Part I. Talks

Section C. Effects of Magnetic Fields on Highly Energetic Processes and Emission from Astrophysical Plasmas



Title: Interaction of Gravitationally Contracting Gas Having Angular Momentum with Magnetic Field, and the Acceleration and Collimation of Astrophysical Jets
Authors: Y. Uchida, M. Nakamura, T. Miyagoshi, T. Kobayashi, T. Mukawa, and S. Hirose
Affil: Physics Department, Science University of Tokyo, Shinjuku-ku, Tokyo 162-8601, Japan
Abstract: In the present paper, we stress the importance of the magnetic field in the problem of acceleration and collimation of astrophysical jets, and discuss our proposed generic picture for such ``central gravitator + jets + lobes" systems and inherent interpretations of the various observational characteristics of such systems: Mechanisms are proposed for (1) the enhanced liberation of gravitational energy at the central object, (2) the transfer of a part of the liberated energy along the large-scale magnetic field by large-amplitude, torsional Alfven wave trains that form collimated jets (we call this a sweeping pinch process), (3) the dumping of the transferred energy at the end of the jets when they impinge on the denser region outside the border of the ``cavity" from which the mass contracted to the central condensation (central gravitator + accretion disk, as well as the larger-scale condensation surrounding them), and (4) the formation of wiggled jets and lobes as helical kinks and the tucked-up magnetic field produced in the sweeping pinch process, respectively.


Title: A Three-dimensional Outer-magnetospheric Gap Model for Gamma-ray Pulsars: I. The Crab Pulsar
Authors: K. S. Cheng(1), M. Ruderman(2), and L. Zhang(1)
Affil: (1) Department of Physics, the University of Hong Kong, P.R. China (2) Department of Physics, Columbia University, U.S.A.
Abstract: We use a three-dimensional pulsar magnetosphere model to study the geometry of outer-magnetospheric gaps. The vertical size of the ``outer gap'' is first determined by a self-consistent model in which the outer gap size is limited by pair production from collisions between (1) thermal photons produced from polar cap heating by backflow ``outer gap'' current, and (2) the curvature photons emitted by gap-accelerated charged particles. The transverse size of the outer gap is also determined by local pair production limits. In principle, there are two topologically disconnected outer gaps in the magnetosphere of a pulsar. Both incoming and outgoing particle flows are allowed. However, the emission morphologies produced by incoming particle flow is severely restricted by local pair production in the gap and the absorption of magnetic pair production near the star. Double-peaked light curves with strong bridges are most common. From the three-dimensional structure of the outer gap and its local properties, we calculate the emission morphologies and phase-resolved spectra of gamma-ray pulsars. Applications to the Crab pulsar illustrate the model.


Title: Accreting Plasmas in Black Hole Magnetospheres
Author: M. Takahashi
Affil: Department of Physics and Astronomy, Aichi University of Education, Kariya, Aichi 448-8542, Japan
Abstract: We present a fully relativistic study on the standing shock formation for magnetohydrodynamical plasmas in a stationary and axisymmetric black hole magnetosphere. We express all the postshock physical quantities in terms of the relativistic compression ratio. Then, the downstream state of a shocked plasma is determined by the upstream state of the accretion. We also discuss the dragging-effects of the rotating black hole on the shock conditions.


Title: Magnetohydrodynamic Turbulence in Accretion Discs
Authors: U. Torkelsson(1), A. Brandenburg(2), A. Nordlund(3), and R. F. Stein(4)
Affil: (1) Chalmers University of Technology Goteborg University, Department of Theoretical Physics, Astrophysics Group, S-412 96 Gothenburg, Sweden (2) Department of Mathematics, University of Newcastle upon Tyne, NE1 7RU, U.K. (3) Theoretical Astrophysics Center, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark (4) Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, U.S.A.
Abstract: We present results from numerical simulations of magnetohydrodynamic turbulence in accretion discs. Our simulations show that the turbulent stresses that drive the accretion are less stratified than the matter; thus, the surface layers are more strongly heated than the interior of the disc.


