bluuebunny/crossref_metadata_2025_split huggingface dataset:
Super-Hard X-Ray Emission from η Carinae Observed with Suzaku
Authors: Sekiguchi Akiko , Tsujimoto Masahiro , Kitamoto Shunji , Ishida Manabu , Hamaguchi Kenji , Mori Hideyuki , Tsuboi Yohko 
Published: March 2014

Abstract
We present the Suzaku results of $\eta$ Carinae in the 5–50 keV range conducted twice around the apastron in 2005 August for 50 ks and in 2006 February for 20 ks. The X-ray Imaging Spectrometer (XIS) produced hard (5–12 keV) band spectra, resolving K shell lines from highly ionized Fe and Ni. The Hard X-ray Detector yielded a significant detection in the super-hard (15–50 keV) band, which was uncontaminated by near-by sources. We constrained the temperature of the optically thin thermal plasma emission dominant in the hard band to be 3–4 keV using the K-shell line features with the XIS. We found significant excess emission above the thermal emission in the super-hard band with the PIN, confirming the previous INTEGRAL ISGRI report. The entire 5–50 keV spectra were fitted by a combination of a thermal plasma model plus a flat power-law, or a very hot thermal bremsstrahlung model for the excess emission. No significant change of the excess emission was found at different epochs within the systematic and statistical uncertainties, and no flare-like flux amplification was seen in the hard band, indicating that the excess emission is a steady phenomenon. We argue that the super-hard emission is attributable to the inverse Compton of stellar UV photons by non-thermal electrons or to the thermal bremsstrahlung of very hot plasma, and not to the bremsstrahlung by non-thermal electrons colliding with cold ambient matter.
Radio Variability and Relativistic Beaming Effect for Blazars
Authors: Fan Jun-Hui , Huang Yong , He Tang-Mei , Yang Jiang He , Hua Tong Xu , Liu Yi , Wang Yong Xiang 
Published: March 2014

Abstract
In this paper, using a database of the University of Michigan Radio Astronomy Observatory at the radio frequencies (8 GHz and 14.5 GHz), we determined the variability time scales, and calculated the brightness temperature for 86 radio sources (29 BL Lacertae objects—BLs and 57 flat spectrum radio quasars—FSRQs). The time scales were found in the range of from 3 months to 16.27 years with an averaged value scale of 2.34 years. We obtained the following results: (1) The brightness temperature is in the range of log $T_{\rm b,var}$$=$ 10.98 to $T_{\rm b,var}$$=$ 15.35, which suggests that the Doppler factors are in the range of $\delta$$=$ 0.73 to $\delta$$=$ 20.74. The averaged values are $\langle\delta\rangle$$=$ 5.95$\pm$2.93 for 57 FSRQs and $\langle\delta\rangle$$=$ 5.08$\pm$2.63 for 29 BLs. (2) The radio luminosity, $L_{\rm ob}$, is found to be correlated with the radio Doppler factor, $\delta$, log$L_{\rm ob}$$=$ (0.58$\pm$0.10) log$\delta^{3}$$+$ 43.49$\pm$0.21. (3) The viewing angles and the Lorentz factors were determined for 53 sources (15 BLs and 38 FSRQS) with available superluminal velocity (Zhang & Fan 2008, Chin. J. Astron. Astrophys, 8, 385). The averaged values are $\Gamma$$=$ 24.1$\pm$17.35 and $\theta$$=$ 8$.^\circ$7$\pm$3$.^{\circ}$5 for the FSRQs, and $\Gamma$$=$ 13.5$\pm$11.16 and $\theta$$=$ 12$^{\circ}\pm$7$^{\circ}$ for the BLs.
Spectroscopic Observations of the WZ Sge-Type Dwarf Nova GW Librae during its 2007 Superoutburst
Authors: Hiroi Kazuo , Nogami Daisaku , Ueda Yoshihiro , Moritani Yuuki , Soejima Yuichi , Imada Akira , Hashimoto Osamu , Kinugasa Kenzo , Honda Satoshi , Narusawa Shin-ya , Sakamoto Makoto , Iizuka Ryo , Matsuda Kentaro , Naito Hiroyuki , Iijima Takashi , Fujii Mitsugu 
Published: March 2014

