방향성 분포를 이용한 초고에너지 우주선의 기원 연구

Abstract

To search the sources of ultra-high energy cosmic rays (UHECR), a variety of research has been done for a half century. However, the sources of UHECR are still unclear because of the statistical limitations caused by the small number of observational data. We investigated where the UHECRs came from using arrival direction (AD) distributions. First, we set up source models for the Monte-Carlo simulation describing the phenomena that the UHECR can go through during their journey from their origin to Earth. We introduced the smearing angle, θs, and the source fraction, fs, in the model. The smearing angle is the parameter to describe the deflection by the magnetic fields, and the source fraction adjusts the isotropic background fraction in the UHECR flux. Then, we extracted the natures of the observed AD distributions and the expected AD ones from the simulation using our reduction methods, such as right ascension distribution, auto-angular distance distribution, correlational angular distance distribution, and nearest-neighbor angular distance distribution, and compared the two distributions by statistical test methods. We adopted the Kuiper test for the statistical test methods. We tested anisotropy and correlation with active galactic nuclei (AGN) using observational data: the Pierre Auger Observatory (PAO) and the Telescope Array (TA) experiment. We found that the PAO and TA data are consistent with the isotropic distribution. Also, the results of correlation tests with AGNs showed that we could exclude the AGN dominant source models with a relatively small smearing angle. According to parameter estimations, it required more isotropic components or larger deflection angle than conventional estimations to describe the observational data. In conclusion, we could not confirm where UHECRs come from using AD distribution so far. If we can accumulate more observational data in the future, we can take a step forward.