GAMMA-RAYS AND NEUTRINOS FROM A POWERFUL COSMIC ACCELERATOR

The powerful radio quasar 3C273 will possibly reveal its nature as an efficient proton accelerator up to energies of the order of 10(11) GeV in the near future. It is shown in this paper that the shock-accelera ted protons expected to be present in the quasar's plasma jet induce a n unsaturated synchrotron cascade with electromagnetic radiation emerg ing in the x-ray and gamma-ray ranges. While (including the synchrotro n emission from the accelerated primary electrons) the broadband nonth ermal emission from 3C273 can be explained over the observed 18 orders of magnitude, a flattening of the spectrum at the highest observed en ergies (a few GeV) is predicted that could be falsified by the Energet ic Gamma Ray Experiment Telescope on board the Compton Gamma Ray Obser vatory. Above almost-equal-to 100 GeV the cascade spectrum dramaticall y steepens again due to the absorption of the gamma-ray photons by the host galaxy's strong infrared photon field from extended dust clouds, in accordance with the nondetection of 3C273 by Cherenkov telescopes. However, neutrinos from the hadronic interactions initiating the casc ade are not damped and reach terrestrial experiments without any modif ication of their injected flux. In contrast with the neutrino flux fro m pp interactions, which are energetically unimportant in jets, pgamma interactions generate a flat neutrino flux. Therefore it is emphasize d that one must not simply normalize the expected neutrino flux by the observed gamma-ray flux. Hence it is shown that the expected neutrino flux in the energy range relevant for underwater or under-ice detecto rs is much lower than assumed by many authors. On the other hand, with an increasing number of cosmic gamma-ray sources at known positions, their neutrino detection should be feasible when it is realized that t he angular resolution is the crucial design property for neutrino dete ctors.