Abstract
We carried out an international spectroscopic observation campaign of the dwarf nova GW Librae (GW Lib) during its 2007 superoutburst. Our observation period covered the rising phase of the superoutburst, maximum, slowly decaying phase (plateau), and long fading tail phase after the rapid decline from the plateau. The spectral features dramatically changed during the observations. In the rising phase, only absorption lines of H$\alpha$, H$\beta$, and H$\gamma$ were present. Around the maximum, the spectrum showed singly peaked emission lines of H$\alpha$, He i 5876, He i 6678, He ii 4686, and C iii/N iii as well as absorption lines of the Balmer components and HeI. These emission lines significantly weakened during the latter part of the plateau phase. In the fading tail phase, all of the Balmer lines and He i 6678 were in emission, as observed in quiescence. We find that the center of the H$\alpha$ emission component was mostly stable over the whole orbital phase, being consistent with the low inclination of the system. Compared with the observational results of WZ Sagittae during its 2001 superoutburst, the same type of stars as GW Lib seen with a high inclination angle, we interpret that the change of the H$\alpha$ profile before the fading tail phase can be attributed to a photoionized region formed at the outer edge of the accretion disk, irradiated from the white dwarf and inner disk.
Light-Time Effect in the Early-Type Close Binary ZZ Cassiopeiae
Authors: Wen-Ping Liao , Sheng-Bang Qian 
Published: March 2014

Abstract
CCD observations of the eclipsing binary ZZ Cas were carried out during three nights from 2007 to 2008. Based on our new CCD times of light minimum and all available photoelectric and CCD data compiled from the literature, orbital period changes of ZZ Cas were analyzed. It was discovered that there may exist two cyclic variations (i.e., $P_3$$=$ 13.63 yr and $A_3$$=$ 0.02406 d, $P_4$$=$ 3.89 yr and $A_4$$=$ 0.00295 d). ZZ Cas is composed of early type component stars; the two cyclic variations can be explained by the light-time effect via the presence of the third and fourth bodies in the system. Minimal masses of $M_{3}$$=$ 5.00 $M_{\odot}$ and $M_{4}$$=$ 1.21$M_{\odot}$ were also calculated, respectively. These conclusions are in agreement with the result of previous investigations, that the additional bodies should contribute 23.6% to the total light of the system (Zasche 2009, New Astron., 14, 129), when the inclinations of the third and the fourth bodies are $i_3$$=$$i_4$$=$ 58$.\circ$9. The third and fourth bodies orbit the eclipsing binary at orbital distances of $a_3$$=$ 11.74AU and $a_4$$=$ 6.14AU, respectively.
Suzaku Observations of SN 1987A
Authors: Sturm Richard , Haberl Frank , Hasinger Günther , Kenzaki Kyoko , Itoh Masayuki 
Published: March 2014

Abstract
We report on Suzaku observations of SN1987A in the Large Magellanic Cloud, performed in 2005 November and 2006 June. The observations provide medium resolution X-ray spectra during the phase of the interaction between the supernova blast wave and the inner circumstellar ring. The Suzaku observations complement XMM-Newton and Chandra observations and were used to investigate the spectral evolution of SN1987A. The spectra were analyzed with two-temperature emission model from shocked gas. For the flux in the soft band (0.5−2.0 keV) we obtained 25.7$_{-1.9}^{+1.4}$$\times$ 10$^{-13}$ergcm$^{-2}$ (2005) and 30.8$_{-1.7}^{+1.4}$$\times$ 10$^{-13}$ergcm$^{-2}$ (2006). The exponential rise seen in the soft X-ray light curve of SN1987A till $\sim$6500 d after the explosion slowed down significantly between the Suzaku observations. Recent Chandra and XMM-Newton observations confirm this evolution. SN1987A continues to brighten exponentially, but with longer characteristic timescale. This must be caused by a less rapidly increasing emission measure.
NH3 in the Galactic Center is Formed under Cool Conditions
Authors: Nagayama Takumi , Omodaka Toshihiro , Handa Toshihiro , Toujima Hideyuki , Sofue Yoshiaki , Sawada Tsuyoshi , Kobayashi Hideyuki , Koyama Yasuhiro 
Published: March 2014

