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 $\approx1$ 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 $\sim 1.2$ 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