bluuebunny/crossref_metadata_2025_split huggingface dataset:
Suzaku Observations of Tycho’s Supernova Remnant
Authors: Tamagawa Toru , Hayato Asami , Nakamura Satoshi , Terada Yukikatsu , Bamba Aya , Hiraga Junko S. , Hughes John P. , Hwang Una , Kataoka Jun , Kinugasa Kenzo , Kunieda Hideyo , Tanaka Takaaki , Tsunemi Hiroshi , Ueno Masaru , Holt Stephen S. , Kokubun Motohide , Miyata Emi , Szymkowiak Andrew , Takahashi Tadayuki , Tamura Keisuke , Ueno Daisuke , Makishima Kazuo 
Published: March 2014

Abstract
Tycho’s supernova remnant was observed by the XIS and HXD instruments onboard the Suzaku satellite on 2006 June 26–29 for 92 ks. The spectrum up to 30 keV was well fitted with a two-component model, consisting of a power-law with a photon index of 2.7 and a thermal bremsstrahlung model with a temperature of 4.7 keV. The former component can alternatively be modeled as synchrotron emission from a population of relativistic electrons with an estimated roll-off energy of around 1 keV. In the XIS spectra, in addition to the prominent Fe K$\alpha$ line (6.445 keV), we observed for the first time significant K$\alpha$ line emission from trace species Cr and Mn at energies of 5.48 keV and 5.95 keV, respectively. Faint K$\beta$ lines from Ca (4.56 keV) and Fe (7.11 keV) were also seen. The ionization states of Cr and Mn, based on their line centroids, are estimated to be similar to that of Fe K$\alpha$ (FeXV or XVI).
X-Ray Studies of HESS J1837$-$069 with Suzaku and ASCA: a VHE Gamma-Ray Source Originated from the Pulsar Wind Nebula
Authors: Anada Takayasu , Ebisawa Ken , Dotani Tadayasu , Bamba Aya 
Published: March 2014

Abstract
We present ASCA and Suzaku studies of the TeV source HESS J1837$-$069, which has not been identified in other wavelengths. We confirm the presence of two X-ray sources in the Suzaku XIS image, AX J1838.0$-$0655 and AX J1837.3$-$0652, near both ends of the elongated TeV emission region. The XIS spectra of the two sources were reproduced by an absorbed power-law model, whose parameters are all consistent with those determined by the ASCA data. Recently, 70.5 ms X-ray pulsation has been detected with RXTE in the sky region including HESS J1837$-$069 (Gotthelf & Halpern 2008, ApJ, 681, 515). Using the ASCA GIS data, which has both timing and imaging capabilities, we identified the pulsation source as AX J1838.0$-$0655. The pulse periods determined by ASCA and Suzaku, and that reported with RXTE indicate steady spin-down at $\dot{P}$$=$ 4.917(4)$\times$10$^{-14}$s s$^{-1}$. These results suggest that AX J1838.0$-$0655 is an intrinsically stable source, and presumably a pulsar wind nebula (PWN). We discuss the possibility that AX J1838.0$-$0655 is associated with HESS J1837$-$069 and the VHE $\gamma$-ray emission is originated from the PWN.
Suzaku Observation of HESS J1825$-$137: Discovery of Largely-Extended X-Rays from PSR J1826$-$1334
Authors: Uchiyama Hideki , Matsumoto Hironori , Tsuru Takeshi Go , Koyama Katsuji , Bamba Aya 
Published: March 2014

Abstract
We observed the brightest part of HESS J1825$-$137 with the Suzaku XIS, and found diffuse X-rays extending at least up to 15$^\prime$ ($\sim$17 pc) from the PSR J1826$-$1334. The spectra have no emission line, and were fitted with an absorbed power-law model. The X-rays, therefore, are likely to be due to synchrotron emission from a pulsar wind nebula. The photon index near the pulsar ($r$$\leq$ 1${\rlap{\hskip.75pt{^\prime}}\hskip.75pt.\hskip1pt}$5) is $\Gamma$$=$ 1.7, while those in $r$$=$ 1${\rlap{\hskip.75pt{^\prime}}\hskip.75pt.\hskip1pt}$5–16${}^\prime$ are nearly constant at $\Gamma$$=$ 2.0. The spectral energy distribution of the Suzaku and H.E.S.S. results are naturally explained by a combined process; synchrotron X-rays and $\gamma $-rays by the inverse Compton of the cosmic microwave photons by high-energy electrons in a magnetic field of $\sim$7$\mu$G. If the electrons are accelerated at the pulsar, the electrons must be transported over 17 pc in the synchrotron lifetime of 1900 yr, with a velocity of $\geq$8.8 $\times$ 10$^{3}$km s$^{-1}$.
X-Ray Observations of the Sagittarius D H ii Region toward the Galactic Center with Suzaku
Authors: Sawada Makoto , Tsujimoto Masahiro , Koyama Katsuji , Law Casey J. , Tsuru Takeshi Go , Hyodo Yoshiaki 
Published: March 2014

