An ASCA observation of Seyfert galaxy NGC 3227 showed flares with a linear increase and exponential decrease similar to that of solar flares. We derive a scaling law relating the loop length of a magnetic flux tube to rise and decay times of the flare using cooling mechanisms suitable for the central engine of a Seyfert galaxy. The predicted loop lengths are consistent with physical constraints on the plasma dynamics, suggesting that the same mechanism which explains solar flares may explain variability in Seyfert galaxies.

We present the initial results from our search for hidden blazars via CIV emission line variability among radio loud quasars. The implications on models of quasar Broad Emission Line Regions are discussed, and we focus on the tidally disrupted star model.

The Hard X-ray Telescope (HXT: Kosugi et al. 1991) onboard Yohkoh has observed that, in impulsive solar flares, a hard X-ray source is located above the apex of a soft X-ray flaring loop, in addition to double footpoint sources (Masuda et al. 1994, 1995). This observation suggests that flare energy-release, probably magnetic reconnection, takes place not in the soft X-ray loop but above the loop. It is important to derive the hard X-ray spectrum of the above-the-looptop source accurately in order to understand how electrons are energized there. The above-the-looptop source was most clearly observed during the 13 January 1992 flare. However, the count rate, especially in the H-band (53–93 keV), is too small to synthesize high-quality images and to derive an accurate spectrum.

The unique Galactic object SS433 contains the best-studied relativistic jets, and their physical parameters (velocity, temperature, density) are known to an astronomically unprecedented accuracy, i.e., to factors of order unity. The comparison of numerical simulations of these jets with observations provides deeper insight into the SS433/W50 system and is ideal for testing our understanding of the jet phenomenon in general.

The aim of this work is to demonstrate the properties of the magnetospheric model around Kerr black holes, so-called the “flywheel” (rotation powered) model. The fly-wheel engine of the BH accretion disk system is applied to the statistics of QSOs/AGNs. Nitta, Takahashi, & Tomimatsu clarified the individual evolution of the Kerr black-hole fly-wheel engine, which is parameterized by black-hole mass, initial Kerr parameter, magnetic field near the horizon, and a dimensionless small parameter. We impose a statistical model for the initial mass function of an ensemble of black holes using the Press-Schechter formalism. With the help of additional assumptions, we can discuss the evolution of the luminosity function and the spatial number density (population) of QSOs/AGNs. The result explains well the decrease of very bright QSOs and decrease of population after z ~ 2.

X-ray emission observed from the SS433/W50 system has been interpreted as resulting from the interaction of the binary jets with the surrounding medium. We have been carrying out millimetre wavelength measurements of this system. We find no evidence for the association of a molecular cloud with the eastern jet, but we do find evidence for a strong association with the western jet.

The structural parameters of the supermassive object at the Galactic Center and its high-energy radiation are estimated according to observations in near-infrared radiation, under the model of a supermassive object with magnetic monopoles.

Present observational techniques provide stellar spectra with high resolution at a high signal-to-noise ratio over the complete wavelength range—from the far infrared to X-rays.

The effects of Non-“Local Thermal Equilibrium” (NLTE) are particularly important for hot stars, hence the use of reliable NLTE stellar model atmosphere fluxes is required for an adequate spectral analysis.

State-of-the-art NLTE model atmospheres include metal-line blanketing of millions of lines of all elements from hydrogen up to the iron-group elements, and thus permit precise analyses of extremely hot compact stars, e.g., central stars of planetary nebulae, PG 1159 stars, white dwarfs, and neutron stars. Their careful spectroscopic study is of great interest in several branches of modern astrophysics, e.g., stellar and galactic evolution, and interstellar matter.

Supernova remnant shocks produce a rich spectrum of lines in the ultraviolet. Among these are important diagnostic resonance lines of O VI, C III, and N III which lie in the bandpass observable with the recently launched Far Ultraviolet Spectroscopic Explorer. We present an overview of a PI program to observe several supernova remnants using this new telescope.

We explain why compact sources are nonlinear and investigate the nonlinearity of MCG-6-30-15. We argue that the central engine of this Seyfert nucleus is compact and show that it exhibits a specific nonlinear behavior similar to that of a system in a critically self-organized state.

The 3-ms, X-ray pulsar RX J1824.2-2R52P has been identified at the 2-σ level as a possible X-ray counterpart of the radio pulsar PSR 1821-24. The present work uses archival HST data for M28 to set upper limits on the optical V-band magnitude of PSR 1821–24 / RX J1824.2-2R452P. The optical limit extends the multiwavelength observations for this source and would provide constraints for theoretical models of pulsar emission.

The principal mechanism for neutron-star cooling during the early period of its thermal evolution is the emission of neutrinos. Because the neutrino luminosity is very large compared to the photon luminosity, most approximations leave any small effects upon the photon luminosity during the early part of the evolution as ignorable. However, for a field strength of H ~ 1012 gauss, taking those effects into consideration in terms of a decreased photon flux from the surface means that the energy not released from the surface as photons is still trapped within the star. Energy conservation requires that neutrino emission must make up for the difference, thereby modifying the onset of the photon era of cooling. A magnetic field of large magnitude will change the surface temperature. A proper treatment of the neutron-star cooling problem in a large magnetic field requires that tangential heat flow be taken into account. This presentation shows the preliminary results of a study that is leading toward a full two-dimensional calculation of the thermal evolution.

