TAROGE experiment and reconstruction technique for near-horizon impulsive radio signals induced by Ultra-high energy cosmic rays

Taiwan Astroparticle Radiowave Observatory for Geo-synchrotron Emissions (TAROGE) is antenna arrays sitting on high coastal mountains of Taiwan, pointing to the Pacific Ocean for the detection of near-horizon extensive air showers (EAS) induced by ultra-high energy cosmic rays and Earth-skimming tau neutrinos. TAROGE would improve the detection capability by collecting both the direct emissions and the ocean-reflected signals on a vast area of ocean which is visible from Taiwan’s high mountains. Four TAROGE stations in Taiwan have been deployed in the past few years. Angular resolution is crucial for discriminating between cosmic ray and neutrino events, the major systematic error of event direction reconstruction in TAROGE experiment comes from interference between direct and ground-reflected signals. We developed a new angular reconstruction method based on mapping and unfolding of differential response between channels which can be feasibly measured with a drone-borne calibration pulser. We achieved a sub-degree angular resolution for near horizon events. In this paper, we discuss details of the method and the results. A brief status report of the TAROGE project also will be reported.