Abstract
We present a Suzaku X-ray study of the Sagittarius D (Sgr$\;$D) H ii region in the Galactic center region. Two 18$^{\prime}$$\times$ 18$^{\prime}$ images by the X-ray Imaging Spectrometer (XIS) encompass the entire Sgr$\;$D complex. Thanks to the low background, XIS discovered two diffuse sources with low surface brightness and obtained their high signal-to-noise ratio spectra. One is associated with the core of the Sgr$\;$D H ii region, arising from a young stellar cluster. The other object is new and reported here for the first time. We also present 3.5 cm and 6.0 cm radio continuum maps of the new source using the 100-m Green Bank Telescope. We conclude that the source is a new supernova remnant (SNR; G1.2$-$0.0) based on: (1) the 0.9$\pm$0.2 keV thermal X-ray spectrum with emission lines from highly ionized atoms; (2) the diffuse nature with an apparent extent of $\sim$10 pc at the Galactic center distance inferred from the X-ray absorption ($\sim$8.5 $\times$ 10$^{22}$cm$^{-2}$); and (3) the nonthermal radio continuum spectral index ($\sim-$0.5). Our discovery of an SNR in the Sgr$\;$D H ii region leads to a revision of the view of this system, which had been considered to be a thermal H ii region and its environment.
A New Supernova Remnant Candidate and an Associated Outflow in the Sagittarius C Region
Authors: Tsuru Takeshi Go , Nobukawa Masayoshi , Nakajima Hiroshi , Matsumoto Hironori , Koyama Katsuji , Yamauchi Shigeo 
Published: March 2014

Abstract
We present the Suzaku results on a new candidate of a supernova remnant (SNR) in the Sagittarius C region. We detected diffuse X-rays of an elliptical shape (G359.41$-$0.12) and a chimney-like structure (the Chimney), both of which were fitted with a thin thermal the model of $k_{\rm B}T$$\sim$ 1 keV temperature. The absorption columns are same between these two structures, indicating that both are located at the same distance in the same line of sight. The narrow band image and one-dimensional profile of S xv K$\alpha$ at 2.45 keV show that the Chimney is emanating from G359.41$-$0.12. Therefore, these two sources are physically connected with each other. The sum of the thermal energies of the Chimney and G359.41$-$0.12 is estimated to be 1.4 $\times$ 10$^{50}$erg, typical for a galactic SNR. G359.41$-$0.12 is likely to be a new SNR candidate and the Chimney is an associated outflow.
X-Ray Reflection Nebulae with Large Equivalent Widths of the Neutral Iron K$\alpha$ Line in the Sagittarius C Region
Authors: Nakajima Hiroshi , Tsuru Takeshi Go , Nobukawa Masayoshi , Matsumoto Hironori , Koyama Katsuji , Murakami Hiroshi , Senda Atsushi , Yamauchi Shigeo 
Published: March 2014

