General Relativistic Effect of Gravitomagnetic Charge on Pulsar Magnetosphere and Particle Acceleration in a Polar Cap

We study magnetospheric structure surrounding rotating magnetized neutron star with nonvanishing NUT (Newman-Tamburino-Unti) parameter. For the simplicity of calculations Goldreich-Julian charge density is analyzed for the aligned neutron star with zero inclination between magnetic field, gravitomagnetic field and rotation axis. From the system of Maxwell equations in spacetime of slowly rotating NUT star, second-order differential equation for electrostatic potential is derived. Analytical solution of this equation indicates the general relativistic modification of an accelerating electric field and charge density along the open field lines by the gravitomagnetic charge. The implication of this effect to the magnetospheric energy loss problem is underlined. In the second part of the paper we derive the equations of motion of test particles in magnetosphere of slowly rotating NUT star. Then we analyze particle motion in the polar cap and show that NUT parameter can significantly change conditions for particle acceleration.Comment: 21 pages, 6 figures, accepted for publication in Ap

Pulsar Polar Cap Heating and Surface Thermal X-Ray Emission I. Curvature Radiation Pair Fronts

We investigate the effect of pulsar polar cap (PC) heating produced by positrons returning from the upper pair formation front. Our calculations are based on a self-consistent treatment of the pair dynamics and the effect of electric field screening by the returning positrons. We calculate the resultant X-ray luminosities, and discuss the dependence of the PC heating efficiencies on pulsar parameters, such as characteristic spin-down age, spin period, and surface magnetic field strength. In this study we concentrate on the regime where the pairs are produced in a magnetic field by curvature photons emitted by accelerating electrons. Our theoretical results are not in conflict with the available observational X-ray data and suggest that the effect of PC heating should significantly contribute to the thermal X-ray fluxes from middle-aged and old pulsars. The implications for current and future X-ray observations of pulsars are briefly outlined.Comment: 28 pages, 7 figures, accepted for publication in Ap

Pair Multiplicities and Pulsar Death

Through a simple model of particle acceleration and pair creation above the polar caps of rotation-powered pulsars, we calculate the height of the pair-formation front (PFF) and the dominant photon emission mechanism for the pulsars in the Princeton catalog. We find that for most low- and moderate-field pulsars, the height of the pair formation front and the final Lorentz factor of the primary beam is set by nonresonant inverse Compton scattering (NRICS), in the Klein-Nishina limit. NRICS is capable of creating pairs over a wide range of pulsar parameters without invoking a magnetic field more complicated than a centered dipole, although we still require a reduced radius of curvature for most millisecond pulsars. For short-period pulsars, the dominant process is curvature radiation, while for extremely high-field pulsars, it is resonant inverse Compton scattering (RICS). The dividing point between NRICS dominance and curvature dominance is very temperature-dependent; large numbers of pulsars dominated by NRICS at a stellar temperature of $10^6$ K are dominated by curvature at $10^5$ K. We apply these results to pulsar death-line calculations and to the issue of particle injection into the Crab Nebula.Comment: 14 pages, 7 figures, to appear in Ap

Effects of Rotation and Relativistic Charge Flow on Pulsar Magnetospheric Structure

We propose an analytical 3-D model of the open field-line region of a neutron star (NS) magnetosphere. We construct an explicit analytic solution for arbitrary obliquity (angle between the rotation and magnetic axes) incorporating the effects of magnetospheric rotation, relativistic flow of charges (e.g. primary electron beam) along the open field lines, and E X B drift of these charges. Our solution employs the space-charge-limited longitudinal current calculated in the electrodynamic model of Muslimov & Tsygan (1992) and is valid up to very high altitudes nearly approaching the light cylinder. We assume that in the innermost magnetosphere, the NS magnetic field can be well represented by a static magnetic dipole configuration. At high altitudes the open magnetic field lines significantly deviate from those of a static dipole and tend to focus into a cylindrical bundle, swept back in the direction opposite to the rotation, and also bent towards the rotational equator. We briefly discuss some implications of our study to spin-powered pulsars.Comment: 24 pages, 3 figures, accepted for publication in Ap

