Global structure of the pulsar force-free magnetosphere revisited

A new model of the pulsar force-free magnetosphere is suggested, which includes the presence of the polar, outer and slot gaps. It is based on a new exact solution of the pulsar equation in the form of an offset monopole and the resultant split-offset monopole scheme.Comment: 3 pages, 2 figures; to appear in Proceedings of IAUS 291 "Neutron Stars and Pulsars: Challenges and Opportunities after 80 years", J. van Leeuwen (ed.

Mechanisms of the physical connection between the radio- and high-energy emissions of pulsars

The high-energy emission mechanisms based on the radio photon reprocessing by the ultrarelativistic plasma particles in the open field line tube of a pulsar are considered. The particles are believed to acquire relativistic gyration energies as a result of resonant absorption of pulsar radio emission. The spontaneous synchrotron re-emission of these particles falls into the optical and soft X-ray ranges and can at least partially account for the pulsar non-thermal high-energy emission. Besides that, the radio photons, which are still below the resonance, can be deposited into the high-energy range by means of the scattering off the gyrating particles. This process can also markedly contribute to the pulsar high-energy emission and underlie the potentially observable features of the radio -- high-energy connection. Based on the theory developed, we interpret the manifestations of the radio -- high-energy connection already observed in the Crab and Vela pulsars. Furthermore, it is shown that generally the most prominent connection is expected at the lowest radio frequencies, beyond the low-frequency turnover of a pulsar.Comment: 5 pages, 2 figures. To appear in the Proceedings of The Low-Frequency Radio Universe Conference held at NCRA-TIFR, Pune, 8-12 December 2008, eds. D.J. Saikia, D. Green, Y. Gupta, and T. Ventur

On the Global Structure of Pulsar Force-free Magnetosphere

The dipolar magnetic field structure of the neutron star is modified by the plasma originating in the pulsar magnetopshere. In the simplest case of a stationary axisymmetric force-free magnetosphere, a self-consistent description of the fields and currents is given by the well-known pulsar equation. Here we revise the commonly used boundary conditions of the problem in order to incorporate the plasma-producing gaps and to provide a framework for a truly self-consistent treatment of the pulsar magnetosphere. The generalized multipolar solution of the pulsar equation is found, which, as compared to the customary split monopole solution, is suggested to better represent the character of the dipolar force-free field at large distances. In particular, the outer gap location entirely inside the light cylinder implies that beyond the light cylinder the null and critical lines should be aligned and go parallel to the equator at a certain altitude. Our scheme of the pulsar force-free magnetosphere, which will hopefully be followed by extensive analytic and numerical studies, may have numerous implications for different fields of pulsar research.Comment: 5 pages, 2 figures; accepted for publication in Ap

Physics of radio emission in gamma-ray pulsars

Propagation of radio emission in pulsar magnetosphere is reviewed. The effects of polarization transfer, induced scattering and reprocessing to high energies are analysed with an especial emphasis on the implications for the gamma-ray pulsars. The possibilities of the pulsar plasma diagnostics based on the observed radio pulse characteristics are outlined as well. As an example, the plasma number density profiles obtained from the polarization data for the Vela and the gamma-ray millisecond pulsars J1446-4701, J1939+2134 and J1744-1134 are presented. The number densities derived tend to be the highest/lowest when the radio pulse leads/lags the gamma-ray peak. In the PSR J1939+2134, the plasma density profiles for the main pulse and interpulse appear to fit exactly the same curve, testifying to the origin of both radio components above the same magnetic pole and their propagation through the same plasma flow in opposite directions. The millisecond radio pulse components exhibiting flat position angle curves are suggested to result from the induced scattering of the main pulse by the same particles that generate gamma-rays. This is believed to underlie the wide-sense radio/gamma-ray correlation in the millisecond pulsars. The radio quietness of young gamma-ray pulsars is attributed to resonant absorption, whereas the radio loudness to the radio beam escape through the periphery of the open field line tube.Comment: 25 pages, 5 figures. Invited contribution to a Special Collection 'Plasma Physics of Gamma Ray Emission from Pulsars and their Nebulae' ed. by J. Arons and D. Uzdensk

Elastic Properties of KH2PO4 at the ferroelectric phase transition

We report results of ultrasonic studies of a single crystal of KDP in the temperature range 2-300 K. The longitudinal and transverse sound velocities along [001] and [100] directions were obtained as functions of temperature. The analysis of the temperature evolution of pseudomoduli $c_{11}$ and $c_{33}$ in the ferroelectric phase shows that these quantities can be approximated by the expression $c_{ii}\sim(T-T_0)^{0.5}$ in the temperature range 0.001K$<T_c-T<$0.2K

