Solitary Magnetic Bubbles

Stability and attractor property of free-floating axisymmetric magnetic bubbles in high-conductivity plasmas is (tentatively, numerically) demonstrated. The existence of compact non-singular axisymmetric magnetic equilibria is proved. Being attractors, the solitary magnetic bubbles should exist in nature.Comment: 7 pages, 26 figure

Three Form Inflation

It is noted that inflation driven by a three form with arbitrary self coupling satisfies a consistency relation $n_S-1=2n_T$, between spectral indices of scalar and tensor cosmological perturbations. The standard consistency relation for the ratio of the amplitudes of perturbations is only valid for quadratic self coupling of the three form.Comment: 4 page

Power of a Turbulent Pulsar

We speculate that stationary force-free pulsar magnetospheres are screw unstable, and the spin-down power of real pulsars is carried by turbulent Poynting jets. The turbulent jet entrains poloidal flux as it propagates away from the star. Due to poloidal flux entrainment, poloidal field inside the jet decreases at a slower rate than the dipole's $r^{-3}$, and the pulsar power increases accordingly: $L\sim (\mu ^2\Omega^4/c^3)(\Omega R/c)^{-\alpha}$, where $\mu$ is the magnetic dipole, $\Omega$ is the frequency, $R$ is the neutron star radius, and $\alpha \lesssim 1$ is an index which depends on spin-dipole angle. Our speculation is of interest because it seems to provide the only possible explanation (without fine-tuning) of observed pulsar braking indices.Comment: 5 page

GRB: magnetic fields, cosmic rays, and emission from first principles?

We describe a scenario for large-scale magnetic field generation and particle acceleration in a collisionless collision of cold plasma clouds. A first-principle (i.e. using particles) numerical simulation of this process might be possible. Our scenario is essentially 3D. We argue that {\it large-scale} magnetic fields are not generated in 2D, even in collisionless plasma. We calculate and numerically simulate magnetic field generation by relativistic collisionless Kelvin-Helmholtz instability in 2D. Collisionless tangential discontinuity might be more important than collisionless shock, because tangential discontinuity remains unstable even in the hydro limit, when the shock stabilizes.Comment: 5 page

Distances and moments of inertia of Fermi Pulsars

Measurement of distances and moments of inertia of pulsars must be useful, for instance, for three-dimensional mapping of the dispersion and rotation measures, constraining the nuclear equation of state, etc. The distances and moments of inertia can be measured by fitting the gamma-ray lightcurves of pulsars, because the gamma-ray emission seems to be governed by easily calculable physics. The (first-principle) theoretical lightcurves have been computed only for weak pulsars (pair production near the light cylinder much smaller than Goldreich-Julian [1] per rotation), and at insufficient accuracy; but, since this computation has been done by a self-taught numericist, it must be possible to improve the theoretical accuracy for weak pulsars, and also to extend the computation to non-weak pulsars. To invite the computational effort of better-equipped researchers, we describe an (entirely obvious) procedure for measuring the distances and moments of inertia for weak pulsars.Comment: 2 page

Landau Damping and Alfven Eigenmodes of Neutron Star Torsion Oscillations

Torsion oscillations of the neutron star crust are Landau damped by the Alfven continuum in the bulk. For strong magnetic fields (in magnetars), undamped Alfven eigenmodes appear.Comment: 5 pages, 1 figur

Collisionless Halos Around Black Holes

When a black hole accretes slowly, the radiative cooling of the infalling gas is weak and the accretion disk does not form. A hot collisionless quasi-spherical halo is formed instead. The properties of such halos are discussed. The rate of accretion, the radiative efficiency, and the temperature and density near the hole are evaluated.Comment: 7 pages, Proceedings IAU Symposium 19

Spin 3/5 Black Hole in GRO J1655-40?

When a bright spot in a high-inclination disk orbits a black hole, its light is periodically lensed and Doppler shifted. If the spots occupy a narrow range of radii, a quasi-periodic oscillation (QPO) will result. I calculate the QPO frequency assuming that the spots appear near r_max - the radius of the maximal proper radiation flux from the disk. The calculated frequency depends on the black hole mass and spin. For the microquasar GRO J1655-40, the black hole mass is known and a 300 Hz QPO was observed. The inferred black hole spin is about 60% of the maximal. The orbit precession frequency at r_max is 20Hz, this QPO was also observed in GRO J1655-40. An approximate formula for r_max is given.Comment: 4 pages, submitted to Ap

Ultra-Relativistic Blast Wave: Stability and Strong Non-Universality

Linear eigenmodes of a spherically symmetrical ultra-relativistic blast wave (the Blandford-McKee, BMK, solution) are calculated. The BMK solution is shown to be stable and strongly non-universal. It is stable because all the eigenmodes decay. Non-universality of the BMK solution (BMK is not an intermediate asymptotic) is a consequence of causality. In terms of eigenmodes -- some eigenmodes decay too slowly. For each degree l, there exists an eigenmode which decays at the smallest rate. The amplitude of this eigenmode, defined as relative perturbation of energy behind the shock front, is constant at early time. Later, when the blast wave slows down to Gamma = l/10, an oscillatory decay commences, and the amplitude drops to less than 10% of the initial value at Gamma = l/100. The non-universality is surprisingly strong. Near the end of the ultra-relativistic stage, perturbations with l<200, that is more than 10,000 different harmonics, are suppressed by less than a factor of 10. Spherical symmetry is only reached by the time the blast wave slows down to non-relativistic velocities, when the Sedov/Taylor/von Neumann solution sets in.Comment: 6 pages, submitted to ApJ

The radiation belt of the Sun

For a given solar magnetic field, the near-Sun (phase-space) density of cosmic ray electrons and positrons of energy above about 10GeV can be calculated from first principles, without any assumptions about the cosmic ray diffusion. This is because the sunlight Compton drag must be more important than diffusion. If the solar magnetic field has an appreciable dipole component, the electron/positron density should have a belt-like dent, perhaps extending to several solar radii. The belt structure appears because the quasi-bound orbits are depopulated by the sunlight Compton drag.Comment: 2 pages, 1 figur