Abstract
It is an open question as to why the temperature of molecular gas in the Galactic center region is higher than that of dust. To address this problem, we made simultaneous observations in the NH$_3$ ($J,K$) $=$ (1, 1), (2, 2), and (3, 3) lines of the central molecular zone (CMZ) using the Kagoshima 6-m telescope. The ortho-to-para ratio of NH$_3$ molecules in the CMZ is 1.5–3.5 at most in the observed area. This ratio is higher than the statistical equilibrium value, and suggests that the formation temperature of NH$_3$ is 11–20 K. This temperature is similar to the dust temperature estimated from the submillimeter and infrared continuum. This result suggests that the NH$_3$ molecules in the CMZ were produced on dust grains with the currently observed temperature (11–20 K), and they were released into the gas phase by supernova shocks or collisions of dust particles. The discrepancy between warm molecular gas and cold dust can be explained by transient heating of the interstellar media in the CMZ approximately $10^5$ yr ago when NH$_3$ molecules were released from the dust.
Particle Propagation in the Galactic Center and Spatial Distribution of Non-Thermal X-Rays
Authors: Dogiel Vladimir A. , Chernyshov Dmitrii , Yuasa Takayuki , Cheng Kwong-Sang , Bamba Aya , Inoue Hajime , Ko Chung-Ming , Kokubun Motohide , Maeda Yoshitomo , Mitsuda Kazuhisa , Nakazawa Kazuhiro , Yamasaki Noriko Y. 
Published: March 2014

Abstract
We showed that if the non-thermal emission from the galactic center in the range 14–40 keV is due to inverse bremsstrahlung emission of subrelativistic protons, their interactions with hot and cold fractions of the interstellar medium are equally important. Our estimation shows that about 30% of the total non-thermal flux from the GC in the range 14–40 keV is generated in regions of cold gas while the rest is produced by proton interaction with hot plasma. From the spatial distribution of 6.7 keV iron line we concluded the spatial distribution of hot plasma is strongly non-uniform that should be taken into account in analysis of proton propagation in the GC. From the Suzaku data we got independent estimates for the diffusion coefficient of subrelativistic protons in the GC, which was in the range 10$^{26}$–10$^{27} $cm$^{2} $s$^{-1}$.
Metallicity Measurements of Pleiades Young Dwarfs
Authors: Funayama Hitoshi , Itoh Yoichi , Oasa Yumiko , Toyota Eri , Hashimoto Osamu , Mukai Tadashi 
Published: March 2014

Abstract
We present metallicity analyses of A, F, and G stars in the Pleiades cluster. High-resolution spectroscopic observations of 25 stars were made with the HIDES spectrograph on the Okayama 1.88-m telescope and the GAOES spectrograph on the Gunma 1.5-m telescope. The resultant optical spectra had an S$/$N of 70–220. We measured the equivalent widths of $\sim $60 neutral iron and $\sim $15 single-ionized iron absorption lines to determine stellar parameters and metallicities. We derived the metallicities of 22 stars by adapting the method of equivalent-width measurements. The average metallicity was $+$0.03$ \pm $0.05 dex. The dispersion was comparable to the statistical uncertainties of the metallicity measurements; in addition, the metallicities of all 22 stars fell within the dispersion range, indicating their uniform metallicities. A comparison of our results with previous studies confirmed a high probability of metallicity homogeneity in Pleiades.
WD+MS Systems as Progenitors of Type Ia Supernovae with Different Metallicities
Authors: Meng Xiangcun , Yang Wuming , Geng Xuemin 
Published: March 2014

Abstract
The single-degenerate model for the progenitors of type Ia supernovae (SNe Ia) is one of the two most popular models, in which a carbon–oxygen white dwarf accretes hydrogen-rich material from its companion, increases its mass to the Chandrasekhar mass limit, and then explodes as a SN Ia. Incorporating the prescription of Hachisu et al. (1999a, ApJ, 519, 314) for the accretion efficiency into Eggleton’s stellar evolution code and assuming that the prescription is valid for all metallicities, we carried out a detailed binary evolution study with different metallicities. We showed the initial and final parameter space for SNe Ia in a (log$ P$–$M_{\rm 2}$) plane. The positions of some famous recurrent novae in the (log$ P$–$M_{2}$) plane, as well as a supersoft X-ray source (SSS), RX J0513.9$-$6951 are well explained by our model, and our model can also explain the space velocity and mass of Tycho G, which is now suggested to be a companion star of Tycho’s supernova. Our study indicates that a SSS, V Sge, is a potential progenitor of supernovae, like SN 2002ic, if the delayed dynamical-instability model in Han and Podsiadlowski (2006, MNRAS, 368, 1095) is appropriate.
Viscous Accreting Magnetofluids around a Static Compact Object in Final Stages of Accretion Flow
Authors: Ghanbari Jamshid , Shaghaghian Mahboobeh 
Published: March 2014

