Observation of In-Ice Askaryan Radiation from High-Energy Cosmic Rays

Area of Science:

• Particle Physics
• Radio Astronomy
• Glaciology

Background:

• High-energy cosmic rays create particle cascades when interacting with dense media like ice.
• Askaryan radiation, a predicted coherent radio emission, has not been definitively observed from such in-ice cascades.
• The Askaryan Radio Array (ARA) is designed to detect radio signals from cosmic ray interactions in the Antarctic ice sheet.

Purpose of the Study:

• To present the first experimental evidence of in-ice Askaryan radiation.
• To analyze 13 previously identified radio signal events originating from below the Antarctic ice surface.
• To determine the origin of these radio signals and compare them with theoretical predictions.

Main Methods:

• Reanalysis of 208 days of data from the Askaryan Radio Array (ARA).
• Detailed examination of event rates, arrival directions, signal shapes, spectral content, and polarization of radio signals.
• Comparison of observed signal characteristics with predictions for in-ice Askaryan radiation and alternative sources like geomagnetic charge separation.

Main Results:

• Observed radio signals are consistent with in-ice Askaryan radiation from cosmic ray air shower cores.
• The angular radiation pattern for bright events suggests an extended, cascade-like emitter.
• The event rate is inconsistent with background noise and on-surface events at a significance of 5.1σ, strongly supporting an in-ice origin.

Conclusions:

• The study provides the first experimental evidence for in-ice Askaryan radiation.
• The findings confirm that high-energy particle cascades in the Antarctic ice sheet produce detectable coherent radio emission.
• This observation opens new avenues for studying ultra-high-energy cosmic rays using radio detection techniques in ice.