Abstract
This paper reports on the first results of a Suzaku observation in the Sgr C region. We detected four diffuse clumps with strong line emission at 6.4 keV, K$\alpha$ from neutral or low-ionized Fe. One of them, M359.38$-$0.00, was newly discovered with Suzaku. The X-ray spectra of the two bright clumps, M359.43$-$0.07 and M359.47$-$0.15, after subtracting the galactic center diffuse X-ray emission (GCDX), exhibit a strong K$\alpha$ line from Fe i with large equivalent widths ($EW$s) of 2.0–2.2 keV and a clear K$\beta$ of Fe i. The GCDX in the Sgr C region is composed of the 6.4 keV- and 6.7 keV-associated components. These were phenomenologically decomposed by taking relations between the $EW$s of the 6.4 keV and 6.7 keV lines. Then, the former $EW$s against the associated continuum in bright clump regions were estimated to be 2.4$^{+2.3}_{-0.7}$keV. Since the two different approaches give similar large $EW$s of 2 keV, we strongly suggest that the 6.4 keV clumps in the Sgr C region are due to X-ray reflection/fluorescence (the X-ray reflection nebulae).
Time Variability of the Neutral Iron Lines from the Sagittarius B2 Region and Its Implication of a Past Outburst of Sagittarius A$^\ast$
Authors: Inui Tatsuya , Koyama Katsuji , Matsumoto Hironori , Tsuru Takeshi Go 
Published: March 2014

Abstract
We investigated long-term X-ray behavior from the Sgr B2 complex using archival data of the X-ray satellites Suzaku, XMM-Newton, Chandra, and ASCA. The observed region of the Sgr B2 complex included two prominent spots in the FeI K$\alpha$ line at 6.40 keV, a giant molecular cloud, M0.66$-$0.02, known as the “Sgr B2 cloud” and an unusual X-ray source, G0.570$-$0.018. Although these 6.40 keV spots have spatial extensions of a few parsec scale, the morphology and flux of the 6.40 keV line has been time variable for 10 years, in contrast to the constant flux of the Fe XXV K$\alpha$ line at 6.67 keV in the Galactic diffuse X-ray emission. This time variation is mostly due to M0.66$-$0.02; the 6.40 keV line flux declined in 2001, and decreased to 60% in the time span 1994–2005. The other spot, G0.570$-$0.018, is found to be conspicuous only in the Chandra observation in 2000. From the long-term time variability ($\sim$10 years) of the Sgr B2 complex, we infer that the Galactic Center black hole Sgr A$^\ast$ was X-ray bright in the past 300 years, and exhibited a time variability with a period of a few years.
X-Ray Spectroscopy of the Classical Nova V458 Vulpeculae with Suzaku
Authors: Tsujimoto Masahiro , Takei Dai , Drake Jeremy J. , Ness Jan-Uwe , Kitamoto Shunji 
Published: March 2014

Abstract
We conducted a target of opportunity X-ray observation of the classical nova V458 Vulpeculae 88 d after the explosion using the Suzaku satellite. With a $\sim$20 ks exposure, the X-ray Imaging Spectrometer detected X-ray emission significantly harder than typical super-soft source emission. The X-ray spectrum shows K$\alpha$ lines from N, Ne, Mg, Si, and S, and L-series emission from Fe in highly ionized states. The spectrum can be described by a single-temperature ($\sim$0.64 keV) thin thermal plasma model in collisional equilibrium with a hydrogen-equivalent extinction column density of $\sim$3 $\times$ 10$^{21}$cm$^{-2}$, a flux of $\sim$10$^{-12}$ergs$^{-1}$cm$^{-2}$, and a luminosity of $\sim$6 $\times$ 10$^{34}$ergs$^{-1}$ in the 0.3–3.0 keV band at an assumed distance of 13 kpc. We found a hint of an enhancement of N and deficiencies of O and Fe relative to other metals. The observed X-ray properties can be interpreted as the emission arising from shocks of ejecta from an ONe-type nova.
Chemical Abundances of Outer Halo Stars in the Milky Way
Authors: Ishigaki Miho , Chiba Masashi , Aoki Wako 
Published: March 2014