Abstract
The dynamics of the stationary axisymmetric configuration of accreting magnetofluids surrounding a non-rotating compact object in the final stages of accretion flow is presented here. We discuss two classes of solutions for the angular momentum: a Keplerian solution, which demands no accretion flow for the fluids, and a non-Keplerian solution, which requires a radial inflow velocity for the matter. For the special case of no presence of electromagnetic fields, two sets of self-consistent analytical solutions of fully relativistic fluid equations are obtained separately for two different equations of state. The effect of the bulk viscosity coefficient on the physical functions was investigated for each state, as well as the bounds that exert on the free parameters due to last stages of the accretion-flow condition. To resolve the magnetohydrodynamical equations, we were inspired by previous sets of solutions, since the magnetofluid equations are just the same as the fluid ones in the case of vanishing electromagnetic fields. The azimuthal current in magnetofluids doesn’t modify the dipolar configuration of the central object magnetic field, owing to the lack of a finite resistivity. The presence of this magnetic field doesn’t affect the azimuthal velocity of the plasma, but does slow down its radial inflow, and decrease the density and pressure of the plasma. Despite the role importance of the bulk viscosity on the fluids’ dynamics in the absence of electromagnetic fields, exerting the magnetic field decreases this role.
Observational Appearance and Spectrum of Black-Hole Winds with Supercritical Accretion Disks
Authors: Fukue Jun 
Published: March 2014

Abstract
We examine the observational appearance and expected spectra of an optically thick, spherically symmetric, relativistic wind (a black-hole wind), blowing off from the central region of a geometrically thick supercritical accretion disk. Due to the relativistic limb-darkening (center-brightening) effect as well as the usual Doppler boost, the black-hole wind becomes luminous as the wind speed increases. We found that the spectra of the black-hole wind is somewhat similar to a blackbody one, while the spectra of a naked supercritical accretion disk is known to have a flat spectral energy distribution (SED) when viewing from the pole-on direction. In the case of a black-hole wind with a supercritical accretion disk, the spectra generally becomes a hybrid type, but we found that in almost all cases the characteristic flat SED of a supercritical disk disappears. That is, when the speed of the wind gas is low, the apparent photosphere of the black-hole wind becomes larger than the supercritical region. In this case the spectra of a black-hole wind dominates. As the wind speed increases, the apparent photosphere shrinks and the spectra of the disk emergent. However, when the wind speed becomes sufficiently high, the inner part of the naked supercritical disk is not seen, even if the inclination angle is small.
Spectral Variation of the Seyfert 1 Galaxy MCG –6–30–15 Observed with Suzaku
Authors: Miyakawa Takehiro , Ebisawa Ken , Terashima Yuichi , Tsuchihashi Fuminori , Inoue Hajime , Zycki Piotr 
Published: March 2014

Abstract
We have investigated the spectral variation of the Seyfert 1 galaxy MCG $-$6–30–15 observed with Suzaku in 2006 January for three separate periods spreading over fourteen days. We found that the time-averaged continuum energy spectrum between 1 keV and 40 keV can be approximated with a spectral model composed of a direct power-law component, its reflection component, two warm absorbers with different ionization states, and neutral absorption. We have taken two approaches to study its spectral variation at various timescales. The first approach was to make intensity-sliced spectra, and to study any correlation between the intensity and the spectral shape. The second approach was to study spectral changes between the intervals when the source flux is above (“bright state”) and below (“faint state”) the average for fixed time-intervals. In both approaches, we found a clear correlation between the intensity in the 6–10 keV band and the spectral ratio of 0.5–3.0 keV$/$6.0–10 keV. Such a spectral variation requires a change of the apparent slope of the direct component, whereas the shape and intensity of the reflection component are invariable. The observed apparent spectral change is explained by the variation of the ionization degree of one of the two warm absorbers due to the intrinsic source luminosity variation. The current results suggest that the warm absorber has a critical role to explain the observed continuum spectral shape and the variation of MCG $-$6–30–15, which is essential to constrain the parameters of the putatively broadened iron line emission feature.
Tidal Mechanism as an Impossible Cause of the Observed Secular Increase of the Astronomical Unit
Authors: Itoh Yousuke 
Published: March 2014

Abstract
Krasinsky and Brumberg (2004, Celest. Mech. Dyn. Astron., 90, 267) reported a secular increase in the Astronomical Unit (AU) of 15 meters per century. Recently, Miura et al. (2009, PASJ, 61, 1247) proposed that angular-momentum transfer from the rotation of the Sun to the orbital motion of the solar-system planets may explain the observed increase of the AU. They assumed that the tidal effect between the planets and the Sun is the cause of this transfer. Here, we claim that a tidal effect cannot be a cause of this type of transfer to explain the increase of the AU.
Suzaku and XMM-Newton Observations of Diffuse X-Ray Emission from the Eastern Tip Region of the Carina Nebula
Authors: Ezoe Yuichiro , Hamaguchi Kenji , Gruendl Robert A. , Chu You-Hua , Petre Robert , Corcoran Michael F. 
Published: March 2014

