bluuebunny/crossref_metadata_2025 huggingface dataset:
A Time-Variable X-Ray Echo: Indications of a Past Flare of the Galactic-Center Black Hole
Authors: Koyama Katsuji , Inui Tatsuya , Matsumoto Hironori , Tsuru Takeshi Go
Published: March 2014

A time-variability study of the neutral iron line flux at 6.40keV in the Sgr B2 region from data of Suzaku and Chandra is presented. The highly ionized iron line at 6.68keV is due to Galactic Center Diffuse X-rays, and is thus time invariable. By comparing the 6.68keV and 6.40keV line fluxes, we found that the 6.40keV flux from the Sgr B2 complex region is time variable; particularly the giant molecular cloud M 0.66$-$0.02, known as “Sgr B2 cloud” is highly variable. The variability of the 6.40keV line in intensity and spatial distribution strongly supports the scenario that the molecular clouds in the Sgr B2 region are X-ray Reflection Nebulae irradiated by the Galactic Center black hole Sgr A$^*$.
Detection of a Rare Supersoft Outburst Event during a Suzaku Observation of 1E0102.2$-$7219
Authors: Takei Dai , Tsujimoto Masahiro , Kitamoto Shunji , Morii Mikio , Ebisawa Ken , Maeda Yoshitomo , Miller Eric D.
Published: March 2014

We report on the detection of a transient X-ray source toward the Small Magellanic Cloud (SMC) using the X-ray Imaging Spectrometer (XIS) on board the Suzaku telescope. The source was detected at the edge of the XIS image during a routine observation of the calibration source 1E0102.2$-$7219, a supernova remnant in the SMC. We constrained the source position using ray-tracing simulations. No such transient source was found at the position in the other Suzaku observations, nor in all of the available archived images of other X-ray missions for the last $\sim$28 years. The XIS spectrum can be explained by a single blackbody with a temperature of $\sim$72 eV, and an interstellar extinction of $\sim$4.9$\times$10$^{20}$ H atoms cm$^{-2}$, consistent with the value to the SMC. An additional absorption edge at $\sim$0.74 keV was also confirmed, which is presumably due to absorption by helium-like oxygen ions. Assuming that the source is at the distance of the SMC, the X-ray luminosity in the 0.2-2.0 keV band is $\sim$10$^{37}$ erg s$^{-1}$ and the radius of the source is $\sim$10$^{8}$ cm. The XIS light curve shows about a two-fold decline in X-ray flux during the 24 ks observation. Together with the archived data, the X-ray flux in the burst is at least three-orders of magnitude brighter than the undetected quiescent level. All of these properties are often seen among supersoft sources (SSSs). We conclude that the transient source is another example of SSS in the SMC.
Discovery of a Bright Transient Ultraluminous X-Ray Source, Suzaku J1305–4931 in NGC4945
Authors: Isobe Naoki , Kubota Aya , Makishima Kazuo , Gandhi Poshak , Griffiths Richard E. , Dewangan Gulab C. , Itoh Takeshi , Mizuno Tsunefumi
Published: March 2014

An X-ray source, Suzaku J1305$-$4931, was discovered in the south-west arm of a nearby Seyfert II galaxy, NGC4945, at 0.5-10keV flux of $2.2 \times 10^{-12}$ergcm$^{-2}$s$^{-1}$ during a Suzaku observation conducted on 2006 January 15-17. It was undetectable in a shorter observation on 2005 August 22-23, with an upper limit of $1.7 \times 10^{-14}$ergcm$^{-2}$s$^{-1}$. At a distance of 3.7Mpc, the bolometric luminosity of the source became $L_{\rm bol} = 4.4 \times 10^{39} \alpha$ergs$^{-1}$, where $\alpha = ({\rm\cos} 60^\circ \!/ \cos i)$ and $i$ is the disk inclination. The time-averaged X-ray spectrum of the source is described by a multi-color disk model, with an innermost disk temperature of $T_{\rm in} = 1.69_{-0.05}^{+0.06}$keV. It varied by a factor of $2$ in intensity, following a clear correlation of $L_{\rm bol} \propto T_{\rm in}^4$. The innermost disk radius is inferred to stay constant at $R_{\rm in} = 79_{-3.9}^{+4.0} \alpha^{1/2}$ km, suggesting the presence of a standard accretion disk. Relating $R_{\rm in}$ with the last stable orbit around a non-rotating black hole yields a rather low black-hole mass, $\sim 9 \alpha^{1/2}$ solar masses, which would imply that the source is shining at a considerable super-Eddington luminosity. These results can be better interpreted by invoking sub-Eddington emission from a rapidly spinning black hole with 20-130 solar masses.
In-Orbit Timing Calibration of the Hard X-Ray Detector on Board Suzaku
Authors: Terada Yukikatsu , Enoto Teruaki , Miyawaki Ryouhei , Ishisaki Yoshitaka , Dotani Tadayasu , Ebisawa Ken , Ozaki Masanobu , Ueda Yoshihiro , Kuiper Lucien , Endo Manabu , Fukazawa Yasushi , Kamae Tsuneyoshi , Kawaharada Madoka , Kokubun Motohide , Kuroda Yoshikatsu , Makishima Kazuo , Masukawa Kazunori , Mizuno Tsunefumi , Murakami Toshio , Nakazawa Kazuhiro , Nakajima Atsushi , Nomach Masaharu , Shibayama Naoki , Takahashi Tadayuki , Takahashi Hiromitsu , Tashiro Makoto S. , Tamagawa Toru , Watanabe Shin , Yamaguchi Makio , Yamaoka Kazutaka , Yonetoku Daisuke
Published: March 2014

