bluuebunny/crossref_metadata_2025 huggingface dataset:
Slow and Fast Transitions in the Rising Phase of Outbursts from NS–LMXB Transients, Aquila X-1 and 4U 1608−52
Authors: Asai Kazumi , Matsuoka Masaru , Mihara Tatehiro , Sugizaki Mutsumi , Serino Motoko , Nakahira Satoshi , Negoro Hitoshi , Ueda Yoshihiro , Yamaoka Kazutaka
Published: March 2014

We analyzed the initial rising behaviors of X-ray outbursts from two transient low-mass X-ray binaries (LMXBs) containing a neutron-star (NS), Aquila X-1 (Aql X-1) and 4U 1608$-$ 52, which are continuously being monitored by MAXI/GSC in 2–20 keV, RXTE/ASM in 2–10 keV, and Swift/BAT in 15–50 keV. We found that the observed ten outbursts can be classified into two types based on the patterns of the relative intensity evolutions in the two energy bands below/above 15 keV. One type behaves as the 15–50 keV intensity achieves the maximum during the initial hard-state period, and drops greatly at the hard-to-soft state transition. On the other hand, the other type does as both the 2–15 keV and 15–50 keV intensities achieve the maximums after the transition. The former have the longer initial hard-state ($ \gtrsim$ 9 d) than the latter ($ \lesssim$ 5 d). Therefore, we named them as slow-type (S-type) and fast-type (F-type), respectively. These two types also show differences in the luminosity at the hard-to-soft state transition as well as in the average luminosity before the outburst started, where the S-type are higher than the F-type in both. These results suggest that the X-ray radiation during the pre-outburst period, which heats up the accretion disk and delays the disk transition (i.e., from a geometrically thick disk to a thin one), would determine whether the following outburst becomes S-type or F-type. The luminosity when the hard-to-soft state transition occurs is higher than $ \sim$ 8 $ \times$ 10$ ^{36}$ erg s$ ^{-1}$ in the S-type, which corresponds to 4% of the Eddington luminosity for a 1.4 NS.
An Attempt to Describe Frequency-Correlations among kHz QPOs and HBOs by Two-Armed Vertical p-Mode Oscillations: Case of No Magnetic Field
Authors: Kato Shoji
Published: March 2014

The trapping of two-armed ($ m$$ =$ 2) vertical p-mode oscillations in relativistic disks is examined. The disks are assumed to be isothermal in the vertical direction, but are truncated at a certain height by the presence of corona. The same issues were examined in a previous paper (Kato 2012a). In this paper, unlike the previous paper, however, we do not use the approximation that the oscillations are nearly vertical, but limit to a simpler case of no magnetic field. As in the previous paper, the results suggest that the two basic oscillation modes [both are the fundamental ($ n$$ =$ 1) in the vertical direction, but in the horizontal direction one is the fundamental ($ n_{\rm r}$$ =$ 0) and the other the first overtone ($ n_{\rm r}$$ =$ 1)] correspond to the twin kHz QPOs. Second, the oscillation mode, which is the first overtone ($ n$$ =$ 2) in the vertical direction and the fundamental in the horizontal direction ($ n_{\rm r}$$ =$ 0), will correspond to the horizontal branch oscillation (HBO) of Z-sources. The latter suggests that the horizontal branch of Z-sources is a sequence of temperature change in disks whose vertical thickness is strongly terminated. The temperature increases leftward along the sequence from the apex between the normal and horizontal branches.
Search for Diffuse X-Rays from the Bow Shock Region of Runaway Star BD +43 3654 with Suzaku
Authors: Terada Yukikatsu , Tashiro Makoto S. , Bamba Aya , Yamazaki Ryo , Kouzu Tomomi , Koyama Shu , Seta Hiromi
Published: March 2014

The bow shocks of runaway stars with strong stellar winds of over 2000 km s$ ^{-1}$ can serve as particle acceleration sites. The conversion from stellar wind luminosity into particle acceleration power has an efficiency of the same order of magnitude as those in supernova remnants, based on the radio emission from the bow shock region of runaway star BD $ +$ 43 3654 (Benaglia et al. 2010, A&A, 517, L10). If this object exhibits typical characteristics, then runaway star systems can contribute a non-negligible fraction of Galactic cosmic-ray electrons. To constrain the maximum energy of accelerated particles from measurements of possible non-thermal emissions in the X-ray band, Suzaku observed BD $ +$ 43 3654 in 2011 April with an exposure of 99 ks. Because the onboard instruments have a stable and low background level, Suzaku detected a possible enhancement over the background of 7.6 $ \pm$ 3.4 counts arcmin$ ^{-2}$ at the bow shock region, where the error represents the 3 $ \sigma$ statistics only. However, the excess is not significant within the systematic errors of non-X-ray and cosmic-ray backgrounds of the X-ray Imaging Spectrometer, which are $ \pm$ 6.0 and $ \pm$ 34 counts arcmin$ ^{-2}$ , respectively, and the 3 $ \sigma$ upper limit in the X-ray luminosity from the shock region, which is 1.1 $ \times$ 10$ ^{32}$ erg s$ ^{-1}$ per 41.2 arcmin$ ^2$ in the 0.5 to 10 keV band. This result leads to three conclusions: (1) a shock-heating process is inefficient on this system; (2) the maximum energy of electrons does not exceed $ \sim$ 10 TeV, corresponding to a Lorentz factor of less than $ 10^7$ ; and (3) the magnetic field in the shock acceleration site might not be as turbulent as those in pulsar wind nebulae and supernova remnants.
Recombining Plasma and Hard X-Ray Filament in the Mixed-Morphology Supernova Remnant W 44
Authors: Uchida Hiroyuki , Katsuji Koyama , Yamaguchi Hiroya , Sawada Makoto , Ohnishi Takao , Tsuru Takeshi Go , Tanaka Takaaki , Yoshiike Satoshi , Fukui Yasuo
Published: March 2014

