bluuebunny/crossref_metadata_2025 huggingface dataset:
Detection of Strong Fe-K Lines from the Spiral Galaxies NGC 1365 and NGC 1386
Authors: Iyomoto Naoko , Makishima Kazuo , Fukazawa Yasushi , Tashiro Makoto , Ishisaki Yoshitaka
Published: March 2014

Two spiral galaxies, NGC 1365 and NGC 1386, were observed in X-rays with ASCA. Both galaxies exhibit hard X-ray emission from point-like sources at the nuclei. The continuous spectrum of NGC 1365 was fitted well with a power-law of photon index 0.8−0.2+0.7, whose 2–10 keV luminosity is (3.8±0.5) × 1040 erg s−1 for an assumed distance of 18.4 Mpc. NGC 1386 has an absorbed [NH = (2.8+2.7−2.6) × 1023) cm−2] power-law continuum, whose 2–10 keV luminosity (at 18.4 Mpc) is (2.6−2.0+3.2) × 1040 erg s−1 after removing the absorption. A broad (σ = 0.20+0.16−0.08 keV) Fe-K emission line centered at 6.61−0.06+0.08 keV was detected from the NGC 1365 nucleus at an equivalent width of 2.1+2.1−0.3 keV. The Fe-K line was also detected from NGC 1386 at an equivalent width of 1.6−1.2+7.9 keV and at a similar energy as the NGC 1365 line. These spectral features indicate that both galaxies host low-luminosity active galactic nuclei (LLAGNs).
Confirmation of the SU UMa-Type Nature of the Suggested Intermediate Polar VZ Pyxidis
Authors: Kato Taichi , Nogami Daisaku
Published: March 2014

We observed VZ Pyx (=H0857–242), a suspected intermediate polar (IP), during a bright outburst in 1996 May. Time-resolved CCD photometry revealed superhumps with a period of 0.07576 (± 0.00003) d, confirming the SU UMa-type nature of the object. Unlike other intermediate polars, the superhump and outburst properties of VZ Pyx are quite similar to those of non-magnetic dwarf novae, suggesting a minor effect of global magnetism on the outburst mechanism of this system. If VZ Pyx is really proven to be an IP by future detection of X-ray pulses, this system might provide a unique opportunity to investigate what mechanisms regulate the accretion process and disk instabilities in magnetic dwarf novae.
Fokker-Planck Models of Star Clusters with Anisotropic Velocity Distributions III. Multi-mass Clusters
Authors: Takahashi Koji
Published: March 2014

The evolution of globular clusters driven by two-body relaxation was investigated by means of a numerical integration of the two-dimensional Fokker-Planck equation in energy-angular momentum space. The two-dimensional Fokker-Planck equation allows the development of velocity anisotropy. We include a spectrum of stellar masses in this paper. The radial anisotropy develops, that is, the radial velocity dispersion exceeds the tangential one, in the outer halo of multi-mass clusters as in single-mass clusters. However, the evolution of the velocity anisotropy significantly depends on the stellar mass in some cases. In fact, the tangential-velocity dispersion becomes dominant around the half-mass radius for massive components in clusters with a steep mass function. The development of this tangential anisotropy is closely related to the initial cooling of the massive components toward energy equipartition. Our simulation results suggest that multi-mass anisotropic King-Michie models are not always appropriate for describing the velocity anisotropy in globular clusters.
Infrared Identification of SiO Maser Sources toward the SGR B2 Molecular Cloud
Authors: Deguchi Shuji , Shiki Shigetomo , Matsumoto Shigeru , Jiang B. W. , Nakada Yoshikazu , Wood Peter R.
Published: March 2014

J, H, and K imaging observations have been made in order to identify infrared counterparts for 6 new SiO maser sources toward the Sgr B2 molecular cloud. Only two of these 6 new sources were previously identified with known objects in other catalogues: one with an OH/IR object, another with an IRAS point source. With the imaging observations, we find infrared counterparts for four of the objects: #1, #2, #4, and #7. These are late-type stars either nearby or near to the galactic center. The remaining two sources of which we could not find counterparts can be candidates of young stellar objects with SiO masers. However, it is highly possible that these two are late-type stars located behind the galactic-center molecular cloud, suffering from very high dust extinction.
The 1993 Superoutburst of T Leonis: Early Appearance of Superhumps during a Precursor Outburst
Authors: Kato Taichi
Published: March 2014

We observed the SU UMa-type dwarf nova T Leo during a precursor to the superoutburst in 1993 January. V-band time-resolved CCD photometry revealed the existence of superhumps even during a precursor outburst, which otherwise closely resembled a normal outburst. This finding not only provides observational evidence of the suspected idea that a tidal instability starts to work in precursor outbursts of precursor-superoutburst complexes, but also severely constrains the growth time of superhumps to less than 10 to 20 orbital cycles.
Maximum Visible Polarization of 4179 Toutatis in the Apparition of 1996
Authors: Ishiguro Masateru , Nakayama Hiroyuki , Kogachi Motofumi , Mukai Tadashi , Nakamura Ryosuke , Hirata Ryuko , Okazaki Akira
Published: March 2014

Our visible polarimetry of asteroid 4179 Toutatis during the apparition of 1996 has revealed the existence of a maximum polarization Pmax of (7.0 ± 0.2)% at a phase angle (Sun-asteroid-observer angle) αmax of 107°±10α at an effective wavelength of 0.53 μm. This is the second significant report of Pmax and αmax for the asteroids; the first one for 1685 Toro by Kiselev et al. (1990, AAA51.098.084) has large uncertainties. A comparison of our values of Pmax and {αmax with those of laboratory measurements reported by Bowell et al. (1972, Proc. Lunar Sci. Conf.) as well as Shkuratov and Opanasenko (1992, AAA56.094.027) suggests that the Toutatis' surface is covered with a material having similar polarimetric properties to those of lunar fines with a size of less than 80 μm. Furthermore, our multi-channel polarimetry has confirmed a decrease in the polarization with increasing wavelength.
NMA CS J = 2–1 Line Observations of IRAS 19550+3248
Authors: Lee Ho-Gyu , Koo Bon-Chul , Park Yong-Sun , Roh Duk-Gyoo , Hong Seung-Soo , Hayashi Masahiko
Published: March 2014

