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

白光太阳耀斑发射高度及其硬X射线源研究

• 批准号: 1459930
• 负责人: Juan Carlos Martinez Oliveros
• 金额: $ 39万
• 依托单位: University of California-Berkeley
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-06-01 至 2020-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1459930&HistoricalAwards=false
• 关键词: Study; Emission; Heights; White; Light

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.

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法包括X射线，无线电和色球光谱线。大部分的耀斑被认为是可见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，甚至可以在其他恒星上观察到。虽然白色光发射是有史以来第一次发现的太阳耀斑的表现形式，但在1959年9月1日著名的卡林顿事件中，它的起源仍然不清楚。 这项研究将比较白光和硬X射线耀斑起源的太阳大气层高度的观测和建模，并通过这一点能够阐明和区分竞争性耀斑的产生机制。 通过这种方式，研究解决了与太阳低层大气中耀斑能量转移有关的基本问题，研究结果将提供关于太阳耀斑和日冕物质抛射的生成、能量学和动力学的重要信息，从而对空间气象事件的起始提供重要的认识。这项研究工作也将对研究燃烧的恒星产生重大影响，因为同样的加速和辐射产生过程也在起作用。这些恒星耀斑在白色光下被探测到，但是来自加速电子的硬X射线辐射太微弱而无法直接测量。这项工作的结果将更好地定义太阳耀斑发射的白色光和硬X射线之间的关系。 这些信息反过来将有助于研究恒星耀斑，包括粒子加速和耀斑恒星的大气条件。令人困惑的是，太阳耀斑在低层大气中产生白光（WL）连续辐射的实际机制还没有得到更好的理解。 WL连续体与太阳耀斑的脉冲阶段（即粒子加速的阶段）的关联已被解释为一种迹象，表明在日冕中加速的非热粒子可以深入到低层太阳大气中，加热这些层并导致强烈的WL发射。然而，耀斑加速的电子撞击色球层的碰撞范围相对较短，因此它们能够深入穿透，正如WL和硬X射线（HXR）时间剖面的密切相关所表明的那样，这是令人惊讶的。产生观察到的WL连续谱的其他方法包括通过质子（而不是电子）的能量沉积或通过UV或X射线连续谱的“辐射回温”。阿尔夫文波的能量传输也可能是重要的，色球层中的复合辐射也是如此。WL和HXR在太阳大气中的排放高度之间的比较将支持或排除许多这些提出的生成机制，从而提供了WL耀斑生成以及太阳耀斑的整体能量学的更好的理解。 本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。将研究太阳大气中的绝对高度和这两种发射的相对高度。将观测到的高度与通过辐射流体动力学模型RADYN和三维辐射MHD模型RADMHD进行的理论建模的结果进行比较。导出的高度和模型比较将揭示太阳大气层外WL耀斑源的起源层，并将提供新的见解WL耀斑发射，太阳物理学中的一个重要和理解不足的问题的产生。源高度将使用SDO航天器上的HMI仪器（用于白光源）、RHESSI（用于硬X射线源）和双STEREO航天器上的EUVI仪器的数据作为背景数据来确定，以便提供替代视角，从而进行精确的高度测量。地面GONG++网络将用于验证建模结果。ROSA和IBIS仪器的多波长观测将用于描述白光耀斑能量学的特征。