K.-I. Seon

Results of Ginga/ROSAT Simultaneous Observation of the X-Ray Burst Source 1735–444

We present a detailed analysis of simultaneous Ginga and ROSAT observations of the X-ray burst source 1735-444, during which the source was in an unusually high luminosity state. The source shows the characteristics of an atoll source in the high-intensity (banana) state, with a general correlation between intensity and spectral hardness. A blackbody component contributes ~15%-20% of the total flux when the conventional two-component model is used to fit the spectra. We also observed a bright burst with radius expansion at this very high luminosity. The burst spectrum could not be described by a simple blackbody model. We discuss possible explanations.

New features of the X-ray dip source X1755-338

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Beam-plasma discharge and the boundary effects

Abstract A simulation of the beam-plasma discharge is attempted in this paper by using a particle-in-cell code in a one-dimensional system. Two different boundary conditions are adopted in the present study. When the open boundary condition is used, the stagnation region expands slowly and most ionization occurs only in a limited region near the beam injection boundary. The electrostatic energy deposited from the beam is inversely proportional to the electron-neutral collision frequency. When this open boundary is replaced by a grounded conducting wall, the stagnation point formed initially near the emitter moves quickly toward the wall and significant ionization is observed in the entire system. Beam-plasma instability is observed in the late evolution of the bounded system.

Key Science Programs for the Spear Mission

Figure 1 shows three models of the state of interstellar gas. The upper model, derrived from Slavin and Cox (1992,1993) shows hot gas concentrated in isolated supernova remnants, with FUV emission arising in the interface regions between the hot gas and the neutral ISM.. The middle model show the distribution of emission that would be expected in a Galactic fountain model. (Shull & Slavin 1994) Emission in these models, which is primarily concentrated toward the Galactic poles, tends to be brighter in OVI λλ 1032,1038 emission than in CIV λλ 1550 emission. In contrast, a McKee Ostriker type model (McKee & Ostriker 1977, bottom) including a pervasive hot (106) K ISM results in emission primarily at hot/cold interfaces. This results in a low contrast sky that is brighter in CIV emission than in OVI . Of course, none of these models is likely to be an accurate representation of the real FUV sky. MHD simulations of interstellar matter indicate that reality is likely to be more complex that any of these models could indicate. Reality is likely a combination of all three models with active processes leading to strong variations over the sky. The all-sky maps arising from the SPEAR mission will result in a significant increase in our understanding of the global state of interstellar gas.

BAFFLE DESIGN OF FIMS

FIMS (Far-ultraviolet IMaging Spectrograph) is the main payload of STSAT-1 satellite which was successfully launched on September 27, 2003. The optical system of FIMS consists of two sets of parabolic cylinder mirror, slit, ellipsoidal reflection grating, and baffle system. We designed two types of baffle system for the FIMS: FOV baffle and order baffle. FOV baffle in the mirror house controls the field of view, and the order baffle in the vacuum box blocks the rays reflected rays by different orders.