Understanding the sources and chemical composition of the most energetic extraterrestrial radiation or "cosmic rays" is a major thrust of current astrophysics research. Particles with enormous energies regularly strike the Earth from within our galaxy and beyond. Understanding the origins of these particles will require accurate models of the most violent processes in the universe. However, progress in the field of high-energy cosmic rays is currently limited by the rarity of the most interesting rays striking Earth. Indeed, the continuation of the field beyond the current generation of observatories may become financially and practically impossible if new ways are not found to achieve remote coverage over large portions of the Earth's surface.
With this award, these scientists will investigate a new technique: the remote sensing via bistatic radar technology of cosmic ray induced extensive air showers. They build on experience gained by the MARIACHI project in developing this technique, the opportunity afforded by the location of the northern hemisphere's largest cosmic ray observatory, the Telescope Array, in Utah, and the donation of analog television transmission equipment to this effort by a local television station. The successful outcome of these studies would be the development of a new detection technique with the potential of having a transformative effect on the field of ultra-high energy cosmic ray research.
For Broader Impacts, this project has potential for connecting the local community to the astrophysics research currently being conducted in Utah. Radar techniques similar to those being used for cosmic ray studies have long been utilized in the study of micrometeors, and this group has already hosted public events in which visitors to the Millard County Cosmic Ray Center "listen" to meteor showers and learn about the cosmic ray project. It will also connect with their successful ASPIRE program.
The purpose of this research is to develop a new remote sensing technique for the study of high-energy cosmic rays. The technique we are investigating makes use of bistatic radar technology. Like radar systems used in tracking airplanes or cars on the highway, our system works by detecting reflected radio waves. Under this grant, we commissioned a 2 kW transmitter facility broadcasts a very-high frequency (VHF) radio wave, which in principle will be deflected by the atmospheric ionization produced by the cosmic ray's passage. This is an interdisciplinary project involving both physicists and electrical engineers, and has provided PhD dissertation research projects for physics and engineering students. While no definitive evidence was found for air shower radar echoes, we made progress on understanding how to operate such an observatory and on the technical issues involved in analyzing the data. Also, we spent a substantial amount of time simulating air shower echoes and learning their properties. The work begun under this grant led directly to our obtaining support for the creation of a substantially more sensitive observatory employing a 40 kW transmitter, a high-gain phased transmitting antenna array which brings the total effective radiated power to 8 MW, and a data acquisition system featuring a 250 MS/s sampling rate receiver. This new observatory is currently collecting data.
