Common envelope: enthalpy consideration

In this Letter we discuss a modification to the criterion for the common envelope (CE) event to result in envelope dispersion. We emphasize that the current energy criterion for the CE phase is not sufficient for an instability of the CE, nor for an ejection. However, in some cases, stellar envelopes undergo stationary mass outflows, which are likely to occur during the slow spiral-in stage of the CE event. We propose the condition for such outflows, in a manner similar to the currently standard $\alpha_{\rm CE}\lambda$-prescription but with an addition of $P/\rho$ term in the energy balance equation, accounting therefore for the enthalpy of the envelope rather than merely the gas internal energy. This produces a significant correction, which might help to dispense with an unphysically high value of energy efficiency parameter during CE phase, currently required in the binary population synthesis studies to make the production of low-mass X-ray binaries (LMXBs) with a black hole companion to match the observations.Comment: 4 pages, 1 figure, ApJL accepte

Jet confinement by magneto-torsional oscillations

Many quasars and active galactic nuclei (AGN) appear in radio, optical, and X-ray maps, as a bright nuclear sources from which emerge single or double long, thin jets. When observed with high angular resolution these jets show structure with bright knots separated by relatively dark regions. Nonthermal nature of a jet radiation is well explained as the synchrotron radiation of the relativistic electrons in an ordered magnetic field. We consider magnetic collimation, connected with torsional oscillations of a cylinder with elongated magnetic field, and periodically distributed initial rotation around the cylinder axis. The stabilizing azimuthal magnetic field is created here by torsional oscillations, where charge separation is not necessary. Approximate simplified model is developed. Ordinary differential equation is derived, and solved numerically, what gives a possibility to estimate quantitatively the range of parameters where jets may be stabilized by torsional oscillations.Comment: accepted for publication in Astrophysics and Space Scienc

Dynamic confinement of jets by magneto-torsional oscillations

Many quasars and active galactic nuclei (AGN) appear in radio, optical, and X-ray maps, as a bright nuclear sources from which emerge single or double long, thin jets (Thomson et al., 1993). When observed with high angular resolution these jets show structure with bright knots separated by relatively dark regions. High percentages of polarization, sometimes more then 50% in some objects, indicates the nonthermal nature of the radiation which is well explained as the synchrotron radiation of the relativistic electrons in an ordered magnetic field. A strong collimation of jets is most probably connected with ordered magnetic fields. The mechanism of magnetic collimation, first suggested by Bisnovatyi-Kogan et al. (1969), was based on the initial charge separation, leading to creation of oscillating electrical current, which produces azimuthal magnetic field, preventing jet expansion and disappearance. Here we consider magnetic collimation, connected with torsional oscillations of a cylinder with elongated magnetic field. Instead of initial blobs with charge separation, we consider a cylinder with a periodically distributed initial rotation around the cylinder axis. The stabilizing azimuthal magnetic field is created here by torsional oscillations, where charge separation is not necessary. Approximate simplified model is developed. Ordinary differential equation is derived, and solved numerically, what gives a possibility to estimate quantitatively the range of parameters where jets may be stabilized by torsional oscillations.Comment: Accepted for publication in Month. Not. R.A.

Origin of GRB Afterglows in the Model of Galactic Neutron Stars

The launch of the Beppo-Sax satellite gave a unique opportunity to investigate gamma ray bursts (GRB) in different spectral regions. The large diversity of the afterglow behavior creates additional problems for the cosmological model with a fireball. Formation of the afterglow giving the observed diversity of properties is suggested in the Galactic neutron star model of GRBs. It is based on the transient accretion disc formation around the neutron star with a low-mass brown companion irradiated by the neutron star.Comment: Talk at the Workshop "Gamma-Ray Bursts in the Afterglow Era", Rome, November 3-6. To appear in A&A Supp

High Velocity Neutron Stars as a Result of Asymmetric Neutrino Emission

Formation of a neutron star is accompanied by neutrino emission carring about 10% of the rest energy of the star. Toroidal field produced by twisting of a dipole field in differentially rotating star is antisymmetric. Its summation with antisymmetric toroidal field results in braking of mirror symmetry of the magnetic field . For large magnetic field the neutron decay rate depends on its strength. Neutrino is emitted more in one direction leading to flux asymmetry and recoil of the neutron star. Estimations show that the neutron star can reach velocities $\sim 1000$ km/s for 3% asymmetry of the neutrino flux.Comment: Latex, no figures, 5 page