We have carried out CS J=2–1 line observations of IRAS 19550+3248 using the Nobeyama Millimeter Array. IRAS 19550+3248 is a class-I young-stellar object (YSO) deeply embedded in a small molecular cloud. The CS core associated with IRAS 19550 + 3248 comprises a compact component and extended, weak, diffuse emission. The size of the whole structure is 0.24 pc × 0.1 pc. The total mass is 4.9 M⊙ and most of the mass resides in the compact component. The deconvolved size of the compact component is 0.07 pc × 0.06 pc. The IR source is located at 0.03 pc southeast of the CS peak position. The CS core associated with IRAS 19550 + 3248 has a large (∼ 2.4 km s−1) velocity dispersion. Our results indicate that the large velocity dispersion results from small (< 0.05 pc) clumps moving supersonically in the beam. Individual clumps have a linewidth of ∼ 0.7 km s−1, but the velocity dispersion among the clumps is large. Using a three-dimensional, non-LTE radiative transfer calculation, we have shown that the observed profile can be explained by a clumpy core with a mass of 3.3–3.9 M⊙. The virial mass is greater than the mass derived from the total flux by an order of magnitude. The large discrepancy may indicate that the clumps are not gravitationally bound to form the CS core, but are dispersing. We discuss the origin of the dispersal. We also detected weak, high-velocity (HV) CS emission, which is considered to be a dense part of the outflow. We compare its properties with those of the CO outflow previously detected in this region.
Measurement of the Sunyaev-Zel'dovich Effect toward Abell 2218 at 36 GHz
Authors: Tsuboi Masato , Miyazaki Atsushi , Kasuga Takashi , Matsuo Hiroshi , Kuno Nario
Published: March 2014

We performed a millimeter-wave observation of the Sunyaev-Zel'dovich effect toward a moderately distant cD cluster of galaxies, Abell 2218, at 36 GHz using the Nobeyama 45-m telescope. The antenna temperature decrement of the cosmic microwave background radiation (CMB) was measured to be ΔTA* = −0.52 ± 0.15 mK at the central peak position of X-ray emission in the cluster. Assuming that the hot gas in the cluster has isothermality, spherical symmetry, and the β-model density distribution, the Sunyaev-Zel'dovich effect is inferred to be ΔT0RJ = −0.68 ± 0.19 mK at the Rayleigh-Jeans limit. A combination of this Sunyaev-Zel'dovich effect and X-ray surface brightness suggests that the Hubble constant is H0 (q0 = 0.5) = 54+51−21 km s−1 Mpc−1.
ASCA Measurements of Silicon and Iron Abundances in the Intracluster Medium
Authors: Fukazawa Yasushi , Makishima Kazuo , Tamura Takayuki , Ezawa Hajime , Xu Haiguang , Ikebe Yasushi , Kikuchi Ken'ichi , Ohashi Takaya
Published: March 2014

We analyzed the ASCA X-ray data of 40 nearby clusters of galaxies, whose intracluster-medium temperature distributes in the range of 0.9–10 keV. We measured the Si and Fe abundances of the intracluster medium, spatially averaging over each cluster, but excluding the central ∼ 0.15 h50−1 Mpc region in order to avoid any possible abundance gradients and complex temperature structures. The Fe abundances of these clusters are 0.2–0.3 solar, with only weak dependence on the temperature of the intracluster medium, hence on the cluster richness. In contrast, the Si abundance is observed to increase from 0.3 to 0.6–0.7 solar from the poorer to richer clusters. These results suggest that the supernovae of both type-Ia and type-II significantly contribute to the metal enrichment of the intracluster medium, with the relative contribution of type-II supernovae increasing towards richer clusters. We suggest a possibility that a considerable fraction of type-II supernova products escaped from poorer systems.
A Geometrical Relationship between Broad-Line Clouds and an Accretion Disk around Active Galactic Nuclei
Authors: Nishiura Shingo , Murayama Takashi , Taniguchi Yoshiaki
Published: March 2014

Recent hard X-ray spectroscopy of active galactic nuclei has strongly suggested that double-peaked, very broad Fe K emission arises from an accretion disk around the central engine. Model fitting of the observed Fe K emission line profile makes it possible to estimate a probable inclination angle of the accretion disk. In order to study the geometrical relationship between the accretion disk and broad emission-line regions (BLRs), we investigate the correlation between the inclination angle of the accretion disk and the velocity width of BLRs for 18 type-1 Seyfert galaxies. We found that there may be a negative correlation between them, i.e., Seyfert nuclei with a more face-on accretion disk tend to have larger BLR velocity widths, suggesting that the BLRs are not coplanar with respect to the accretion disk. The most probable interpretation may be that the BLRs arise from outer parts (r ∼ 0.01 pc) of a warped accretion disk illuminated by the central engine.
ASCA Observations of a Nearby and Massive Galaxy Cluster Abell 3627
Authors: Tamura Takayuki , Fukazawa Yasushi , Kaneda Hidehiro , Makishima Kazuo , Tashiro Makoto , Tanaka Yasuo , Böhringer Hans
Published: March 2014

