Magnetocentrifugal launching of jets from discs around Kerr black holes

Strong magnetic fields modify particle motion in the curved space–time of spinning black holes and change the stability conditions of circular orbits. We study conditions for magnetocentrifugal jet launching from accretion discs around black holes, whereby large-scale black hole lines anchored in the disc may fling tenuous coronal gas outwards. For a Schwarzschild black hole, magnetocentrifugal launching requires that the poloidal component of magnetic fields makes an angle less than  60°  to the outward direction at the disc surface, similar to the Newtonian case. For prograde rotating discs around Kerr black holes, this angle increases and becomes  90°  for footpoints anchored to the disc near the horizon of a critically spinning   a = M   black hole. Thus, a disc around a critically spinning black hole may centrifugally launch a jet even along the rotation axis.     

Maser Emission of Relativistic Electrons Spiralling and Drifting in Curved Magnetic Fields

Synchro-curvature radiation describes the emission from a relativistic charged par- ticle which is moving and spiralling in a curved magnetic field. We investigate the maser emission for synchro-curvature radiation including drift of the guiding center of the radiating electron. It is shown that under some conditions the absorption coefficient can be negative, so maser can happen. These conditions are different from those needed for maser emission of curvature radiation including drift of the charged particles. We point out that our results, in- cluding the emissivity, can reduce to these of curvature radiation. Previously it was found that synchro-curvature radiation can not generate maser in vacuum, but we argue that synchro- curvature radiation including drift can generate maser even in vacuum. We discuss the possi- bilities of the potential applications of the synchro-curvature maser in modeling gamma ray bursts and pulsars.     

Revision of the basic equations of wave distribution function analysis

The basic equations of wave distribution function analysis are rewritten in forms that treat the electric and magnetic fields of the waves in a more symmetrical way than the original equations do, and are slightly better for computing.     

Interaction between nulls and emission in the pulsar B0834+06

We present a detailed study of the single pulses of the bright radio pulsar B0834+06, and offer evidence that the dominant periodic modulation in this pulsar's emission governs the occurrence of nulls. The nulls of B0834+06 constitute approximately 9 per cent of the total pulses and we demonstrate that they do not occur at random in the pulse sequence. On the contrary, they are found to occur preferentially close to the minimum of the pulsar's emission cycle, whose period jitters around a central value of P ₃≈ 2.17 rotation periods. It is likely that the intrinsic duration of the nulls averages about 0.2 times the pulsar rotation period. Surprisingly, the clearly distinct population of nulls and partial nulls of B0834+06 exhibit a two-peak profile slightly broader than that of the normal emission. This is in contrast to the profile of extremely weak normal pulses, which is narrower than the overall profile. A flow/counterflow model for the pulsar's two components can reproduce the essential observed features of the emission in its dominant mode, with nulls occurring at the point where the minima of the two systems are aligned. This suggests that the observed nulling rate is determined by the chance positioning of our sightline with respect to the system. If the flow is interpreted as part of a circulating carousel, a fit yields a best estimate of 14 'sparks'.     

Magnetic reconnection via tearing instability in a rotating viscous fluid

The resistive tearing instability of a sheet pinch, first investigated by Kuang & Roberts (1990) for the case of a rapidly rotating inviscid fluid, is studied for arbitrary rotation rate in a visco‐resistive fluid. Altogether there are three regimes of the resistive tearing instability which correspond to the particular parameter domain in the (Ω, P_m) plane. Here Ω is the angular velocity of the medium which is normalized to the Alfvén time and P_m is the magnetic Prandtl number. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrostatic dust-cyclotron waves in plasmas with opposite polarity grains

The dispersion relation is derived for electrostatic dust-cyclotron (EDC) waves in a collisional plasma with dust grains having both positive and negative charges. The critical electric fields for excitation of two EDC modes in such a plasma are numerically calculated for a laboratory-type plasma.     

Numerical simulations of aligned neutron star magnetospheres

We present detailed numerical simulations of the magnetosphere of an isolated neutron star in which the spin and magnetic dipole axes of the star are aligned. We demonstrate that stable charge distributions are always found, rather than particle outflows. A stable magnetosphere consists of a dome above the polar cap containing plasma of one charge and an equatorial belt containing plasma of the other sign: E · B =0 inside both of these. These are separated by a vacuum gap in which E · B ≠0 ( ρ =0 instead). We show that the charge distribution used in the 'standard' Goldreich–Julian pulsar model is inherently unstable: it collapses to a stable configuration that is very similar to the others illustrated here. An instructive video of this collapse is available at http://spacsun.rice.edu/~ian/. For typical pulsars, the stable solution has no particles near to the light cylinder, and if there were any there then their loss from the system would not lead to a replacement from the star (in contradiction to the explicit assumption used in the Goldreich–Julian model). We discuss the generic effects of pair creation, in particular as an additional source of ionization in the vacuum gap. The overall effect is simply to reduce the value of E · B in the vacuum gap so that the pair-production rate drops towards zero. A dome, disc and gap geometry is still the resulting solution. In conclusion, we confirm previous studies that the aligned rotator cannot make an active pulsar.