We report on new features of the typical mixed-morphology supernova remnant W 44. In X-ray spectra obtained with Suzaku, radiative recombination continua of highly ionized atoms were detected for the first time. The spectra are well reproduced by a thermal plasma in a recombining phase. The best-fit parameters suggest that the electron temperature of the shock-heated matter rapidly cooled down from $\sim$ 1 keV to $\sim$ 0.5 keV, possibly due to adiabatic expansion (rarefaction), occurred $\sim$ 20000 yr ago. We also discovered hard X-ray emission, which shows an arclike structure spatially correlating with a radio continuum filament. The surface-brightness distribution has a clear anticorrelation with $^{12}$ CO ($J$  $=$ 2–1) emission from a molecular cloud observed with NANTEN2. While the hard X-ray is most likely due to a synchrotron enhancement in the vicinity of the cloud, no current model can quantitatively predict the observed flux.
Low-Resolution Spectroscopy of the Recurrent Nova T Pyxidis at its Early Stage of the 2011 Outburst
Authors: Imamura Kazuyoshi , Tanabe Kenji
Published: March 2014

We present our observational results of the recurrent nova T Pyx at its early stage of the 2011 outburst, using a low-resolution spectrograph ($ R$$ \approx$ 400) attached to a 28 cm telescope. The total number of nights of our observation was 11, among which 9 nights were during the pre-maximum stage. As a result, we obtained a detailed evolutional feature of this recurrent nova on the way to its maximum light. At first, on the earliest three nights (25–21 days before maximum), broad and prominent emission lines, such as Balmer series, He I, He II, N II, N III, and O I together with the P Cyg profile, are seen on the spectra. The blueshifted absorption minima of H$ \alpha$ yields a maximum expansion velocity of approximately 2200 km s$ ^{-1}$ , and the velocity gradually decreases. Then, helium and nitrogen lines are weakened day by day. After that (18 days before maximum light), Fe II (multiplets) lines emerge on the spectra. These lines are then strengthened day by day, and the P Cyg profiles also become more prominent. Accordingly, the expansion velocities turn to gradual increase. In addition, during the pre-maximum stage, the nova spectral type of T Pyx is thought to evolve from the He$ /$ N type to the Fe II one.
Phase Relationship between Polar Faculae and Sunspot Numbers Revisited: Wavelet Transform Analyses
Authors: Deng Linhua , Qu Zhongquan , Dun Guangtao , Xu Chenglin
Published: March 2014

Cross-correlation analysis and wavelet transform methods are proposed to investigate the phase relationship between the polar faculae (PF) and the sunspot numbers (SNs). It was found that: (1) the PF begin 52 months earlier than the SNs on the average of the considered time interval, which should lead to phase asynchrony between them; (2) the length of the Schwabe cycle for the PF obviously differs from that for the SNs at all time points, and the mean length of the Schwabe cycle of the PF (10.28 yr) is slightly smaller than that of the SNs (10.37 yr); (3) the phase relationship between the PF and the SNs is not only time-dependent but also frequency-dependent.
Is the Cygnus Superbubble a Hypernova Remnant?
Authors: Kimura Masashi , Tsunemi Hiroshi , Tomida Hiroshi , Sugizaki Mutsumi , Ueno Shiro , Hanayama Takanori , Yoshidome Koshiro , Sasaki Masayuki
Published: March 2014

We present here an observation of the Cygnus Superbubble (CSB) using the Solid-state slit camera (SSC) aboard the Monitor of All-sky X-ray Image (MAXI). The CSB is a large diffuse structure in the Cygnus region with enhanced soft X-ray emission. By utilizing the CCD spectral resolution of the SSC, we detected Fe, Ne, Mg emission lines from the CSB for the first time. The best-fit model implies a thin hot plasma of $ kT$$ \approx$ 0.3 keV with a depleted abundance of 0.26 $ \pm$ 0.1 solar. Joint spectrum fittings of the ROSAT/PSPC data and MAXI/SSC data enabled us to measure precise values of $ N_{\rm H}$ and the temperature inside the CSB. The results show that all of the regions in the CSB have a similar $ N_{\rm H}$ and temperature, indicating that the CSB is a single unity. An energy budgets calculation suggests that (2–3) $ \times$$ 10^{6}$ yr of stellar wind from the Cyg OB2 is sufficient to power up the CSB, whereas due to its off-center position, the origin of the CSB is most likely to be a Hypernova.
An X-Ray Detected Group of Quiescent Early-Type Galaxies at z = 1.6 in the Chandra Deep Field South
Authors: Tanaka Masayuki , Alexis Finoguenov , Mirkazemi Mohammad , Wilman David J. , Mulchaey John S. , Ueda Yoshihiro , Xue Yongquan , Brandt William N. , Cappelluti Nico
Published: March 2014

We report the discovery of an X-ray group of galaxies located at a high redshift of $ z$  $ =$ 1.61 in the Chandra Deep Field South. Based on 4 Ms Chandra data, the group is first identified as an extended X-ray source. We have used a wealth of deep multi-wavelength data to identify the optical counterpart—our red sequence finder detects a significant over-density of galaxies at $ z$  $ \sim$ 1.6. The brightest group galaxy is spectroscopically confirmed at $ z$  $ =$ 1.61, based on published spectroscopic redshifts. Using this as a central redshift of the group, we measure an X-ray luminosity of $ L_{0.1{\rm-}2.4\rm keV}$  $ =$ (1.8 $ \pm$ 0.6) $ \times$ 10$ ^{43}$ erg s$ ^{-1}$ , which then translates into a group mass of (3.2 $ \pm$ 0.8) $ \times$ 10$ ^{13}$  $ M_{\odot}$ . This is the lowest-mass group ever confirmed at $ z$  $ >$ 1.5. Deep optical–nearIR images from CANDELS reveal that the group exhibits a surprisingly prominent red sequence, and most of the galaxies are consistent with a formation redshift of $ z_{\rm f}$  $ =$ 3. A detailed analysis of the spectral energy distributions of the group member candidates confirms that most of them are indeed passive galaxies. Furthermore, their structural parameters measured from near-IR CANDELS images show that they are morphologically early-type. The newly identified group at $ z$  $ =$ 1.61 is dominated by quiescent early-type galaxies, and the group appears to be similar to those in the local Universe. One possible difference is the high fraction of AGN—38$ ^{+23}_{\hskip.4mm-20}$ % of the bright group member candidates are AGN, which might indicate a role for AGN in the quenching of star formation. However, a statistical sample of high-$ z$ groups is needed to draw a general picture of groups at this redshift. Such a sample will hopefully be available in near-future surveys.
K-Shell Line Distribution of Heavy Elements along the Galactic Plane Observed with Suzaku
Authors: Uchiyama Hideki , Nobukawa Masayoshi , Go tsuru Takeshi , koyama Katsuji
Published: March 2014

