Synchro-curvature radiation of charged particles in the strong curved magnetic fields

It is generally believed that the radiation of relativistic particles in a curved magnetic field proceeds in either the synchrotron or the curvature radiation modes. In this paper we show that in strong curved magnetic fields a significant fraction of the energy of relativistic electrons can be radiated away in the intermediate, the so-called synchro-curvature regime. Because of the persistent change of the trajectory curvature, the radiation varies with the frequency of particle gyration. While this effect can be ignored in the synchrotron and curvature regimes, the variability plays a key role in the formation of the synchro-curvature radiation. Using the Hamiltonian formalism, we find that the particle trajectory has the form of a helix wound around the drift trajectory. This allows us to calculate analytically the intensity and energy distribution of prompt radiation in the general case of magnetic bremsstrahlung in the curved magnetic field. We show that the transition to the limit of the synchrotron and curvature radiation regimes is determined by the relation between the drift velocity and the component of the particle velocity perpendicular to the drift trajectory. The detailed numerical calculations, which take into account the energy losses of particles, confirm the principal conclusions based on the simplified analytical treatment of the problem, and allow us to analyze quantitatively the transition between different radiation regimes for a broad range of initial pitch angles. We argue that in the case of realization of specific configurations of the electric and magnetic fields, the gamma-ray emission of the pulsar magnetospheres can be dominated by the component radiated in the synchro-curvature regime.Comment: this article supersedes arXiv:1207.6903 and arXiv:1305.078

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

On transition of propagation of relativistic particles from the ballistic to the diffusion regime

A stationary distribution function that describes the entire processes of propagation of relativistic particles, including the transition between the ballistic and diffusion regimes, is obtained. The spacial component of the constructed function satisfies to the first two moments of the Boltzmann equation. The angular part of the distribution provides accurate values for the angular moments derived from the Boltzmann equation, and gives a correct expression in the limit of small-angle approximation. Using the derived function, we studied the gamma-ray images produced through the $pp$ interaction of relativistic particles with gas clouds in the proximity of the accelerator. In general, the morphology and the energy spectra of gamma-rays significantly deviate from the "standard" results corresponding to the propagation of relativistic particles strictly in the diffusion regime

Mechanics and kinetics in the Friedmann-Lemaitre-Robertson-Walker space-times

Using the standard canonical formalism, the equations of mechanics and kinetics in the Friedmann-Lemaitre-Robertson-Walker (FLRW) space-times in Cartesian coordinates have been obtained. The transformation law of the generalized momentum under the shift of the origin of the coordinate system has been found, and the form invariance of the Hamiltonian function relative to the shift transformation has been proved. The general solution of the collisionless Boltzmann equation has been found. In the case of the homogeneous distribution the solutions of the kinetic equation for several simple, but important for applications, cases have been obtained

Angular, spectral, and time distributions of highest energy protons and associated secondary gamma-rays and neutrinos propagating through extragalactic magnetic and radiation fields

The angular, spectral and temporal features of the highest energy protons and accompanying them secondary neutrinos and synchrotron gamma-rays propagating through the intergalactic magnetic and radiation fields are studied using the analytical solutions of the Boltzmann transport equation obtained in the limit of the small-angle and continuous-energy-loss approximation.Comment: 21 pages, 13 figure

Non-variable cosmologically distant gamma-ray emitters as an imprint of propagation of ultra-high-energy protons

The acceleration cites of ultra-high-energy (UHE) protons can be traced by the footprint left by these particles propagating through cosmic microwave background (CMB) radiation. Secondary electrons produced in extended region of several tens of Mpc emit their energy via synchrotron radiation predominantly in the initial direction of the parent protons. It forms a non-variable and compact (almost point-like) source of high energy gamma rays. The importance of this effect is increased for cosmologically distant objects; because of severe energy losses, UHE protons cannot achieve us even in the case of extremely weak intergalactic magnetic fields. Moreover, at high redshifts the energy conversion from protons to secondary particles becomes significantly more effective due to the denser and more energetic CMB in the past. This increases the chances of UHE cosmic rays to be traced by the secondary synchrotron gamma radiation. We discuss the energy budget and the redshift dependence of the efficiency of energy transfer from UHE protons to synchrotron radiation. The angular and spectral distributions of radiation in the gamma- and X-ray energy bands are calculated and discussed in the context of their detectability by Fermi LAT and Chandra observatories

Synchrotron-to-curvature transition regime of radiation of charged particles in a dipole magnetic field

The details of trajectories of charged particles become increasingly important for proper understanding of processes of formation of radiation in strong and curved magnetic fields. Because of damping of the perpendicular component of motion, the particle's pitch angle could be decreased by many orders of magnitude leading to the change of the radiation regime -- from synchrotron to the curvature mode. To explore the character of this transition, we solve numerically the equations of motion of a test particle in a dipole magnetic field, and calculate the energy spectrum of magnetic bremsstrahlung self-consistently, i.e. without a priori assumptions on the radiation regime. In this way we can trace the transitions between the synchrotron and curvature regimes, as well as study the third (intermediate or the so-called synchro-curvature) regime. We briefly discuss three interesting astrophysical scenarios, the radiation of electrons in the pulsar magnetosphere in the polar cap and outer gap models, as well as the radiation of ultrahigh energy protons in the magnetosphere of a massive black hole, and demonstrate that in these models the synchrotron, synchro-curvature and curvature regimes can be realized with quite different relative contributions to the total emission

Very-high-energy gamma-ray emission from high-redshift blazars

We study the possible detection of and properties of very high-energy (VHE) gamma-ray emission (in the energy band above 100 GeV) from high redshift sources. We report on the detection of VHE gamma-ray flux from blazars with redshifts z>0.5. We use the data of Fermi telescope in the energy band above 100 GeV and identify significant sources via cross-correlation of arrival directions of individual VHE gamma-rays with the positions of known Fermi sources. There are thirteen high-redshift sources detected in the VHE band by Fermi/LAT telescope. The present statistics of the Fermi signal from these sources is too low for a sensible study of the effects of suppression of the VHE flux by pair production through interactions with Extragalactic Background Light photons. We find that the detection of these sources with ground-based gamma-ray telescopes would be challenging. However, several sources including BL Lacs PKS 0426-380 at z=1.11, KUV 00311-1938 at z=0.61, B3 1307+433 at z=0.69, PG 1246+586 at z=0.84, Ton 116 at z=1.065 as well as a flat-spectrum radio quasar 4C +55.17 at z=0.89 should be detectable by HESS-II, MAGIC-II and CTA. A high-statistics study of a much larger number of VHE gamma-ray sources at cosmological distances would be possible with the proposed high-altitude Cherenkov telescope [email protected]: 10 pages, 14 figure