bluuebunny/crossref_metadata_2025_split huggingface dataset:
Accretion of stellar winds onto Sgr A*
Authors: Cuadra Jorge , Nayakshin Sergei 
Published: May 2007

AbstractWe report a 3-dimensional numerical study of the accretion of stellar winds onto Sgr A*, the super-massive black hole at the centre of our Galaxy. Compared with previous investigations, we allow the stars to be on realistic orbits, include the recently discovered slow wind sources, and allow for optically thin radiative cooling. We first show the strong influence of the stellar dynamics on the accretion onto the central black hole. We then present more realistic simulations of Sgr A* accretion and find that the slow winds shock and rapidly cool, forming cold gas clumps and filaments that coexist with the hot X-ray emitting gas. The accretion rate in this case is highly variable on time-scales of tens to hundreds of years. Such variability can in principle lead to a strongly non-linear response through accretion flow physics not resolved here, making Sgr A* an important energy source for the Galactic centre.
Short-term variability of Sgr A*
Authors: Morris M. R. , Hornstein S. D. , Ghez A. M. , Lu J. R. , Matthews K. , Baganoff F. K. 
Published: May 2007

AbstractObservations of Sgr A* over the past 4 years with the Keck Telescope in the near-infrared, coupled with millimeter and submillimeter observations, show that the 3.7×106M⊙Galactic Black Hole, Sagittarius A*, displays continuous variability at all these wavelengths, with the variability power concentrated on characteristic time scales of a few hours, and with a variability fraction that increases with wavelength. We review the observations indicating that the few-hour time scale for variability is reproduced at all accessible wavelengths. Interpreted as a dynamical time, this time scale corresponds to a radial distance of 2 AU, or ∼25 Schwarzschild radii. Searches for quasi-periodicities in the near-infrared data from the Keck Telescope have so far been negative. One interpretation of the character of these variations is that they result from a recurring disk instability, rather than from variations in the mass accretion rate flowing through the outer boundary of the emission region. However, neither a variable accretion rate nor a mechanism associated with a jet can presently be ruled out.
Ultra-luminous X-ray sources: X-ray binaries in a high/hard state?
Authors: Kuncic Z. , Soria R. , Hung C. K. , Freeland M. C. , Bicknell G. V. 
Published: May 2007

AbstractWe examine the possibility that Ultraluminous X-ray sources (ULXs) represent the extreme end of the black hole X-ray binary (XRB) population. Based on their X-ray properties, we suggest that ULXs are persistently in a high/hard spectral state and we propose a new disk–jet model that can accomodate both a high accretion rate and a hard X-ray spectrum. Our model predicts that the modified disk emission can be substantially softer than that predicted by a standard disk as a result of jet cooling and this may explain the unusually soft components that are sometimes present in the spectra of bright ULXs. We also show that relativistic beaming of jet emission can indeed account for the high X-ray luminosities of ULXs, but strong beaming produces hard X-ray spectra that are inconsistent with observations. We predict the beamed synchrotron radio emission should have a flat spectrum with a flux density ≲0.01 mJy.
Optical, ultraviolet and X-ray analysis of the black hole candidate BG Geminorum
Authors: Elebert P. , Callanan P. J. , Russell L. , Shaw S. E. 
Published: May 2007

AbstractWe present the first high resolution optical spectrum of the black hole candidate BG Geminorum, as well as UV spectroscopy from the Hubble Space Telescope, and X-ray data from INTEGRAL. The UV spectra suggest the presence of material in BG Gem with velocities possibly as high as ∼1000 km s−1, suggesting an origin at a distance of ∼0.7 R⊙ from a 3.5 M⊙ object; if real, this would be strong evidence that the primary in BG Gem is indeed a black hole. In contrast, the upper limit provided by the INTEGRAL data gives a maximum X-ray luminosity of only ∼0.1 of the Eddington luminosity.
Uncertainty principle for the entropy of black holes, de Sitter and Rindler spaces
Authors: Hara Tetsuya , Sakai Keita , Kunitomo Shuhei , Kajiura Daigo 
Published: May 2007

AbstractBy a simple physical consideration and uncertain principle, we derive that temperature is proportional to the surface gravity and entropy is proportional to the surface area of the black hole. We apply the same consideration to de Sitter space and estimate the temperature and entropy of the space, then we deduce that the entropy is proportional to the boundary surface area. By the sameconsideration, we estimate the temperature and entropy in the uniformly accelerated system (Rindler space). The cases in higher dimensions are considered.
Intensity and polarization light-curves from radiatively-driven clouds
Authors: Horák Jiří , Karas Vladimír 
Published: May 2007

AbstractWe study linear polarization from scattering of light on a cloud of relativistic electrons. We assume that the cloud is hovering above an accretion disc, or it is in an accelerated motion underthe combined influence of the radiation and gravitational fields near an accreting black hole. Atfirst we derive simple and general analytical formulae for the Stokes parameters. These formulae are then used in calculations of the temporal evolution of the observed signal.We find that higher-order images can significantly enhance the observed flux. Possible targets where the effect should be searched are accreting super-massive black holes and Galactic microquasars exhibiting episodic accretion/ejection events.
Fe K line profile in PG quasars: the averaged shape and Eddington ratio dependence
Authors: Inoue H. , Terashima Y. , Ho L. C. 
Published: May 2007

