Centaurus A as a point source of Ultra-High Energy Cosmic Rays

Abstract

We probe the possibility that Centaurus A (Cen A) is a point source of ultra-high energy cosmic rays (UHECR) observed by 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 $f_{\mathrm{C}}$ of the whole UHECR with energy above $5.5\times 10^{19}\mathrm{eV}$ and the isotropic background contributes the remaining $1-f_{\mathrm{C}}$ fraction. The effect of the intergalactic magnetic fields on the bending of the trajectory of Cen A originated UHECR is parameterized by the gaussian smearing angle ${\theta }_s$. Using the correlational angular distance distribution (CADD), we identify the excess of UHECR in the Cen A direction and fit the CADD of the observed PAO data by varying two parameters $f_{\mathrm{C}}$ and ${\theta }_s$ of the Cen A dominance model. The best-fit parameter values are $f_{\mathrm{C}}\approx 0.1$ (The corresponding Cen A fraction observed at PAO is $f_{\mathrm{C},\mathrm{PAO}}\approx 0.15$, that is, about 10 out of 69 UHECR.) and ${\theta }_s=5^{\circ }$ with the maximum probability $P_{\max }=0.29$. Considering the uncertainty concerning the assumption of isotropic background in the Cen A dominance model, we extend the viable parameter ranges to the $2\sigma$ band, $0.09\lesssim f_{\mathrm{C},\mathrm{PAO}}\lesssim 0.25$ and $0^{\circ }\lesssim {\theta }_s\lesssim 20^{\circ }$. This result supports the existence of a point source extended by the intergalactic magnetic fields in the direction of Cen A. If Cen A is actually the source responsible for the observed excess of UHECR, the average deflection angle of the excess UHECR implies the order of $10\mathrm{nG}$ intergalactic magnetic field in the vicinity of Cen A.

12 pages, 7 figures

References in corpus (9)

• Update on the correlation of the highest energy cosmic rays with nearby extragalactic matter
• High-energy Particle Acceleration and Production of Ultra-high-energy Cosmic Rays in the Giant Lobes of Centaurus A
• Search for Correlations between HiRes Stereo Events and Active Galactic Nuclei
• Searching for a Correlation Between Cosmic-Ray Sources Above 10^{19} eV and Large-Scale Structure
• Search for Anisotropy of Ultra-High Energy Cosmic Rays with the Telescope Array Experiment
• Cross-Correlation between UHECR Arrival Distribution and Large-Scale Structure
• The Centaurus A Ultrahigh-Energy Cosmic Ray Excess and the Local Extragalactic Magnetic Field
• Statistical Analysis of the Correlation between Active Galactic Nuclei and Ultra-High Energy Cosmic Rays
• Update on tests of the Cen A neutron-emission model of highest energy cosmic rays

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• High-Energy Gamma Rays and Neutrinos from Nearby Radio Galaxies
• Ultrahigh-energy neutrinos as a probe of espresso-shear acceleration in jets of Centaurus A
• A Study on Anisotropy in the Arrival Directions of Ultra-High-Energy Cosmic Rays Observed by Pierre Auger Observatory
• Ultra high-energy cosmic rays from beyond the Greisen-Zatsepin-Kuz'min horizon