Title: Plasma Masers in Radio Pulsars
Authors: M. Lyutikov(1), R. Blandford(1), and G. Machabeli(2)
Affil: (1) Canadian Institute for Theoretical Astrophysics, 60 St. George Street, Toronto, Canada (2) Abastumani Astrophysics Observatory, A. Kazbegi Av. 2a, Tbilisi 380060, Republic of Georgia
Abstract: Relativistic plasma masers operating on the anomalous cyclotron-Cherenkov resonance (omega - k_|| v_|| + omega_B gamma_[res] = 0) and on the Cherenkov-drift resonance (omega - k_|| v_|| - k_x u_d = 0) are capable of explaining the main observational characteristics of pulsar radio emission. Both electromagnetic instabilities are due to the interaction of the fast particles of the primary beam and from the tail of the distribution with the normal modes of a strongly magnetized, one-dimensional electron-positron plasma. In a typical pulsar, both resonances occur in the outer parts of the magnetosphere at r_[res] ~ 10^9 cm.


Title: The Physics of Soft Gamma Repeaters
Author: C. Thompson
Affil: University of North Carolina, Department of Physics and Astronomy, Chapel Hill, NC 27599, U.S.A.
Abstract: I describe the evidence that Soft Gamma Repeaters are magnetars---neutron stars in which a decaying magnetic field (rather than rotation) is the dominant source of free energy. The focus here is on the bursting emission of these sources and on direct physical diagnostics of very strong magnetic fields (B > (or approximately) 10 B_[QED] = 4.4x10^[14] G). I also summarize the trapped fireball model of SGR outbursts, the influence of QED processes on their spectra and lightcurves, and the genetic connection between neutron star magnetism and the violent fluid motions in a collapsing supernova core.


Title: The Magnetic Fields of the Universe and Their Origin
Authors: S. A. Colgate & H. Li
Affil: Los Alamos National Lab, T-6, MS B288, Los Alamos, NM 87545, U.S.A.
Abstract: Recent rotation-measure observations of a dozen or so galaxy clusters have revealed a surprisingly large number of magnetic fields whose estimated energy and flux are, on average, ~10^[58] ergs and ~10^[41] G cm^2, respectively. These quantities are so much larger than any coherent sums of individual galaxies within the cluster that an efficient galactic dynamo is required. We associate these fields with single AGNs within the cluster and, therefore, with all galaxies during their AGN phase. Only the central, massive black hole (BH) has the necessary binding energy, ~10^[61] ergs. Only the accretion disk during the BH formation has the winding number, ~10^[11] turns, necessary to make the gain and magnetic flux. We present a model of a BH accretion-disk dynamo that might create these magnetic fields, where the helicity of the "alpha-omega" dynamo is driven by star-disk collisions. The back reaction of the saturated dynamo forms a force-free field helix that carries the energy and flux of the dynamo and redistributes them within the clusters.


Title: Jets from Black Hole Magnetospheres
Authors: K. Shibata(1), S. Koide(2), T. Kudoh(3), and S. Aoki(4)
Affil: (1) Kwasan Observatory, Kyoto University, Yamashina, Kyoto 607-8471, Japan (2) Faculty of Engineering, Toyama University, Toyama 930-8555, Japan (3) National Astronomical Observatory, Mitaka, Tokyo 181-8588, Japan (4) Dept. of Astronomy, Univ. Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
Abstract: Recent general-relativistic MHD simulations of jets ejected from black-hole magnetospheres (for both Schwarzschild and Kerr holes) have revealed that (1) strong shock waves are formed in the accretion flow inside 3 r_s, (2) jets show two-layered shell structure consisting of a gas-pressure driven jet and a magnetically driven jet, the former being accelerated from a high-pressure region heated by strong shocks, and (3) in the case of a Kerr hole, magnetically driven jets are produced from the ergosphere by the effect of frame dragging.