We report on the global distribution of the intensities of the K-shell lines from He-like and H-like ions of S, Ar, Ca, and Fe along the Galactic plane. From the profiles, we clearly separate the Galactic center X-ray emission (GCXE) and the Galactic ridge X-ray emission (GRXE). The intensity profiles of the He-like K$ \alpha $ lines of S, Ar, Ca, and Fe along the Galactic plane are approximately similar to each other, while not for the H-like Ly$ \alpha $ lines. In particular, the profiles of H-like Ly$ \alpha $ of S and Fe show remarkable contrast: a large excess of Fe, and almost no excess of S lines in GCXE compared to GRXE. Although the prominent K-shell lines are represented by $ \sim$ 1 keV and $ \sim$ 7 keV temperature plasmas, these two temperatures are not equal between GCXE and GRXE. In fact, a spectral analysis of GCXE and GRXE revealed that the $ \sim$ 1 keV plasma in GCXE has a lower temperature than that in GRXE, and vice versa for the $ \sim$ 7 keV plasma.
Moment Approach to Determining the Orbital Elements of an Astrometric Binary with a Low Signal-to-Noise Ratio
Authors: Iwama Hirofumi , Asada Hideki , Yamada Kei
Published: March 2014

A moment approach to the orbit determination of an astrometric binary with a low signal-to-noise ratio from astrometric observations alone is proposed, especially aiming at a close binary system with a short orbital period, such as Cyg X-1, and also at a star wobbled by planets. As an exact solution to the nonlinearly coupled equation, the orbital elements are written in terms of the second and third moments of projected positions that are measured by astrometry. This may hold the possibility of the true orbit estimate.
Evidence for Recombining Plasma in the Supernova Remnant G346.6–0.2
Authors: Yamauchi Shigeo , Nobukawa Masayoshi , Koyama Katsuji , Yonemori Manami
Published: March 2014

We present Suzaku results of the supernova remnant (SNR) G346.6$-$ 0.2. The X-ray emission has a center-filled morphology with a size of 6$ '$$ \times$ 8$ '$ within the radio shell. Neither an ionization equilibrium nor non-equilibrium (ionizing) plasma can reproduce the spectra remaining shoulder-like residuals in the 2–4 keV band. These structures are possibly due to a recombination of free electrons to the K-shell of He-like Si and S. The X-ray spectra were well-fitted with a plasma model in a recombination-dominant phase. We propose that the plasma was in a nearly full ionized state at a high temperature of $ \sim$ 5 keV, and then the plasma changed to a recombining phase due to selective cooling of electrons to a lower temperature of $ \sim$ 0.3 keV. G346.6$-$ 0.2 would be in an epoch of the recombining phase.
The GENJI Programme: Gamma-Ray Emitting Notable AGN Monitoring by Japanese VLBI
Authors: Nagai Hiroshi , Kino Motoki , Niinuma Kotaro , Akiyama Kazunori , Hada Kazuhiro , Koyama Shoko , Orienti Monica , Hiura Koichiro , Sawada-Satoh Satoko , Honma Mareki , Giovannini Gabriele , Giroletti Marcello , Shibata Katsunori , Sorai Kazuo
Published: March 2014

We introduce the gamma-ray emitting notable active galactic nucleus (AGN) monitoring by Japanese VLBI programme, which is the monitoring of gamma-ray bright AGNs with the VLBI Exploration of Radio Astrometry (VERA) array. This programme aims to conduct dense monitoring at 22 GHz toward the $ \gamma$-ray emitting AGNs to investigate the time variation of the radio core and possible ejection of a new radio component, the motion of jets, and their relations with the emission at other wavelengths, especially at $ \gamma$-rays. We are currently monitoring 8 notable $ \gamma$-ray-emitting AGNs (DA 55, 3C 84, M 87, PKS 1510$-$ 089, DA 406, NRAO 530, BL Lac, and 3C 454.3) about once every two weeks. This programme is promising for tracing the trend of radio time variation on shorter time scale than conventional VLBI monitoring programmes and is complementary to data of other programmes (e.g., MOJAVE; Boston University Blazar Project). In particular, we successfully carried out quick follow-up observations after the GeV $ \gamma$-ray flare in NRAO 530 and 3C 454.3 reported by the Fermi Gamma-ray Space Telescope. Here, we present the initial results of morphology and light curves for the first 7-month operation.
Long-Term Variability of the O VII Line Intensity toward the Lockman Hole Observed with Suzaku from 2006 to 2011
Authors: Yoshitake Hiroshi , Sakai Kazuhiro , Mitsuda Kazuhisa , Yamasaki Noriko Y. , Takei Yoh , Yamamoto Ryo
Published: March 2014