The results obtained from ASCA observations of the cluster of galaxies Abell 3627 are presented. This cluster, located behind the Milky Way, was recently found to be a nearby, X-ray bright, and very rich cluster. Pointed observations onto the central region of the cluster gave a gas temperature of ∼ 7 keV and a metallicity of about 0.2 solar. An offset pointing to a substructure elongated to the south-east of the cluster center gave a significantly lower temperature of ∼ 5 keV. The 2–10 keV luminosity within a radius of 40′ (1.1 Mpc) is estimated to be 3.7 × 1044 erg s−1 . The X-ray data imply a cluster mass of about 4× 1014 M⊙ within 40′.
Hydrodynamical Simulation of Clusters of Galaxies in X-Ray, mm, and submm Bands: Determination of Peculiar Velocity and the Hubble Constant
Authors: Yoshikawa Kohji , Itoh Makoto , Suto Yasushi
Published: March 2014

We have performed a series of simulations of clusters of galaxies on the basis of the smoothed particle hydrodynamics technique in a spatially flat cold dark matter universe with Ω0 =0.3, λ0 =0.7, and H0=70 km s−1 Mpc−1 as one of the most successful representative cosmological scenarios. In particular, we focused on the Sunyaev–Zel'dovich effect in submm and mm bands, and estimated the reliability of the estimates of the global Hubble constant H0 and the peculiar velocity of clusters vr. Our simulations indicate that the fractional uncertainties of the estimates of H0 amount to ∼ 20%, mainly due to the departure from the isothermal and spherical gas density distribution. We find a systematic underestimate bias of H0 by ∼ 20% for clusters at z ≈ 1, but not at z ≈ 0. The gas temperature drop in the central regions of our simulated clusters leads to an underestimate bias of vr by ∼ 5% at z ≈ 0 and by ∼ 15% at z ≈ 1 in addition to the statistical errors of the comparable amount due to the non-spherical gas profile.
Is M82 a Disk-Truncated Bulge by a Close Encouter with M81?
Authors: Sofue Yoshiaki
Published: March 2014

The rotation curve of the small-mass starburst galaxy M82 has a steep nuclear rise, peaking at 200 pc radius, which then declines in a Keplerian fashion. This rotation curve mimics that for a central bulge of spiral galaxies with a high concentration of stellar mass. The declining rotation indicates that its extended disk mass is missing. In order to explain this peculiar rotation characteristic, we propose a hypothesis that M82 is a surviving central bulge of a much larger disk galaxy, whose outer disk was truncated during a close encounter with M81. We simulated a tidal truncation of the disk of a companion galaxy by a tidal penetration through its more massive parent galaxy. The model can well reproduce the observed peculiar feature of M82.
Radiative Disk Winds in Supersoft X-Ray Sources
Authors: Hachiya Masao , Tajima Yukiko , Fukue Jun
Published: March 2014

Since they depend on inclination angles, P Cyg profiles observed in CVs strongly suggest the existence of accretion disk winds in CVs. Recently, X-ray observations revealed bipolar outflows in SSXSs. The wind velocity measured in these observations is about 3000–5000 km s−1 , which is of the order of the escape velocity of white dwarfs. Hence, it is supposed that the winds originate from the inner disk and/or the boundary layers between the disk and white dwarf. We examined radiatively-accelerated accretion-disk winds, and found that the terminal speed of the wind emanating from the inner disk becomes $\sim 0.6 \sqrt{GM/R_\ast}, $ where M is the white dwarf mass and R⋆ the inner radius of the disk (= the white dwarf radius).
ASCA Observations of the Seyfert 2 Galaxy NGC 7582: An Obscured and Scattered View of the Hidden Nucleus
Authors: Xue Sui-Jian , Otani Chiko , Mihara Tatehiro , Cappi Massimo , Matsuoka Masaru
Published: March 2014

ASCA observations of the Seyfert 2 galaxy NGC 7582 revealed that it was highly variable on the timescale of ∼ 2×104 s in the hard X-ray band (2–10 keV), while the soft X-ray (0.5–2 keV) flux remained constant during the observations. The normalized variability amplitude in the hard X-ray band was σRMS ≈ 0.3, which is the same level as that of Seyfert 1 galaxies of the same luminosity ∼ 3 × 1042 erg s−1 (2–10 keV). The spectral analysis suggests that this object is seen through an obscuring torus with the thickness of NH ∼ 1.0× 1023 cm−2 . The hard X-rays are an absorbed direct continuum from a hidden Seyfert 1 nucleus, while the soft X-rays are dominated by the scattered central continuum from an extended spatial region. We have an obscured/absorbed and a scattered view of this source as expected from the unification model for Seyfert galaxies. More interestingly, the inferred column density increased by ∼ 4×1022 cm−2 from 1994 to 1996, suggesting a “patchy” torus structure, namely the torus might be composed of many individual clouds. The observed iron-line feature near 6.4 keV with the equivalent width of 170 eV is also consistent with the picture of the transmission of nuclear X-ray continuum through a non-uniform torus.
Transition Radius from Cooling-Dominated to Advection-Dominated Regimes in Two Temperature Disks
Authors: Kato Shoji , Nakamura Kenji E.
Published: March 2014