The hard X-ray detector (HXD) aboard the X-ray satellite Suzaku is designed to have a good timing capability with a 61$\mu$s time resolution. In addition to detailed descriptions of the HXD timing system, results of in-orbit timing calibration and the performance of the HXD are summarized. The relative accuracy of time measurements of the HXD event was confirmed to have an accuracy of $1.9\times 10^{-9}$s s$^{-1}$ per day, and the absolute timing was confirmed to be accurate to 360$\mu$s or better. The results were achieved mainly through observations of the Crab pulsar, including simultaneous ones with RXTE, INTEGRAL, and Swift.
Suzaku Observation of the Metallicity in the Hot Interstellar Medium of the Isolated Elliptical Galaxy NGC 720
Authors: Tawara Yuzuru , Matsumoto Chiho , Tozuka Miyako , Fukazawa Yasushi , Matsushita Kyoko , Anabuki Naohisa
Published: March 2014

The metal abundances in the interstellar medium of the isolated elliptical galaxy NGC 720 were studied with the CCD X-ray Imaging Spectrometer (XIS) aboard the Suzaku satellite. The high detection efficiency along with the excellent spectral resolution of the XIS allowed the K-shell lines of O and Mg to be clearly resolved, and the abundances of O, Ne, Mg, Si, and Fe to be measured with good accuracy for the region within a 3$'$ radius of NGC 720. The abundances of O and Mg were well determined to be 0.4 and 0.5 solar respectively, meaning stellar metallicity of mass-losing stars in NGC 720 was also well determined. The abundance of Fe was determined to be about 0.7 solar, while the O$/$Fe, Ne$/$Fe abundance ratios were found to be about 0.5 and Mg$/$Fe, Si$/$Fe were found to be 0.7 in solar units. Relative errors of 30% for the O$/$Fe, Ne$/$Fe, Mg$/$Fe abundance ratios are the lowest among isolated elliptical galaxies so far observed. The higher abundance of Fe than those of O, Ne, and Mg supplied by stellar mass loss indicates that iron is enhanced by SN Ia in NGC 720. These abundance ratios are consistent with those in the ISM of NGC 1399, NGC 1404, and in the ICM of the Fornax cluster observed with Suzaku.
Suzaku Observations of AWM 7 Cluster of Galaxies: Temperatures, Abundances, and Bulk Motions
Authors: Sato Kosuke , Matsushita Kyoko , Ishisaki Yoshitaka , Yamasaki Noriko Y. , Ishida Manabu , Sasaki Shin , Ohashi Takaya
Published: March 2014

We carried out 3 observations of the cluster of galaxies AWM 7, for the central region and $20'$-east and $20'$-west offset regions, with Suzaku. Temperature and abundance profiles were measured out to 27$'\simeq$570$\;h_{70}^{-1}$kpc, which corresponded to $\sim$0.35$r_{180}$. The temperature of the intra-cluster medium (ICM) slightly decreased from 3.8keV at the center to 3.4keV in the $\sim$0.35$r_{180}$ region, indicating a flatter profile than those in other nearby clusters. The abundance ratio of Si to Fe was almost constant in our observations, while the Mg-to-Fe ratio increased with radius from the cluster center. The O to Fe ratio in the west region showed an increase with radius, while that in the east region was almost flat, though the errors were relatively large. These features suggest that the enrichment process is significantly different between products of type II supernovae (O and Mg) and those by type Ia supernovae (Si and Fe). We also examined the positional shift of the central energy of a He-like Fe-K$\alpha$ line, in search of possible rotation of the ICM. The 90% upper limit for the line-of-sight velocity difference was derived to be $\Delta v \lesssim 2000$kms$^{-1}$, suggesting that the ellipticity of AWM 7 is rather caused by a recent directional infall of gas along the large-scale filament.
Restoring the Suzaku Source Position Accuracy and Point-Spread function
Authors: Uchiyama Yasunobu , Maeda Yoshitomo , Ebara Masatoshi , Fujimoto Ryuichi , Ishisaki Yoshitaka , Ishida Manabu , Iizuka Ryo , Ushio Masayoshi , Inoue Hirohiko , Okada Shunsaku , Mori Hideyuki , Ozaki Masanobu
Published: March 2014

We present an empirical correction of sky coordinates of X-ray photons obtained with the X-ray Imaging Spectrometer (XIS) aboard the Suzaku satellite to improve the source position accuracy and restore the point-spread function (PSF). The XIS images are known to have an uncertainty in position of up to $1′$, and to show considerable degradations of the PSF. These problems are caused by a drifting of the satellite attitude due to thermal distortion of the side panel #7, where the attitude control system is mounted. We found that the position error averaged over a pointing observation can be largely reduced by using the relation between the deviation of the source position in the DETX direction and the ecliptic latitude of the pointing target. We parameterized the wobbling of the source position synchronized with the 96-minute satellite orbital period with temperatures of onboard radiators and elapsed time since the night-day transition of the spacecraft. We developed software, aeattcor, to correct the image drift using these parameters, and applied it to 27 point-source images taken in the Suzaku initial science-operation phase. We show that the radius of the 90% error circle of the source position was reduced to $19′$ and the PSF was sharpened. These improvements have enhanced the scientific capability of the Suzaku XIS.
Identification of the Exciting Source of CO Outflow in the Star-Formation Region GGD 12-15
Authors: Sato Yaeko , Tamura Motohide , Kandori Ryo , Nakajima Yasushi , Kusakabe Nobuhiko , Hashimoto Jun , Kudo Tomoyuki , Saito Hiroo , Kitamura Yoshimi , Kawamura Akiko , Nishiyama Shogo , Sunada Kazuyoshi , Ueno Munetaka
Published: March 2014