Long-term time variabilities of the O VII (0.57 keV) emission in the soft X-ray diffuse background were studied using six Suzaku annual observations of the blank sky towards the Lockman Hole made from 2006 to 2011. After time intervals in which the emission was enhanced on time scales of a few tens of ks were removed, the O VII intensity was found to be constant from 2006 to 2009 within 90% statistical errors. The intensity in 2010 and 2011 was higher by 2–3 LU ($ =$ photons s$ ^{-1}$ cm$ ^{-2}$ sr$ ^{-1}$ ) than the earlier values. The most plausible origin of the fast variable component is Solar wind charge exchange (SWCX). The intensity increase is not positively correlated with the proton flux at the L1 point. Since all of the observations were made in the same season of a year, the variation cannot be explained by parallax of the SWCX-induced X-ray emission from the Heliosphere. We consider that it is related to geometrical changes of slow and fast solar wind structures associated with the 11 year solar activity. The observed variation was compared with that expected from the SWCX-induced X-ray emission model.
Density Profile of a Cool Core of Galaxy Clusters
Authors: Ota Naomi , Onzuka Kiyokazu , Masai Kuniaki
Published: March 2014

The density profile of a cool core of intracluster gas is investigated for a cluster of galaxies that is initially in the virial equilibrium state, and then undergoes radiative cooling. The initial gas profile is derived under the assumption that the gas is hydrostatic within the dark-matter potential presented by the “NFW” or King model, and has a polytropic profile. The contribution of masses of gas and galaxies to the potential in the calculation is ignored compared to the dark matter. The temperature and density profiles of gas in its quasi-hydrostatic cooling phase, which is expected to last for $ \sim$ Gyr, are then calculated for different initial gas profiles. It is found that in the quasi-hydrostatic cooling phase, while the temperature decreases to about one-third, the density increases by a factor of 4–6 at the cluster center in comparison with its initial polytropic value, though the profiles over the core depend on the dark-matter potential. Hence, the core radius in the quasi-hydrostatic cooling gas appears to be smaller than that in the initial polytropic gas. We compared the density profile of the cool core with observations to find that, while the initial density is around the upper bounds of large-core ($ >$ 100 kpc) clusters, most likely relaxed, but the cooling is not yet significant, the central density under quasi-hydrostatic cooling falls between the mid- and high-values of small ($ <$ 100 kpc)- or cool-core clusters. It is also found for the quasi-hydrostatic cooling gas that the entropy profile roughly agrees with the best-fit model to the ACCEPT cluster sample with a low central entropy; also, the pressure gradient in the core is close to that of the REXCESS sample. X-ray surface brightness calculated for the quasi-hydrostatic cooling gas is well represented by the conventional double $ \beta $-model, giving a physical basis for applying the double $ \beta $-model to cool-core clusters.
Detection of a 522 s Pulsation from the Transient X-Ray Source Suzaku J0102.8–7204 (SXP 523) in the Small Magellanic Cloud
Authors: Wada Qazuya , Tsujimoto Masahiro , Ebisawa Ken , Miller Eric D.
Published: March 2014

During a routine calibration observation of 1E 0102.2$-$ 7219 in the Small Magellanic Cloud (SMC), carried out in 2012 October for the Suzaku satellite, we detected a transient X-ray source at (RA, Dec) $ =$ (01$ ^{\rm h}$ 02$ ^{\rm m}$ 47$ ^{\rm s}$ , $-$ 72$ ^\circ$ 04$ ^{\rm m}$ 54$ ^{\rm s}$ ) in the equinox J2000.0 with a positional uncertainty of $ \sim$ 14. We conducted a temporal and spectral analysis of the source and found a coherent pulse signal with a period of 522.3 $ \pm$ 0.1 s. We also found a featureless spectrum described by a single power-law model with a photon index of 1.0$ ^{+0.1}_{-0.1}$ and a 0.5–10 keV luminosity of $ \sim$ 8.8 $ \times$ 10$ ^{35}$ erg s$ ^{-1}$ at an assumed distance of 60 kpc. The Suzaku source is likely to be the counterpart of 2XMM J010247.4$-$ 720449, which has been observed several times, including outburst detected by Swift. Based on the X-ray characteristics from our data, as well as the transient record and optical and near-infrared features described in the literature, we conclude that this source is a high-mass X-ray binary pulsar with a Be star companion in the SMC, which is known to harbor an exceptionally large ($ \sim$ 80) number of such sources compared to that in our Galaxy.
The Cause of the Superoutburst in SU UMa Stars is Finally Revealed by Kepler Light Curve of V1504 Cygni
Authors: Osaki Yoji , Kato Taichi
Published: March 2014

We have studied the short-cadence Kepler light curve of an SU UMa star, V1504 Cyg, which covers a period of $ \sim$ 630 d. All superoutbursts in V1504 Cyg have turned out to be of precursor-main types, and the superhump first appears near the maximum of the precursor. The superhumps grow smoothly from the precursor to the main superoutburst, showing that the superoutburst was initiated by a tidal instability (as evidenced by the growing superhump) as envisioned in the thermal-tidal instability (TTI) model proposed by Osaki (1989, PASJ, 41, 1005). We performed a power spectral analysis of the light curve of V1504 Cyg. One of the outstanding features is the appearance of a negative superhump extending over around 300 d, well over a supercycle. We found that the appearance of the negative superhump tends to decrease the frequency of occurrence of normal outbursts. Two types of supercycles are recognized in V1504 Cyg, which are similar to those of the Type L and Type S supercycles in the light curve of VW Hyi, a prototype SU UMa star, introduced by Smak (1985, Acta Astron., 35, 357). It is found that the Type L supercycle is the one accompanied by the negative superhump, and Type S is that without the negative superhump. If we adopt a tilted disk as an origin of the negative superhump, two types of the supercycles are understood to be due to a difference in the outburst interval, which is in turn caused by a difference in mass supply from the secondary to different parts of the disk. The frequency of the negative superhump varies systematically during a supercycle in V1504 Cyg. This variation can be used as an indicator of the disk-radius variation, and we have found that the observed disk-radius variation in V1504 Cyg fits very well with a prediction of the TTI model.
Spectral Evolution of a New X-Ray Transient MAXI J0556−332 Observed by MAXI, Swift, and RXTE
Authors: Sugizaki Mutsumi , Yamaoka Kazutaka , Matsuoka Masaru , Kennea Jamie A. , Mihara Tatehiro , Hiroi Kazuo , Ishikawa Masaki , Isobe Naoki , Kawai Nobuyuki , Kimura Masashi , Kitayama Hiroki , Kohama Mitsuhiro , Matsumura Takanori , Morii Mikio , Nakagawa Yujin E. , Nakahira Satoshi , Nakajima Motoki , Negoro Hitoshi , Serino Motoko , Shidatsu Megumi , Sootome Tetsuya , Sugimori Kousuke , Suwa Fumitoshi , Toizumi Takahiro , Tomida Hiroshi , Tsuboi Yoko , Tsunemi Hiroshi , Ueda Yoshihiro , Ueno Shiro , Usui Ryuichi , Yamamoto Takayuki , Yamauchi Makoto , Yamazaki Kyohei , Yoshida Atsumasa
Published: March 2014