Optically thin advection-dominated flows are known to be unable to extend outward beyond a certain critical (transition) radius in disk accretion. Outside of the radius, the disks are cooling-dominated. The advection-dominated self-similar steady flows cannot join thermally to the cooling-dominated steady standard disks, unless there is some external heating at the transition zone. We examine, under the condition of no such heating, the radius rtr of the transition analytically when the advection-dominated inner flows are two-temperature ones. The results are almost the same as those obtained by Honma (1996, AAA 65.067.241) to a one-temperature disk: i.e., rtr/rg ∼ 5.5 × 102(α4/ṁ2), where α is the viscosity parameter and ṁ is the mass accretion rate normalized by the critical accretion rate defined by the Eddington luminosity. This coincidence with the one-temperature case comes from the fact that the transition occurs after the ion temperature in the advection-dominated region decreases sharply outwards.
On Search and Detection of Hard X-Ray Emission from Orion-Like Complexes Produced by a Flux of Subrelativistic Nuclei
Authors: Dogiel Vladimir A. , Ichimura Atsushi , Inoue Hajime , Masai Kuniaki
Published: March 2014

We analyze the origin of the Orion γ-rays discovered by the COMPTEL telescope and possibilities to search Orion-like sources with X-ray telescopes. We have shown that if these γ-rays are produced by a flux of carbon and oxygen subrelativistic nuclei (as it is usually assumed) then we expect a flux of continuous and line X-ray emission. We showed that in addition to the bremsstrahlung and inverse bremsstrahlung radiation a significant part of the continuous X-ray flux is generated by radiative capture of background electrons. The calculations showed also that the 6.4 keV iron line is the most prominent in the Orion X-ray spectrum, if the nuclei fill the whole volume of the Orion complex. The line flux is estimated by Lx ∼ 4 · 1040 ph s−1. Since the region of the emission is expected to be extended (the total area is about 100 square degrees) the intensity of the line near Earth is 4.6 · 10−3 ph cm−2 s−1 sr−1. This value is below the 3σ level of the ASCA telescope. Therefore, a search of distant (point-like) Orion-like candidates with X-ray telescopes seems to be more perspective. As an example, we analyze the flux of the 6.4 keV iron line observed with ASCA in the direction of the galactic center. If this line is emitted by an Orion-like object in the center of the Galaxy then we expect that there is a powerful source of subrelativistic cosmic rays with energies ≤ 25 MeV n−1 as well as γ-rays in the range 3 to 7 MeV. Their luminosities are Ln ∼ 4 · 1043 n s−1 and Lγ ∼ 1041 ph s−1, respectively.
Wind from T Tauri Stars
Authors: Kiguchi Masayoshi , Narita Shinji , Hayashi Chushiro
Published: March 2014

Previously, it was shown by DeCampli that an isothermal wind of T Tauri stars cannot explain both the mass-loss rates and X-ray observations. Since the assumption of an isothermal wind does not hold in general, we recalculated the structure of a steady and spherically symmetric stellar wind, taking the heating luminosity and its range as input parameters. Our result shows that when the heating luminosity becomes greater than 10−4L⊙, a sonic point lies inside the heating region, contrary to the case of the solar wind. In this case, there exist two solutions for the same heating luminosity and the same mass-loss rate. In one solution, heat is transported by conduction, and in the other solution it is transported by convection. When the heating luminosity is as high as 1 L⊙, the mass-loss rate is about 10−9 ∼ 10−8M⊙ yr−1 . In the former solution, the corona shines with a temperature of about 7 × 107 K and with an X-ray luminosity of about 10−3L⊙, in agreement with X-ray observations. However, the time scale of the angular-momentum loss is greater than 108 yr and this solution, itself, may be insufficient for the angular-momentum loss. This result stems from the smallness of the viscosity coefficient. If global magnetic fields exist, this problem may be solved. In the latter solution, the temperature is at most 4 × 106K, but the time scale of the angular-momentum loss becomes about 107 yr even if magnetic fields do not exist.
Near-Infrared Observations of IRAS Sources with SiO Masers in the Direction of the Near End of the Galactic Bar
Authors: Deguchi Shuji , Matsumoto Shigeru , Wood Peter R.
Published: March 2014

In order to investigate the kinematics of stars in the direction of the near end of the galactic bar, J, H, and K photometric observations were made for 67 IRAS sources in the galactic plane $(15^\circ\lt l\lt 25^\circ$ and $|b| \lt 3^\circ)$. SiO maser emission has previously been detected for all of these sources; they are well-confirmed, mass-losing, late-type stars having accurate radial velocities derived from the SiO observations. For 61 sources, single near-infrared counterparts are found within the $\sim 20^{\prime\prime}$ error ellipse of the IRAS positions, and for the other 6 sources, multiple candidates or candidates with a low confidence level are found. From the J, H, K-band and IRAS 12 and 25 μm intensities, we estimated the spectral energy distributions of the 61 sources. After correcting for interstellar extinction, the bolometric corrections to the 12 μm fluxes of the sources were calculated. The distances from the Sun have been obtained assuming a constant stellar luminosity $(L=8000 L_\odot)$ for the sources. The stars with a large deviation of motion from the galactic rotation are found to fall at a distance of ∼ 5.5 kpc from the Sun. This fact might indicate that the stellar motion deviates strongly from smooth galactic rotation near to the tip of the bar.
Oxygen Abundances in Late-B through F Supergiants
Authors: Takeda Yoichi , Takada-Hidai Masahide
Published: March 2014

A spectral-synthesis analysis was performed for twenty-six late-B through F supergiants (including Cepheids) in order to determine their photospheric oxygen abundances from the O I 6156–8 feature, while taking into account the non-LTE effect, which is progressively Teff-dependent from ≲ 0.1 dex for F-type supergiants to ∼ 0.4 dex for late-B ones in terms of the non-LTE abundance correction. The resulting oxygen abundances show a moderate underabundance relative to the Sun $([\textrm O/\textrm H]{\sim -0.3} $) along with a remarkably small scatter (within ± 0.1 dex) over this wide temperature range. Considering the recent evidence that the solar oxygen abundance is mildly enhanced by 0.2−0.3 dex relative to that of the galactic gas which forms young stars, we conclude that the original O-composition in the atmosphere of these supergiants had suffered almost no appreciable alteration during their past evolutionary history, even though signs of significant mixing of CN-cycle or NeNa-cycle products are evident. This excludes the possibility of any global-mixing mechanism, such that producing a significant reduction of oxygen due to a deep dredge-up of considerable ON-processed material, whatever the details of the envelope-mixing process for these relatively massive stars may be.
Two-Dimensional Accretion Disks at Subcritical Luminosity
Authors: Fujita Mitsutaka , Okuda Toru
Published: March 2014

