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arXiv · 1803.05436

Evidence for a New Component of High-Energy Solar Gamma-Ray Production

Tim Linden·Bei Zhou·John F. Beacom·Annika H. G. Peter·Kenny C. Y. Ng·Qing-Wen Tang
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Abstract

The observed multi-GeV gamma-ray emission from the solar disk --- sourced by hadronic cosmic rays interacting with gas, and affected by complex magnetic fields --- is not understood. Utilizing an improved analysis of the Fermi-LAT data that includes the first resolved imaging of the disk, we find strong evidence that this emission is produced by two separate mechanisms. Between 2010-2017 (the rise to and fall from solar maximum), the gamma-ray emission is dominated by a polar component. Between 2008-2009 (solar minimum) this component remains present, but the total emission is instead dominated by a new equatorial component with a brighter flux and harder spectrum. Most strikingly, although 6 gamma rays above 100 GeV are observed during the 1.4 years of solar minimum, none are observed during the next 7.8 years. These features, along with a 30-50 GeV spectral dip which will be discussed in a companion paper, were not anticipated by theory. To understand the underlying physics, Fermi and HAWC observations of the imminent Cycle 25 solar minimum are crucial.

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Tim Linden, Bei Zhou, John F. Beacom, Annika H. G. Peter, Kenny C. Y. Ng, Qing-Wen Tang. 2018-03-14. Evidence for a New Component of High-Energy Solar Gamma-Ray Production. https://doi.org/10.1103/physrevlett.121.131103

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