Shigetomo Shiki

SiO Maser Sources toward the Sagittarius B2 Molecular Cloud

We have detected six new SiO maser sources toward the Sagittarius B2 molecular cloud. One is identified with an OH 1612 MHz maser source that was previously found by the VLA, and another associated with an IRAS source. The other four sources are not associated with any known OH/IR or IRAS sources. The spatial density and the kinematic property for these sources are found to be similar to those of the OH/IR sources near the Galactic center. This fact suggests that they are mostly stellar SiO maser sources in front of (or behind) the Sgr B2 molecular cloud. A possibility of association with young stellar objects, however, cannot be completely ruled out for the one SiO source (17450-2808) that is associated with an IRAS source exhibiting infrared colors of young objects.

Early (<0.3 Days) R-Band Light Curve of the Optical Afterglow of GRB 030329

We observed the optical afterglow of the bright gamma-ray burst GRB 030329 on the night of 2003 March 29 using the Kiso Observatory (University of Tokyo) 1.05 m Schmidt telescope. Data were taken from March 29 13:21:26-17:43:16 UT (0.072-0.253 days after the burst) using an RC-band filter. The obtained RC-band light curve has been fitted successfully by a single-power-law function with a decay index of 0.891 ± 0.004. These results remain unchanged when incorporating two early photometric data points at 0.065 and 0.073 days, reported by Price et al. using the Siding Spring Observatory 40 inch (1.0 m) telescope, and when also including data from the Russian-Turkish 1.5 m Telescope (Burenin et al.) covering about 0.3 days. Over the period of 0.065-0.285 days after the burst, any deviation from the power-law decay is smaller than ±0.007 mag. The temporal structure reported by Uemura et al. does not show up in our R-band light curve.

Characteristics of Superconducting series array tunnel junctions for heavy ions

Heavy ion detection experiments were carried out with superconducting series array tunnel junctions. /sup 40/Ar beam from linear accelerator was introduced to a cryostat and stopped in a substrate on which series array tunnel junctions were fabricated. An energy resolution of 4.2% was obtained for 191 MeV /sup 40/Ar, but linearity proved poor for energy ranges from 136 MeV to 191 MeV.

Application of a Self-Organizing State Space Model to the Leonid Meteor Storm in 2001

The Leonids show meteor storms in a period of 33 years, and known as one of the most active meteor showers. It has recently shown a meteor stream consisting of several narrow dust trails made by meteoroids ejected from a parent comet. Hence, an analysis of the temporal behavior of the meteor flux is important to study the structure of the trails. However, statistical inference for the count data is not an easy task, because of its Poisson characteristics. We carried out a wide-field video observation of the Leonid meteor storm in 2001. We formulated a state-of-the-art statistical analysis, which is called a self-organizing state space model, to infer the true behavior of the dust density of the trails properly from the meteor count data. {}From this analysis, we found that the trails have a fairly smooth spatial structure, with small and dense clumps that cause a temporal burst of meteor flux. We also proved that the time behavior (trend) of the fluxes of bright meteors and that of faint meteors are significantly different. In addition we comment on some other application of the self-organizing state-space model in fields related to astronomy and astrophysics.