Centaurus a as a Point Source of Ultrahigh Energy Cosmic Rays

Abstract

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 × 10 19 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.

One-zone synchrotron self-Compton model for the core emission of Centaurus A revisited

“…Still, these are well below the observed CR flux at such energies. In the light of recent results suggesting Cen A to be the origin of some UHECR events observed by PAO (Farrar et al 2013;Kim 2013) and our model results, the core of Cen A cannot be the production site of UHECR.…”

“…Cen A has been under consideration as a potential source of ultra high energy cosmic rays (UHECR) from as early as 1978 (Cavallo 1978), and its proximity to our galaxy compared to all other AGN has even inspired models where it is the sole originator of UHECR (Biermann & de Souza 2012). Recently, the Pierre Auger Observatory (PAO) has shown an excess in UHECR within 18 • of Cen A (Pierre Auger Collaboration et al 2007) and, although that region contains a high density of nearby galaxies, further analysis has shown that some of those UHECR may have originated from Cen A itself (Farrar et al 2013;Kim 2013). For our two models we have obtained distributions for both the escaping protons and neutrons.…”

TANAMI monitoring of Centaurus A: The complex dynamics in the inner parsec of an extragalactic jet

“…A detailed scrutiny of possible high-energy emission processes in Cen A's inner parsec jet system is very important given the suggested positional coincidence of Cen A with ultra-highenergy cosmic rays observed by the Pierre Auger Observatory (e.g., Romero et al 1996;Honda 2009;Anchordoqui et al 2001Anchordoqui et al , 2011Kim 2013). Furthermore, it has recently been shown that the brightest extragalactic jets inside the fields of the first two PeV neutrino events detected by IceCube (IceCube Collabora-tion 2013; Aartsen et al 2013) are capable, from a calorimetric point of view, of producing the observed neutrino flux (Krauß et al 2014).…”

Ultra-high energy cosmic rays

“…Conversely they can be used to extract information about the galactic and the intergalactic magnetic fields by examining the distribution of events around point sources. This direction was tried for an AGN in Centaurus A, around which an appreciable number of events were found in the Auger experiment [11]. The TA hot spot may play a similar role, but in a different way, because no known source candidate is found around it yet.…”