Matter-induced vertices for photon splitting in a weakly magnetized plasma

We evaluate the three-photon vertex functions at order $B$ and $B^{2}$ in a weak constant magnetic field at finite temperature and density with on shell external lines. Their application to the study of the photon splitting process leads to consider high energy photons whose dispersion relations are not changed significantly by the plasma effects. The absorption coefficient is computed and compared with the perturbative vacuum result. For the values of temperature and density of some astrophysical objects with a weak magnetic field, the matter effects are negligible.Comment: 14 pages, 1 figure. Accepted for publication in PR

Density Matrix Functional Calculations for Matter in Strong Magnetic Fields: I. Atomic Properties

We report on a numerical study of the density matrix functional introduced by Lieb, Solovej and Yngvason for the investigation of heavy atoms in high magnetic fields. This functional describes {\em exactly} the quantum mechanical ground state of atoms and ions in the limit when the nuclear charge $Z$ and the electron number $N$ tend to infinity with $N/Z$ fixed, and the magnetic field $B$ tends to infinity in such a way that $B/Z^{4/3}\to\infty$. We have calculated electronic density profiles and ground state energies for values of the parameters that prevail on neutron star surfaces and compared them with results obtained by other methods. For iron at $B=10^{12}$ G the ground state energy differs by less than 2 \% from the Hartree-Fock value. We have also studied the maximal negative ionization of heavy atoms in this model at various field strengths. In contrast to Thomas-Fermi type theories atoms can bind excess negative charge in the density matrix model. For iron at $B=10^{12}$ G the maximal excess charge in this model corresponds to about one electron.Comment: Revtex, 13 pages with 6 eps figures include

On non-axisymmetric magnetic equilibria in stars

In previous work stable approximately axisymmetric equilibrium configurations for magnetic stars were found by numerical simulation. Here I investigate the conditions under which more complex, non-axisymmetric configurations can form. I present numerical simulations of the formation of stable equilibria from turbulent initial conditions and demonstrate the existence of non-axisymmetric equilibria consisting of twisted flux tubes lying horizontally below the surface of the star, meandering around the star in random patterns. Whether such a non-axisymmetric equilibrium or a simple axisymmetric equilibrium forms depends on the radial profile of the strength of the initial magnetic field. The results could explain observations of non-dipolar fields on stars such as the B0.2 main-sequence star tau-Sco or the pulsar 1E 1207.4-5209. The secular evolution of these equilibria due to Ohmic and buoyancy processes is also examined.Comment: 13 pages, 12 figures. Accepted by MNRA

Formation of Millisecond Pulsars from Accretion Induced Collapse and Constraints on Pulsar Gamma Ray Burst Models

We study accretion induced collapse of magnetized white dwarfs as an origin of millisecond pulsars. We apply magnetized accretion disk models to the pre-collapse accreting magnetic white dwarfs and calculate the white dwarf spin evolution. If the pulsar magnetic field results solely from the flux-frozen fossil white dwarf field, a typical millisecond pulsar is born with a field strength $\sim 10^{11}-10^{12}G$. The uncertainty in the field strength is mainly due to the uncertain physical parameters of the magnetized accretion disk models. A simple correlation between the pulsar spin $\Omega_*$ and the magnetic field $B_*$, $(\Omega_*/10^4s^{-1})\sim (B_{*}/10^{11}G)^{-4/5}$, is derived for a typical accretion rate \sim 5\times 10^{-8}M_{\sun}/yr. This correlation remains valid for a wide pre-collapse physical conditions unless the white dwarf spin and the binary orbit are synchronized prior to accretion induced collapse. We critically examine the possibility of spin-orbit synchronization in close binary systems. Using idealized homogeneous ellipsoid models, we compute the electromagnetic and gravitational wave emission from the millisecond pulsars and find that electromagnetic dipole emission remains nearly constant while millisecond pulsars may spin up rather than spin down as a result of gravitational wave emission. We also derive the physical conditions under which electromagnetic emission from millisecond pulsars formed by accretion induced collapse can be a source of cosmological gamma-ray bursts. We find that relativistic beaming of gamma-ray emission and precession of gamma-ray emitting jets are required unless the dipole magnetic field strengths are $>10^{15}$G; such strong dipole fields are in excess of those allowed from the accretion induced collapse formation process except in spin-orbit synchronization.Comment: 36 pages, AASLATEX, 4 ps figures, Ap

Absorption of Electro-magnetic Waves in a Magnetized Medium

In continuation to our earlier work, in which the structure of the vacuum polarisation tensor in a medium was analysed in presence of a background electro-magnetic field, we discuss the absorptive part of the vacuum polarization tensor. Using the real time formalism of finite temperature field theory we calculate the absorptive part of 1-loop vacuum polarisation tensor in the weak field limit ($eB < m^2$). Estimates of the absorption probability are also made for different physical conditions of the background medium.Comment: 9 Pages. One figure. LaTe

