Physics of Interpulse Emission in Radio Pulsars

The magnetized induced Compton scattering off the particles of the ultrarelativistic electron-positron plasma of pulsar is considered. The main attention is paid to the transverse regime of the scattering, which holds in a moderately strong magnetic field. We specifically examine the problem on induced transverse scattering of the radio beam into the background, which takes place in the open field line tube of a pulsar. In this case, the radiation is predominantly scattered backwards and the scattered component may grow considerably. Based on this effect, we for the first time suggest a physical explanation of the interpulse emission observed in the profiles of some pulsars. Our model can naturally account for the peculiar spectral and polarization properties of the interpulses. Furthermore, it implies a specific connection of the interpulse to the main pulse, which may reveal itself in the consistent intensity fluctuations of the components at different timescales. Diverse observational manifestations of this connection, including the moding behavior of PSR B1822-09, the peculiar temporal and frequency structure of the giant interpulses in the Crab pulsar, and the intrinsic phase correspondence of the subpulse patterns in the main pulse and the interpulse of PSR B1702-19, are discussed in detail. It is also argued that the pulse-to-pulse fluctuations of the scattering efficiency may lead to strong variability of the interpulse, which is yet to be studied observationally. In particular, some pulsars may exhibit transient interpulses, i.e. the scattered component may be detectable only occasionally.Comment: 28 pages, 2 figures. Accepted for publication in Ap

Radial growth of functions from the Korenblum space

We study radial behavior of analytic and harmonic functions, which admit a certain majorant in the unit disk. We prove that extremal growth or decay may occur only along small sets of radii and give precise estimates of these exceptional sets.Comment: 18 page

On the Axisymmetric Force-Free Pulsar Magnetosphere

We investigate the axisymmetric magnetosphere of an aligned rotating magnetic dipole surrounded by an ideal force-free plasma. We concentrate on the magnetic field structure around the point of intersection of the separatrix between the open and closed field-line regions and the equatorial plane. We first study the case where this intersection point is located at the Light Cylinder. We find that in this case the separatrix equilibrium condition implies that all the poloidal current must return to the pulsar in the open-field region, i.e., that there should be no finite current carried by the separatrix/equator current sheet. We then perform an asymptotic analysis of the pulsar equation near the intersection point and find a unique self-similar solution; however, a Light Surface inevitably emerges right outside the Light Cylinder. We then perform a similar analysis for the situation where the intersection point lies somewhere inside the Light Cylinder, in which case a finite current flowing along the separatrix and the equator is allowed. We find a very simple behavior in this case, characterized by a 90-degree angle between the separatrix and the equator and by finite vertical field in the closed-field region. Finally, we discuss the implications of our results for global numerical studies of pulsar magnetospheres.Comment: 31 pages, including 5 figure

Disk Diffusion Propagation Model for the Outburst of XTE J1118+480

We present a linear diffusion model for the evolution of the double-peaked outburst in the transient source XTEJ1118+480. The model treats the two outbursts as episodic mass deposition at the outer radius of the disk followed by evolution of disk structure according to a diffusion process. We demonstrate that light curves with fast-rise, exponential decay profile are a general consequence of the diffusion process. Deconvolution of the light curve proves to be feasible and gives an input function specifying mass deposition at the outer disk edge as well as the total mass of the disk, both as functions of time. The derived evolution of total disk mass can be correlated with the observed evolution of the ~0.1 Hz QPO in the source reported in Wood et al. (2000).Comment: 26 pages, 6 figures, accepted for publication in Ap

Interpretation of the Low-Frequency Peculiarities in the Radio Profile Structure of the Crab Pulsar

The theory of magnetized induced scattering off relativistic gyrating particles is developed. It is directly applicable to the magnetosphere of a pulsar, in which case the particles acquire gyration energies as a result of resonant absorption of radio emission. In the course of the radio beam scattering into background the scattered radiation concentrates along the ambient magnetic field. The scattering from different harmonics of the particle gyrofrequency takes place at different characteristic altitudes in the magnetosphere and, because of the rotational effect, gives rise to different components in the pulse profile. It is demonstrated that the induced scattering from the first harmonic into the state under the resonance can account for the so-called low-frequency component in the radio profile of the Crab pulsar. The precursor component is believed to result from the induced scattering between the two states well below the resonance. It is shown that these ideas are strongly supported by the polarization data observed. Based on an analysis of the fluctuation behaviour of the scattering efficiencies, the transient components of a similar nature are predicted for other pulsars.Comment: 9 pages, no figures. Accepted for publication in MNRA

