On the nature of Off-pulse emission from pulsars

In Basu et al. 2011 we reported the detection of Off-pulse emission from two long period pulsars B0525+21 and B2045-16. The pulsars were observed at a single epoch using the 325 MHz frequency band of the Giant Meterwave Radio Telescope (GMRT). In this paper we report a detailed study of the Off-pulse emission from these two pulsars using multiple observations at two different frequencies, 325 MHz and 610 MHz bands of GMRT. We report detection of Off-pulse emission during each observation and based on the scintillation effects and spectral index of Off-pulse emission we conclude a magnetospheric origin. The magnetospheric origin of Off-pulse emission gives rise to various interesting possibilities about its emission mechanism and raises questions about the structure of the magnetosphere.Comment: 13 pages, 6 figures, accepted for publication in the Ap

On the nature of radio pulsars with long periods

It is shown that the drift waves near the light cylinder can cause the modulation of the emission with periods of the order several seconds. These periods explain the intervals between successive pulses observed in "magnetars" and radio pulsars with long periods. The model under consideration makes it possible to calculate the real rotation periods of the host neutron stars. They are less than 1 sec for the investigated objects. The magnetic fields at the surface of the neutron star of the order 10^(11)-10^(13) G and equal to the usual fields for known radio pulsarsComment: 18 pages, 4 figure

On the Nature of Pulsar Radio Emission

A theory of pulsar radio emission generation, in which the observed waves are produced directly by maser-type plasma instabilities operating at the anomalous cyclotron-Cherenkov resonance $\omega- k_{\parallel} v_{\parallel} + \omega_B/ \gamma_{res}=0$ and the Cherenkov-drift resonance $\omega- k_{\parallel} v_{\parallel} - k_{\perp} u_d =0$, is capable of explaining the main observational characteristics of pulsar radio emission. The instabilities are due to the interaction of the fast particles from the primary beam and the tail of the distribution with the normal modes of a strongly magnetized one-dimensional electron-positron plasma. The waves emitted at these resonances are vacuum-like, electromagnetic waves that may leave the magnetosphere directly. In this model, the cyclotron-Cherenkov instability is responsible for core emission pattern and the Cherenkov-drift instability produces conal emission. The conditions for the development of the cyclotron-Cherenkov instability are satisfied for both typical and millisecond pulsars provided that the streaming energy of the bulk plasma is not very high $\gamma_p \approx 10$. In a typical pulsar the cyclotron-Cherenkov and Cherenkov-drift resonances occur in the outer parts of magnetosphere at $r_{res} \approx 10^9 cm$. This theory can account for various aspects of pulsar phenomenology including the morphology of the pulses, their polarization properties and their spectral behavior. We propose several observational tests for the theory. The most prominent prediction are the high altitudes of the emission region and the linear polarization of conal emission in the plane orthogonal to the local osculating plane of the magnetic field.Comment: 39 pages, 10 figure

Unraveling the nature of coherent pulsar radio emission

Forty years have passed since the discovery of pulsars, yet the physical mechanism of their coherent radio emission is a mystery. Recent observational and theoretical studies strongly suggest that the radiation outcoming from the pulsar magnetosphere consists mainly of extraordinary waves polarized perpendicular to the planes of pulsar dipolar magnetic field. However, the fundamental question whether these waves are excited by maser or coherent curvature radiation, remains open. High quality single pulse polarimetry is required to distinguish between these two possible mechanisms. Here we showcase such {\it decisive} strong single pulses from 10 pulsars observed with the GMRT, showing extremely high linear polarization with the position angle following locally the mean position angle traverse. These pulses, which are relatively free from depolarization, must consist of exclusively single polarization mode. We associate this mode with the extraordinary wave excited by the coherent curvature radiation. This crucial observational signature enables us to argue, for the first time, in favor of the coherent curvature emission mechanism, excluding the maser mechanism.Comment: 11 pages, 3 figures, accepted for publication in Astrophysical Journal Letter

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

Radio Emission Signatures in the Crab Pulsar

Our high time resolution observations of individual pulses from the Crab pulsar show that both the time and frequency signatures of the interpulse are distinctly different from those of the main pulse. Main pulses can occasionally be resolved into short-lived, relatively narrow-band nanoshots. We believe these nanoshots are produced by soliton collapse in strong plasma turbulence. Interpulses at centimeter wavelengths are very different. Their dynamic spectrum contains regular, microsecond-long emission bands. We have detected these bands, proportionately spaced in frequency, from 4.5 to 10.5 GHz. The bands cannot easily be explained by any current theory of pulsar radio emission; we speculate on possible new models.Comment: 26 pages, 10 figures, to appear in Ap

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

Curvature-drift instability fails to generate pulsar radio emission

The curvature drift instability has long been considered as a viable mechanism for pulsar radio emission. We reconsidered this mechanism by finding an explicit solution describing propagation of short-wave electro-magnetic waves in a plasma flow along curved magnetic field lines. We show that even though the waves could be amplified, the amplification factor remains very close to unity therefore this mechanism is unable to generate high brightness temperature emission from initial weak fluctuations.Comment: to appear in Ap

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