Generation of the electrostatic field in the pulsar magnetosphere plasma

The behaviour of a relativistic electron-positron plasma in the pulsar magnetosphere is investigated. The equation of the motion of the magnetospheric plasma is discussed, from which it follows that, if the plasma particle radial velocity ${V_r}>{c/{\sqrt 2}}$ (where c is the speed of light), the centrifugal acceleration changes its sign and the particle braking begins. The stability of the magnetospheric plasma with respect to the radially oriented potential perturbations is discussed and the possibility of the electrostatic field generation in this plasma along the pulsar magnetic field lines is shown.Comment: Plain LaTe

Transverse quasilinear relaxation in inhomogeneous magnetic field

Transverse quasilinear relaxation of the cyclotron-Cherenkov instability in the inhomogeneous magnetic field of pulsar magnetospheres is considered. We find quasilinear states in which the kinetic cyclotron-Cherenkov instability of a beam propagating through strongly magnetized pair plasma is saturated by the force arising in the inhomogeneous field due to the conservation of the adiabatic invariant. The resulting wave intensities generally have nonpower law frequency dependence, but in a broad frequency range can be well approximated by the power law with the spectral index -2. The emergent spectra and fluxes are consistent with the one observed from pulsars.Comment: 14 Pages, 4 Figure

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

Weak turbulence theory of the non-linear evolution of the ion ring distribution

The nonlinear evolution of an ion ring instability in a low-beta magnetospheric plasma is considered. The evolution of the two-dimensional ring distribution is essentially quasilinear. Ignoring nonlinear processes the time-scale for the quasilinear evolution is the same as for the linear instability 1/t_ql gamma_l. However, when nonlinear processes become important, a new time scale becomes relevant to the wave saturation mechanism. Induced nonlinear scattering of the lower-hybrid waves by plasma electrons is the dominant nonlinearity relevant for plasmas in the inner magnetosphere and typically occurs on the timescale 1/t_ql w(M/m)W/nT, where W is the wave energy density, nT is the thermal energy density of the background plasma, and M/m is the ion to electron mass ratio, which has the consequence that the wave amplitude saturates at a low level, and the timescale for quasilinear relaxation is extended by orders of magnitude

Close range photogrammetry in the survey of the coastal area geoecological conditions (on the example of Portugal)

Close range digital photogrammetry, which involves the application of unmanned aerial vehicle (UAV), has been used in a growing number of diverse applications across different scientific disciplines. Our objective was to use the mentioned method in the survey of the contemporary geoecological conditions of the coastal area on the example of Portuguese northwest coastal zone. The coastal zone can be subdivided into two geomorphological sectors: Sector 1, between the Minho River and the town of Espinho, where the coastal segments consist of estuaries, sandy and shingle beaches with rocky outcrops, and Holocene dune systems. The estuaries and the foredunes in particular are very degraded by human activities; and Sector 2, between Espinho and the Mondego Cape, where coastal lagoons and Holocene dune systems occur. We chose two beaches for surveying – Aguçadoura and Ramalha to which the drone swinglet CAM took the photos. We used the ground control software eMotion 2 to plan the flights over the study area and controlled the drone’s trajectory during flight. After processing the obtained images in the program of AgisoftPhotoscanPro, we generated the 2D orthophotos and 3D digital elevation models (DEM) of the research sections. At this stage of study we derived the above product without using the ground control points, or we used only the camera GPS data. Based on these models the compilation of the large-scale maps of high resolution (1cm-5cm) will be possible in the GISs for monitoring and management of the geoecological state of the mentioned beaches in case to precise the x, y and z values of the models with the geodetic device of Differential GPSs in the selected ground control points (GCP).We are grateful to the European Commission ERASMUS-MUNDUS Action-2 ELECTRA program and the Earth Sciences Centre of the University of Minho (Braga, Portugal) in supporting us to conduct the field works and research.info:eu-repo/semantics/publishedVersio