AbstractFe K emission line is a powerful probe of the inner part of an accretion disk. We analyze X-ray spectra of 43 Palomar-Green (PG) quasars taken from Boroson & Green (1992) observed with XMM-Newton and make an averaged Fe K line profile. We study the Eddington ratio dependence of the Fe K line profile. The width of the Fe line becomes broader (σ=0.1 to 0.7 keV) and its peak energy becomes higher (6.4 to 6.8 keV) as the Eddington ratio gets larger.These results indicate that the physical state of the accretion disk, such as the geometrical structure and/or ionization state, changes with the Eddington ratio.
The capture of main sequence stars and giant stars by a massive black hole
Authors: Lu Y. , Huang Y. F , Zheng Z. , Zhang S. N. 
Published: May 2007

AbstractSince the mass-radius relation is quite different for a main sequence (MS) star and a giant (G) star, we find that the radiation efficiencies in the star capture processes by a black hole (BH) are also very different. This may provide a useful way to distinguish the capture of MS and G stars. Comparing with observations of the very high energy (VHE) gamma-ray emissions, we argue the event that triggers the gamma-ray emission in the energy range 4–40 TeV should be a G star capture. On the other hand, the capture of MS stars by the massive BH is required when the measured spectrum of VHE gamma-rays extends from 109 to 1015 eV.
Low-frequency, one-armed oscillations in black hole accretion flows obtained from direct 3D MHD simulations
Authors: Machida Mami , Matsumoto Ryoji 
Published: May 2007

AbstractWe present the results of global 3D MHD simulations of optically thin black hole accretion flows. The initial disk is embedded in a low density, spherical, isothermal halo and threaded by weak (β ≡ Pgas/Pmag = 100) toroidal magnetic field. General relativistic effects are simulated by using the pseudo-Newtonian potential. When the Maxwell stress in the innermost region of the disk is reduced due to the loss of magnetic flux or by decrease of disk temperature, inner torus is created around 4 – 10rs. We found that in such an inner torus, one-armed (m = 1) density enhancement grows and that the inner torus oscillates quasi-periodically. The oscillation period is about 0.1s when we assume a 10M⊙ black hole. This frequency agrees with the low-frequency QPOs observed in low/hard state of black hole candidates. The disk ejects winds whose opening angle is about 30 degree. The maximum velocity of the wind is about 0.05c.
Masses of radiation pressure supported stars in extreme relativistic realm
Authors: Mitra Abhas 
Published: May 2007

AbstractWe discuss that in the extreme relativistic limit, i.e., when z ≫ 1, where z is the surface gravitational redshift, there could be radiation pressure supported and dominated stars with arbitrary gravitational mass, high or low. Such objects are called Eternally Collapsing Objects (ECOs). ECOs are practically as compact as Schwarzschild black holes (BH) and, observationally, are likely to be mistaken as BHs. Further since any object undergoing continued collapse must first become an ECO before becoming a true BH state characterized by M = 0, the observed BH Candidates are ECOs.
Radiation spectra from MHD simulations of low angular momentum flows
Authors: Moscibrodzka Monika A. , Proga Daniel , Czerny Bożena , Siemiginowska Aneta 
Published: May 2007

AbstractWe perform Monte Carlo calculation to determine the radiation spectra from magnetized, low angular momentum accretion flow. Magneto-hydrodynamical simulation (with angular momentum parameter lambda of about 2 Rg c) was performed by Proga & Begelman 2003. Because simulation neglect radiative cooling, we compute electron temperature separately, including ohmic heating, parametrized with small δ coefficient, ion-electron coupling, radiative cooling and advection. Radiation spectra are obtained taking into account, thermal synchrotron and bremsstrahlung radiation, self absorption and Comptonization processes.We show which parts of the flow are responsible for characteristic spectral features and how the spectrum changes in different accretion states. We compare our results with Galactic Center black hole radiation spectra, where low angular momentum accretion is suggested. Accretion state changes seems to be a promising model for the flaring behavior of Galactic Center black hole. We also show the radiation intensity maps in radio and X-rays energy band for viewing angle i = 90°.
Can gravitational microlensing be used to probe geometry of a massive black-hole?
Authors: Popović Luka Č , Jovanović Predrag 
Published: May 2007

AbstractHere we discuss the possibility to use gravitational microlensing in order to probe the geometry around a massive black hole. Taking into account that lensed quasars are emitting X-rays which come from the heart of these objects, we investigated the influence of microlensing on the Fe Kα line shape originated in Schwarzschild and Kerr metrics.
Exact solutions for discs around stationary black holes
Authors: Požár N. , Semerák O. , Šácha J. , Žáček M. , Zellerin T. 
Published: May 2007

