皮埃尔·奥格天文台观测到的具有非对称着陆点的陆地伽马射线闪
A Terrestrial Gamma-ray Flash with an Asymmetric Footprint Observed at the Pierre Auger Observatory
- Observatorio Pierre Auger（皮埃尔·奥热天文台）
- University of California, Santa Cruz（加州大学圣克鲁兹分校）
- University of New Hampshire（新罕布什尔大学）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
皮埃尔·奥格天文台观测到一例具非对称着陆点的陆地伽马射线闪，经三角定位其源高2.3±0.5公里，模拟显示其天顶角大于75°，该结构无法用传统均匀电场模型解释。
AI中文摘要：
皮埃尔·奥格天文台是位于阿根廷海拔1400米处、面积达3000平方公里的探测器阵列，具备绘制陆地伽马射线闪（TGF，与闪电相关的短时间强伽马射线暴）完整着陆点的能力，这与绝大多数仅在空间单个探测器中探测到TGF的情况形成对比。本文利用该能力对2007年的一个事件开展两项重要分析，该事件因具有大着陆点和高信号质量被选中：首先，利用伽马射线到达探测器阵列的时间，独立于任何闪电通道信息，将TGF的源三角定位到地面以上2.3±0.5公里的高度；确定源位置后，可分析TGF相对于该源在地面的空间分布，不仅发现TGF着陆点一侧的通量比另一侧高一个数量级，还发现其具有由两个强度明显峰值组成的非对称方位结构，这两个峰值彼此偏移约120°，这种方位结构在传统的TGF均匀电场模型下不可能出现。利用Geant4对相对论逃逸电子雪崩谱的准直束进行模拟，尝试重建该TGF的源几何结构，发现其可能在θ>75°的范围内有显著分量，其中θ为天顶角（偏离天底的角度）。
英文摘要：
The Pierre Auger Observatory, a $3000km^2$ detector array that sits 1400m above sea level in Argentina, has the ability to map the entire footprint of Terrestrial Gamma-ray Flashes (TGFs), which are short, intense bursts of gamma rays associated with lightning. This is in contrast to the vast majority of TGF detections that only occur in a single detector in space. In this paper we leverage this capability to perform two important analyses on an event from 2007, chosen for its large footprint and high signal quality. First, we triangulate the source of the TGF to $2.3\pm0.5$km height above ground level using the arrival time of the gamma rays themselves at the detector array, independently of any information regarding the lightning channel. With the source position established, we can analyze the spatial distribution of the TGF on the ground with respect to that source. Not only do we find that one side of the TGF footprint shows an order of magnitude higher flux than the other, but we also find an asymmetric azimuthal structure consisting of two clear peaks in intensity. These peaks are offset by about $120^o$ from each other. This azimuthal structure is not possible under the traditional uniform electric-field model of a TGF. Using Geant4 simulations of collimated beams of the relativistic runaway electron-avalanche spectrum, we attempt to reconstruct the source geometry of the TGF and find that it likely had significant components in the $θ> 75^o$ range, where $θ$ is the off-nadir angle.
