S. Uemura

A Quadruple Magnetic Source Model for Arcade Flares and X-Ray Arcade Formations outside Active Regions. II. Dark Filament Eruption and the Associated Arcade Flare

A 2.5-dimensional MHD simulation based on the quadruple magnetic source model (Uchida et al.) was performed to deal with a dark filament eruption and the associated arcade flare. The numerical results are summarized as follows:

Observations Of Flares And Active Regions From Yohkoh, and Magnetodynamic Models Explaining Them

We discuss here some of the new aspects about solar flares and active regions found by the Solar X-ray Satellite Yohkoh, by taking advantage of the wider dynamic range and higher cadence observations with higher spatial resolution compared with the previous satellites. Those new aspects have lead us to new ways of understandings, with contradictions to the previous views about flares and active regions that are widely conceived for a long time. We give some models that explain those newly revealed observational results.

Magnetodynamic Formation Of Jets In Accretion Process Of Magnetized Mass Onto The Central Gravitator — Cases Of Forming Stars And Active Galactic Nuclei

A magnetodynamic model to deal with the acceleration and collimation of jets as a part of the global process of gravitational contraction of the magnetized gas to the central gravitator is discussed. We first review its application to the star forming jet case with several observational supporting evidence. Then, a justification will be given for the extension of this to the AGN jet case, despite of the difference in orders of magnitudes in the scales as well as in the physical parameters. The results of actual application of this magnetodynamic mechanism to the AGN case will be presented together with the discussions for the origin of the radio lobes and hotspots, and we show that this mechanism can explain the enhancement of accretion and the formation of the jet + lobe system consistently with the genetic consideration of the system.

A Magnetohydrodynamic Model to Dark Filament Eruption and Arcade Flaring

We performed a 2.5-dimensional magnetohydrodynamic simulation for dark filament eruption and arcade flaring in the solar corona. The simula- tion was based on the quadruple magnetic source model created by Uchida (1980). The results of the simulation are summarized as follows (See CD- ROM for details.). In a quadruple source field energized by the photospheric motion, a certain amount of gas can be supported quasi-stably in the current sheet region. This “dark filament” gas contains a helical magnetic island and prevents magnetic reconnection (Figure 1: Time=0.0). After the dark filament gas is squeezed out both upwards (dark filament rise) and downwards (down-pressed S-shaped X-ray filament) by external triggers, magnetic reconnection can occur, releasing the stored magnetic stress energy (Figure 1: Time=18.5-21.5). (The erupted gas oscillates above the arcade and does not go away in this case, which may be due to the 2.5- dimensional approximation.) Thus, it is shown that this model can explain several key characteristic features of dark filament eruption as well as the arcade flaring found by Yohkoh.

Generation of Current System and Energy Deposition in a Magnetohydrodynamic Model for the Production of Radio Jets from Active Galactic Nuclei (AGN’s)

We have performed 2.5D MHD numerical simulations based on our model of the MHD jet formation (Uchida and Shibata 1985). We have already shown also in the case of AGN jets that a magnetically driven, well-collimated jets can be accelerated in the direction of the rotating axis of the accretion disk around the central object (Uchida and Shibata 1986, Matsumoto et al. 1996). In this model, it is our concept that the jets are formed by the interaction between the accretion disk and a large scale magnetic field. By this interaction, angular momentum of the disk gas is taken away, and the gas of the disk accretes towards the central massive blackhole, and the gravitational potential energy of the disk is continuously liberated in a much enhanced way. At the same time, a large scale magnetic field is helically twisted and this twist propagates as non-linear torsional Alfven wave. We consider the generation, transfer, and depositon of the electromagnetic energy according to this MHD model of jets formation.

On Magnetodynamic Jet Formation from Accretion Process Of Magnetized GAS in AGN Core

In this paper, we discuss the extension of the Sweeping Magnetic Twist model to the situation of AGN jets from its accretion disk in the core. The model was first proposed for the star formation bipolar flow case by Uchida and Shibata (1985) with a genetic consideration. The gravitational contraction of the interstellar gas permeated by the large scale magnetic field ends up with an accretion disk whose angular momentum axis is parallel to the large scale field, and the field in the disk is stretched by the differential rotation into the azimuthal direction. The magnetic tension exerts braking to the rotation of the disk material and enhances the accretion, while the external part of the field lines is dragged, and the non-linear torsional Alfven waves are emitted along the large scale field. Those pinch the hourglass shaped field into the form of slender jets along the axis. The earlier phases in this scenario, providing the disk with an hourglass-shaped field as assumed in the initial work, have actually been verified recently by Tomisaka (1998) by using an adaptive mesh simulation.

Contraction of magnetized gas to the central gravitator and the production of magnetically accelerated jets

Abstract A magnetodynamic model proposed and worked on by Uchida and collaborators for the star formation jets (bipolar flows), by taking a genetic point of view into account, is reviewed. A large scale magnetic field, which is week in the primordial gas but intensified in the gravitational contraction of the gas, assists the continuous accretion of the gas to the central gravitator by extracting angular momentum from the rotating disk, and this process creates a large amplitude torsional Alfven wave that swirls up the gas into the direction of the axis. This torsional Alfven wave, as it propagates, pinches the large scale field into a slender strong field structure which we identify with the collimated jet. The rationale for extending this mechanism to the AGN jet cases is given, and some results of application to the AGN jet case are presented, with interpretation of some characteristic features like the wiggling of the jets, extended radio lobes and the hotspots at the end of the jets.

Solar Arcade Flarings as Magnetodynamic Process of Mass and Energy Shedding from Energized Magnetic Regions

Prototypes of magnetic actions in producing and shedding the X-ray-emitting high temperature plasmas in various astrophysical objects are witnessed in the spatially-resolved form on the Sun by the Solar X-ray Satellite “Yohkoh”. The most prominent of those are arcade flarings seen as powerful arcade flares in active regions with strong magnetic field. Larger scale fainter X-ray arcade formation observed at high latitudes, shedding a large amount of mass and energy as CME’s (coronal mass ejections) also belongs to this category. Since some features found by the new observation by Yohkoh are incompatible with the so-called “classical model of arcade flarings”, we advance an alternative model based on the quadruple magnetic sources in the photosphere.