CENTAURUS A AS A POINT SOURCE OF ULTRAHIGH ENERGY COSMIC RAYS

We probe the possibility that Centaurus A (Cen A) is a point source of ultrahigh energy cosmic rays (UHECRs) observed by Pierre Auger Observatory (PAO), through the statistical analysis of the arrival direction distribution. For this purpose, we set up the Cen A dominance model for the UHECR sources, in which Cen A contributes the fraction f C of the whole UHECR with energy above 5.5 × 1019 eV and the isotropic background contributes the remaining 1 – f C fraction. The effect of the intergalactic magnetic fields on the bending of the trajectory of Cen A originated UHECRs is parameterized by the Gaussian smearing angle θ s. For the statistical analysis, we adopted the correlational angular distance distribution (CADD) for the reduction of the arrival direction distribution and the Kuiper test to compare the observed and the expected CADDs. We identify the excess of UHECRs in the Cen A direction and fit the CADD of the observed PAO data by varying two parameters f C and θ s of the Cen A dominance model. The best-fit parameter values are f C ≈ 0.1 (the corresponding Cen A fraction observed at PAO is f C,PAO ≈ 0.15, that is, about 10 out of 69 UHECRs) and θ s = 5° with the maximum likelihood L max = 0.29. This result supports the existence of a point source smeared by the intergalactic magnetic fields in the direction of Cen A. If Cen A is actually the source responsible for the observed excess of UHECRs, the rms deflection angle of the excess UHECRs implies the order of 10 nG intergalactic magnetic field in the vicinity of Cen A.