Time structure of gamma-ray signals generated in line-of-sight interactions of cosmic rays from distant blazars

Blazars are expected to produce both gamma rays and cosmic rays. Therefore, observed high-energy gamma rays from distant blazars may contain a significant contribution from secondary gamma rays produced along the line of sight by the interactions of cosmic-ray protons with background photons. Unlike the standard models of blazars that consider only the primary photons emitted at the source, models which include the cosmic-ray contribution predict that even ~10 TeV photons should be detectable from distant objects with redshifts as high as z> 0.1. Secondary photons contribute to signals of point sources only if the intergalactic magnetic fields are very small, below ~10 femtogauss, and their detection can be used to set upper bounds on magnetic fields along the line of sight. Secondary gamma rays have distinct spectral and temporal features. We explore the temporal properties of such signals using a semi-analytical formalism and detailed numerical simulations, which account for all the relevant processes, including magnetic deflections. In particular, we elucidate the interplay of time delays coming from the proton deflections and from the electromagnetic cascade, and we find that, at multi-TeV energies, secondary gamma-rays can show variability on timescales of years for femtogauss magnetic fields.Comment: 25 pages, 9 figure

TeV gamma rays from blazars beyond z=1?

At TeV energies, the gamma-ray horizon of the universe is limited to redshifts z<<1, and, therefore, any observation of TeV radiation from a source located beyond z=1 would call for a revision of the standard paradigm. While robust observational evidence for TeV sources at redshifts z>1 is lacking at present, the growing number of TeV blazars with redshifts as large as z~0.5 suggests the possibility that the standard blazar models may have to be reconsidered. We show that TeV gamma rays can be observed even from a source at z>1, if the observed gamma rays are secondary photons produced in interactions of high-energy protons originating from the blazar jet and propagating over cosmological distances almost rectilinearly. This mechanism was initially proposed as a possible explanation for the TeV gamma rays observed from blazars with redshifts z~0.2, for which some other explanations were possible. For TeV gamma-ray radiation detected from a blazar with z>1, this model would provide the only viable interpretation consistent with conventional physics. It would also have far-reaching astronomical and cosmological ramifications. In particular, this interpretation would imply that extragalactic magnetic fields along the line of sight are very weak, in the range 0.01 < fG < 10 fG, assuming random fields with a correlation length of 1 Mpc, and that acceleration of E> 0.1 EeV protons in the jets of active galactic nuclei can be very effective.Comment: 8 pages, 4 figure

Propagation and radiation of ultrarelativistic particles in magnetic fields in different astrophysical environments

The thesis work presents the results of theoretical studies of different scenarios for the propagation and the radiation of ultrarelativistic particles depending on the environment determined by the magnetic and low energy radiation fields. First, using the analytical solution of Boltzmann equation in the small-angle approximation, we have accurately calculated the angular, energy, and time distributions of the ultrahigh energy protons, gamma rays produced by synchrotron radiation of secondary electrons and positrons, and secondary neutrinos from the source of cosmic rays embedded in the magnetized environment of the level of B ∼ 10^(−9) G. The second part considers the scenario explaining TeV gamma radiation from distant blazars by secondary gamma rays produced by cosmic rays along the line of sight in the weak magnetic field of the level of B ∼ 10^(−15) G. We have studied the possibility of detection of TeV radiation from blazars with redshifts greater than z = 1. Finally, the last chapter of the work is addressed to the radiation of charged particles in the extremely strong magnetic fields of compact objects such as pulsar and black hole. We have studied the synchrotron and curvature radiation regimes and transition between them showing the strong sensitivity of radiation spectra on the pitch angle