We report on the spectral evolution of a new X-ray transient, MAXI J0556$-$ 332, observed by MAXI, Swift, and RXTE. The source was discovered on 2011 January 11 (MJD $ =$ 55572) by the MAXI Gas Slit Camera all-sky survey at ($ l$, $ b$) $ =$ (238.$ ^{\!\!\!\circ}$ 9, $-$ 25.$ ^{\!\!\!\circ}$ 2), relatively away from the Galactic plane. Swift/XRT follow-up observations identified it with a previously uncatalogued bright X-ray source, which led to optical identification. For more than one year since its appearance, MAXI J0556$-$ 332 has been X-ray active, with a 2–10 keV intensity above 30 mCrab. The MAXI/GSC data revealed rapid X-ray brightening in the first five days, and a hard-to-soft transition in the meantime. For the following $ \sim$ 70 days, the 0.5–30 keV spectra, obtained by the Swift/XRT and the RXTE/PCA on an almost daily basis, show a gradual hardening, with large flux variability. These spectra are approximated by a cutoff power-law with a photon index of 0.4–1 and a high-energy exponential cutoff at 1.5–5 keV, throughout the initial 10 months where the spectral evolution is mainly represented by a change of the cutoff energy. To be more physical, the spectra are consistently explained by thermal emission from an accretion disk plus Comptonized emission from a boundary layer around a neutron star. This supports the source identification as being a neutron-star X-ray binary. The obtained spectral parameters agree with those of neutron-star X-ray binaries in the soft state, whose luminosity is higher than 1.8 $ \times$ 10$ ^{37}$ erg s$ ^{-1}$. This suggests a source distance of $ >$ 17 kpc.
Gravitational-Wave Memory from the Relativistic Jet of Gamma-Ray Bursts
Authors: Akiba Shota , Nakada Megumi , Yamaguchi Chiyo , Iwamoto Koichi
Published: March 2014

The gravitational-wave (GW) memory from a radiating and decelerating point mass is studied in detail. It is found that for isotropic photon emission the memory generated from the photons is essentially the same as the memory from the point mass that radiated the photons, so that it is anti-beamed. On the other hand, for anisotropic emission the memory from the photons may have a non-vanishing amplitude, even if it is seen at small viewing angles. In the decelerating phases of gamma-ray burst (GRB) jets the kinetic energy of the jet is converted into the energy of gamma-ray photons. It would then be possible to observe a variation in the GW memory associated with GRB jets on the timescale of the gamma-ray emission if the emission is partially anisotropic. Such anisotropy in gamma-ray emission has been suggested by polarizations detected in recent observations of GRBs. The GW memory from GRB jets would provide clues for clarifying the geometry of the jets and the emission mechanism in GRBs. Thus, it will be an interesting target for the next-generation detectors of GWs.
Long-Period Meteor Streams and the Dispersion of Semimajor Axes of Meteor Orbits
Authors: Hajduková Mária
Published: March 2014

The present work is based on an analysis of a large statistical sample of meteor orbits collected in the Japanese shower catalogue (SonotaCo 2009, WGN, 37, 55) of 114280 video observed meteors. The shower meteor data were selected and analysed with the aim of determining the orbits' distribution in major meteor streams with heliocentric velocities close to the parabolic limit, in which the errors in the velocity determination correspond to large differences in the reciprocal semimajor axis, 1$ /a$ . The contribution of the real dispersion of the semimajor axes, $ a$ , can be deduced from the high proportion of hyperbolic orbits in the analysed streams, where an excess over the parabolic value can be regarded as being entirely due to measurement errors. The orbital dispersion described by the median absolute deviation in terms of 1$ /a$ was found to be $ \pm$ 0.083 AU$ ^{-1}$ for the Leonids and $ \pm$ 0.080 AU$ ^{-1}$ for the Orionids, and slightly smaller for the Perseid and Lyrid meteor streams ($ \pm$ 0.055 and $ \pm$ 0.047 AU$ ^{-1}$ ). The proximity of the parabolic limit caused a strong influence of observational effects; however, a significant contribution of the real dispersion is involved.
Multicolor Photometry of an Outburst of a New WZ Sge-Type Dwarf Nova, OT J012059.6+325545
Authors: Nakagawa Shinichi , Noguchi Ryo , Iino Eriko , Ogura Kazuyuki , Matsumoto Katsura , Arai Akira , Isogai Mizuki , Uemura Makoto
Published: March 2014

