Differentially rotating force-free magnetosphere of an aligned rotator: analytical solutions in split-monopole approximation

In this paper we consider stationary force-free magnetosphere of an aligned rotator when plasma in the open field line region rotates differentially due to presence of a zone with the accelerating electric field in the polar cap of pulsar. We study the impact of differential rotation on the current density distribution in the magnetosphere. Using split-monopole approximation we obtain analytical expressions for physical parameters of differentially rotating magnetosphere. We find the range of admitted current density distributions under the requirement that the potential drop in the polar cap is less than the vacuum potential drop. We show that the current density distribution could deviate significantly from the ``classical'' Michel distribution and could be made almost constant over the polar cap even when the potential drop in the accelerating zone is of the order of 10 per cents of the vacuum potential drop. We argue that differential rotation of the open magnetic field lines could play an important role in adjusting between the magnetosphere and the polar cap cascade zone and could affect the value of pulsar breaking index.Comment: 15 pages, 15 figures; accepted for publication in MNRA

Optical counterparts of cosmological GRBs due to heating of ISM in the parent galaxy

We investigated influence of cosmological GRB on the surrounding interstellar medium. It was shown that \gamma-radiation from the burst heats interstellar gas to the temperatures > 10^4 K up to the distance \sim 10 pc. For high density ISM optical and UV radiation of the heated gas can be observed on the Eath several years as a GRB`s counterpartComment: 2 pages, 1 figure; presented at the Rome Conference on Gamma Ray Bursts in the Afterglow Ag

A model for nulling and mode changing in pulsars

We propose that in some pulsars the magnetosphere has different states with different geometries or/and different distributions of currents, it occasionally switches between them. These states have different spindown rates and emission beams, in some of the states no radioemission is produced at all. Switching into a different state manifests as a mode change when we see different parts of the emission beam or the beams in different states have significantly different geometries, it manifests as nulling when we either miss the new beam or no radioemission is generated in the new state. We show that modest variations in the beam shape can be accompanied by large variations in the pulsar spindown rate W - the dependence of W on the opening angle of the emission beam $\alpha$ can be as strong as W\propto\alpha^4. We speculate about physical mechanisms which may cause reconfiguration of the magnetosphere.Comment: 5 pages, 1 figure; MNRAS, in pres

On the nature of QPO in the tail of SGR giant flares

A model is presented for the quasiperiodic component of magnetar emission during the tail phase of giant flares. The model invokes modulation of the particle number density in the magnetosphere. The magnetospheric currents are modulated by torsional motion of the surface and we calculate that the amplitude of neutron star surface oscillation should be ~1% of the NS radius in order to produce the observed features in the power spectrum. Using an axisymmetric analytical model for structure of the magnetosphere of an oscillating NS, we calculate the angular distribution of the optical depth to the resonant Compton scattering. The anisotropy of the optical depth may be why QPO are observed only at particular rotational phases.Comment: 7 pages, 4 figures, emulateapj styl