Abstract
We present the chemical abundances of 57 metal-poor ([Fe$/$H] $&lt; -$1) stars that are likely constituents of the outer stellar halo in the Milky Way. Almost all of the sample stars have an orbit reaching a maximum vertical distance ($Z_{\rm max}$) of $&gt;$ 5 kpc above and below the Galactic plane. High-resolution ($R \sim$ 50000$-$55000), high signal-to-noise (S$/$N $&gt;$ 100) spectra for the sample stars obtained with Subaru/HDS were used to derive the chemical abundances of Na, Mg, Ca, Ti, Cr, Mn, Fe, Ni, Zn, Y, and Ba with an LTE abundance analysis code. The resulting abundance data were combined with those presented in the literature that mostly targeted at smaller $Z_{\rm max}$ stars, and both data were used to investigate any systematic trends in detailed abundance patterns depending on their kinematics. It was shown that, in the metallicity range of $-$2 $&lt;$ [Fe$/$H] $&lt; -$1, the [Mg$/$Fe] ratios for stars with $Z_{\rm max} &gt;$ 5 kpc are systematically lower ($\sim$ 0.1 dex) than those with a smaller $Z_{\rm max}$. For this metallicity range, a modest degree of depression in the [Si$/$Fe] and the [Ca$/$Fe] ratios was also observed. This result of lower [$\alpha/$Fe] for the assumed outer halo stars is consistent with previous studies that found a signature of lower [$\alpha/$Fe] ratios for stars with extreme kinematics. The distribution of the [Mg$/$Fe] ratios for the outer halo stars partly overlaps with that for stars belonging to the Milky Way dwarf satellites in the metallicity interval of $-$2 $&lt;$ [Fe$/$H] $&lt; -$1 and spans a range intermediate between the distributions for the inner halo stars and the stars belonging to the satellites. Our results confirm the inhomogeneous nature of the chemical abundances within the Milky Way stellar halo, depending on the kinematic properties of the constituent stars, as suggested by earlier studies. Possible implications for the formation of the Milky Way halo and its relevance to the suggested dual nature of the halo are discussed.
Dwarf Novae in the Shortest Orbital Period Regime. I A New Short Superhump Period Dwarf Nova, OT J055717+683226
Authors: Uemura Makoto , Arai Akira , Kato Taichi , Maehara Hiroyuki , Nogami Daisaku , Kubota Kaori , Moritani Yuuki , Imada Akira , Omodaka Toshihiro , Oizumi Shota , Ohsugi Takashi , Yamashita Takuya , Kawabata Koji S. , Isogai Mizuki , Nagae Osamu , Sasada Mahito , Miyamoto Hisashi , Uehara Takeshi , Tanaka Hiroyuki , Matsui Risako , Fukazawa Yasushi , Sato Shuji , Kino Masaru 
Published: March 2014

Abstract
We report on the observation of a new dwarf nova (DN), OT J055717$+$683226 (OT: optical transient), during the period of its first-recorded superoutburst in 2006 December. Our observation shows that this object is an SU UMa-type dwarf nova having a very short superhump period of 76.67$\pm$0.03 min (0.05324$\pm$0.00002 d). The next superoutburst was observed in 2008 March. The recurrence time of superoutbursts (supercycle) is, hence, estimated to be $\sim$480 d. The supercycle ($\sim$ 480 d) is much shorter than those ($&gt;rsim$10 yr) of WZ Sge-type dwarf novae which are in the major of dwarf novae in the shortest orbital period regime ($\lesssim$85 min). Using a hierarchical cluster analysis, we divided the dwarf nova in the shortest orbital period regime in seven groups. We found that objects, which have short supercycles, small outburst amplitudes, and large superhump period excesses compared with those of WZ Sge stars, form a small group. OT J055717$+$683226 probably belongs to this group.
Bayesian Approach to Find a Long-Term Trend in Erratic Polarization Variations Observed in Blazars
Authors: Uemura Makoto , Kawabata Koji S. , Sasada Mahito , Ikejiri Yuki , Sakimoto Kiyoshi , Itoh Ryosuke , Yamanaka Masayuki , Ohsugi Takashi , Sato Shuji , Kino Masaru 
Published: March 2014

Abstract
We developed a method of separating a long-term trend from observed temporal variations of polarization in blazars using a Bayesian approach. The temporal variation of the polarization vector is apparently erratic in most blazars, while several objects have occasionally exhibited systematic variations, for example an increase of the polarization degree associated with a flare of the total flux. We assume that the observed polarization vector is a superposition of two distinct components: a long-term trend and a short-term variation component responsible for short flares. Our Bayesian model estimates a long-term trend that satisfies the condition that the total flux correlates with the polarized flux of the short-term component. We demonstrate that assumed long-term polarization components are successfully separated by the Bayesian model for artificial data. We applied this method to the three photopolarimetric data of OJ 287, S5 0716$+$714, and S2 0109$+$224. Simple and systematic long-term trends were obtained in OJ 287 and S2 0109$+$224, while no such trend was confirmed in S5 0716$+$714. We propose that the apparently erratic variations of polarization in OJ 287 and S2 0109$+$224 are due to the presence of the long-term polarization component. The behavior of polarization in S5 0716$+$714 during the period of observation implies the presence of a number of polarization components showing variations on a quite short time-scale.
Photometric Investigation and Possible Light-Time Effect in the Orbital Period of a Marginal Contact System, CW Cassiopeiae
Authors: Jiang Tian-Yu , Li Li-Fang , Han Zhan-Wen , Jiang Deng-Kai 
Published: March 2014