We present our photometric studies of a newly discovered optical transient, OT J012059.6$ +$ 325545, which underwent a large outburst during the period between 2010 November and 2011 January. The amplitude of the outburst was $ \sim$ 8 mag. We performed simultaneous multicolor photometry using g$ '$-, $ R_{\rm C}$-, and $ i'$-band filters from the early stage of the outburst. Time-resolved photometry during its early stage revealed periodic variations with double-peaked profiles, which are referred to as early superhumps, with amplitudes of $ \sim$ 0.08 mag. After rapid fading in the main outburst, we found rebrightening phenomena, which occurred at least nine times. The large amplitude of the outburst, early superhumps, and rebrightening phenomena are typical features of WZ Sge-type dwarf novae. We detected color variations within early superhump modulations, which established this objects as the second system of WZ Sge-type dwarf nova, next to V445 And. We carried out numerical calculations of the accretion disk to explain both of the modulations and the color variations of the early superhump. This modeling of the disk height supports the idea that height variations within the outer disk can produce early-superhump modulations, though we cannot rule out an idea that temperature asymmetry may also play a role.
Active Galactic Nucleus and Extended Starbursts in a Midstage Merger VV 114
Authors: Iono Daisuke , Saito Toshiki , Yun Min S. , Kawabe Ryohei , Espada Daniel , Hagiwara Yoshiaki , Imanishi Masatoshi , Izumi Takuma , Kohno Kotaro , Motohara Kentaro , nakanishi Kouichiro , Sugai Hajime , Tateuchi Ken , Tamura Yoichi , Ueda Junko , Yoshii Yuzuru
Published: March 2014

High-resolution ($ \sim$ 0$ .\!\!\!''$ 4) Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 0 observations of HCO$ ^+$ (4–3) and HCN (4–3) toward a midstage infrared bright merger, VV 114, have revealed a compact nuclear ($ <$ 200 pc) and extended ($ \sim$ 3–4 kpc) dense gas distribution across the eastern part of the galaxy pair. We have found a significant enhancement of HCN (4–3) emission in an unresolved compact and broad (290 km s$ ^{-1}$ ) component found in the eastern nucleus of VV 114, and suggest dense gas associated with the surrounding material around an Active Galactic Nucleus (AGN), with a mass upper limit of $ \lesssim$ 4 $ \times$ 10$ ^{8}$  $ M_{\odot}$ . The extended dense gas is distributed along a filamentary structure with resolved dense gas concentrations ($ \sim$ 230 pc; $ \sim$ 10$ ^{6}$  $ M_{\odot}$ ) separated by a mean projected distance of $ \sim$ 600 pc, many of which are generally consistent with the location of star formation traced in Pa$ \alpha$ emission. Radiative-transfer calculations suggest moderately dense ($ n_{\rm H_2}$  $ =$ 10$ ^{5}$ –10$ ^{6}$ cm$ ^{-3}$ ) gas averaged over the entire emission region. These new ALMA observations demonstrate the strength of the dense gas tracers for identifying both the AGN and the star-formation activity in a galaxy merger, even in the most dust-enshrouded environment in the local universe.
Evidence for a Cool Disk and Inhomogeneous Coronae from Wide-Band Temporal Spectroscopy of Cygnus X-1 with Suzaku
Authors: Yamada Shin’ya , Makishima Kazuo , Done Chris , Torii Shunsuke , Noda Hirofumi , Sakurai Soki
Published: March 2014

Unified X-ray spectral and timing studies of Cygnus X-1 in the low/hard and hard intermediate state were conducted in a model-independent manner, using broadband Suzaku data acquired on 25 occasions from 2005 to 2009 with a total exposure of $\sim$ 450 ks. The unabsorbed 0.1–500 keV source luminosity changed over 0.8%–2.8% of the Eddington limit for 14.8 solar masses. Variations on short (1–2 seconds) and long (days to months) time scales require at least three separate components: a constant component localized below $\sim$ 2 keV, a broad soft one dominating in the 2–10 keV range, and a hard one mostly seen in the 10–300 keV range. In view of the truncated disk/hot inner-flow picture, these are respectively interpreted as emission from the truncated cool disk, a soft Compton component, and a hard Compton component. Long-term spectral evolution can be produced by the constant disk increasing in temperature and luminosity as the truncation radius decreases. The soft Compton component likewise increases, but the hard Compton does not, so that the spectrum in the hard intermediate state is dominated by the soft Compton component; on the other hand, the hard Compton component dominates the spectrum in the dim low/hard state, probably associated with a variable soft emission providing seed photons for the Comptonization.
Quasars with Anomalous Hβ Profiles. I. Demographics
Authors: Steinhardt Charles L. , Silverman John D.
Published: March 2014

The H$\beta$ emission line in a typical Type I quasar is composed of a broad base and a narrow core, with the core velocity characteristic of narrow-line region emission, and line-fitting routines typically assume this picture. We test the effects of removing this constraint, and find a substantial group of Type I quasars in the Sloan Digital Sky Survey catalog with H$\beta$ emission line cores broader than 1200 km s$^{-1}$, above the velocity believed possible for gas in the quasar narrow-line region. We identify this group of “anomalous H$\beta$ quasars” (AHQs) as a distinct population because of a variety of spectral and photometric signatures common to these AHQs but atypical of other quasars. These features are similar to some aspects of narrow-line Seyfert 1s and correlations identified by Eigenvector 1, but also contain distinct features that make it difficult to classify AHQs. We demonstrate that AHQs comprise at least 11% and most likely approximately one quarter of the SDSS Type I quasar population at 0.2 $<$  z  $<$ 0.8. For AHQs, the [O iii]$\lambda$ 4959, 5007 profile is often better fit by de-linking it from the H$\beta$ core, while a more standard linked fit produces a tight correlation between narrow- and broad-line velocities. We find that [O iii] in AHQs sometimes has a standard narrow-line profile and other times matches the H$\beta$ core, but is rarely in between the two, implying that the broadened core emission arises from a distinct physical region. Another feature of AHQs is a diminished [O ii] line, which might indicate a connection between AHQs and the interstellar mediums of their host galaxies, through reduced photoionization or star formation. We find that it is difficult to produce AHQs using the current quasar standard model.
Suzaku X-Ray Observations of the Accreting NGC 4839 Group of Galaxies and a Radio Relic in the Coma Cluster
Authors: Akamatsu Hiroki , Inoue Susumu , Sato Takuya , Matsusita Kyoko , Ishisaki Yoshitaka , Sarazin Craig L.
Published: March 2014