We present results of near-infrared imaging polarimetry of the GGD 12-15 region with the IRSF 1.4m telescope and the SIRIUS camera/SIRPOL polarimeter and mid-infrared imaging with the AKARI telescope and the Infra-Red Camera (IRC). Two infrared sources, IRS 9E and IRS 9M near an H$_{\mathrm{2}}$O maser source situated on both sides around a VLA source (VLA 7), have been believed to be two bipolar lobes associated with a massive CO outflow. However, our polarimetric observations have revealed that IRS 9E is stellar-like, and not part of a reflection nebula. Furthermore, IRS 9M itself is not stellar, but a bipolar nebula, extending north-south. Both polarization vector maps and polarized intensity images show that the true illuminating source, IRS 9Mc, is not resolved, and is situated near the peak of the intensity image. Our astrometry also indicates that the position of IRS 9Mc does not coincide with the water maser position, but rather coincides with the VLA 7 position. We suggest that the unresolved illuminating source IRS 9Mc is the true exciting source of the CO outflow, corresponding to a mid-infrared source detected by AKARI with a lower spatial resolution. Fluxes of the newly identified source at 1 to 11$\mu$m were derived by separating contributions from nearby infrared sources; the spectral energy distribution is consistent with that of a class I/0 source.
Radial Velocity Search for Extrasolar Planets in Visual Binary Systems
Authors: Toyota Eri , Itoh Yoichi , Ishiguma Shinichiro , Urakawa Seitaro , Murata Daisuke , Oasa Yumiko , Matsuyama Hiroko , Funayama Hitoshi , Sato Bun’ei , Mukai Tadashi
Published: March 2014

We searched for extrasolar planets in visual binary systems using precise Doppler-shift measurements taken over a period of 4 yr. Using the HIgh Dispersion Echelle Spectrograph (HIDES) equipped on the Okayama Astrophysical Observatory (OAO) 188 cm reflector, we achieved a radial-velocity precision of about 10 ms$^{-1}$. We monitored both primary and secondary stars of six visual binary systems, and primary stars of three visual binaries. Among them, three objects show large radial-velocity variations. ADS 7311 A exhibits a decreasing trend in radial velocity with a best-fit slope of $-$30 ms$^{-1}$yr$^{-1}$, while 31 Dra A shows an increasing trend with a best-fit slope of $+$220 ms$^{-1}$yr$^{-1}$. These long-term trends in radial velocity may be attributable to unseen companions. BDS 10966 A shows a periodic variation in radial velocity with a period of 840 d and a semiamplitude of about 120 ms$^{-1}$, implying an association of a planetary-mass companion, rotational modulation, or nonradial oscillation of the photosphere. In any case, we should mention the nonassociation between BDS 10966 A and B, suggested by the different proper motions, radial velocities, and Hipparcos parallaxes.
Nobeyama Millimeter Array Observations of the Nuclear Starburst of M 83: A GMA Scale Correlation between Dense Gas Fraction and Star Formation Efficiency
Authors: Muraoka Kazuyuki , Kohno Kotaro , Tosaki Tomoka , Kuno Nario , Nakanishi Kouichiro , Handa Toshihiro , Sorai Kazuo , Ishizuki Sumio , Okuda Takeshi
Published: March 2014

We present aperture synthesis high-resolution ($\sim$7$^{\prime\prime}$$\times$ 3$^{\prime\prime}$) observations in CO ($J$$=$ 1–0), HCN ($J$$=$ 1–0), and 95 GHz continuum emission toward the central ($\sim$1.5 kpc) region of the nearby barred spiral galaxy M 83 with the Nobeyama Millimeter Array. Our high-resolution CO ($J$$=$ 1–0) mosaic map depicts the presence of molecular ridges along the leading sides of the stellar bar and a nuclear twin peak structure, whereas the distributions of the HCN ($J$$=$ 1–0) emission that traces dense molecular gas ($n_{\rm H_2}$$\gt$ a few $\times$ 10$^{4}$cm$^{-3}$) and the 95 GHz continuum emission that traces massive starburst show nuclear single-peak structures. The HCN ($J$$=$ 1–0) and the 95 GHz continuum peaks are not spatially coincident with the optical starburst regions traced by the HST $V$-band image, suggesting the existence of deeply buried ongoing starburst due to strong extinction ($A_{V}$$\sim$ 5 mag) near these peaks. We found that the HCN ($J$$=$ 1–0)$/$CO ($J$$=$ 1–0) intensity ratio, $R_{\rm HCN/CO}$, correlates well with the extinction-corrected star formation efficiency (SFE) in the central region of M 83 at a resolution of 7$^{\prime\prime}$.5 ($\sim$160 pc). This suggests that SFE is controlled by a dense gas fraction traced by $R_{\rm HCN/CO}$, even on a Giant Molecular cloud Association (GMA) scale. Moreover, the correlation between $R_{\rm HCN/CO}$ and SFE in M 83 seems to be almost coincident with that among the Gao and Solomon (2004 a, ApJ, 606, 271) sample. This suggests that the correlation between $R_{\rm HCN/CO}$ and the SFE on a GMA ($\sim$160 pc) scale found in M 83 is the origin of the global correlation on a few kpc scale shown by Gao and Solomon (2004a).
Time-Evolution of Peak Energy and Luminosity Relation within Pulses for GRB 061007: Probing Fireball Dynamics
Authors: Ohno Masanori , Ioka Kunihito , Yamaoka Kazutaka , Tashiro Makoto , Fukazawa Yasushi , Nakagawa Yujin E.
Published: March 2014

We performed a time-resolved spectral analysis of a bright, long gamma-ray burst GRB 061007 using Suzaku/WAM and Swift/BAT. Because of the large effective area of the WAM, we can investigate the time evolution of the spectral peak energy $E^{\rm t}_{ \rm peak}$ and the luminosity $L^{\rm t}_{\rm iso}$ with 1-s time resolution, and we find that the time-resolved pulses also satisfy the $E_{\rm peak}$–$L_{\rm iso}$ relation, which was found for the time-averaged spectra of other bursts, suggesting the same physical conditions in each pulse. Furthermore, the initial rising phase of each pulse could be an outlier of this relation with higher $E^{\rm t}_{ \rm peak}$ value by a factor of 2. This difference could suggest that the fireball radius expands by a factor of 2–4 and/or bulk Lorentz factor of the fireball is decelerated by a factor of $\sim$4 during the initial phase, providing a new probe of fireball dynamics in real time.
Unified Rotation Curve of the Galaxy — Decomposition into de Vaucouleurs Bulge, Disk, Dark Halo, and the 9-kpc Rotation Dip —
Authors: Sofue Yoshiaki , Honma Mareki , Omodaka Toshihiro
Published: March 2014