Abstract
The first complete charge-coupled device (CCD) light curves in $B$ and $V$ passbands of a neglected contact binary system, CW Cassiopeiae (CW Cas), are presented. They were analyzed simultaneously by using the Wilson and Devinney (WD) code (1971, ApJ, 166, 605). The photometric solution indicates that CW Cas is a W-type W UMa system with a mass ratio of $m_{2}/m_{1} =$ 2.234, and that it is in a marginal contact state with a contact degree of $\sim$ 6.5% and a relatively large temperature difference of $\sim$ 327 K between its two components. Based on the minimum times collected from the literature, together with the new ones obtained in this study, the orbital period changes of CW Cas were investigated in detail. It was found that a periodical variation overlaps with a secular period decrease in its orbital period. The long-term period decrease with a rate of $dP/dt = -$3.44 $\times$ 10$^{-8} $d yr$^{-1}$ can be interpreted either by mass transfer from the more-massive component to the less-massive with a rate of ${d}m_{2}/dt = -$3.6 $\times$ 10$^{-8} M_{\odot} $yr$^{-1}$, or by mass and angular-momentum losses through magnetic braking due to a magnetic stellar wind. A low-amplitude cyclic variation with a period of $T =$ 63.7 yr might be caused by the light-time effect due to the presence of a third body.
NANTEN Survey of Molecular Clouds toward the Galactic Center; Association of Compact Astronomical Objects
Authors: Takeuchi Tomotake , Yamamoto Hiroaki , Torii Kazufumi , Kudo Natsuko , Hayakawa Takahiro , Kawamura Akiko , Mizuno Norikazu , Onishi Toshikazu , Mizuno Akira , Ogawa Hideo , Fukui Yasuo 
Published: March 2014

Abstract
In order to better understand molecular clouds and their properties toward the Galactic center region, we have analyzed the NANTEN database of $^{12}$CO ($J =$ 1–0) and $^{13}$CO ($J =$ 1–0) to search for associations with candidates for young high-mass star-forming regions, such as IRAS point sources, radio continuum sources, recombination line sources, maser line sources, and other molecular line sources. We have also compared the data with TeV $\gamma$-ray sources. The analyzed region covers $-$12$^{\circ} \leq l \leq$ 12$^{\circ}$ and $-$1${\rlap{\hskip.75pt{^\circ}}\hskip.75pt.\hskip1pt}$5 $\leq b \leq$ 1${\rlap{\hskip.75pt{^\circ}}\hskip.75pt.\hskip1pt}$5 for $^{12}$CO, and $-$6$^{\circ} \leq l \leq$ 8$^{\circ}$ and $-$1$^{\circ} \leq b \leq$ 1$^{\circ}$ for $^{13}$CO. As a result, we identified 167 IRAS point sources, 73 recombination line sources, 58 maser sources, 107 radio continuum sources, and 77 molecular line sources associated with 169 positions with the CO emission. The associations among the objects with known velocity are fairly certain (68%), while those with only positional coincidence are less reliable (32%). We present a catalog of these CO clouds in a form useful for future follow-up studies. As specific examples of usage of the catalog, we highlight three outstanding regions of active star formation: W 28, W 30, and W 31. In particular, we have discovered that the W 30 region shows a striking correlation between the extended TeV $\gamma$-ray source and the molecular gas. This is a second case of such a good correlation identified from the NANTEN dataset subsequent to W 28 (Aharonian et al. 2008, A&A, 481, 401). We suggest that the pulsar PSR J1803$-$2137 near the molecular features may play a role in $\gamma$-ray production. The W 31 region exhibits another active star formation, while no $\gamma$-ray source is yet known.
Dwarf Novae in the Shortest Orbital Period Regime: II. WZ Sge Stars as the Missing Population near the Period Minimum
Authors: Uemura Makoto , Kato Taichi , Nogami Daisaku , Ohsugi Takashi 
Published: March 2014

