96 research outputs found
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 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
G for typical neutron star and up to 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
Particle acceleration through multiple conversions from a charged into a neutral state and back
We propose a new way of quick and very efficient acceleration of protons
and/or electrons in relativistic bulk flows. The new mechanism takes advantage
of conversion of particles from the charged state (protons or
electrons/positrons) into neutral state (neutrons or photons) and back. In most
cases, the conversion is photon-induced and requires presence of intense
radiation fields, but the converter acceleration mechanism may also operate via
inelastic nucleon-nucleon collisions.
Like in the traditional model -- ``stochastic'' (or diffusive) acceleration,
-- the acceleration cycle in our scenario consists of escape of particles from
the relativistic flow followed by their return back after deflection from the
ambient magnetic field. The difference is that the charge-changing reactions,
which occur during the cycle, allow accelerated particles to increase their
energies in each cycle by a factor roughly equal to the bulk Lorentz factor
squared.
The emerging spectra of accelerated particles can be very hard and their
cut-off energy in some cases is larger than in the standard mechanism. This
drastically reduces the required energy budget of the sources of the
highest-energy particles observed in cosmic rays. Also, the proposed
acceleration mechanism may serve as an efficient means of transferring the
energy of bulk motion to gamma-radiation and, if the accelerated particles are
nucleons, routinely produces high-energy neutrinos at relative
efficiency.Comment: extended version, 10 pages, submitted to Phys. Rev.
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
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