137 research outputs found
Quasi-linear diffusion driving the synchrotron emission in active galactic nuclei
We study the role of the quasi-linear diffusion (QLD) in producing X-ray
emission by means of ultra-relativistic electrons in AGN magnetospheric flows.
We examined two regions: (a) an area close to the black hole and (b) the outer
magnetosphere. The synchrotron emission has been studied for ultra-relativistic
electrons and was shown that the QLD generates the soft and hard X-rays, close
to the black hole and on the light cylinder scales respectively. By considering
the cyclotron instability, we show that despite the short synchrotron cooling
timescales, the cyclotron modes excite transverse and longitudinal-transversal
waves. On the other hand, it is demonstrated that the synchrotron reaction
force and a force responsible for the conservation of the adiabatic invariant
tend to decrease the pitch angles, whereas the diffusion, that pushes back on
electrons by means of the aforementioned waves, tends to increase the pitch
angles. By examining the quasi-stationary state, we investigate a regime in
which these two processes are balanced and a non-vanishing value of pitch
angles is created.Comment: 4 pages, 3 figure
Nonthermal emission model of isolated X-ray pulsar RX J0420.0-5022
In the present paper an alternative theoretical interpretation to the
generally assumed thermal emission models of the observed X-ray spectrum of
isolated pulsar RX J0420.0-5022 is presented. It is well known that the
distribution function of relativistic particles is one-dimensional at the
pulsar surface. However, cyclotron instability causes an appearance of
transverse momenta of relativistic electrons, which as a result, start to
radiate in the synchrotron regime. On the basis of the Vlasov's kinetic
equation we study the process of the quasi-linear diffusion (QLD) developed by
means of the cyclotron instability. This mechanism provides generation of
optical and X-ray emission on the light cylinder lengthscales. The analysis of
the three archival XMM-Newton observations of RX J0420.0-5022 is performed.
Considering a different approach of the synchrotron emission theory, the
spectral energy distribution is obtained that is in a good agreement with the
observational data. A fit to the X-ray spectrum is performed using both the
present synchrotron emission model spectrum absorbed by cold interstellar
matter and generally assumed absorbed black-body model.Comment: 7 pages, 1 figures; accepted to Advances in Astronomy and Space
Physic
On The Recently Discovered Pulsations From RX J1856.5-3754
An explanation of the recently discovered 7 s pulsations from the isolated
neutron star RX J1856.5-3754 is presented. It is assumed that the real spin
period of this source is s, whereas the observed spin-modulation is
caused by the presence of a nearly transverse, very low frequency drift waves
in the pulsar magnetosphere. It is supposed that the period of the drift wave
is equal to a recently observed one. The simulated lightcurve is plotted, the
angular parameters are defined and the value of the pulsed fraction of only
is explained.Comment: 7 pages, 2 figure
The influence of corotation on the high energy synchrotron emission in Crab-like pulsars
For Crab-like pulsars we consider the synchrotron mechanism influenced by
relativistic effects of rotation to study the production of the very high
energy (VHE) pulsed radiation. The process of quasi-linear diffusion (QLD) is
applied to prevent the damping of the synchrotron emission due to extremely
strong magnetic field. By examining the kinetic equation governing the QLD,
apart from the synchrotron radiative force, we taken into account the the
so-called reaction force, that is responsible for corotation and influences
plasma processes in the nearby zone of the light cylinder (LC) surface. We have
found that the relativistic effects of rotation significantly change efficiency
of the quasi-linear diffusion. In particular, examining magnetospheric
parameters typical for Crab-like pulsars, it has been shown that unlike the
situation, where relativistic effects of rotation are not important, on the LC
surface, the relativistic electrons via the synchrotron mechanism may produce
photons even in the TeV domain. It is shown that the VHE radiation is strongly
correlated with the relatively low frequency emission.Comment: 5 pages, 2 figure
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