To examine subcritical accretion disks, we performed two-dimensional axisymmetric calculations by solving a set of fully non-linear hydrodynamic equations coupled with radiation transport. Focusing on the accretion disks of neutron stars near to the Eddington luminosity LE, we obtained thermally stable accretion disks where the radiation pressure and electron scattering are dominant. The thermally stable disks are interpreted in terms of the slim accretion-disk theory. While the accretion disks are unstable to convection and convective cells generally stretch from the disk mid-plane to the disk surface in the inner disk. It has been found that convection is an important energy-transfer mechanism along the vertical direction of the disk. A very rarefied, hot, and optically thin region is formed along the rotational axis of the disk. The relativistic jet with a collimation angle of less than 10° is generated in the rarefied optically thin region, mainly due to the dominant radiation-pressure force. The results of subcritical accretion onto a neutron star are discussed in relation to SS 433.
A Peculiar X-Ray Transient Source, AX J1842.8–0423, Discovered with ASCA
Authors: Terada Yukikatsu , Kaneda Hidehiro , Makishima Kazuo , Ishida Manabu , Matsuzaki Keiichi , Nagase Fumiaki , Kotani Taro
Published: March 2014

A new transient X-ray source, AX J1842.8-0423, was discovered with ASCA in 1996 October in the Scutum arm region. The source exhibited an absorption-corrected 2–10 keV flux of 5.2 × 10−12 erg s−1 cm−2, with insignificant intensity variability. The continuous spectrum is approximated by a power-law of photon index 2.9, absorbed by a hydrogen column of NH ∼ 5 × 1022 cm−2. The spectrum also exhibits the Fe-K emission line with an extremely large equivalent width of ∼ 4000 eV, of which the centroid energy is ∼ 6.8 keV. The overall spectrum can be reproduced by a thin-thermal plasma-emission model having a temperature of ∼ 5.1 keV, on the condition that the heavy-element abundance is allowed to increase to $3.0^{+4.3}_{-0.9}$ solar abundance. The source was undetectable in a previous observation in 1993 October, as well as in a subsequent observation in 1996 April. The overall source behavior is thus quite peculiar, but may be explained in terms of a close binary involving a magnetized white dwarf viewed from pole-on inclination, where the unusually strong Fe-K line may be the result of resonant scattering of line photons.
Pair Plasma Dominance in the 3C 279 Jet on Parsec Scales
Authors: Hirotani Kouichi , Iguchi Satoru , Kimura Moritaka , Wajima Kiyoaki
Published: March 2014

We have investigated whether a pc-scale jet of 3C 279 is dominated by a normal plasma or an electron-positron plasma. By analyzing Very Long Baseline Interferometry data between 1983 and 1990, and utilizing the theory of synchrotron self-absorption, we have derived the lower limits for the proper electron number density. Comparing the lower limit with another independent constraint for the electron density that is deduced from the kinetic luminosity, we find that the core and components C3 and C4 are likely dominated by an electron-positron plasma.
Spectroscopic Studies of the Solar Corona I. Spatial Variations in Line Parameters of Green and Red Coronal Lines
Authors: Singh Jagdev , Ichimoto Kiyoshi , Imai Hideki , Sakurai Takashi , Takeda Aki
Published: March 2014

We obtained simultaneously profiles of the coronal green line (FeXIV 5303 A) and red line ([FeX] 6374 A) on a number of days at several regions covering an area of about 200″ × 500″ in the solar corona. The intensity, velocity, and width for both of these lines were computed by making a Gaussian fit to the observed line profile. We find that in coronal structures the spatial variations in the red and green line intensities are correlated. The ratio of green- to red-line intensities varies between 0.6–9.2 for different coronal structures. The value of the intensity ratio in an individual coronal structure also varies with height above the solar limb along the structure. The range of values of the intensity ratio observed implies that most of the structures under investigation had a temperature in the range of 1.2–1.6 × 106 K. Also, we find that in coronal structures the width of the red line increases with height above the limb, whereas the green-line width in the same region decreases with height. This behavior of the line widths can be explained if we assume the mixing of plasma in the middle and higher portions of the coronal structures by microturbulence or traveling waves, which have been detected recently. No Ha loops and activity were seen in these regions during the observation periods.
Optical and CO Radio Observations of Poor Cluster Zwicky 1615.8+3505
Authors: Tomita Akihiko , Maehara Hideo , Takeuchi Tsutomu T. , Nakanishi Kouichiro , Honma Mareki , Tutui Yoshinori , Sofue Yoshiaki
Published: March 2014

The cluster Zwicky 1615.8+3505 is considered to be a dynamically young poor cluster. To investigate the morphology and star-formation activity of galaxies under the environment of a dynamically young poor cluster, we have performed V, R, and I surface photometry, optical low-resolution spectroscopy, and 12CO (J=1–0) line observations for member galaxies. Our data show that more than 90% of the observed galaxies show regular morphologies and no star-formation activities, indicating that the environment does not affect these galaxy properties. Among sixteen galaxies observed, only NGC 6104 shows a significant star-formation activity, and shows a distorted morphology, indicating a tidal interaction. This galaxy contains double knots, and only one knot possesses Seyfert activity, though the sizes and luminosities are similar to each other; we also discuss this feature.
Radiation Hydrodynamical Mass Accretion onto Galactic Nuclei Driven by Circumnuclear Starbursts
Authors: Ohsuga Ken , Umemura Masayuki , Fukue Jun , Mineshige Shin
Published: March 2014