Based on Suzaku X-ray observations, we studied the hot gas around the NGC 4839 group of galaxies and a radio relic in the outskirts of the Coma cluster. We found a gradual decline in the gas temperature from 5 keV around NGC 4839 to 3.6 keV at the radio relic, across which there is a further, steeper drop down to 1.5 keV. This drop as well as the observed surface brightness profile are consistent with a shock with Mach number ${\cal M} =$ 2.2 $\pm$ 0.5 and velocity $v_{\rm s} =$ (1410 $\pm$ 110) km s$^{-1}$. A lower limit of $B \gt $ 0.33 $\mu$G was derived based on the magnetic field strength around the relic from the upper limits to inverse Compton X-ray emission. Although this suggests that the non-thermal electrons responsible for the relic are generated by diffusive shock acceleration (DSA), the relation between the measured Mach number and the electron spectrum inferred from radio observations are inconsistent with that expected from the simplest, test-particle theory of DSA. Nevertheless, DSA is still viable if it is initiated by the injection of a pre-existing population of non-thermal electrons. Combined with previous measurements, the temperature profile of Coma in the southwest direction is shallower outside NGC 4839, and also slightly shallower in the outermost region. The metal abundance around NGC 4839 is confirmed to be higher than that in its vicinity, implying a significant peak in the abundance profile that decreases to 0.2 solar toward the outskirts. We interpret these facts as being due to ram pressure stripping of metal-enriched gas from NGC 4839 as it falls into Coma. The relic shock may result from the combined interaction of pre-existing intracluster gas, gas associated with NGC 4839, and cooler gas flowing in from the large-scale structure filament in the southwest.
Multi-Epoch VERA Observations of Sagittarius A*. I. Images and Structural Variability
Authors: Akiyama Kazunori , Takahashi Rohta , Honma Mareki , Oyama Tomoaki , Kobayashi Hideyuki
Published: March 2014

We report on the results of multi-epoch observations of Sgr A$^*$ with VLBI Exploration of Radio Astrometry (VERA) at 43 GHz, carried out from 2004 to 2008. We detected a time variation of the flux at the 11% level and the intrinsic size at 19%. In addition, comparisons with previous Very Long Baseline Array (VLBA) results showed that Sgr A$^*$ underwent a flaring event for at least longer than 10 d in 2007 May. The intrinsic size of Sgr A$^*$ remained unchanged within the 1 $\sigma$ level from the size before/after the flaring event, indicating that the brightness temperature of Sgr A$^*$ was increased. The flaring event occurred within 31 d, which is shorter than the refractive time scale. Moreover it is difficult to explain the increase in the spectral index at the flaring event by a simple interstellar scattering model. Hence, the flaring event is most likely associated with changes in the intrinsic properties of Sgr A$^*$. We considered the origin of the brightness temperature variation, and concluded that the flaring event of Sgr A$^*$ could be explained by the continuous heating of electrons, such as a standing shock in accretion flow.
Submillimeter ALMA Observations of the Dense Gas in the Low-Luminosity Type-1 Active Nucleus of NGC1097
Authors: Izumi Takuma , Kohno Kotaro , Martín Sergio , Espada Daniel , Harada Nanase , Matsushita Satoki , Hsieh Pei-Ying , Turner Jean L. , Meier David S. , Schinnerer Eva , Imanishi Masatoshi , Tamura Yoichi , Curran Max T. , Doi Akihiro , Fathi Kambiz , Krips Melanie , Lundgren Andreas A. , Nakai Naomasa , Nakajima Taku , Regan Michael W. , Sheth Kartik , Takano Shuro , Taniguchi Akio , Terashima Yuichi , Tosaki Tomoka , Wiklind Tommy
Published: March 2014

We present the first 100 pc scale view of the dense molecular gas in the central ∼1.3 kpc of the type-1 Seyfert NGC 1097, traced by HCN (J = 4–3) and HCO+ (J = 4–3) lines afforded with ALMA band 7. This galaxy shows significant HCN enhancement with respect to HCO+ and CO in the low-J transitions, which seems to be a common characteristic in AGN environments. Using the ALMA data, we consider the characteristics of the dense gas around this AGN, and search for the mechanism of HCN enhancement. We find a high HCN (J = 4–3) to HCO+ (J = 4–3) line ratio in the nucleus. The upper limit of the brightness temperature ratio of HCN (v  2 = 11f , J = 4–3) to HCN (J = 4–3) is 0.08, which indicates that IR pumping does not significantly affect the pure rotational population in this nucleus. We also find a higher HCN (J = 4–3) to CS (J = 7–6) line ratio in NGC 1097 than in starburst galaxies, which is more than 12.7 on the brightness temperature scale. Combined with similar observations from other galaxies, we tentatively suggest that this ratio appears to be higher in AGN-host galaxies than in pure starburst ones, similar to the widely used HCN to HCO+ ratio. LTE and non-LTE modeling of the observed HCN and HCO+ lines using J = 4–3 and 1–0 data from ALMA, and J = 3–2 data from SMA, reveals a high HCN to HCO+ abundance ratio (5 ≤ [HCN]/[HCO+] ≤ 20: non-LTE analysis) in the nucleus, and that the high-J lines (J = 4–3 and 3–2) are emitted from dense (104.5 cm-3 ≤ n  H2 ≤ 106 cm-3), hot (70K ≤ T  kin ≤ 550 K) regions. Finally we propose that “high-temperature chemistry” is more plausible to explain the observed enhanced HCN emission in NGC 1097 than pure gas-phase PDR/XDR chemistry.
A Relation of the PAH3.3μm Feature with Star-forming Activity for Galaxies with aWide Range of Infrared Luminosity
Authors: Yamada Rika , Oyabu Shinki , Kaneda Hidehiro , Yamagishi Mitsuyoshi , Ishihara Daisuke , Kim Ji Hoon , Im Myungshin
Published: March 2014

