Study of the Emission Heights of White-Light Solar Flares and their Hard X-Ray Sources

太阳耀斑是太阳系中观测到的能量最大的爆炸。观察太阳耀斑的不同方式包括X射线、射电和色球光谱线。很大比例的耀斑被认为是可见光光谱中相关增亮的结果，因此被称为白光耀斑。白光发射是大型太阳耀斑的标志，甚至在其他恒星上也能观察到。虽然白光发射是迄今检测到的第一次太阳耀斑的表现，但在1959年9月1日著名的所谓卡林顿事件中，它的来源仍然不清楚。这项研究将比较观测和模拟太阳大气中白光耀斑和硬X射线耀斑起源的高度，并通过这一点来阐明和区分相互竞争的耀斑产生机制。通过这种方式，调查解决了与低太阳大气中耀斑能量转移有关的基本问题，其结果将提供关于太阳耀斑和日冕物质抛射的产生、能量和动力学的重要信息，从而为空间气象事件的发生提供关键的理解。这项研究工作也将对耀斑恒星的研究产生重大影响，因为同样的加速和辐射产生过程也在发挥作用。这些恒星耀斑可以在白光下探测到，但来自加速电子的硬X射线发射太微弱，无法直接测量。这一努力的结果将更好地定义太阳耀斑发射的白光和硬X射线之间的关系。这些信息反过来将有助于对恒星耀斑的研究，包括粒子加速和耀斑恒星的大气条件。令人费解的是，太阳耀斑在较低大气中产生白光(WL)连续辐射的实际机制尚未得到更好的了解。WL连续体与太阳耀斑的脉冲阶段，即粒子被加速的阶段，被解释为一个迹象，即在日冕中加速的非热粒子可以深入到较低的太阳大气，加热这些层并产生强烈的WL发射。然而，耀斑加速的电子撞击色球的碰撞距离相对较短，因此它们穿透深度的能力令人惊讶，正如WL和硬X射线(HXR)时间分布的密切关联所表明的那样。产生观测到的WL连续体的其他方法包括通过质子(而不是电子)沉积能量，或者通过紫外线或X射线连续体“辐射回暖”。阿尔文波的能量传输也可能是重要的，色球中的复合辐射也是如此。太阳大气中WL和HXR排放的高度之间的比较将支持或排除许多拟议的产生机制，从而提供对WL耀斑产生以及太阳耀斑整体能量学的更多了解。这项研究的主要目的是确定大样本耀斑的白光和硬X射线(HXR)源在太阳大气中的高度。我们将研究太阳大气中的绝对高度以及这两种辐射相互之间的高度。观测高度将与通过辐射流体动力学模型RADYN和三维辐射MHD模型RADMHD进行的理论模拟结果进行比较。得出的高度和模型比较将揭示太阳外层大气WL耀斑源的哪一层起源，并将为WL耀斑发射的产生提供新的见解，这是太阳物理学中一个重要而鲜为人知的问题。将使用SDO航天器上的人机界面仪器(白光源)、RHESSI(硬X射线源)和双立体声航天器上的EUVI仪器的数据作为背景数据来确定震源高度，以便提供另一种视角，从而实现精确的高度测量。将使用地面共用++网络来验证建模结果。来自ROSA和IBIS仪器的多波长观测将被用来表征白光耀斑的能量学。

A solar flare is the most energetic explosion observed in the solar system. Different ways of viewing solar flares include X-rays, radio and chromospheric spectral lines. A large percentage of flares are recognized as a result of associated brightening in the visible light spectrum, and thus are called white-light flares. White-light emission is a signature of large solar flares and can be observed even on other stars. Though the white light emission was the first manifestation of a solar flare ever detected, in the famous so-called Carrington event of September 1, 1959, its origin is still not understood. This study will compare observation and modeling of the heights in the solar atmosphere where the white-light and hard-X-ray flares originate and through this be able to elucidate and distinguish between competing flare generation mechanisms. In this way, the investigation tackles fundamental issues related to flare energy transfer in the lower solar atmosphere and the results will provide important information about the generation, energetics and dynamics of solar flares and coronal mass ejections, providing crucial understanding of the initiation of space weather events. The research effort will also have major consequences for the study of flaring stars, since the same acceleration and radiation generation processes are at work. These stellar flares are detected in white light, but hard X-ray emission from accelerated electrons is too faint to be directly measured. The results from this effort will better define the relationship between white light and hard X-ray emissions from solar flares. This information, in turn, will aid the investigation of stellar flares, including particle acceleration and atmospheric conditions of flaring stars.It is puzzling that the actual mechanism by which solar flares generate white-light (WL) continuum radiation in the lower atmosphere is not better understood. The association of WL continuum with the impulsive phase of a solar flare, that is, the phase in which particles are accelerated, has been interpreted as an indication that non-thermal particles accelerated in the corona can penetrate deep into the lower solar atmosphere, heating those layers and causing intense WL emission. However, flare-accelerated electrons hitting the chromosphere have relatively short collisional ranges, and so their ability to penetrate deeply, as indicated by the close correlation of WL and hard X-ray (HXR) time profiles, is surprising. Other methods of generating the observed WL continuum include energy deposition by protons (instead of electrons) or "radiative back-warming" by the UV or X-ray continua. Alfvenic wave transport of energy could also be significant, as could recombination radiation in the chromosphere. Comparison between the heights of WL and HXR emissions in the solar atmosphere will support or rule out many of these proposed generation mechanisms, thereby providing a greater understanding of WL flare generation as well as the overall energetics of solar flares. The main objective of this study is the determination of the heights in the solar atmosphere of white-light and hard X-ray (HXR) sources for a large sample of flares. Both absolute heights in the solar atmosphere and heights of the two types of emission relative to each other will be studied. The observed heights will be compared with the results of theoretical modeling performed via the radiation hydrodynamic model RADYN and the 3D radiative MHD model RADMHD. The derived heights and model comparisons will reveal in which layers of the outer solar atmosphere WL flare sources originate and will provide new insight into the generation of WL flare emission, an important and poorly-understood problem in solar physics. Source heights will be determined using data from the HMI instrument aboard the SDO spacecraft (for white-light sources), the RHESSI (for hard X-ray sources), and the EUVI instruments on the twin STEREO spacecraft, as context data, in order to provide an alternate viewing angleand thus precise height measurements. The ground-based GONG++ network will be used to validate the modeling results. Multiwavelength observations from the ROSA and IBIS instruments will be used to characterize white-light flare energetics.