We explore the radiation hydrodynamical evolution of a galactic nuclear gas disk exposed to intense radiation from circumnuclear starbursts. The evolution is characterized by two stages. First, the disk is radially contracted by the radiation force. Subsequently, the surface stratum of the disk avalanches onto the center due to the removal of angular momenta by radiation drag. The mass accretion via a radiatively-driven avalanche was analyzed quantitatively while assuming a torus shape of the circumnuclear starburst regions. As a result, it was found that the mass-accretion rate is sensitively dependent upon the extension of the starburst regions. For an optically thick disk, the mass-accretion rate is roughly in proportion to the ratio of the thickness to the curvature radius of the torus. The rate is also dependent upon the rotation law of the disk. We investigated the evolution of the disk surface density resulting from radiatively-driven mass accretion. It was found that for a more intensive starburst the central concentration of surface density becomes more conspicuous. The present results seem to be significant when considering the evolution of starburst nuclei, for instance, in luminous IRAS galaxies.
Relativistic Radiative Jets Confined by a Disk Corona
Authors: Fukue Jim
Published: March 2014

We examine steady relativistic jets, emanating from an inner accretion disk, driven by disk radiation fields, and confined by an isothermal corona. In order to describe the radiation fields produced by the standard accretion disk, we derive bridging formulae which approximately represent the components of the radiation fields from a near-disk regime to a distant regime. We use a streamline approach, where the dynamical equations are expressed by the streamline coordinates, and a cold approximation, where the pressure-gradient force is ignored. When the effect of a corona is ignored, the jet streamlines widen due to the centrifugal force, since the jet gas emanating from the disk has angular momentum. When the corona is considered, on the other hand, the jet flow is remarkably collimated by the corona gas. As a result, radiative winds from an inner disk forms hollow cylindrical jets. The present radiative jets have a terminal speed, where the radiation force is balanced by the gravitational and radiation drag forces. The terminal speed VQQ is not sensitive to the corona properties, but depends on the disk luminosity L<\ normalized by the Eddington one LE-. The terminal speed VQQ of the present model is approximately expressed as ^oo/c ∼ (0.5/rd )°′9 (rd – 0.5), where Td =L^/LE-. For the Eddington luminosity (Fd = 1), the terminal speed is about 0.27 c, which is very close to the speed of SS 433 jets.
Two-Dimensional Simulations of Relativistic Extragalactic Jets Crossing an ISM/ICM Interface
Authors: Zhang Hui-Min , Koide Shinji , Sakai Jun-Ichi
Published: March 2014

We have performed two-dimensional relativistic hydrodynamical simulations of initially conical axisymmetric jets using a newly developed relativistic magnetohydrodynamic simulation code. The simulation code employs a simplified total variation diminishing method. These jets emerge from the atmospheres of active galaxies and then cross a pressure-matched interface into a hotter, but less-dense, intraclustermedium, whereupon they are accelerated and collimated. We compared the nonrelativistic and relativistic jets to find any relativistic effects in this kind of propagation processes. The simulation results show that there are clear relativistic effects as well as interface impacts in several aspects. Compared with a nonrelativistic jet propagating in a uniform medium, three results are notable: (1) when a jet propagates from a higher density medium region to lower density region, the variation in the amplitude of the Mach disk between concave and convex is greater; nonrelativistic jets show this feature more obviously; (2) the interface causes the jet to undergo a quasi-periodical shrinkage and expansion, which may correspond to a chain of knots in an extragalactic jet; (3) the jet head advance velocity formula,v^=v0y/rj/(l + y/v)i should be replaced by vh = t>o7o VWU + loy/rj), where vo and 70 are the velocity of the inflowing jet fluid and its Lorentz factor, respectively, and eta is the initial ratio of jet density to medium density.
Gravitational Microlens Mapping of a Quasar Accretion Disk
Authors: Mineshige Shin , Yonehara Atsunori
Published: March 2014

Since the radiation from different portions in the central region of a quasar can be successively amplified during a microlensing event, microlensing light curves provide fruitful information regarding the emissivity distribution of an accretion disk located at the quasar center. We present a basic methodology of how to map the emissivity distribution of the disk as a function of the radial distance from the center, Q(r), from ‘observed’ microlens light curves during a caustic crossing event. Our proposed method is based on the standard inversion technique, the so-called regularization method, and Abel's transformation of the one-dimensional luminosity profile integrated along the line parallel to the caustics. This technique will be used to map the disk structure in Q2237+0305, for which the HST and AXAF observations are scheduled. A reconstruction of the image on length scales of several to ten AUs is quite feasible for this source, as long as the measuring errors are within 0.02 mag and the observation time intervals are one week or less.
Discovery of Large Doppler Factors in Radio-Loud Active Galactic Nuclei
Authors: Fujisawa Kenta , Kobayashi Hideyuki , Wajima Kiyoaki , Hirabayashi Hisashi , Kameno Seiji , Inoue Makoto
Published: March 2014