We present a unified rotation curve of the Galaxy re-constructed from existing data by re-calculating the distances and velocities for a set of Galactic constants, $R_0$$=$ 8 kpc and $V_0$$=$ 200 km s$^{-1}$. We decomposed it into a bulge with de Vaucouleurs-law profile of half-mass scale radius 0.5 kpc and mass 1.8 $\times$ 10$^{10}M_\odot$, an exponential disk of scale radius 3.5 kpc and 6.5 $\times$ 10$^{10}M_\odot$, and an isothermal dark halo of terminal velocity 200 km s$^{-1}$. A $r^{1/4}$-law fit was obtained for the first time for the Milky Way’s rotation curve. After fitting by these fundamental structures, two local minima, or dips, of the rotation velocity are prominent at radii 3 and 9 kpc. The 3-kpc dip is consistent with the observed bar. It is alternatively explained by a massive ring with the density maximum at a radius of 4 kpc. The 9-kpc dip is clearly exhibited as the most peculiar feature in the Galactic rotation curve. We explain it by a massive ring of amplitude as large as 0.3 to 0.4-times the disk density with the density peak at a radius of 11 kpc. This great ring may be related to the Perseus arm, while no peculiar feature of HI-gas is associated.
A Chain of Dark Clouds in Projection Against the Galactic Center
Authors: Nagayama Takahiro , Sato Shuji , Nishiyama Yuka , Murai Shogo , Nagata Tetsuya , Hatano Hirofumi , Kurita Mikio , Tamura Motohide , Nakajima Yasushi , Sugitani Koji , Oka Tomoharu , Sofue Yoshiaki
Published: March 2014

In a $J$, $H$, and $K_{\rm S}$ band survey of the Galactic center region over an area of 2${}^\circ$$\times$ 5${}^\circ$, we have found many dark clouds, among which a distinguished chain of dark clouds can be identified with a quiescent CO cloud. The distances of the clouds are estimated to be 3.2–4.2 kpc, corresponding to the Norma arm, by our new method for determining the distances to dark clouds using the cumulative number of stars against the $J-K_{\rm S}$ color. By adopting these estimated distances, the size and total mass of the cloud are estimated to be $\sim$70 pc in length and 6 $\times$ 10$^4$$M_\odot$, respectively. Three compact HII regions exist in the cloud, indicating that star-forming activities are going on at the cores of the quiescent CO cloud on the spiral arm.
Diffuse 18  $\mu$m Emission around TYC 3159-6-1 Discovered by the AKARI MIR All-Sky Survey
Authors: Takita Satoshi , Kitamura Yoshimi , Kataza Hirokazu , Ishihara Daisuke , Ueno Munetaka , Fujiwara Hideaki , Ikeda Norio , Kawamura Akiko , Murakami Hiroshi , Okamoto Yoshiko K. , Onaka Takashi , Oyabu Shinki , Sakon Itsuki , Takahashi Hidenori
Published: March 2014

We report on observations of the mysterious object TYC 3159-6-1 located toward the Cygnus X region. It shows interesting characteristics in the AKARI mid-infrared All-Sky Survey. The central star is clearly detected as a point source at 9 $\mu$m, while no point-like source, but a large shell-like structure is seen around the source at 18 $\mu$m. The optical spectrum indicates the presence of the weak H$\alpha$emission on the red smooth continuum, whereas the mid-infrared $N$band spectrum shows neither excess emission nor significant silicate absorption. Interferometric continuum observations at 104 GHz do not show any appreciable peak at the position of the star. On the basis of these observations, we investigate three possibilities of concerning the nature of TYC 3159-6-1: a nearby young stellar object, a heavily extincted high-mass star, and an asymptotic giant branch (AGB) star with a detached shell. We conclude that none of these cases can account for the observations consistently, and the nature of TYC 3159-6-1 remains a mystery.
Relativistic Variable Eddington Factor in a Relativistic Plane-Parallel Flow
Authors: Fukue Jun
Published: March 2014

We examine the behavior of the variable Eddington factor for a relativistically moving radiative flow in the vertical direction. We adopt the “one-tau photo-oval” approximation in the comoving frame. Namely, the comoving observer sees radiation coming from a closed surface where the optical depth measured from the observer is unity; such a surface is called a one-tau photo-oval. In general, the radiative intensity emitted by the photo-oval is non-uniform and anisotropic. Furthermore, the photo-oval surface has a relative velocity with respect to the comoving observer, and therefore the observed intensity suffers from the Doppler effect and aberration. In addition, the background intensity usually depends on the optical depth. All of these introduce anisotropy to the radiation field observed by the comoving observer. As a result, the relativistic Eddington factor, $f$, generally depends on the optical depth $\tau$, the four velocity $u$, and the velocity gradient $du/d\tau$. In the case of a plane-parallel vertical flow, we found that the relativistic variable Eddington factor, $f$, generally decreases as the velocity gradient increases, but it increases as the velocity increases for some cases. When the comoving radiation field is uniform, it is well approximated by $3f \sim 1/$[ $1$$+$ (16$/$15)($-{du}/{\gamma d\tau}$) $+$ ($-{du}/{\gamma d\tau}$)$^{1.6-2}$]. When the radiation field in the inertial frame is uniform, on the other hand, it is expressed as $f$$=$ ($1+3\beta^2$)$/$($3+\beta^2$). These relativistic variable Eddington factors can be used in various relativistic radiatively-driven flows, such as black-hole accretion flows, relativistic astrophysical jets and outflows, and relativistic explosions like gamma-ray bursts.
Dependence of Spectral State Transition and Disk Truncation on Viscosity Parameter $\alpha $
Authors: Qiao Erlin , Liu Bi Fang
Published: March 2014