Particle Acceleration in Pair-Starved Pulsars

We investigate the physical situation above the pulsar polar cap (PC) where the accelerating primaries (electrons) are not capable of producing sufficient numbers of electron-positron pairs at low altitudes (within 1-2 stellar radii above the PC surface) to screen the accelerating electric field, and continue accelerating up to, at least, very high altitudes nearly approaching the light cylinder. We derive an analytic solution for the parallel electric field valid at high altitudes. The solution is based on the physical condition of asymptotic vanishing of the rotationally induced transverse electric field within the magnetic flux tube. This condition constrains the asymptotic value of the effective space charge that determines the distribution of the parallel electric field within the magnetic tube. Our estimates of low- to high-altitude values of the parallel electric field imply the occurrence of a regime of primary acceleration (with the characteristic Lorentz factor up to 1-2 X 10^7) all the way from the PC to the light cylinder limited by curvature-radiation reaction. In this model the primary outflow becomes asymptotically force-free, and may turn into a relativistic wind beyond the light cylinder. Such a solution will apply to both older pulsars producing only inverse Compton scattering pairs and younger very high B pulsars (magnetars). We suggest that pulsars, which are lying below the pair death line, may be radio-quiet gamma-ray sources.Comment: 20 pages, accepted for publication in Ap

The Role of Media Resources in the Process of Self-Education

This article discusses media resources influence in self-education. Methods of formation of students' media-information competencies in the organization of self -education of students through media resources, ensuring their activity and independence in cognitive activity, the formation of professional skills, and the development of creative and critical thinking skills are covered. The technique proposed in media instruction models is more often than not based on cycles (pieces, modules) of imaginative and play errands that are effectively utilized by instructors in the course and out of course exercises

Gamma-ray emission from rotation-powered pulsars

Using a simplified model of cascade pair creation over pulsar polar caps presented in two previous papers, we investigate the expected gamma-ray output from pulsars' low altitude particle acceleration and pair creation regions. We divide pulsars into several categories, based on which mechanism truncates the particle acceleration off the polar cap, and give estimates for the expected luminosity of each category. We find that inverse Compton scattering above the pulsar polar cap provides the primary gamma rays which initiate the pair cascades in most pulsars. This reduces the expected $\gamma$-ray luminosity below previous estimates which assumed curvature gamma ray emission was the dominant initiator of pair creation in all pulsars.Comment: 10 pages, 5 figures, to be published in Ap

Pulsar Polar Cap Heating and Surface Thermal X-Ray Emission II. Inverse Compton Radiation Pair Fronts

We investigate the production of electron-positron pairs by inverse Compton scattered (ICS) photons above a pulsar polar cap (PC) and surface heating by returning positrons. This paper is a continuation of our self-consistent treatment of acceleration, pair dynamics and electric field screening above pulsar PCs. We calculate the altitude of the inverse Compton pair formation fronts, the flux of returning positrons and present the heating efficiencies and X-ray luminosities. We revise pulsar death lines implying cessation of pair formation, and present them in surface magnetic field-period space. We find that virtually all known radio pulsars are capable of producing pairs by resonant and non-resonant ICS photons radiated by particles accelerated above the PC in a pure star-centered dipole field, so that our ICS pair death line coincides with empirical radio pulsar death. Our calculations show that ICS pairs are able to screen the accelerating electric field only for high neutron star surface temperatures and magnetic fields. We argue that such screening at ICS pair fronts occurs locally, slowing but not turning off acceleration of particles until screening can occur at a curvature radiation (CR) pair front at higher altitude. In the case where no screening occurs above the PC surface, we anticipate that the pulsar gamma-ray luminosity will be a substantial fraction of its spin-down luminosity. The X-ray luminosity resulting from PC heating by ICS pair fronts is significantly lower than the PC heating luminosity from CR pair fronts, which dominates for most pulsars. PC heating from ICS pair fronts is highest in millisecond pulsars, which cannot produce CR pairs, and may account for observed thermal X-ray components in the spectra of these old pulsars.Comment: 29 pages, 10 figures, accepted for publication in Ap

Pulsar X-Ray and Gamma-Ray Pulse Profiles: Constraint on Obliquity and Observer Angles

We model the thermal X-ray profiles of Geminga, Vela and PSR 0656+14, which have also been detected as gamma-ray pulsars, to constrain the phase space of obliquity and observer angles required to reproduce the observed X-ray pulsed fractions and pulse widths. These geometrical constraints derived from the X-ray light curves are explored for various assumptions about surface temperature distribution and flux anisotropy caused by the magnetized atmosphere. We include curved spacetime effects on photon trajectories and magnetic field. The observed gamma-ray pulse profiles are double peaked with phase separations of 0.4 - 0.5 between the peaks. Assuming that the gamma-ray profiles are due to emission in a hollow cone centered on the magnetic pole, we derive the constraints on the phase space of obliquity and observer angles, for different gamma-ray beam sizes, required to produce the observed gamma-ray peak phase separations. We compare the constraints from the X-ray emission to those derived from the observed gamma-ray pulse profiles, and find that the overlapping phase space requires both obliquity and observer angles to be smaller than 20-30 degrees, implying gamma-ray beam opening angles of at most 30-35 degrees.Comment: 29 pages, 9 embedded figures, AASTEX v.4, To appear in ApJ, June 20, 1998 (Vol. 499