For star-forming galaxies, we investigated a global relation between the polycyclic aromatic hydrocarbon (PAH) emission luminosity at 3.3μm, LPAH3.3, and the infrared (8–1000μm) luminosity, LIR, to understand how the PAH3.3μm feature relates to star-formation activity. With AKARI, we performed near-infrared (2.5–5μm) spectroscopy of 184 galaxies having LIR ∼ 108–1013L⊙. We classified the samples into infrared galaxies (IRGs: LIR < 1011L⊙), luminous infrared galaxies (LIRGs: LIR ∼ 1011–1012L⊙) and ultra-luminous infrared galaxies (ULIRGs: LIR > 1012L⊙). We excluded sources likely to be contaminated by AGN activity, based on the restframe equivalent width of the PAH emission feature (<40 nm) and the power-law index, representing the slope of continuum emission (Γ > 1; Fv ∝ λΓ). Of these samples, 13 IRGs, 67 LIRGs, and 20 ULIRGs show the PAH emission feature at λrest = 3.3μm in their spectra. We find that the LPAH3.3/LIR ratio considerably decreases toward the luminous end. Utilizing the mass and temperature of dust grains as well as the Brα emission for the galaxies, we discuss the cause of the relative decrease in the PAH emission with LIR.
Secular Influence of Solar Dark-Matter Accretion upon the Evolution of Orbits of Planets
Authors: Li Lin-Sen
Published: March 2014

This paper examines the secular influence of solar dark-matter accretion on the evolution of the orbital elements of planets. The solutions of the perturbation equations are given by using the mean anomaly as the fast variable of integration. The theoretical results obtained are secular rates in the semi-major axis, eccentricity, orbital period, and the time of perihelion passage. The results obtained are applied to the orbital evolution of major planets and of some near-Earth asteroids in our solar system.
Density-Independent Smoothed Particle Hydrodynamics for a Non-Ideal Equation of State
Authors: Hosono Natsuki , Saitoh Takayuki R. , Makino Junichiro
Published: March 2014

The smoothed particle hydrodynamics (SPH) method is a useful numerical tool to study a variety of astrophysical and planetlogical problems. However, it turned out that the standard SPH algorithm has problems in dealing with hydrodynamical instabilities. This problem is due to the assumption that the local density distribution is differentiable. In order to solve this problem, a new SPH formulation, which does not require the differentiability of the density, was proposed. This new SPH method improved the treatment of hydrodynamical instabilities. This method, however, is applicable only to the equation of state (EOS) of an ideal gas. In this paper, we describe how to extend the new SPH method to non-ideal EOS. We present the results of various standard numerical tests for non-ideal EOS. Our new method works well for non-ideal EOS. We conclude that our new SPH can handle hydrodynamical instabilities for an arbitrary EOS, and that it is an attractive alternative to the standard SPH.
The 9 and 18 Micrometer Luminosity Functions of Various Types of Galaxies with AKARI: Implication for the Dust Torus Structure of AGN
Authors: Toba Yoshiki , Oyabu Shinki , Matsuhara Hideo , Malkan Matthew A. , Ishihara Daisuke , Wada Takehiko , Ohyama Youichi , Takita Satoshi , Yamauchi Chisato
Published: March 2014

We present the 9 and 18μm luminosity functions (LFs) of galaxies at 0.006 ≤ z ≤ 0.8 (with an average redshift of ∼0.04) using the AKARI mid-infrared all-sky survey catalog. We selected 243 galaxies at 9μm and 255 galaxies at 18μm from the Sloan Digital Sky Survey (SDSS) spectroscopy region. These galaxies were then classified by their optical emission lines, such as the line width of Hα or by their emission line ratios of [O III]/Hβ and [N II]/Hα into five types: Type 1 active galactic nuclei (AGN) (Type 1); Type 2 AGN (Type 2); low-ionization narrow emission line galaxies (LINER); galaxies with both star formation and narrow-line AGN activity (composite galaxies); and starforming galaxies (SF). We found that (i) the number density ratio of Type 2 to Type 1 AGNs is 1.73±0.36, which is larger than a result obtained from the optical LF and (ii) this ratio decreases with increasing 18μm luminosity.
Study of Superoutbursts and Superhumps in SU UMa Stars by the Kepler Light Curves of V344Lyrae and V1504 Cygni
Authors: Osaki Yoji , Kato Taichi
Published: March 2014

We have studied the short-cadence Kepler public light curves of two SU UMa stars, V344 Lyr and V1504 Cyg, extending over a period of more than two years by using power spectral analysis. We determined the orbital period of V344 Lyr to be Porb = 0.087903(1)d. We also reanalyzed the frequency variation of the negative superhump in a complete supercycle of V1504 Cyg with additional data of the O – C diagram, confirming that its characteristic variation is in accordance with the thermal-tidal instability model. We present a new two-dimensional period analysis based on a new method of a least absolute shrinkage and selection operator (Lasso). The new method gives very sharp peaks in the power spectra, and it is very useful for studying the frequency variation in cataclysmic variable stars. We have analyzed simultaneous frequency variations of the positive and negative superhumps. If they are appropriately converted, it is found that they vary in unison, indicating that they represent a disk-radius variation. We have also studied the frequency (or period) variations of positive superhumps during superoutbursts. These variations can be understood in a qualitative way by combining the disk-radius variation and the variation of pressure effects during a superoutburst. A sudden excitation of oscillation with a frequency range near to the negative superhump (which we call “impulsive negative superhump”) was observed in the descending branch of several outbursts of V344 Lyr. These events seem to have occurred just prior to the next superoutburst, and to act as a “lead” of the impending superoutburst.