A wealth of Galactic accreting X-ray binaries has been observed in both the low/hard and high/soft states. The transition between these two states has often been detected. Observations show that the transition luminosity between these two states is different for different sources, ranging from 1% to 4% of the Eddington luminosity $L_{\rm Edd}$. Even for the same source, the transition luminosity at different outbursts can be different. The transition can occur at luminosities from 0.0069 to 0.15 $L_{\rm Edd}$. In order to investigate the underlying physics, we study the influence of viscosity parameter $\alpha $ on the transition luminosity on the basis of the disk-corona model for black holes. We calculate the mass-evaporation rate for a wide range of viscosity parameters such as 0.1 $\le$$\alpha $$\le$ 0.9. Fitting the numerical results, we obtain fitting formulae for both the transition accretion rate and the corresponding radius as a function of $\alpha $. We find that the transition luminosity is very sensitive to the value of $\alpha $, $L/L_{\rm Edd}\propto\alpha^{2.34}$. For 0.1 $\le$$\alpha $$\le$ 0.6, the transition luminosity varies by two orders of magnitude, from 0.001 to 0.2$L_{\rm Edd}$. Comparing with observations, we find that transition luminosity can be fitted by adjusting the value of $\alpha $, and the model-determined values of $\alpha $ are mostly in the range of observationally inferred values. We also investigate the truncation of the disk in the low/hard state for some luminous sources. Our results agree roughly with the observations.
Toward First-Principle Simulations of Galaxy Formation: II. Shock-Induced Starburst at a Collision Interface during the First Encounter of Interacting Galaxies
Authors: Saitoh Takayuki R. , Daisaka Hiroshi , Kokubo Eiichiro , Makino Junichiro , Okamoto Takashi , Tomisaka Kohji , Wada Keiichi , Yoshida Naoki
Published: March 2014

We investigated the evolution of interacting disk galaxies using high-resolution $N$-body/SPH simulations, while taking into account the multiphase nature of the interstellar medium. In our high-resolution simulations, a large-scale starburst occurred naturally at the collision interface between two gas disks at the first encounter, resulting in the formation of star clusters. This is consistent with observations of interacting galaxies. The probability distribution function (PDF) of the gas density showed a clear change during the galaxy–galaxy encounter. The compression of gas at the collision interface between the gas disks first appears as an excess at $n_{\rm H}$$\sim$ 10 cm$^{-3}$ in the PDF, and then it moves to higher densities ($n_{\rm H}$$\gtrsim$ 100 cm$^{-3}$) in a few times 10$^7$ years, where starburst takes place. After the starburst, the PDF goes back to a quasi-steady state. These results give a simple picture of starburst phenomena in galaxy–galaxy encounters.
Abundance Inhomogeneity in the Northern Rim of the Cygnus Loop
Authors: Uchida Hiroyuki , Tsunemi Hiroshi , Katsuda Satoru , Kimura Masashi , Kosugi Hiroko , Takahashi Hiroaki
Published: March 2014

We observed the northern rim of the Cygnus Loop with the Suzaku observatory in 5 pointings (P21–P25). From a spatially resolved analysis, all of the spectra were well fitted by a single component of the non-equilibrium ionization plasma model. From the best-fit parameters, we found that the abundances of the heavy elements are significantly lower than the solar values, except for those at the outermost edge in P21 and P22. The origin of the depleted metal abundances is still unclear, while such deficiencies have been reported from many other rim observations of the Loop. To explain these depletions at the rim regions, we considered several possibilities. The effects of resonance-line-scattering and grain condensation lower the values of the abundances. However, these are not sufficient to account for the observed abundance depletion.
Black-Hole Winds with a Variable Eddington Factor
Authors: Akizuki Chizuru , Fukue Jun
Published: March 2014

We solve one-dimentinal spherically symmetric, optically thick black-hole winds under general relativity with the help of a variable Eddington factor, $f$($\tau$, $\beta$), where $\tau$ is the optical depth and $\beta$ is the flow velocity normalized by the speed of light. Relativistic radiation hydrodynamics under the moment formalism has several complex problems, such as a closure relation. Conventional relativistic moment equations closed with the traditional Eddington approximation in the comoving frame have a singularity, beyond which the flow cannot be accelerated. In order to avoid such a pathological behavior inherent in the relativistic moment formalism, we use a variable Eddington factor that depends on the flow velocity as well as the optical depth, for the case of spherically symmetric flow. We find luminous winds that can be accelerated by radiation pressure from a close vicinity to a black hole up to nearly the speed of light in a general-relativistic gravitational field.
Search for Remnant Clouds Associated with the TW Hya Association
Authors: Tachihara Kengo , Neuhäuser Ralph , Fukui Yasuo
Published: March 2014

We report on a search for the parental molecular clouds of the TW Hya association (TWA), using CO emission and NaI absorption lines. TWA is the nearest young ($\sim$50 pc; $\sim$10 Myr) stellar association; yet in spite of its youth there has been no detection of any associated natal molecular gas, as is the case with other typical young clusters. Using infrared maps as a guide, we conducted a CO cloud survey toward a region with a dust extinction of $E$($B-V$) $\gt$ 0.2 mag, or $A_{V}$$\gt$ 0.6 mag. CO emission was detected in the direction of three IR dust clouds, and we rejected one cloud out of the TWA, because no interstellar Na absorption was detected in the nearby Hipparcos stars, implying that it is too distant to relate to the TWA. The two other clouds exhibit only faint and small-scale CO emission. Interstellar NaI absorptions of Hipparcos targets (HIP 57809, HIP 64837, and HIP 64925, at distances of 133, 81, and 101 pc, respectively) by these clouds were also detected. We conclude that only a small fraction of the interstellar matter (ISM) toward the infrared (IR) dust cloud is located at a distance less than 100 pc, which may be all that is left out of the remnant clouds of TWA; the remaining remnant cloud dissipated within the last $\sim$1 Myr. Such a short-dissipation timescale may be due to an external perturbation or kinematic segregation that has a large stellar proper motion relative to the natal cloud.
Modified Slim-Disk Model Based on Radiation-Hydrodynamic Simulation Data: The Conflict between Outflow and Photon Trapping
Authors: Takeuchi Shun , Mineshige Shin , Ohsuga Ken
Published: March 2014

