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

观测到太阳大气层最外层称为日冕的地方偶尔会发生突然爆发。日冕喷发释放了大量的能量。释放的一小部分能量储存在喷发地点和较低的太阳大气层区域。沉积的能量使这些区域在极端紫外线(EUV)下显得非常明亮，并发出X射线和较少频率的伽马射线。辐射的突然闪光，通常被称为极紫外线、X射线和伽马射线耀斑或事件，只有使用特殊的探测器才能观察到，因为人眼对这些波长波段不敏感。因为太阳喷发发生得很快，所以相关耀斑的寿命也相对较短。特别是，伽马射线耀斑的持续时间通常很短，大约为10-100秒。然而，观测到的一些伽马射线耀斑持续时间长达数小时，比同时发生的极紫外线耀斑和X射线耀斑要长得多。这项为期3年的研究项目的目的是为了更好地了解太阳如何产生长持续时间的伽马射线发射。该项目的主要科学目标是通过综合分析伽马射线、白光、极紫外光和射电观测以及太阳高能粒子的现场观测，确定日冕物质抛射(CME)驱动的激波是否是产生在100 MeV能量下观测到的持续伽马射线发射(SGRE)事件的高能质子的主要来源。费米卫星上的大面积望远镜(LAT)观测表明，SGRE事件相当常见。在低太阳大气中，300 MeV的质子与物质的相互作用被认为会产生中性介子，这些介子会迅速衰变成100 MeV的伽马射线，但高能质子的来源存在争议。建议的来源既包括耀斑，也包括CME驱动的冲击。最近发现的分米-百米II型射电爆发与SGRE事件之间的关系，为CME-Shock作为高能质子源提供了支持。将通过对CME驱动的激波的运动学和空间范围以及在SGRE事件期间观测到的相关的II型射电爆发和SEP事件的性质的统计分析，来研究CME-Shock模式是否有效地描述了SGRE事件。这些分析将通过比较似乎很符合日冕物质抛射-激波模型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激波的性质的不同来进行。次要的科学目标是确定相关的日冕物质抛射和SEP事件的特征，这可以为SGRE事件期间粒子加速和迁移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智力优势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.