20206-05-06 シカゴ大学（Chicago）
Scientists at work installing cables and electronic components for the Askaryan Radio Array, a detector for incoming cosmic particles located at the South Pole.Image credit: ARA Collaboration / NSF / Jeffrey Donenfeld
＜関連情報＞
- https://news.uchicago.edu/story/deep-ice-antarctic-detectors-pick-incoming-cosmic-rays-outer-space
- https://journals.aps.org/prl/abstract/10.1103/xwqy-yzrk
高エネルギー宇宙線による氷内アスカリアン放射の観測 Observation of In-Ice Askaryan Radiation from High-Energy Cosmic Rays
N. Alden, S. Ali, P. Allison, S. Archambault, J. J. Beatty, D. Z. Besson, A. Bishop, P. Chen, Y. C. Chen et al. (ARA Collaboration)
Physical Review Letters Published: 17 April, 2026
DOI: https://doi.org/10.1103/xwqy-yzrk
Abstract
We present the first experimental evidence for in-ice Askaryan radiation—coherent charge-excess radio emission—from high-energy particle cascades developing in the Antarctic ice sheet. In 208 days of data recorded with the phased array instrument of the Askaryan Radio Array, a previous analysis has incidentally identified 13 events with impulsive radio frequency signals originating from below the ice surface. We here present a detailed reanalysis of these events. The observed event rate, radiation arrival directions, signal shape, spectral content, and electric field polarization are consistent with in-ice Askaryan radiation from cosmic ray air shower cores impacting the ice sheet. For the brightest events, the angular radiation pattern favors an extended cascadelike emitter over a pointlike source. An origin from the geomagnetic separation of charges in cosmic ray air showers is disfavored by the arrival directions and polarization. Considering the arrival angles, timing properties, and impulsive nature of the passing events, the event rate is inconsistent with the estimation of the combined background from thermal noise events and on-surface events at the level of 5.1.