Photon trapping and outflow are two key physics issues associated with supercritical accretion flow. We investigated the conflict between these two processes based on two-dimensional radiation-hydrodynamic (RHD) simulation data, and constructed a simplified (radially) one-dimensional model. Mass loss due to outflow, which is not considered in the slim-disk model, reduces the surface density of the flow, and if very significantly, it can totally suppress the photon-trapping effects. If photon trapping is very significant, conversely, outflow can be suppressed because the radiation-pressure force is reduced. To see what actually occurs, we examined the RHD simulation data and evaluated the accretion and outflow rates as functions of the radius. We have found that the accretion rate monotonically decreases, while the outflow rate increases, as the radius decreases. However, the accretion remains constant at small radii, inside several Schwarzschild radii, since the outflow is suppressed by photon trapping effects. To understand the conflict between the photon trapping and outflow in a simpler way, we modeled the radial distribution of the accretion rate from our simulation data, and built up a new (radially) one-dimensional model, which is similar to the slim-disk model, but incorporates mass loss effects due to the outflow. We find that the surface density (and, hence, the optical depth) is greatly reduced even inside the trapping radius, compared to the case without outflow, whereas the effective temperature distribution hardly changes. That is, the emergent spectra do not sensitively depend on the amount of mass outflow. We conclude that the slim-disk approach is valid for interpreting observations, even if the outflow is taken into account. The observational implications of our findings are briefly discussed in relation to ultra-luminous X-ray sources.
Eruptions of Magnetic Ropes in Two Homologous Solar Events of 2002 June 1 and 2: a Key to Understanding an Enigmatic Flare
Authors: Meshalkina Nataliya S. , Uralov Arkadiy M. , Grechnev Victor V. , Altyntsev Alexander T. , Kashapova Larisa K.
Published: March 2014

The goal of this paper is to understand the drivers, configurations, and scenarios of two similar eruptive events, which occurred in the same solar active region 9973 on 2002 June 1 and 2. The June 2 event was previously studied by Sui, Holman, and Dennis (2006, ApJ, 646, 605; 2008, Adv. Space Res., 41, 976), who concluded that it was challenging for popular flare models. Using multi-spectral data, we analyzed a combination of the two events. Each of the events exhibited an evolving cusp-like feature. We have revealed that these apparent “cusps” were most likely mimicked by twisted magnetic flux ropes, but unlikely to be related to the inverted Y-like magnetic configuration in the standard flare model. The ropes originated inside a funnel-like magnetic domain whose base was bounded by an EUV ring structure, and the top was associated with a coronal null point. The ropes appear to be the major drivers for the events, but their rise was not triggered by reconnection in the coronal null point. We propose a scenario and a three-dimensional scheme for these events in which the filament eruptions and flares were caused by interaction of the ropes.
A Massive Substellar Companion to the Massive Giant HD 119445
Authors: Omiya Masashi , Izumiura Hideyuki , Han Inwoo , Lee Byeong-Cheol , Sato Bun’ei , Kambe Eiji , Kim Kang-Min , Yoon Tae Seog , Yoshida Michitoshi , Masuda Seiji , Toyota Eri , Urakawa Seitaro , Takada-Hidai Masahide
Published: March 2014

We detected a brown dwarf-mass companion around the intermediate-mass giant star HD 119445 (G6III) using the Doppler technique. This discovery is the first result from a Korean$-$Japanese planet search program based on precise radial velocity measurements. The radial velocity of this star exhibits a periodic Keplerian variation with a period, semiamplitude, and eccentricity of 410.2 d, 413.5 ms$^{-1}$, and 0.082, respectively. Adopting a stellar mass of 3.9$M_{\odot}$, we were able to confirm the presence of a massive substellar companion with a semimajor axis of 1.71AU and a minimum mass of 37.6$M_{\mathrm{J}}$, which falls in the middle of the brown dwarf-mass region. This substellar companion is the most massive ever discovered within 3AU of a central intermediate-mass star. The host star also ranks among the most massive stars with substellar companions ever detected by the Doppler technique. This result supports the current view of substellar systems that more massive substellar companions tend to exist around more massive stars, and may further constrain substellar system formation mechanisms.
A Study of Combining Technique of Single-Dish and Interferometer Data: Imaging Simulations and Analysis
Authors: Kurono, Yasutaka , Morita Koh-Ichiro , Kamazaki Takeshi
Published: March 2014

We have investigated a technique of combining single-dish data and interferometer data in the spatial frequency domain, using imaging simulations and analytical considerations. Our study shows that there is an optimum of the relative weights between the visibility data of a single-dish and an interferometer. The quality of the reconstructed combined image achieves the highest values at relative weights where the mean of the difference between the synthesized beam and the CLEAN beam is close to zero. We also examined the ($u$,$v$)-range that can be effectively used for the data combining by considering a blurring effect due to a pointing error. The error in single-dish deconvolution caused by the beam approximation is small with a large diameter of the single-dish aperture. The diameter should be at least 1.7-times larger than the minimum baseline of the interferometer for an amplitude accuracy better than 10%. Furthermore, we derived an estimate of the noise variance in the combined image, which agrees with our simulation results. The noise-added simulations demonstrate that there is a threshold of the noise level of the single-dish image, beyond which a large-scale error is emphasized in the combined image. We should take observation times to make at least the same noise level at the border of the spatial frequency between the single-dish and the interferometer. Although our examinations were assumed to use the 45 m telescope and NMA, our results concerning the required conditions for observations and data processes can be used in a general case of heterogeneous array imaging.
The Origin of an Extended X-Ray Emission Apparently Associated with the Globular Cluster 47 Tucanae
Authors: Yuasa Takayuki , Nakazawa Kazuhiro , Makishima Kazuo
Published: March 2014

