A Terrestrial Gamma-ray Flash with an Asymmetric Footprint Observed at the Pierre Auger Observatory
Year: 2026
Type: preprint
Abstract: 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.
Source: arXiv (Cornell University)
Language: English
Subfield: Atmospheric Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: green
Funders: National Science Foundation, U.S. Department of Energy, Grainger Foundation, Strong, Ministerio de Ciencia, Innovación y Universidades, European Commission, Deutsche Forschungsgemeinschaft, Ministerstvo Školství, Mládeže a Tělovýchovy, Grantová Agentura České Republiky, Fonds De La Recherche Scientifique - FNRS, Consejo Nacional de Investigaciones Científicas y Técnicas, Fonds Wetenschappelijk Onderzoek, Consejo Nacional de Ciencia y Tecnología, Nederlandse Organisatie voor Wetenschappelijk Onderzoek, Ministério da Ciência, Tecnologia e Inovação, Centre National de la Recherche Scientifique, Istituto Nazionale di Astrofisica, Universidad Nacional Autónoma de México, Benemérita Universidad Autónoma de Puebla, Xunta de Galicia, Istituto Nazionale di Fisica Nucleare, Ministerium für Kultur und Wissenschaft des Landes Nordrhein-Westfalen, Helmholtz Alliance for Astroparticle Physics, Ministero dell'Università e della Ricerca, Agencia Nacional de Promoción Científica y Tecnológica, European Regional Development Fund, Agencia Estatal de Investigación, Institut National de Physique Nucléaire et de Physique des Particules, NextGenerationEU
Awards: G1086978037, G1105844351, Pierre Auger Project, G1151900320, G1496055848, G1603472241, G1610934229, G1727275246, G176604203, G1840991089, G1935710221, G2230854319, G2296507700, Runaway Discharges and Their Roles in Atmospheric Processes, G291036901, G318412399, G3286760496, G3346696926, G3405914644, G3490171961, G3523651922, G3694284866, G3735356012, G3755077010, G3886017652, G3999575733, G410571670, Race in the Histories of Science and Medicine: A Review Essay and a Research Agenda, G4212894969, G4280972364, G4320224000, G4462967385, G451917667, G523076202, G545007060, G5616713406, G5635532810, G5641063287, G584027024, G585908603, G5860975833, G589433610, G5916014575, G593054264, G5967599077, G6010476436, G6230683201, Pierre Auger Observatory - participation of the Czech Republic, Astrophysics Center for Multimessenger studies in Europe, G6520718613, G6761430300, G6869766708, G6958583472, G7517989378, STUDIES OF HIGH ENERGY PARTICLE ASTROPHYSICS, G7720562802, G7745284665, G7805626310, G7863371703, G8037394432, Galactic and Extragalactic Cosmic Rays, Neutrinos and Gamma Rays, G8140083606, G8262994006, G8497050386, G86560745, G8800403394
OpenAlex ID: W7204892103