We use optical and X-ray data to investigate the atmosphere of the isolated neutron star RX J185635-3754. The space motion suggests an origin about 2 million years ago in the Upper Cen-Lup OB association.

Relativistic electrons may be effectively accelerated by turbulent Alfvén waves in radio jets. The acceleration spectrum is a power law with the electron energy as high as γ ~ 106, but the spectrum index is ~ 1.2 in the condition of diffusion approximation, which is less than the observation value.

“Transient brightenings” (or “microflares”) regularly deposit 1027 ergs of energy in the solar corona, and account for perhaps 20% of the active corona's power (Shimizu 1995). We assume these events correspond to episodes of magnetic reconnection along magnetic separators in the solar corona. Using the techniques of magnetic charge topology, we model active region fields as arising from normally distributed collections of “magnetic charges”, point-like sources/sinks of flux (or field lines). Here, we present statistically determined separator (X-ray loop) lengths, derived from first principles. We are in the process of statistical calculations of heating rates due to reconnection events along many separators.

We study reconnection and chromospheric evaporation in flares using a numerical code including nonlinear, anisotropic heat conduction (Yokoyama & Shibata 1998). The two-dimensional, nonlinear, time-dependent, resistive, compressible MHD equations are solved. The evolution from the rise phase to (the early part of) the decay phase of a solar flare is qualitatively reproduced in this simulation. Based on the results, we obtained a relationship between the flare temperature and the coronal magnetic field strength. We assume that the energy input to a loop balances with the conductive cooling rate, that the temperature at the loop apex is TA ≍ (2QL2/κ0)2/7, where Q is the volumetric heating rate, that L is the half-length of the loop, and that the Spitzer thermal conductivity constant is κ0 = 10−6 CGS. In our simulations, the heating mechanism is magnetic reconnection, so the heating rate is described as Q = B2/(4π) · Vin/L · l/sin Θ, where B is the coronal magnetic field strength, Vin is the inflow velocity (≍ 0.1 VA from our result and also from Petschek's theory), and Θ is the angle between the slow-mode MHD shock and the loop and is approximately given by sin Θ ≍ Vin/VA. By manipulating the equations, we find where ρ is the mass density of the corona. The simulation results show very good agreement with this scaling law.

Five posters in the group of solar physics have been presented at this meeting on “Highly Energetic Physical Processes and Mechanisms for Emissions from Astrophysical Plasmas”. Four of these posters were dealing with aspects of solar flares, the most energetic processes observed in the solar corona, while one poster dealt with active regions. Although the most energetic particles in solar flares (E < 108 eV) do not compete with the most energetic cosmic rays (E > 1018.5 eV) observed in the rest of the universe, similar particle-acceleration mechanisms (electric fields, stochastic acceleration, shocks) are investigated for both phenomena. On the other hand, some highly efficient acceleration mechanisms operating in astrophysical plasmas (e.g., E x B drift in rapidly rotating B-fields on pulsars) are definitely not applicable to solar flares. However, a common theme in both astrophysical and solar acceleration processes is the role of magnetic reconnection, which was also the subject in one or the other form in all of the five presented solar posters. The joint venture of astrophysical and solar participants of this workshop contributed therefore nicely to a cross-fertilization of these common physical themes in both disciplines.

The Sun serves as the local physics laboratory for studying the suprathermal activity phenomena of stars. Scrutiny of the Sun has led to the discovery of a host of previously unknown physical effects, largely within the classical physics of Newton and Maxwell, but including quantum mechanics and lepton physics as well.

I am going to use this opportunity to make some very general remarks. I believe we are about to enter an era that is very different from those we have experienced before, and is probably closest to what those of us who have been around long enough experienced in the 1970s. That was a time of explosive expansion in space astronomy and astrophysics. The intervening two decades have seen major advances in many specific areas, but, since the 1970s period, progress has been more episodic, triggered by the occasional appearance of some new observational tool, new computational tool, or theoretical insight.

Neutron stars can be the underlying source of energetic particle acceleration in several ways. The huge gravitational-collapse energy released in their birth, or the violent fusion at the end of the life of a neutron-star binary, is the energy source for an accelerator in the surrounding medium far from the star. This would be the case for: (a) cosmic rays from supernova explosions with neutron-star remnants; (b) energetic radiation from “plerions” around young neutron stars (e.g., the Crab Nebula, see Pacini 2000); and (c) “afterglow” and γ-rays of cosmic Gamma-Ray Burst (GRB) sources with possible neutron-star central engines. Particles can also be energetically accelerated if a neutron star's gravitational pull sustains an accretion disk fed by a companion. Examples are accretion-powered X-ray pulsars and low-mass X-ray binaries. A third family of “neutron-star powered” accelerators consists of those which do not depend on the surrounding environment. These are the accelerators which must exist in the magnetospheres of many solitary, spinning-down, magnetized neutron stars (“spinsters”) when they are observed as radio pulsars or γ-ray pulsars. (There are probably ~ 103 dead radio pulsars for each one in our Galaxy that is still active; the ratio for γ-ray pulsars may well exceed 105.)