Suzaku investigation into the nature of the nearest ultraluminous X-ray source, M33 X-8

The X-ray spectrum of the nearest ultraluminous X-ray source, M33 X-8, obtained by Suzaku during 2010 January 11 -- 13, was closely analyzed to examine its nature. It is, by far, the only data with the highest signal statistic in 0.4 -- 10 keV range. Despite being able to reproduce the X-ray spectrum, Comptonization of the disk photons failed to give a physically meaningful solution. A modified version of the multi-color disk model, in which the dependence of the disk temperature on the radius is described as r^(-p) with p being a free parameter, can also approximate the spectrum. From this model, the innermost disk temperature and bolometric luminosity were obtained as T_in = 2.00-0.05+0.06 keV and L_disk = 1.36 x 10^39 (cos i)^(-1) ergs/s, respectively, where i is the disk inclination. A small temperature gradient of p = 0.535-0.005+0.004, together with the high disk temperature, is regarded as the signatures of the slim accretion disk model, suggesting that M33 X-8 was accreting at high mass accretion rate. With a correction factor for the slim disk taken into account, the innermost disk radius, R_in =81.9-6.5+5.9 (cos i)^(-0.5) km, corresponds to the black hole mass of M \sim 10 M_sun (cos i)^(-0.5). Accordingly, the bolometric disk luminosity is estimated to be about 80 (cos i)^(-0.5)% of the Eddington limit. A numerically calculated slim disk spectrum was found to reach a similar result. Thus, the extremely super-Eddington luminosity is not required to explain the nature of M33 X-8. This conclusion is utilized to argue for the existence of intermediate mass black holes with M > 100 M_sun radiating at the sub/trans-Eddington luminosity, among ultraluminous X-ray sources with L_disk > 10^(40) ergs/s.Comment: 10 pages, 4 figures, PASJ accepte

ASCA Observations of Two Ultra-Luminous Compact X-Ray Sources in the Edge-on Spiral Galaxy NGC 4565

The edge-on spiral galaxy NGC 4565 was observed for $\sim$ 35 ks with ASCA in the 0.5-10 keV energy band. The X-ray emission was dominated by two bright sources, which can be identified with two point-like X-ray sources seen in the ROSAT HRI image. The observed 0.5-10 keV fluxes of these sources, $1.7 \times 10^{-12} erg/s cm^{-2}$ and $0.7 \times 10^{-12}erg/s cm^{-2}$, %$1.66 \times 10^{-12} erg/s cm^{-2}$ %$0.66 \times 10^{-12} erg/s cm^{-2}$ imply bolometric luminosities of $1.0\times 10^{40} erg/s$ and $4 \times 10^{39} erg/s$, respectively. They exhibit similar spectra, which can be explained by emission from optically thick accretion disks with the inner disk temperature of 1.4-1.6 keV. One of them, coincident in position with the nucleus, shows too low absorption to be the active nucleus seen through the galaxy disk. Their spectra and high luminosities suggest that they are both mass accreting black hole binaries. However the black-hole mass required by the Eddington limit is rather high ($\geq 50 M_{\odot}$), and the observed disk temperature is too high to be compatible with the high black-hole mass. Several attempts are made to solve these problesms.Comment: 20page

X-Ray Spectra of the Narrow-Line Seyfert 1 Galaxy Ton S180 in Comparison with Galactic Black Holes

An analysis was made of 0.3-15 keV X-ray spectra of a Narrow-Line Seyfert 1 Galaxy, Ton S180, using archival data from ASCA, RXTE, and XMM-Newton. At energies above 2.5 keV, a power-law with a photon index of ~ 2.3 successfully and consistently reproduced the spectra from all of these observatories. Assuming this power-law component to extend toward lower energies, a soft excess, which is one of the most remarkable features of Narrow-Line Seyfert 1 Galaxies, is explained by another power-law multiplied by a thermal cutoff at ~ 0.4 keV. Some similarities have been observed between this object and Galactic black hole binaries in very high state, the latter being realized under high accretion rates. Attempts have been made to interpret the soft excess in terms of Comptonization of the disk photons by an electron cloud surrounding the accretion disk, like BHBs in a very high state.Comment: 7 pages, 7 figure

Memory Association in Place Making: A review

AbstractPeople experience present world that is causally connected physically and mentally with past events and objects. This study is to present a synthesis of literature studies from 1990 to 2010 with relation to memory association in place making. Aspects taken into consideration include methodological issue and factor used within the city centre from the person memory and perceptions, followed by the associations between place and memory. In summary, one's memory and perception of the environment are shaped by three components; role of event, history and monument remembrance of a place that enables us to perceive a place through memory association

Comparative study of planning history, spatial development and sociological significance of the back alley in Yangon and Singapore

A comparison of two similar types of back alley spaces: Back Drainage Space (BDS) in Yangon and Back-lane in Singapore, is conducted to find out if there are any relationships between their spatial development and lessons that can be learned from the precedent case in Singapore. Commonalities and differences of the back alley are identified by comparing the historical urban context of their formation and development in British colonial cities. The findings suggest that the back alley spaces in both cities, despite divergent circumstances and development after independence, possess common traits as interstitial space between public and private, with a unique way of spatial management based on informal, mutual agreement, which suggests some useful ideas when considering the role of these spaces in the redevelopment of Yangon in the near future

Disc corona radii and QPO frequencies in black hole binaries: testing Lense– Thirring precession origin

Stellar-mass black hole binary systems in the luminous X-ray states show a strong quasi-periodic oscillation (QPO) in their Comptonized emission. The frequency of this feature correlates with the ratio of a disc to Comptonized emission rather than with total luminosity. Hence, it changes dramatically during spectral transitions between the hard and soft states. Its amplitude is also strongest in these intermediate states, making them an important test of QPO models. However, these have complex spectra which generally require a disc and two separate Comptonization components, making it difficult to uniquely derive the spectral parameters. We build a new energy-conserving model of the accretion flow, SSSED model, which assumes a fixed radial emissivity but with a changing emission mechanism. This is similar to the AGNSED model in XSPEC but tuned to be more suitable for stellar mass black holes. It uses a combination of the disc luminosity and temperature to constrain the inner radius of the (colour temperature corrected) blackbody disc, separating this from the more complex Comptonization spectra emitted inwards of this radius. We show a pilot study of this model fit to hundreds of RXTE spectra of the black hole binary XTE J1550 − 564. We show that the derived disc radius tightly anticorrelates with the central frequencies of the low-frequency QPO detected in the same observations. The relation is consistent with the quantitative predictions of Lense–Thirring precession of the entire inner Comptonization regions for the assumed system parameters. This supports the scenario that low-frequency QPOs are caused by Lense–Thirring precession