Observations of Microwave Continuum Emission from Air Shower Plasmas

TL;DR

This paper explores a novel microwave detection technique for ultra-high energy cosmic ray air showers, demonstrating initial experimental success and potential advantages over existing optical methods in continuous observation conditions.

Contribution

It presents the first experimental evidence of microwave emission from air shower plasmas and develops a prototype detector using satellite TV technology for cosmic ray detection.

Findings

Microwave emission from air ionized by high-energy particles was observed.

Follow-up experiments confirmed initial results with improved precision.

Prototype detectors show potential for continuous cosmic ray observation.

Abstract

We investigate a possible new technique for microwave measurements of ultra-high energy cosmic ray (UHECR) extensive air showers which relies on detection of expected continuum radiation in the microwave range, caused by free-electron collisions with neutrals in the tenuous plasma left after the passage of the shower. We performed an initial experiment at the AWA (Argonne Wakefield Accelerator) laboratory in 2003 and measured broadband microwave emission from air ionized via high energy electrons and photons. A follow-up experiment at SLAC (Stanford Linear Accelerator Center) in summer of 2004 confirmed the major features of the previous AWA observations with better precision and made additional measurements relevant to the calorimetric capabilities of the method. Prompted by these results we built a prototype detector using satellite television technology, and have made measurements indicating possible detection of cosmic ray extensive air showers. The method, if confirmed by experiments now in progress, could provide a high-duty cycle complement to current nitrogen fluorescence observations of UHECR, which are limited to dark, clear nights. By contrast, decimeter microwave observations can be made both night and day, in clear or cloudy weather, or even in the presence of moderate precipitation.