On the Nature of Precursors in the Radio Pulsar Profiles

In the average profiles of several radio pulsars, the main pulse is accompanied by the preceding component. This so called precursor is known for its distinctive polarization, spectral, and fluctuation properties. Recent single-pulse observations hint that the sporadic activity at the extreme leading edge of the pulse may be prevalent in pulsars. We for the first time propose a physical mechanism of this phenomenon. It is based on the induced scattering of the main pulse radiation into the background. We show that the scattered component is directed approximately along the ambient magnetic field and, because of rotational aberration in the scattering region, appears in the pulse profile as a precursor to the main pulse. Our model naturally explains high linear polarization of the precursor emission, its spectral and fluctuation peculiarities as well as suggests a specific connection between the precursor and the main pulse at widely spaced frequencies. This is believed to stimulate multifrequency single-pulse studies of intensity modulation in different pulsars.Comment: 5 pages, no figures. Accepted for publication in MNRAS Letter

On the nature of the variability power decay towards soft spectral states in X-ray binaries. Case study in Cyg X-1

A characteristic feature of the Fourier Power Density Spectrum (PDS) observed from black hole X-ray binaries in low/hard and intermediate spectral states is a broad band-limited noise, characterized by a constant below some frequency (a ``break'' frequency) and a power law above this frequency. It has been shown that the variability of this type can be produced by the inward diffusion of the local driving perturbations in a bounded configuration (accretion disk or corona). In the framework of this model, the perturbation diffusion time t_0 is related to the phenomenological break frequency, while the PDS power-law slope above the ``break'' is determined by the viscosity distribution over the configuration. he perturbation diffusion scenario explains the decay of the power of X-ray variability observed in a number of compact sources (containing black hole and neutron star) during an evolution of theses sources from low/hard to high/soft states. We compare the model predictions with the subset of data from Cyg X-1 collected by the Rossi X-ray Time Explorer (RXTE). Our extensive analysis of the Cyg X-1 PDSs demonstrates that the observed integrated power P_x decreases approximately as a square root of the characteristic frequency of the driving oscillations \nu_{dr}. The RXTE observations of Cyg X-1 allow us to infer P_{dr} and t_0 as a function of \nu_{dr}. Using the inferred dependences of the integrated power of the driving oscillations P_{dr} and t_0 on \nu_{dr} we demonstrate that the power predicted by the model also decays as P_{x,diff} proportional to \nu_{dr}^{-0.5} that is similar to the observed P_{x} behavior.Comment: 15 page, 5 figures, accepted for publication in the Astrophysical Journa

Induced scattering of short radio pulses

Effect of the induced Compton and Raman scattering on short, bright radio pulses is investigated. It is shown that when a single pulse propagates through the scattering medium, the effective optical depth is determined by the duration of the pulse but not by the scale of the medium. The induced scattering could hinder propagation of the radio pulse only if close enough to the source a dense enough plasma is presented. The induced scattering within the relativistically moving source places lower limits on the Lorentz factor of the source. The results are applied to the recently discovered short extragalactic radio pulse.Comment: submitted to Ap

Transformation of the Poynting flux into the kinetic energy in relativistic jets

The acceleration of relativistic jets from the Poynting to the matter dominated stage is considered. The are generally two collimation regimes, which we call equilibrium and non-equilibrium, correspondingly. In the first regime, the jet is efficiently accelerated till the equipartition between the kinetic and electro-magnetic energy. We show that after the equilibrium jet ceases to be Poynting dominated, the ratio of the electro-magnetic to the kinetic energy decreases only logarithmically so that such jets become truly matter dominated only at extremely large distances. Non-equilibrium jets remain generally Poynting dominated till the logarithmically large distances. In the only case when a non-equilibrium jet is accelerated till the equipartition level, we found that the flow is not continued to the infinity but is focused towards the axis at a finite distance from the origin.Comment: Submitted to MNRAS Minor changes in the Conclusion

Very-high-energy gamma radiation associated with the unshocked wind of the Crab pulsar

We show that the relativistic wind in the Crab pulsar, which is commonly thought to be invisible in the region upstream of the termination shock at R < 0.1 pc, in fact could be directly observed through its inverse Compton gamm-ray emission. The search for such specific component of radiation in the gamma-ray spectrum of the Crab can provide unique information about the unshocked pulsar wind that is not accessible at other wavelengths.Comment: 11 pages, 11 figures, to appear in one of the April issues of MNRA