Abstract
The eastern tip region of the Carina Nebula was observed with the Suzaku XIS for 77 ks to conduct a high-precision spectral study of extended X-ray emission. XMM-Newton EPIC data of this region were also utilized to detect point sources. The XIS detected strong extended X-ray emission from the entire field-of-view with a 0.2–5 keV flux of 0.7–4$\times$10$^{-14}$ergs$^{-1}$arcmin$^{-2}$. The emission has a blob-like structure that coincides with an ionized gas filament observed in mid-infrared images. Contributions of astrophysical backgrounds and the detected point sources were insignificant. Thus the emission is diffuse in nature. The X-ray spectrum of the diffuse emission was represented by a two-temperature plasma model with temperatures of 0.3 and 0.6 keV and an absorption column density of 2$\times$10$^{21}$cm$^{-1}$. The X-ray emission showed normal nitrogen-to-oxygen abundance ratios and a high iron-to-oxygen abundance ratio. The spectrally deduced parameters, such as temperatures and column densities, are common to the diffuse X-ray emission near $\eta$ Car. Thus, the diffuse X-ray emission in these two fields may have the same origin. The spectral fitting results are discussed to constrain the origin in the context of stellar winds and supernovae.
X-Ray Spectral Variability of the Seyfert Galaxy NGC 4051 Observed with Suzaku
Authors: Terashima Yuichi , Gallo Luigi C. , Inoue Hirohiko , Markowitz Alex G. , Reeves James N. , Anabuki Naohisa , Fabian Andrew C. , Griffiths Richard E. , Hayashida Kiyoshi , Itoh Takeshi , Kokubun Norihide , Kubota Aya , Miniutti Giovanni , Takahashi Tadayuki , Yamauchi Makoto , Yonetoku Daisuke 
Published: March 2014

Abstract
We report on results from a Suzaku observation of the narrow-line Seyfert 1 NGC 4051. During our observation, large-amplitude rapid variability was seen, and the averaged 2–10 keV flux was 8.1$\times$10$^{-12}$erg s$^{-1}$cm$^{-2}$ which is several times lower than the historical average. The X-ray spectrum hardens when the source flux becomes lower, confirming the trend of spectral variability known for many Seyfert 1 galaxies. The broad-band averaged spectrum and spectra in high- and low-flux intervals were analyzed. The spectra were first fitted with a model consisting of a power-law component, a reflection continuum originating in cold matter, a blackbody component, two zones of ionized absorber, and several Gaussian emission lines. The amount of reflection is rather large ($R$$\sim$ 7, where $R$$=$ 1 corresponds to reflection by an infinite slab), while the equivalent width of the Fe-K line at 6.4 keV is modest (140 eV) for the averaged spectrum. We then modeled the overall spectra by introducing partial covering for the power-law component and reflection continuum independently. The column density for the former is 1$\times$10$^{23}$cm$^{-2}$, while it is fixed at 1$\times$10$^{24}$cm$^{-2}$ for the latter. By comparing the spectra in different flux states, we could identify the causes of spectral variability.
Method of the Particle-in-Cell Simulation for the Y-Point in the Pulsar Magnetosphere
Authors: Umizaki Mitsuhiro , Shibata Shinpei 
Published: March 2014

Abstract
Recent observations in the X-ray and Gamma-ray suggest that the emission region of the pulsar magnetosphere can be multifold. In particular, the open-close boundary of the magnetic field, so-called the Y-point, can be a new candidate place where magnetic field energy converts into plasma heat and/or flow energy. Here, we present a new Particle-in-Cell code, which can be applied to the Y-point of the pulsar magnetosphere in axisymmetric geometry. The electromagnetic solver is used in two-dimensional grid points with cylindrical coordinates ($R$, $z$), while the particle solver operates in three-dimensional Cartesian coordinates ($x$, $y$, $z$), where the Buneman–Boris method is used. The particle motion is treated in special relativity. The inner boundary conditions are set up to generate rotation of the magnetosphere by use of the force-free semi-analytic solution given by Uzdensky (2003, ApJ, 598, 446). The code has been verified by dispersion relations of all wave modes in electron-positron plasmas. The initial test run is also presented to demonstrate the Y-shaped structure at the top of the dead zone on the light cylinder. We suggest that the structure is variable with quasi-periodicity with magnetic reconnection, and that plasma will be accelerated and/or heated. In a time-averaged point of view, the break up of the ideal-MHD (magneto-hydrodynamics) condition takes place in the vicinity of the Y-point.