for the observed hydrogen line and continuum emission. Methods. Flaring atmospheres are considered to be produced by a 1D hydrodynamic response to the injection of an electron beam defining their kinetic temperatures, densities, and macro velocities. We simulated a radiative response in these atmospheres using a fully non-local thermodynamic equilibrium (NLTE) approach for a 5-level plus continuum hydrogen atom model, considering its excitation and ionisation by spontaneous, external, and internal diffusive radiation and by inelastic collisions with thermal and beam electrons. Simultaneous steady-state and integral radiative transfer equations in all optically thick transitions (Lyman and Balmer series) were solved iteratively for all the transitions to define their source functions with the relative accuracy of 10 −5 . The solutions of the radiative transfer equations were found using the L2 approximation. Resulting intensities of hydrogen line and continuum emission were also calculated for Balmer and Paschen series. Results. We find that inelastic collisions with beam electrons strongly increase excitation and ionisation of hydrogen atoms from the chromosphere to photosphere. This leads to an increase in Lyman continuum radiation, which has high optical thickness, and after the beam is off it governs hydrogen ionisation and leads to the long lasting orders of magnitude enhancement of emission in Balmer and Paschen continua. The ratio of Balmer-to-other-continuum head intensities are found to be correlated with the initial flux of the beam. The height distribution of contribution functions for Paschen continuum emission indicate a close correlation with the observations of heights of WL and HXR emission reported for limb flares. This process also leads to a strong increase of wing emission (Stark’s wings) in Balmer and Paschen lines, which is superimposed on large red-shifted enhancements of H α -H γ line emission resulting from a downward motion by hydrodynamic shocks. The simulated line profiles are shown to fit closely the observations for various flaring events.