Downward Gamma Ray Showers from Natural Lightning

已知闪电会产生地面伽马闪光（TGFs），这是一种持续数毫秒的高能伽马射线爆发。 伽马射线是如何产生的，以及它们是否能告诉我们更多关于闪电的信息，几十年来一直是一个活跃的研究领域。 最近，粒子天体物理学界的一个研究小组与闪电研究人员合作，利用位于犹他州的望远镜阵列表面探测器（TASD）获得了伽马射线的新观测结果，这是一个700平方公里的宇宙射线观测站。 该奖项将继续这些调查到生成TGF。 该奖项的主要社会影响将是通过增加对TGFs的了解，这可能会提供有关闪电的更多信息，这是一种众所周知的自然灾害。 该项目还将有助于提供公众宣传机会，以提高人口的科学素养，并为下一代科学家提供培训机会。研究小组将跟进他们先前的奖项，该奖项证明了向下的伽马射线阵雨是在云对地的负闪电开始时产生的。 这一观测是在犹他州西南部使用TASD和闪电测绘阵列（LMA）站的组合进行的。 现在已经发现了这种现象，研究小组计划解决有关伽马射线产生机制的具体问题，并描述发生TGF的闪电事件类型。 将在增加高速宽带甚高频干涉仪和快速电场变化传感器的情况下进行新的观测。 同时，TASD的规模正在扩大，导致可能观察到更多的事件。 该提案的具体目标包括：1）用TASD、LMA、慢和快伽马射线和宽带干涉仪同时观测向下伽马闪光事件，以显著增加向下TGF的样本量，2）通过快E球测量最终确定观测到的伽马闪光是否与初始击穿脉冲（IBP）和高能云内脉冲（EIP）具有预期的相关性，3）继续推进伽马簇射和TASD响应的建模，并使用这些模型进一步表征簇射源大小、高度和伽马射线角分布。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。

Lightning is known to produce Terrestrial Gamma Flashes (TGFs) which are bursts of high-energy gamma rays that last up to a few milliseconds. How the gamma rays are produced and whether they can tell us more about lightning has been an active research area for a couple of decades. Recently, a research team from the particle astrophysics community teamed with lightning researchers to obtain new observations of gamma rays using the Telescope Array Surface Detector (TASD) in Utah, which is a 700 square kilometer cosmic ray observatory. This award will continue these investigations into the generation of TGFs. The main societal impact from this award will be through the increased understanding of TGFs, which may provide additional information on lightning, a well-known natural hazard. The project will also help to provide public outreach opportunities to enhance the scientific literacy of the population and provide training opportunities for the next generation of scientists.The research team will follow up on their prior award which demonstrated that downward gamma ray showers are produced at the beginning of negative cloud-to-ground lightning. This observation was made in southwestern Utah using a combination of the TASD and Lightning Mapping Array (LMA) stations. Now that this phenomenon has been discovered, the research team plans to address specific questions about the mechanisms responsible for gamma ray production and characterization of the types of lightning events in which TGFs occur. New observations will be conducted with the addition of a high-speed broadband VHF interferometer and fast electric field change sensor. Concurrently, the TASD is expanding in size, leading to more events that can potentially be observed. The specific objectives of the proposal include: 1) Simultaneous observation of downward gamma flash events with TASD, LMA, Slow- and Fast Antennas and broadband interferometer to significantly increase the sample size of downward TGFs, 2) Determine conclusively via fast-E spheric measurements whether the observed gamma flashes have the expected correlation with Initial Breakdown Pulses (IBP) and Energetic Intracloud Pulses (EIP), and 3) Continue advances in modeling of gamma showers and the TASD response, and use these models to further characterize shower source size, altitude, and gamma ray angular distribution.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.