Using the Suzaku X-ray Imaging Spectrometer, we performed a 130 ks observation of an extended X-ray emission, which was shown by ROSAT and Chandra observations to apparently associate with the globular cluster 47 Tucanae. The obtained 0.5–6 keV spectrum was successfully fitted with a redshifted thin thermal plasma emission model whose temperature and redshift are 2.2$^{+0.2}_{-0.3} $keV (at the rest frame) and 0.34$ \pm $0.02, respectively. The derived parameters, including the temperature, redshift, and luminosity, indicate that the extended X-ray source is a background cluster of galaxies, and its projected location falls, by chance, on the direction of the proper motion of 47 Tucanae.
Suzaku Observation of the Metallicity in the Interstellar Medium of NGC 4258
Authors: Konami Saori , Sato Kosuke , Matsushita Kyoko , Yamada Shin’ya , Isobe Naoki , Senda Atsushi , Hayato Asami , Gandhi Poshak , Tamagawa Toru , Makishima Kazuo
Published: March 2014

The Suzaku X-ray satellite observed the nearby spiral galaxy NGC 4258 for a total good exposure time of 100 ks. We present an analysis of the Suzaku XIS data, in which we confirm that the 0.5–2 keV spectra of the interstellar medium (ISM) are well-represented by a two-temperature model. The cool and hot ISM temperatures are 0.23 $\pm$ 0.01 and 0.58 $\pm$ 0.01 keV, respectively. Suzaku’s excellent spectral sensitivity has enabled us to measure the metal abundances of O, Ne, Mg, Si, and Fe of the ISM for the first time. The resultant abundance pattern of O, Mg, Si, and Fe is consistent with that of the new solar abundance table of Lodders (2003, ApJ, 591, 1220), rather than Anders and Grevesse (1989, Geochim. Cosmochim. Acta, 53, 197). This suggests that the metal enrichment processes of NGC 4258 and of our Galaxy are similar.
Force-Free Black Hole Magnetospheres
Authors: Okamoto Isao
Published: March 2014

It is argued that a force-free degenerate electrodynamic (FFDE) magnetosphere of a Kerr black hole with 0 $\lt$$\Omega _{\rm F}$$\lt$${\Omega_{\rm H}}$ consists of the outer classical and inner general-relativistic domains. This is described by a simple DC dual-circuit model, with dissipative membranes as two loads at a “force-free infinity surface” (S$_{{\rm ff}\infty }$) with $\omega$$=$ 0 and at a “force-free horizon surface” (S$_{\rm ffH}$) with $\omega$$=$${\Omega_{\rm H}}$, where $\omega$, ${\Omega_{\rm H}}$, and $\Omega _{\rm F}$ are the frame-dragging, the horizon and the field line angular frequencies. It is beneath upper null surface, S$_{\rm N}$, at $\omega$$=$$\Omega _{\rm F}$ between the two domains that dual unipolar batteries (double EMF’s) exist back-to-back, oppositely directed, with a pair-creation gap between. The total energy flux ${\boldsymbol{S}}_E$ is a linear sum of the two fluxes: the hole’s outward spin-down energy flux ${\boldsymbol{S}}_{\rm SD}$ originating at S$_{\rm ffH}$ and the Poynting flux $\boldsymbol{S}_{\rm EM}$ emitted at S$_{\rm N}$ in both the outward and inward directions, with ${\boldsymbol{S}}_E$ being proportional to $\Omega _{\rm F}$, ${\boldsymbol{S}}_{\rm SD}$ to $\omega$ and $\boldsymbol{S}_{\rm EM}$ to ($\Omega _{\rm F}$$-$$\omega$) along each field line. Applying a perturbation method for a split-monopolar field with a spin-parameter $h$$\ll$ 1, the analytic solution of the stream equation is given, and the double eigenvalue problem due to the `criticality condition’ at the outer/inner fast surfaces S$_{\rm oF}$/S$_{\rm iF}$ and the `boundary condition’ at S$_{\rm N}$ is solved to yield the final eigenvalue $\Omega _{\rm F}$, in terms of ${\Omega_{\rm H}}$ and $f_{\rm H}$$=$ 0.5676. The ratio of the output power reaching S$_{{\rm ff}\infty }$ to the dissipation on S$_{\rm ffH}$ is $\epsilon$$=$ 1 $+$ (4$/$5)(1 $-$$f_{\rm H}$) $h^2$.
A Photometric Study of the Near-Contact Binary WY Tauri
Authors: Yang Yuan-Gui
Published: March 2014

CCD photometric observations for the eclipsing binary WY Tauri are firstly presented. Three new minimum timings in 2006 and 2008 have been determined. Using Wilson–Devinney binary code, the photometric solution was simultaneously deduced from $VR$ light curves. Photometric results indicate that WY Tau is a semi-detached binary, whose secondary component fills its Roche lobe. The mass ratio and orbital inclination are $q$$=$ 0.508($\pm$0.006) and $i$$=$ 78${\rlap{\hskip.75pt{^\circ}}\hskip.75pt.\hskip1pt}$0($\pm$0${\rlap{\hskip.75pt{^\circ}}\hskip.75pt.\hskip1pt}$05), respectively. The filling factor of the primary component is 84.9%, indicating that this star is a near-contact binary. Based on all available eclipse timings since 1930, it is found that the ($O-C$) curve may be described by either a long-term period increase or a cyclic variation. The continuous period increase at a rate of $dP/dt$$=$$+$4.65 $\times$ 10$^{-8} $d yr$^{-1}$ may be attributed to mass transferring from the secondary to the primary, identified by the semidetached configuration. With mass transferring, WY Tau may evolve into a contact binary.
GreeM: Massively Parallel TreePM Code for Large Cosmological N-body Simulations
Authors: Ishiyama Tomoaki , Fukushige Toshiyuki , Makino Junichiro
Published: March 2014

In this paper, we describe the implementation and performance of GreeM, a massively parallel TreePM code for large-scale cosmological N-body simulations. GreeM uses a recursive multi-section algorithm for domain decomposition. The size of the domains are adjusted so that the total calculation time of the force becomes the same for all processes. The loss of performance due to non-optimal load balancing is around 4%, even for more than 10$^3$ CPU cores. GreeM runs efficiently on PC clusters and massively-parallel computers, such as a Cray XT4. The measured calculation speed on Cray XT4 is 5 $\times$ 10$^4$ particles per second per CPU core, for the case of an opening angle of $\theta$$=$ 0.5, if the number of particles per CPU core is larger than 10$^6$.
Broad-Band Temporal and Spectral Variation of 36 Active Galactic Nuclei Observed with Suzaku
Authors: Miyazawa Takuya , Haba Yoshito , Kunieda Hideyo
Published: March 2014