We have studied the Doppler factors of active galactic nuclei. The inverse-Compton effect and equipartition models were applied to VLBI observations at 22 GHz. Total flux density measurements at 43 and 92 GHz were made for a reliable estimation of the Doppler factors. We found that two sources (0235+164, 1921–293) have Doppler factors larger than 80, while most have Doppler factors S < 50. The distribution of δ is consistent with the previous results. With the aid of published component motions, we derived a Lorentz factor T > 60 for 0235+164, T > 41 for 1921–293, and a viewing angle p < 1° for both sources. The derived boosting factors of these sources are on the order of 107. An argument is presented based on these large boosting factors that the core consists of Doppler-boosted and non-boosted components. The derived Lorentz factors of the sources exceed the predicted upper bounds of Compton-drag theories.
Discovery of a New X-Ray Pulsar, AX J0049-729, in the Small Magellanic Cloud with ASCA
Authors: Yokogawa Jun , Imanishi Kensuke , Tsujimoto Masahiro , Kohno Makoto , Koyama Katsuji
Published: March 2014

We report on the results of two ASCA observations on an X^ray source, AX J0049–729 (= RX J0049.1–7250), in the Small Magellanic Cloud. A sinusoidal pulsation with a barycentric period of 74.676±0.022 s was found. The pulse fraction was ∼ 70%, independent of the X-ray energy. The spectrum was hard with an absorbed power-law having a photon index of ∼ 1. The X-ray flux was 1.1×10−11 erg s−1 cm−2, and then declined to 1.6×10∼12 erg s−1 cm−2 from the first to the second observations, separated by about one month. Together with the previous results of the Einstein and ROSAT satellites, we found that AX J0049–729 has been in quiescent states, but occasionally showing flare activities. The flux variability, long-pulse period, and hard spectrum support the idea that AX J0049-729 is an X-ray binary pulsar, most likely a Be star binary.
A Quadruple Magnetic Source Model for Arcade Flares and X-Ray Arcade Formations outside Active Regions I. Dark Filament Suspension and the Magnetic Structure in the Pre-Event Regions
Authors: Uchida Yutaka , Hirose Shigenobu , Cable Samuel , Morita Satoshi , Torii Masaya , Uemura Shuhei , Yamaguchi Tomotaka
Published: March 2014

The high-sensitivity, wide dynamic-range observations by the Soft X-ray Telescope (SXT) aboard Yohkoh has enabled us to look into the faint pre-event structures of arcade flares, and of even fainter X-ray arcade formation events outside active regions. What we have found in the pre-event structure of the latter, however, was not a sagged simple (bipolar) arcade, as expected in the classical model, but a “dual-arcades„ type structure in which the inside legs of each “arcade„ cross with the other's, landing at the closer part of the domain of the other. Similar features, together with some other features inexplicable in the classical arcade flare model, were also found in strong arcade flares in active regions seen axis-on at the limb. These features raised a severe problem with the classical “reclosing of the once opened simple arcade„ model(s). In the present paper, we propose interpretations of what we discovered by Yohkoh-SXT by reviving a quadruple source model proposed by one of the authors (YU) years ago, pointing out a serious difficulty in the classical model(s). This model, based on the quadruple magnetic sources in the photosphere, has a “neutral sheet„ already in the pre-event phase in the corona above the field polarity-reversal line in the photosphere, and turns out to explain quite nicely the structures of both faint pre-event corona before arcade formation events, and that of arcade flares discovered by Yohkoh-SXT. A dynamic model of arcade flares and arcade formation events based on this dark filament model will be discussed in the forthcoming Paper II of this series.
Parameters of Black Holes in Sources with Periodic Variability
Authors: Semerák Oldřich , Karas Vladimír , de Felice Fernando
Published: March 2014

We propose a way to deduce the parameters of accreting black holes. The method employs the properties of the spectral features observed in radiation from an accretion disk. It is applicable to sources which exhibit periodic modulation of variability, provided: (i) the gravitational field is determined by the black hole and described by the Kerr metric; (ii) a thin accretion disk of negligible mass lies in the equatorial plane of the hole; (iii) a secondary object (also with negligible mass) moves on a slightly inclined almost circular orbit around the black hole and passes periodically through the disk; (iv) the collisions result in observable photometric and spectroscopic features (temporal variability of the radiation flux and of spectral-line profiles produced in the disk), which show frequencies of the orbital motion and of latitudinal oscillations; (v) one can measure the width of the spectral line from hot spots arising in the disk due to collisions with the orbiter, and/or detect predicted low-frequency oscillations induced in the disk. These frequencies and the line width provide enough information to determine in physical units three parameters characterizing the source: the mass and angular momentum of the central black hole, and radius of the orbit of the secondary.
Gravitational Collapse of Spherical Interstellar Clouds
Authors: Ogino Shinya , Tomisaka Kohji , Nakamura Fumitaka
Published: March 2014

In this paper, the gravitational collapse of spherical interstellar clouds is discussed based on hydrodynamical simulations. The evolution is divided into two phases: former runaway collapse phase, in which the central density increases greatly on a finite time scale, and later contraction, associated with accretion onto a newborn star. The initial density distribution is expressed using a ratio of the gravitational force to the pressure force α. The equation of state for a polytropic gas is used. The central, high-density part of the solution converges on a self-similar solution, which was first derived for the runaway collapse by Larson and Penston (LP). In the later accretion phase, gas behaves like a particle, and the infall speed is accelerated by the gravity of the central object. The solution at this stage is qualitatively similar to the inside-out similarity solutions first found by Shu. However, it is shown that the gas-inflow (accretion) rate is time-dependent, in contrast to the constant rate of the inside-out similarity solutions. For isothermal models in which the pressure is important, 1 ≲ α ≲ 3.35, the accretion rate reaches its maximum when the central part, which obeys the LP solution, contracts and accretes. On the other hand, in isothermal models in which gravity is dominant, α ≳ 3.35, the accretion becomes most active at the epoch when the outer part of the cloud falls onto the center. The effect of the non-isothermal equation of state is discussed.
Evolution of a Luminous Hoyle-Lyttleton Accretor
Authors: Fukue Jun
Published: March 2014

