Coronal-Mass-Ejection-Driven Shocks and Sustained Gamma-Ray Emission Events

突然的爆发偶尔会发生在太阳大气层的最外层，称为日冕。 巨大的能量在日冕爆发中释放出来。 释放的能量的一小部分沉积在喷发地点和太阳大气层的低层区域。 沉积的能量使这些区域在极紫外（EUV）光下显得非常明亮，并发出X射线和较不频繁的伽马射线。 辐射的突然闪光，通常被称为EUV，X射线和伽马射线耀斑或事件，只能使用特殊的探测器观察到，因为人眼对这些波段不敏感。 由于太阳爆发发生得很快，因此相关的耀斑也相对较短。 特别是，伽马射线耀斑的持续时间通常很短，大约10-100秒。 然而，一些伽马射线耀斑被观察到持续长达几个小时，比同时发生的EUV和X射线耀斑长得多。这项为期三年的研究计划旨在更深入了解太阳如何产生长时间的伽马射线辐射。该计划的主要科学目标是利用伽马射线、白光、极紫外线和射电观测以及太阳高能粒子的现场观测。 费米卫星上的大面积望远镜（LAT）的观测表明，SGRE事件相当普遍。 据信300 MeV质子与低太阳大气中的物质相互作用会产生中性π子，后者迅速衰变为100 MeV的γ射线，但高能质子的来源仍存在争议。 建议的来源包括耀斑和CME驱动的冲击。最近发现的一个关系，百米的II型射电爆发和SGRE事件提供了支持CME冲击作为一个源的高能质子。 CME冲击模型是否是一个有效的描述SGRE事件的问题将进行调查，通过进行统计分析的运动学和空间范围的CME驱动的冲击和相关的II型射电爆发和SEP事件期间观察到的SGRE事件的属性。 进行这些分析时，将比较似乎与日冕物质抛射-冲击模型吻合的事件和似乎不符合该模型的事件，并查明喷发情况和相关日冕物质抛射和冲击性质的差异。 第二个科学目标是确定相关的CME和SEP事件的特征，这可以为SGRE事件期间粒子加速和传输的数值模拟工作提供观测约束和参数。 该项目的研究和EPO议程支持AGS部门在发现、学习、多样性和跨学科研究方面的战略目标。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Sudden explosive eruptions are observed to occur occasionally in the outermost part of the Sun’s atmosphere called solar corona. Huge amounts of energy are released in the coronal solar eruptions. A fraction of the released energy is deposited at the eruption site and in the regions of the lower solar atmosphere. The deposited energy makes the regions appear very bright in extreme ultraviolet (EUV) light and emit X-rays and less frequently gamma rays. The sudden flashes of radiation, commonly known as EUV, X-ray, and gamma-ray flares or events, can be observed only using special detectors, because human eye is not sensitive to these wavelength bands. Because solar eruptions occur quickly, the associated flares are also relatively short-lived. Especially, the duration of the gamma-ray flares is typically quite short, around 10–100 seconds. However, some gamma-ray flares are observed to last up to several hours, much longer than the concurrent EUV and X-ray flares. The purpose of this 3-year research project is to better understand how the long-duration gamma-ray emission is produced at the Sun.The primary scientific objective of the project is to determine whether shocks driven by coronal mass ejections (CMEs) are the main source of high-energy protons producing the sustained gamma-ray emission (SGRE) events observed at energies 100 MeV by using combined analysis of gamma-ray, white-light, EUV and radio observations together with in-situ solar energetic particle (SEP) observations. Observations by the Large Area Telescope (LAT) on the Fermi satellite have shown that SGRE events are rather common. Interactions of 300 MeV protons with the material in the low solar atmosphere are believed to produce neutral pions, which promptly decay into the 100 MeV gamma-rays, but the source of the high-energy protons is debated. Suggested sources include both flares and CME-driven shocks. Recent discovery of a relationship between decameter-hectometric type II radio bursts and SGRE events has provided support for CME-shock as a source of high-energy protons. The question whether the CME-shock model is a valid description of SGRE events will be investigated by performing statistical analyses of the kinematics and spatial extent of CME-driven shocks and the properties of the associated type II radio bursts and SEP events observed during the SGRE events. These analyses will be carried out by comparing events that seem to agree well with the CME-shock model with those that do not seem to comply with the model, and by identifying the differences in the circumstances of the eruption and the properties of the associated CMEs and shocks. The secondary scientific objective is to determine the characteristics of the associated CMEs and SEP events, which could provide observational constraints and parameters for numerical modeling efforts of particle acceleration and transport during SGRE events. The research and EPO agenda of this project supports the Strategic Goals of the AGS Division in discovery, learning, diversity, and interdisciplinary research.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.