Abstract
WZ Sge-type dwarf novae are characterized by long recurrence times of outbursts ($\sim$ 10 yr) and short orbital periods ($\lesssim$ 85 min). A significant part of WZ Sge stars may remain undiscovered because of low outburst activity. Recently, the observed orbital period distribution of cataclysmic variables (CVs) has changed partly because outbursts of new WZ Sge stars have been discovered routinely. Hence, estimations of the intrinsic population of WZ Sge stars are important to study the population and the evolution of CVs. In this paper, we present a Bayesian approach to estimate the intrinsic period distribution of dwarf novae from observed samples. In this Bayesian model, we assumed a simple relationship between the recurrence time and the orbital period, which is consistent with observations of WZ Sge stars and other dwarf novae. As a result, the minimum orbital period was estimated to be $\sim $ 70 min. The population of WZ Sge stars exhibited a spike-like feature at the shortest period regime in the orbital period distribution. These features are consistent with the orbital period distribution previously predicted by population synthesis studies. We propose that WZ Sge stars and CVs with a low mass-transfer rate are excellent candidates for the missing population predicted by the evolution theory of CVs.
Suzaku Observations of the Merging Cluster Abell 85: Temperature Map and Impact Direction
Authors: Tanaka Nobuhiro , Furuzawa Akihiro , Miyoshi Shigeru J. , Tamura Takayuki , Takata Tadafumi 
Published: March 2014

Abstract
To investigate the present situation of the merging in the southern outer region of Abell 85, we carried out long-time ($\sim$ 100 ks) observations with Suzaku, and produced an X-ray hardness ratio map. We found a high hardness ratio peak on the east side of a subcluster located south of the cluster; an X-ray spectrum of the region including this peak indicates a high temperature of $\sim$ 8.5 keV. This hot spot has not been reported so far. We consider that this hot spot is a postshock region produced by the infall of the subcluster from the southwest. By using the Rankine–Hugoniot jump conditions for shocks, the Mach number and the infall velocity of the subcluster were obtained as 1.5$\ \pm\ $0.2 and 1950$^{+290}_{-280}\ $km s$^{-1}$, respectively, in the case of merging with the subcluster from the southwest direction. By using the difference in redshift between A 85 and the subcluster obtained from optical observations, the angle between the line of sight and the direction of the motion of the subcluster is estimated to be 75$^{\circ}$$^{+7^{\circ}}_{-8^\circ}$. We estimate the kinetic energy of the subcluster and the energy used for the intracluster medium (ICM) heating to be $\sim$ 10$^{63}$ and $\lesssim\ $8 $\times$ 10$^{60}\ $erg, respectively. This shows that the deceleration of the subcluster by the ICM heating has been negligibly small.
AKARI Infrared Observations of the Edge-On Spiral Galaxy NGC 3079
Authors: Yamagishi Mitsuyoshi , Kaneda Hidehiro , Ishihara Daisuke , Komugi Shinya , Suzuki Toyoaki , Onaka Takashi 
Published: March 2014

Abstract
We present AKARI near- to far-infrared images of the nearby edge-on spiral galaxy NGC 3079 in 10 photometric bands. The spectral energy distribution consists of continuum emission from dust with a single temperature of 28–33 K together with strong mid-infrared emission features from polycyclic aromatic hydrocarbons (PAHs). We derived dust masses of 5.6 $\times$ 10$^{6}\ M$$_{\odot}$ and 1.4 $\times$ 10$^7\ M$$_{\odot}$ for the central 4 kpc region and the whole galaxy, respectively, and found that the gas-to-dust mass ratio is unusually high in the central region ($\sim\ $1100), and even for the whole galaxy ($\sim\ $860). The ratio of the surface brightness distribution at a wavelength of 7$\ \mu$m to that at 11$\ \mu$m suggests that the properties of PAHs have spatial variations. The emission from ionized and neutral PAHs is relatively strong in the center and the disk regions, respectively, suggesting a stronger radiation field, and thus relatively active star formation in the center. Yet, the total infrared luminosities of the galaxy indicate rather low star formation rates. These results suggest that NGC 3079 is in an early-phase starburst stage.