Revisit to centaurus a as a point source of ultra-high-energy cosmic rays

Abstract

The void regions found in the arrival direction distribution of ultra-high-energy cosmic rays (UHECRs) observed by the Pierre Auger Observatory (PAO) may be an important clue in UHECR source hunting. We claim that there is a circular void band structure around the Centaurus A (Cen A) direction. We incorporated this observed void structure in the background contribution into the Cen A dominance model to improve the fitting of the arrival direction distribution. The best fit is obtained for the Cen A contribution fraction fC = 0.14 (The observed fraction at PAO is fC,PAO = 0.27, which means that 18 out of 69 observed UHECR are contributed by Cen A.) and the smearing angle θs = 12° with a maximum likelihood of Lmax= 0.68. The estimate for the intergalactic magnetic fields in the vicinity of the Cen A direction based on the UHECRs contributed by Cen A is B ≈ 24Z−1(lc/Mpc)−1/2 nG.