Kiyoshi Kawabata

Detailed Spectral Study of an Ultra-Luminous Compact X-Ray Source, M81 X-9, in the Disk-Dominated State

We report on the results of detailed spectral studies of the ultra-luminous X-ray source (ULX), M81 X-9 (Holmberg IX X-1), made with XMM-Newton on 2001 April 22 and with ASCA on 1999 April 6. On both occasions, the source showed an unabsorbed 0.5-10 keV luminosity of ~2E40 erg/s (assuming a distance of 3.4Mpc) and a soft spectrum apparently represented by a multi-color disk model with an innermost disk temperature of 1.3-1.5 keV. Adding a power-law model further improved the fit. However, as previously reported, the high luminosity cannot be reconciled with the high disk temperature within a framework of the standard accretion disk radiating at a sub-Eddington luminosity. Therefore, we modified the multi-color disk model, and allowed the local disk temperature to scale as r^(-p) on the distance r from the black hole, with p being a free parameter. We then found that the XMM-Newton and the ASCA spectra can be both reproduced successfully with p~0.6 and the innermost disk temperature of 1.4-1.8 keV. These flatter temperature profiles suggest deviation from the standard Shakura-Sunyaev disk, and are consistent with predictions of a slim disk model.

Methane band photometry of the faded South Equatorial Belt of Jupiter

A preliminary analysis of the limb darkening curves along the unusually faint Jovian South Equatorial Belt (SEB), observed by present authors early 1990 using a CCD camera mounted on the 188 cm reflector (F/4.9 Newton focus) of the Okayama Astrophysical Observatory, is presented : three limb-darkening curves extracted from the CCD images obtained in two strong methane bands at 0.725 and 0.890 μm plus one nearby continuum region (0.750 μm) have been compared with the theoretical computations taking into account the effect of multiple light scattering

Rational approximation formula for Chandrasekhar’s H-function for isotropic scattering

In this work, we first establish a simple procedure to obtain with 11-figure accuracy the values of Chandrasekhar’s H-function for isotropic scattering using a closed-form integral representation and the Gauss-Legendre quadrature. Based on the numerical values of the function produced by this method for various combinations of ϖ0, the single scattering albedo, and μ, the cosine of the zenith angle θ of the direction of radiation emergent from or incident upon a semi-infinite scattering-absorbing medium, we propose a rational approximation formula with μ1/4 and

Spatial periodicity of galaxy number counts, CMB anisotropy, and SNIa Hubble diagram based on the universe accompanied by a non-minimally coupled scalar field

\sqrt{1-\varpi_{0}}

A change of upper cloud structure in Jupiter's South Equatorial Belt during the 1989–1990 event

as the independent variables. This allows us to reproduce the correct values of H(ϖ0,μ) within a relative error of 2.1×10−5 without recourse to any iterative procedure or root-finding process.

CONSTRAINTS ON A-DECAYING COSMOLOGY FROM OBSERVATIONAL POINT OF VIEW

We have succeeded in establishing a cosmological model with a non-minimally coupled scalar field φ that can account not only for the spatial periodicity or the picket-fence structure exhibited by the galaxy N-z relation of the 2dF survey but also for the spatial power spectrum of the cosmic microwave background radiation (CMB) temperature anisotropy observed by the WMAP satellite. The Hubble diagram of our model also compares well with the observation of Type Ia supernovae. The scalar field of our model universe starts from an extremely small value at around the nucleosynthesis epoch, remains in that state for sufficiently long periods, allowing sufficient time for the CMB temperature anisotropy to form, and then starts to grow in magnitude at the redshift z of ∼1, followed by a damping oscillation which is required to reproduce the observed picket-fence structure of the N-z relation. To realize such behavior of the scalar field, we have found it necessary to introduce a new form of potential V(φ)∝φ2exp (−qφ2), with q being a constant. Through this parameter q, we can control the epoch at which the scalar field starts growing.

Discovery of a Compact X-Ray Source in the LMC Supernova Remnant N23 with Chandra

We have analyzed two data sets of Jupiters limb darkening taken before (March 1990) and after (March 1991) a South Equatorial Belt (SEB) disturbance. The vertical aerosol structure has been determined for the SEB, the Equatorial Zone (EZ), and the North Equatorial Belt (NEB). We find that all regions can be well represented with a two-cloud layer model, with slightly higher NH3-cloud top altitude in the EZ than in the two belts. The cloud single-scattering albedos (determined within ±0.003) show little difference in the EZ (from 0.9956 to 0.9952) and the NEB (from 0.9925 to 0.9926) during a 1-year period, while a relatively larger decrease is found in the SEB from 0.9975 to 0.9957, indicating the recovery of the belt through the disturbance. The NH3-cloud top altitude in the SEB shows the most prominent change, lower in 1990 and higher in 1991. We suggest that the brightening and the darkening of the SEB may originate not only from the changes of but also from changes of the ammonia condensation level in the atmosphere, probably due to a decrease of the tropospheric temperature and/or an increase of the ammonia vapor.

Galaxy merging and number vs. apparent magnitude relation for the universe with a time-decaying cosmological term

To constrain the values of the model parameters for the cosmological models involving the time-decaying term, we have computed sets of theoretical predictions for the N-m relation of galaxies as well as the CMB angular power spectrum: three types of variation, viz., , and are thereby assumed following Overduin & Cooperstock (1998), although we concentrate here on the discussion of the results obtained from the first type. Our results for the N-m relation indicate that the observed excess of the galaxy counts N in the faint region beyond the blue apparent magnitude 24 can be reasonably well accounted for with the value of in the range between 0.2 and 1. Furthermore, a comparison of our computational results of the CMB spectra with the observational data shows that the models with a mild degree of the term decay, viz., with the value of 0.4, are favorable. In this case, the age of our universe turns out to be larger than or equal to 14 Gyr, the lower limit inferred from some Uranium datings.