On the very high energy spectrum of the Crab pulsar

In the present paper we construct a self-consistent theory, interpreting the observations of the MAGIC Cherenkov Telescope of the very high energy (VHE) pulsed emission from the Crab pulsar. In particular, 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 simultaneous generation of low (radio) and VHE (0.01-25GeV) emission on the light cylinder scales, in one location of the pulsar magnetosphere. A different approach of the synchrotron theory is considered, giving the spectral index of VHE emission ($\beta=2$) and the exponential cutoff energy (23 GeV) in a good agreement with the observational data.Comment: 8 pages, 0 figure

The generation of connected high and very high energy γ\gamma-rays and radio emission in active galactic nuclei

We consider relativistic electrons in magnetospheric flows close to a supermassive black hole and study the mechanism of quasi-linear diffusion (QLD) to investigate the correlation between $\gamma$-ray and radio emission in active galactic nuclei. Moving in the nonuniform magnetic field the particles experience a force that is responsible for the conservation of the adiabatic invariant. This force, together with the radiation reaction force, tends to decrease the pitch angles. Contrary to this, the QLD attempts to increase the pitch angle, and this maintains the synchrotron emission regime. To examine the balance between the QLD and the aforementioned dissipative factors we investigate the quasi-stationary state by applying the kinetic equation. Considering the magnetospheric plasma close to the supermassive black hole, we examined the efficiency of the QLD for different parameters. By examining the cyclotron instability, we show that despite the efficient dissipative factors, the cyclotron modes excite transverse and longitudinal-transversal waves which leads to the QLD. We find that the QLD provides a connection of emission in the $\gamma$-ray and radio domains. We show that under favourable conditions the radio emission from 22 MHz to 9 GHz on the mpc scale is associated with $\gamma$-ray emission from 900 GeV down to 9 GeV on the same scale.Comment: 5 pages, 5 figure

The spark-associated soliton model for pulsar radio emission

We propose a new, self-consistent theory of coherent pulsar radio emission based on the non-stationary sparking model of Ruderman & Sutherland (1975), modified by Gil & Sendyk (2000) in the accompanying Paper I. According to these authors, the polar cap is populated as densely as possible by a number of sparks with a characteristic perpendicular dimension D approximately equal to the polar gap height scale h, separated from each other also by about h. Each spark reappears in approximately the same place on the polar cap for a time scale much longer than its life-time and delivers to the open magnetosphere a sequence of electron-positron clouds which flow orderly along a flux tube of dipolar magnetic field lines. The overlapping of particles with different momenta from consecutive clouds leads to effective two-stream instability, which triggers electrostatic Langmuir waves at the altitudes of about 50 stellar radii. The electrostatic oscillations are modulationally unstable and their nonlinear evolution results in formation of ``bunch-like'' charged solitons. A characteristic soliton length along magnetic field lines is about 30 cm, so they are capable of emitting coherent curvature radiation at radio wavelengths. The net soliton charge is about 10^21 fundamental charges, contained within a volume of about 10^14 cm^3. For a typical pulsar, there are about 10^5 solitons associated with each of about 25 sparks operating on the polar cap at any instant. One soliton moving relativisticaly along dipolar field lines with a Lorentz factor of the order of 100 generates a power of about 10^21 erg/s by means of curvature radiation. Then the total power of a typical radio pulsar can be estimated as being about 10^(27-28) erg/s.Comment: 27 pages, 5 figures, accepted by Ap

Linear coupling and over-reflection phenomena of magnetohydrodynamic waves in smooth shear flows

Special features of magnetohydrodynamic waves linear dynamics in smooth shear flows are studied. Quantitative asymptotic and numerical analysis are performed for wide range of system parameters when basic flow has constant shear of velocity and uniform magnetic field is parallel to the basic flow. The special features consist of magnetohydrodynamic wave mutual transformation and over-reflection phenomena. The transformation takes place for arbitrary shear rates and involves all magnetohydrodynamic wave modes. While the over-reflection occurs only for slow magnetosonic and Alfv\'en waves at high shear rates. Studied phenomena should be decisive in the elaboration of the self-sustaining model of magnetohydrodynamic turbulence in the shear flows