36 AGN data observed by Suzaku were compiled to examine the temporal variability in different energy bands covered by soft X-ray imaging systems (XRT $+$ XIS: 0.5–10 keV) and Hard X-ray Detector (HXD: 15–50 keV) aboard Suzaku. Three band light curves were obtained in L (0.5–2 keV), M (2–10 keV), and H (15–50 keV) with a time binning of 5760 s. The L-band flux change was almost proportional to that of the M-band without offsets in most of type-1 AGNs. The slope ($=$$dL/dM$) of the correlation changed by more than a factor of 10 from Seyfert 2 to narrow-line Seyfert 1 galaxies (NLS1). The power-law component can explain the slope of Seyfert 1 galaxies with a typical index, $\Gamma$, of 1.9. For NLS1 s with steeper slopes, an additional soft excess component is needed, whose variation should be proportional to that of the power-law component. It gives a new constraint to models for the soft excess component. The H-band flux change is a linear function of the M-band flux with a significant offset in the H-band. The slope can be explained by the power-law component with an absorption column from 10$^{22{-}24} $cm$^{-2}$. The offset can be attributed to the reflection component, which is stable on a time scale of days.
Energy-Scale Calibration of the Suzaku X-Ray Imaging Spectrometer Using the Checker Flag Charge-Injection Technique in Orbit
Authors: Ozawa Midori , Uchiyama Hideki , Matsumoto Hironori , Nakajima Hiroshi , Koyama Katsuji , Tsuru Takeshi Go , Uchino Masahiro , Uchida Hiroyuki , Hayashida Kiyoshi , Tsunemi Hiroshi , Mori Hideyuki , Bamba Aya , Ozaki Masanobu , Dotani Tadayasu , Kohmura Takayoshi , Ishisaki Yoshitaka , Murakami Hiroshi , Kato Takeshi , Kitazono Takeshi , Kimura Yuki , Ogawa Kazuki , Kawai Shusuke , Mori Koji , Prigozhin Gregory , Kissel Steve , Miller Eric D. , LaMarr Beverly , Bautz Marshall
Published: March 2014

The X-ray Imaging Spectrometer (XIS) aboard the Suzaku satellite is an X-ray CCD camera system that has superior performance, such as a low background, high quantum efficiency, and good energy resolution in the 0.2–12 keV band. Because of radiation damage in orbit, however, the charge-transfer inefficiency (CTI) has increased, and hence the energy scale and resolution of the XIS has been degraded since the launch in 2005 July. The CCD has a charge-injection structure, and the CTI of each column and the pulse-height dependence of the CTI are precisely measured by a checker flag charge-injection (CFCI) technique. Our precise CTI correction improved the energy resolution from 230 eV to 190 eV at 5.9 keV in 2006 December. This paper reports on CTI measurements with the CFCI experiments in orbit. Using the CFCI results, we have implemented the time-dependent energy scale and resolution to the Suzaku calibration database.
Broad-Band Spectrum of the Black Hole Candidate IGR J17497$-$2821 Studied with Suzaku
Authors: Paizis Adamantia , Ebisawa Ken , Takahashi Hiromitsu , Dotani Tadayasu , Kohmura Takayoshi , Kokubun Motohide , Rodriguez Jérôme , Ueda Yoshihiro , Walter Roland , Yamada Shin’ya , Yamaoka Kazutaka , Yuasa Takayuki
Published: March 2014

The broad-band 1–300 keV Suzaku spectrum of IGR J17497$-$2821, the X-ray transient discovered by INTEGRAL in 2006 September, is presented. Suzaku observed IGR J17497$-$2821 on September 25, eight days after its discovery, for a net exposure of about 53 ks. During the Suzaku observation, IGR J17497$-$2821 is very bright, 2 $\times$ 10$^{37}\>$erg s$^{-1}$ at 8 kpc in the 1–300 keV range, and shows a hard spectrum, typical of black hole candidates in the low-hard state. Despite the multi-mission X-ray monitoring of the source, only with Suzaku is it possible to obtain a broad-band spectrum in the 1–300 keV range with a very high signal to noise ratio. A sum of a multi-color disc and a thermal Comptonization component with mild reflection is a good representation of our IGR J17497$-$2821 Suzaku spectrum. The spectral properties of the accretion disc as well as the cut-off energy in the spectrum at about 150 keV are clearly detected and constrained. We discuss the implications on the physical model used to interpret the data and the comparison with previous results.
Another Abundance Inhomogeneity in the South East Limb of the Cygnus Loop
Authors: Tsunemi Hiroshi , Kimura Masashi , Uchida Hiroyuki , Mori Koji , Katsuda Satoru
Published: March 2014

We observed the south east (SE) limb of the Cygnus Loop with Suzaku. Our spatially-resolved spectroscopic study shows that a one-$kT_\mathrm{e}$ non-equilibrium ionization model represents our spectra fairly well. We find that the metal abundances obtained are all depleted relative to the solar values with a positional dependence along the radial direction of the Cygnus Loop. The abundances in the very edge of the limb show about half the solar value, whereas other regions inside the Loop show about 0.2-times the solar value, which has been believed to be a typical value for the Cygnus Loop limb. The “enhanced” abundance in the very edge of the SE limb is quite similar to that found in the north-east (NE) limb of the Loop, and thus this is another evidence of an abundance inhomogeneity in the limb regions of the Loop. The radio map shows a quite different feature: the NE limb is in the radio bright region, while the SE limb shows almost no radio. Therefore, the metal abundance variation in the SE limb can not be attributed to non-thermal emission. The abundance inhomogeneity as well as the metal depletion down to 0.2 times the solar value still remain an open question.