We examine the evolution of a Hoyle-Lyttleton accretor, on which mass accretion takes place via the Hoyle-Lyttleton processes, while taking into account the luminosity of the accretor. We consider two cases: (i) a spherical accretor, where the accretor is a spherical radiating source, and (ii) a disk accretor, where the accretor is a disk radiating source. In the well-known case of the classical non-luminous accretor, the growth time depends on the mass, the gas density, and the relative velocity, although the evolution processes are enhanced due to dynamical friction; the evolution time is shortened roughly by a factor of the Coulomb logarithm. In the case of a luminous accretor, we found, the evolutionary picture is drastically changed. The mass of the spherical accretor grows exponentially, but the luminosity approaches the Eddington luminosity, where the evolution timescale is the Eddington timescale, tE (= 4.53 x 108 η yr, η being the efficiency). The mass and the effective luminosity of the disk accretor, on the other hand, diverge to infinity within a finite time, which is shorter than the Eddington timescale by a factor of the Coulomb logarithm. We discuss applications to several astrophysical situations, including a slow mover in giant molecular clouds and a fast runner in Thorne-Żytkow objects.
First Results of a CO Survey of the Large Magellanic Cloud with NANTEN; Giant Molecular Clouds as Formation Sites of Populous Clusters
Authors: Fukui Yasuo , Mizuno Norikazu , Yamaguchi Reiko , Mizuno Akira , Onishi Toshikazu , Ogawa Hideo , Yonekura Yoshinori , Kawamura Akiko , Tachihara Kengo , Xiao Kecheng , Yamaguchi Nobuyuki , Hara Atsushi , Hayakawa Takahiro , Kato Sigeo , Abe Rihei , Saito Hiro , Mano Satoru , Matsunaga Ken'ichi , Mine Yoshihiro , Moriguchi Yoshiaki , Aoyama Hiroko , Asayama Shin-ichiro , Yoshikawa Nao , Rubio Monica
Published: March 2014

A new survey of the LMC has been completed in 2.6 mm carbon monoxide emission with NANTEN. This survey has revealed 107 giant molecular clouds, the first complete sample of giant molecular clouds in a single galaxy at a linear resolution of ∼ 40 pc. The cloud mass ranges from ∼ 6 × 104 to 2 × 106 M⊙, and the total molecular mass has been estimated to be 4–7 × 107 M⊙ for a molecular column density of ≳ 1.0 × 1021 cm-2, corresponding to 5–10% of the atomic mass. The molecular clouds exhibit a good spatial correlation with the youngest stellar clusters whose ages are ≲ 10 Myr, demonstrating that cluster formation is on-going in these clouds. On the other hand, they show little correlation with older clusters or with supernova remnants, suggesting that the molecular clouds are being rapidly dissipated in a several Myrs, probably due to the UV photons of massive stars in clusters.
Discovery of the Carina Flare with NANTEN; Evidence for a Supershell That Triggered the Formation of Stars and Massive Molecular Clouds
Authors: Fukui Yasuo , Onishi Toshikazu , Abe Rihei , Kawamura Akiko , Tachihara Kengo , Yamaguchi Reiko , Mizuno Akira , Ogawa Hideo
Published: March 2014

We present extensive observations of the Carina arm region in the 2.6 mm CO (J = 1−0) emission with the NANTEN telescope in Chile. The observations have revealed 120 molecular clouds which are distributed in an area of 283° < l < 293° and 2° .5 < b < 10°. Because of its vertical elongation to the galactic plane, the clouds are named the Carina flare. H I and far-infrared emission show a cavity-like distribution corresponding to the molecular clouds, and soft X-ray emission appears to fill this cavity. It is shown that the Carina flare represents a supershell at a distance of a few kpc that has been produced by about 20 supernova explosions, or equivalent stellar winds of OB stars, over the last ∼ 2×107 yr. The supershell consisting of molecular and atomic neutral gas involves a total mass and kinetic energy of ≳ 3×105M⊙ and ≳ 3×1050 erg, respectively, and the originally injected energy required is about 100-times this current kinetic energy in the shell. It is unique among supershells known previously because of the following aspects: i) it exhibits evidence for the triggered formation of intermediate-to-high-mass stars and massive molecular clouds of 102 − 104M⊙, and ii) the massive molecular clouds formed are located unusually far above the galactic plane at z ∼ 100–500 pc.
Molecular Clouds and Star Formation in the Southern H II Regions
Authors: Yamaguchi Reiko , Saito Hiro , Mizuno Norikazu , Mine Yoshihiro , Mizuno Akira , Ogawa Hideo , Fukui Yasuo
Published: March 2014

We have carried out extensive 13CO(J = 1−0) observations toward 23 southern H II regions associated with bright-rimmed clouds. In total, 95 molecular clouds have been identified to be associated with the H II regions. Among the 95, 57 clouds \ are found to be associated with 204 IRAS point sources which are candidates for young stellar objects. There is a significant increase of star-formation efficiency on the side facing to the H II regions; the luminosity-to-mass ratio, defined as the ratio of the stellar luminosity to the molecular cloud mass, is higher by an order of magnitude on the near side of the H II regions than that on the far side. This indicates that molecular gas facing to the H II regions is more actively forming massive s\ tars whose luminosity is ≳103L⊙. In addition, the number density of the IRAS point sources increases by a factor of 2 on the near side of the H II regions compared with on the far side. These results strongly suggest that the active formation of massive stars on the near side of the H II regions is due to the effects of the H II regions, such as the compression of molecular material by the ionization/shock fronts. For the whole Galaxy, we estimate that the present star-formation rate under such effects is at least 0.2−0.4 M⊙ yr-1, corresponding to a few 10% by mass.