Off-axis emission from relativistic plasma flows

We show that there is no universal law describing how the spectra and luminosity of synchrotron and inverse Compton radiation from relativistic jets change with increasing observation angle. Instead, the physics of particle acceleration leaves pronounced imprints in the observed spectra and allows for a freedom in numerous modifications of them. The impact of these effects is the largest for high-energy radiation and depends on the details of particle acceleration mechanism(s), what can be used to discriminate between different models. Generally, the beam patterns of relativistic jets in GeV-TeV spectral domain are much wider than the inverse Lorentz factor. The off-axis emission in this energy range appear to be brighter, have much harder spectra and a much higher cut-off frequency compared to the values derived from Doppler boosting considerations alone. The implications include the possibility to explain high-latitude unidentified EGRET sources as off-axis but otherwise typical relativistic-jet sources, such as blazars, and the prediction of GeV-TeV afterglow from transient jet sources, such as Gamma-Ray Bursts. We also discuss the phenomenon of beam-pattern broadening in application to neutrino emission.Comment: Submitted to the Astrophysical Journa

High-energy emission from off-axis relativistic jets

We analyze how the spectrum of synchrotron and inverse Compton radiation from a narrow relativistic jet changes with the observation angle. It is shown that diversity of acceleration mechanisms (in particular, taking the converter mechanism (Derishev et al. 2003) into account) allows for numerous modifications of the observed spectrum. In general, the off-axis emission in GeV-TeV energy range appears to be brighter, has a much harder spectrum and a much higher cut-off frequency compared to the values derived from Doppler boosting considerations alone. The magnitude of these effects depends on the details of particle acceleration mechanisms, what can be used to discriminate between different models. One of the implications is the possibility to explain high-latitude unidentified EGRET sources as off-axis but otherwise typical relativistic-jet sources, such as blazars. We also discuss the broadening of beam pattern in application to bright transient jet sources, such as Gamma-Ray Bursts.Comment: 6 pages, Proceedings of the International Symposium "High Energy Gamma-Ray Astronomy", 26-30 July 2004, Heidelberg, German

Cyclotron line formation in the magnetized atmospheres of compact stars: I. The transfer equations for polarized radiation

We find the forms of the transfer equations for polarized cyclotron radiation in the atmospheres of compact stars, which are simple enough to allow practical implementation and still preserve all important physical effects. We take into account a frequency redistribution of radiation within the cyclotron line as well as the relativistic and quantum-electrodynamic effects. Our analysis is valid for the magnetic fields up to $10^{13}$G and for temperatures well below 500keV.} We present and compare two forms of the radiation transfer equations. The first form, for the intensities of ordinary and extraordinary modes, is applicable for the compact stars with a moderate magnetic field strength up to $10^{11}$G for typical neutron star and up to $10^9$G for magnetic white dwarfs. The second form, for the Stokes parameters, is more complex, but applicable even if a linear mode coupling takes place somewhere in the scattering-dominated atmosphere. Analysing dispersion properties of a magnetized plasma {in the latter case, we describe a range of parameters where the linear mode coupling is possible and essential.Comment: 12 pages, 3 figures, MNRA

MeV-GeV emission from neutron-loaded short gamma-ray burst jets

Recent discovery of the afterglow emission from short gamma-ray bursts suggests that binary neutron star or black hole-neutron star binary mergers are the likely progenitors of these short bursts. The accretion of neutron star material and its subsequent ejection by the central engine implies a neutron-rich outflow. We consider here a neutron-rich relativistic jet model of short bursts, and investigate the high energy neutrino and photon emission as neutrons and protons decouple from each other. We find that upcoming neutrino telescopes are unlikley to detect the 50 GeV neutrinos expected in this model. For bursts at z~0.1, we find that GLAST and ground-based Cherenkov telescopes should be able to detect prompt 100 MeV and 100 GeV photon signatures, respectively, which may help test the neutron star merger progenitor identification.Comment: 13 pages, 2 figures. 1 figure added, minor changes, ApJ accepte

Higher order correction to the neutrino self-energy in a medium and its astrophysical applications

We have calculated the 1/M^4 (M the vector boson mass) order correction to the neutrino self-energy in a medium. The possible application of this higher order contribution to the neutrino effective potential is considered in the context of the Early Universe hot plasma and of the cosmological Gamma Ray Burst fireball. We found that, depending on the medium parameters and on the neutrino properties (mixing angle and mass square difference) the resonant oscillation of active to active neutrinos is possible.Comment: 10 pages, revtex style, uses axodraw.sty, 1 figur