1210.0479 (Jagdish C. Joshi et al.)

Testing Hadronic Models of Gamma Ray Production at the Core of Cen A    [PDF]

Jagdish C. Joshi, Nayantara Gupta

Pierre Auger experiment has observed a few cosmic ray events above 55 EeV from the direction of the core of Cen A.These cosmic rays might have originated from the core of Cen A. High energy gamma ray emission has been observed by HESS from the radio core and inner kpc jets of Cen A. We are testing whether pure hadronic interactions of protons or heavy nuclei with the matter at the core or photo-disintegration of heavy nuclei at the core can explain the cosmic ray and high energy gamma ray observations from the core of Cen A. The scenario of $p-\gamma$ interactions followed by photo-pion decay has been tested earlier by Sahu et al. (2012) and found to be consistent with the observational results. In this paper we have considered some other possibilities (i) the primary cosmic rays at the core of Cen A are protons and the high energy gamma rays are produced in $p-p$ interactions,(ii) the primary cosmic rays are Fe nuclei and the high energy gamma rays are produced in $Fe-p$ interactions and (iii) the primary cosmic rays are Fe nuclei and they are photo-disintegrated at the core. The daughter nuclei de-excite and high energy gamma rays are produced. The high energy gamma ray fluxes expected in each of these cases are compared with the flux observed by HESS experiment to normalise the spectrum of the primary cosmic rays at the core. We have calculated the expected number of cosmic ray nucleon events between 55 EeV and 150 EeV in each of these cases to verify the consistencies of the different scenarios with the observations by Pierre Auger experiment. We find that if the primary cosmic rays are Fe nuclei then their photo-disintegration followed by de-excitation of daughter nuclei can explain the observed high energy particle emissions from the core of Cen A.

View original: http://arxiv.org/abs/1210.0479