Resonant inverse Compton scattering by secondary pulsar plasma

We consider resonant inverse Compton scattering of thermal photons by secondary particles above the pulsar polar gap. The process appears to be an essential energy loss mechanism for the particles. The distribution function of the secondary plasma particles is found to be strongly affected by the scattering. It becomes two-humped implying the development of two-stream instability. The resonantly upscattered Compton photons are found to gain energy of 1 - 10 MeV forming an additional component in the pulsar gamma-ray spectrum. The corresponding gamma-ray flux is estimated as well.Comment: 17 pages, LaTe

Notes on the Vollhardt "invariant" and phase transition in the helical itinerant magnet MnSi

In this paper we argue that rounded "hills" or "valleys" demonstrated by the heat capacity, thermal expansion coefficient, and elastic module are indications of a smeared second order phase transition, which is flattened and spread out by the application of a magnetic field. As a result, some of the curves which display a temperature dependence of the corresponding quantities cross almost at a single point. Thus, the Vollhardt crossing point should not be identified with any specific energy scale. The smeared phase transition in MnSi preceding the helical first order transition most probably corresponds to the planar ferromagnetic ordering, with a small or negligible correlation between planes. At lower temperatures, the system of ferromagnetic planes becomes correlated, acquiring a helical twist

Inexhaustible physics of the helical magnet MnSi: field evolution of the magnetic phase transition inferred from ultrasound studies

The longitudinal and transverse ultrasound speeds and attenuation were measured in a MnSi single crystal in the temperature range of 2 - 40 K and magnetic fields to 7 Tesla. The magnetic phase diagram of MnSi in applied magnetic field appears to depend on the experimental setups, which is related to a difference in demagnetization factors arising due to the disc shape of the sample. The magnetic phase transition in MnSi in zero magnetic field is signified by a quasi discontinuity in the c11 elastic constant, which varies significantly with magnetic field. It is notable that the region where the c11 discontinuity almost vanishes closely corresponds to the extent of skyrmion phase along the magnetic to paramagnetic transition. This implies that the c11 elastic constant is almost continuous through the transition from the skyrmion to paramagnetic phases. A recovery of the discontinuity of c11 and enhanced sound absorption occur at the crossing of the phase transition line and the line of minima in c11. The powerful fluctuations at the minima of c11 make the mentioned crossing point similar to a critical end point, where a second order phase transition meets a first order one. The skyrmion domain in the case of a perpendicular setup with a smaller demagnetization factor has a reduced temperature range, which suggests that the magnetic field inhomogeneity plays an important role in the skyrmion occurrence and, hence, opens a way of skyrmion manipulation. The small anisotropy of the shear moduli in the (001) plane found in the parallel setup is most probably also caused by the magnetic field inhomogeneity, which distorts the hexagonal symmetry of the skyrmion crystal.Comment: 7 pages, 9 figure

On the circular polarization of pulsar radiation

We consider the polarization behaviour of radio waves propagating through an ultrarelativistic highly magnetized electron-positron plasma in a pulsar magnetosphere. The rotation of magnetosphere gives rise to the wave mode coupling in the polarization-limiting region. The process is shown to cause considerable circular polarization in the linearly polarized normal waves. Thus, the circular polarization observed for a number of pulsars, despite the linear polarization of the emitted normal waves, can be attributed to the limiting-polarization effect.Comment: 11 pages, LaTe

Thermal expansion and magneto-volume studies of the itinerant helical magnet MnSi

Thermal expansion and forced magnetostriction of MnSi were measured as a function of temperature down to 5 K and magnetic field to 3 T. The small length (volume) discontinuity at the magnetic phase transition in MnSi decreases with application of magnetic field to a value $\Delta L/L \sim 10^{-7}$, and then suddenly the discontinuity seemingly jumps to zero. Thermal expansivity peaks strongly deteriorate with magnetic fields. No specific features identifying a tricritical point were observed. We propose that the Frenkel concept of heterophase fluctuations may be relevant in the current case. Therefore, we suggest that the magnetic phase transition in MnSi always remains first order at any temperature and magnetic field, but the transition is progressively smoothed by heterophase fluctuations. These results question the applicability of a model of a fluctuation-induced first order phase transition for MnSi. Probably a model of coupling of an order parameter with other degrees of freedom is more appropriate.Comment: 6 figures, 5 page