Seyfert nuclei as sources of ultrahigh-energy cosmic rays |
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| Authors: | A V Uryson |
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| Institution: | (1) Lebedev Physical Institute, Leninskii pr. 53, Moscow, Russia |
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| Abstract: | Particles can be accelerated to ultrahigh energies E≈1021 eV in moderate Seyfert nuclei. This acceleration occurs in shock fronts in relativistic jets. The maximum energy and chemical composition of the accelerated particles depend on the magnetic field in the jet, which is not well known; fields in the range ～5–1000 G are considered in the model. The highest energies of E≈1021 eV are acquired by Fe nuclei when the field in the jet is B≈16 G. When B～(5–40) G, nuclei with Z<10 are accelerated to E≤1020 eV, while nuclei with Z≥10 acquire energies E≥2×1020 eV. Only particles with Z≥23 acquire energies E≤1020 eV when B～1000 G. Protons are accelerated to E<4×1019 eV, and do not fall into the range of energies of interest for any magnetic field B. The particles lose a negligible amount of their energy in interactions with infrared photons in the accretion disk; losses in the thick gas-dust torus are also negligible if the luminosity of the galaxy is L≤1046 erg/s and the angle between the normal to the galactic plane and the line of sight is sufficiently small, i.e., if the axial ratio of the galactic disk is comparatively high. The particles do not lose energy to curvature radiation if their deviations from the jet axis do not exceed 0.03–0.04 pc at distances from the center of R≈40–50 pc. Synchrotron losses are small, since the magnetic field frozen in the galactic wind at R≤40–50 pc is directed (as in the jet) primarily in the direction of motion. If the model considered is valid, the detected cosmic-ray protons could be either fragments of Seyfert nuclei or be accelerated in other sources. The jet magnetic fields can be estimated both from direct astronomical observations and from the energy spectrum and chemical composition of cosmic rays. |
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