Spin-Flavour Oscillations and Neutrinos from SN1987A

The neutrino signal from SN1987A is analysed with respect to spin-flavour oscillations between electron antineutrinos, $\bar{\nu}_{e}$, and muon neutrinos, $\nu_{\mu}$, by means of a maximum likelihood analysis. Following Jegerlehner et al. best fit values for the total energy released in neutrinos, $E_t$, and the temperature of the electron antineutrino, $T_{\bar{\nu}_{e}}$, for a range of mixing parameters and progenitor models are calculated. In particular the dependence of the inferred quantities on the metallicity of the supernova is investigated and the uncertainties involved in using the neutrino signal to determine the neutrino magnetic moment are pointed out.Comment: 14 pages, RevTeX, 4 figures, to appear in Physical Review

Generalized kinetic and evolution equations in the approach of the nonequilibrium statistical operator

The method of the nonequilibrium statistical operator developed by D. N. Zubarev is employed to analyse and derive generalized transport and kinetic equations. The degrees of freedom in solids can often be represented as a few interacting subsystems (electrons, spins, phonons, nuclear spins, etc.). Perturbation of one subsystem may produce a nonequilibrium state which is then relaxed to an equilibrium state due to the interaction between particles or with a thermal bath. The generalized kinetic equations were derived for a system weakly coupled to a thermal bath to elucidate the nature of transport and relaxation processes. It was shown that the "collision term" had the same functional form as for the generalized kinetic equations for the system with small interactions among particles. The applicability of the general formalism to physically relevant situations is investigated. It is shown that some known generalized kinetic equations (e.g. kinetic equation for magnons, Peierls equation for phonons) naturally emerges within the NSO formalism. The relaxation of a small dynamic subsystem in contact with a thermal bath is considered on the basis of the derived equations. The Schrodinger-type equation for the average amplitude describing the energy shift and damping of a particle in a thermal bath and the coupled kinetic equation describing the dynamic and statistical aspects of the motion are derived and analysed. The equations derived can help in the understanding of the origin of irreversible behavior in quantum phenomena.Comment: 21 pages, Revte

The New AM Her System RX J0704.2+6203. Northern Twin of BL Hyi

We report here on the identification and study of the optical counterpart of the ROSAT source RX J0704.2+6203. Extensive spectral and photometric observation showed that the object belongs to the class of magnetic Cataclysmic Variables. We determined the orbital period of the system to be 97.27m and estimated the strength of its magnetic field to be on the order of 20 MG. The system was observed in both high and low states, common for its class. Other parameters of the magnetic close binary system were estimated. The spectral and photometric behavior of the object is similar to that of the well studied polar BL Hyi.Comment: 9 pages, 9 figures, accepted in A&

Two Rare Magnetic Cataclysmic Variables with Extreme Cyclotron Features Identified in the Sloan Digital Sky Survey

Two newly identified magnetic cataclysmic variables discovered in the Sloan Digital Sky Survey (SDSS), SDSSJ155331.12+551614.5 and SDSSJ132411.57+032050.5, have spectra showing highly prominent, narrow, strongly polarized cyclotron humps with amplitudes that vary on orbital periods of 4.39 and 2.6 hrs, respectively. In the former, the spacing of the humps indicates the 3rd and 4th harmonics in a magnetic field of ~60 MG. The narrowness of the cyclotron features and the lack of strong emission lines imply very low temperature plasmas and very low accretion rates, so that the accreting area is heated by particle collisions rather than accretion shocks. The detection of rare systems like these exemplifies the ability of the SDSS to find the lowest accretion rate close binaries.Comment: Accepted for publication in the Astrophysical Journal, vol. 583, February 1, 2003; slight revisions and additions in response to referee's comments; 17 pages, 6 figures, AASTeX v4.

Ohm's Law for Plasma in General Relativity and Cowling's Theorem

The general-relativistic Ohm's law for a two-component plasma which includes the gravitomagnetic force terms even in the case of quasi-neutrality has been derived. The equations that describe the electromagnetic processes in a plasma surrounding a neutron star are obtained by using the general relativistic form of Maxwell equations in a geometry of slow rotating gravitational object. In addition to the general-relativistic effect first discussed by Khanna \& Camenzind (1996) we predict a mechanism of the generation of azimuthal current under the general relativistic effect of dragging of inertial frames on radial current in a plasma around neutron star. The azimuthal current being proportional to the angular velocity $\omega$ of the dragging of inertial frames can give valuable contribution on the evolution of the stellar magnetic field if $\omega$ exceeds $2.7\times 10^{17} (n/\sigma) \textrm{s}^{-1}$ ($n$ is the number density of the charged particles, $\sigma$ is the conductivity of plasma). Thus in general relativity a rotating neutron star, embedded in plasma, can in principle generate axial-symmetric magnetic fields even in axisymmetry. However, classical Cowling's antidynamo theorem, according to which a stationary axial-symmetric magnetic field can not be sustained against ohmic diffusion, has to be hold in the general-relativistic case for the typical plasma being responsible for the rotating neutron star.Comment: Accepted for publication in Astrophysics & Space Scienc