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

On the very high energy (>25GeV) pulsed emission in the Crab pulsar

We have examined the recently detected very high energy (VHE) pulsed radiation from the Crab pulsar. According to the observational evidence, the observed emission (>25GeV) peaks at the same phase with the optical spectrum. Considering the cyclotron instability, we show that the pitch angle becomes non-vanishing leading to the efficient synchrotron mechanism near the light cylinder surface. The corresponding spectral index of the emission equals -1/2. By studying the inverse Compton scattering and the curvature radiation, it is argued that the aforementioned mechanisms do not contribute to the VHE radiation detected by MAGIC.Comment: 11 pages, 1 figur

On the simultaneous generation of high energy emission and submillimeter/infrared radiation from active galactic nuclei

For active galactic nuclei (AGNs) we study the role of the mechanism of quasi-linear diffusion (QLD) in producing the high energy emission in the MeV-GeV domains strongly connected with the submillimeter/infrared radiation. Considering the kinetic equation governing the stationary regime of the QLD we investigate the feedback of the diffusion on electrons. We show that this process leads to the distribution of particles by the pitch angles, implying that the synchrotron mechanism is no longer prevented by energy losses. Examining a reasonable interval of physical parameters, we show that it is possible to produce MeV-GeV gamma-rays, strongly correlated with submillimeter/infrared bands.Comment: 7 pages, 3 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

Cherenkov-drift emission mechanism

Emission of a charged particle propagating in a medium with a curved magnetic field is reconsidered stressing the analogy between this emission mechanism and collective Cherenkov-type plasma emission. It is explained how this mechanism differs from conventional Cherenkov, cyclotron or curvature emission and how it includes, to some extent, the features of each of these mechanisms. Presence of a medium supporting subluminous waves is essential for the possibility of wave amplification by particles streaming along the curved magnetic field with a finite curvature drift. We suggest an analogy between the curvature drift emission and the anomalous cyclotron-Cherenkov emission. Treating the emission in cylindrical coordinates in the plane-wave-like approximation allows one to compute the single particle emissivity and growth rate of the Cherenkov-drift instability. We compare the growth rates calculated using the single particle emissivity and using the dielectric tensor of one dimensional plasma streaming along the curved field. In calculating the single particle emissivity it is essential to know the normal modes of the medium and their polarization which can be found from the dielectric tensor of the medium. This emission mechanism may be important for the problem of pulsar radio emission generation