AbstractBlack holes surrounded by axisymmetric structures prosper in some of the most interesting sources in the universe. However, a consistent exact description of the gravitational field of these systems is still lacking. In a static case, the task reduces to Laplace equation and the fields of multiple sources follow by mere superposition. In a rotating case, non-linearity of the Einstein equations resists simple grasp, but even then the theory of completely integrable systems seems to verge on satisfactory solutions. It seeks them in terms of θ-functions on special manifolds connected – symptomatically – with the names of Riemann and Hilbert.
The X-ray–radio association in RATAN and RXTE monitoring of microquasar GRS 1915+105
Authors: Trushkin S. A. , Kotani T. , Kawai N. , Namiki M. , Fabrika S. N. 
Published: May 2007

AbstractIn the daily RATAN-600 monitoring of the radio variability of the microquasar GRS1915+105 we detected a clear correlation of the flaring radio emission and X-rays “spikes” at 2–12 keV emission (1–2 Crab) detected with RXTE (ASM data) during nine bright (200–600 mJy) radio flares in October 2005. The spectra of these flares in maximum were optically thick at ν<2.3 GHz and optically thin at ν≥2.3 GHz. During radio flares the spectra of the X-ray spikes became definitely softer than those of a quiescent radio state. Thus these data indicated transitions from very high/hard states to high/soft ones during which massive ejections are probably happened, and the ejections are detected as the radio flares.
Flaring activity of microquasars from multi-frequency daily monitoring program with RATAN-600 radio telescope
Authors: Trushkin S. A. , Nizhelskij N. A. , Bursov N. N. , Majorova E. K. 
Published: May 2007

AbstractWe report about the multi-frequency (1–30 GHz) daily monitoring of the radio flux variability of the three microquasars: SS433, GRS1915+105 and Cyg X-3 during 2005–2006. After a quiescent radio emission we have detected a drop down of the fluxes (∼20 mJy) from Cyg X-3, a sign of the following bright flare, and indeed a 1 Jy flare was detected on 2 February 2006 after 18 days of quenched radio emission. The daily spectra of the flare in the maximum was found flat from 2 to 110 GHz, using the quasi-simultaneous observations at 109 GHz with the RT45m telescope and the NMA millimeter array of Nobeyama Radio Observatory in Japan. Several bright radio flaring events (1–15 Jy) followed during the state of highly variable and intense 1–12 keV X-ray emission (∼0.5 Crab), monitored in the RXTE ASM program. We discussed various spectral and temporal characteristics of the detected 180 day light curves from three microquasars in comparison with the Rossi XTE ASM data.
West Antarctic ice sheet change since the Last Glacial Period
Authors: Deen Tara , Hillenbrand Claus‐Dieter , Johnson Joanne , Larter Rob , Livermore Roy , Smith James , Eagles Graeme , Gohl Karsten , Kuhn Gerhard , Schenke Hans‐Werner , Uenzelmann‐Neben Gabriele , Nitsche Frank , Pudsey Carol , Dietrich Reinhard , Udintsev Gleb 
Published: May 2007

The potential for rapid deglaciation, or collapse, of the 2‐million‐square‐kilometer West Antarctic Ice Sheet (WAIS) in response to climate change is one of the most serious environmental threats facing mankind. The WAIS is a marine ice sheet with large parts of its ice grounded below sea level. Complete collapse would result in a global sea level rise of approximately 5 meters, with immense social, economic, and ecological consequences.While most experts consider such a collapse unlikely within the next few centuries, the Amundsen Sea sector has been identified as the most likely site for initiation of collapse, and it alone contains the potential to raise sea level by approximately 1.5 meters [Vaughan, 2007]. This would result in devastating flooding in many low‐lying cities (e.g., New Orleans, London), agricultural areas (e.g., Netherlands, Bangladesh) and atolls (e.g., Maldives).
Eventfulness of Architecture: Teaching about Sacred Architecture Is Teaching about Ritual
Authors: Jones Lindsay 
Published: May 2007

Abstract
In this chapter the author uses architecture as the medium with which to explore ritual. The chapter's author demonstrates the ability of defined spaces to be performative events in themselves. Using comparative analysis, he explains his experiments with two different course structures and projects. Real-world constraints on his students dictated the more successful one for investigating the phenomenon of the ritual eventfulness, apprehensive effect, and even abundant autonomy of buildings, all ways in which our own creations come to structure our reality.
The Multiethnic Church in Society
Authors: Garces-Foley Kathleen 
Published: May 2007

AbstractThis chapter speculates on the future development of multiethnic churches by looking at the factors that propelled Evergreen Baptist Church to its new identity. It is argued that the new Evergreen reflects changing American attitudes toward diversity and a shift toward local engagement within evangelicalism. It is predicted that young adults will continue to play a pivotal role in the success of multiethnic churches. Lastly, after arguing throughout this volume for the influence of society on the development of multiethnic churches, the potential significance of multiethnic churches for societal race relations in light of the Evergreen case study is considered.
The Eagle Returns
Authors: Virani Shafique N. 
Published: May 2007

AbstractAs their wave of devastation swept through the Near East, Mongol hordes led by Hulagu Khan sought the complete extermination of the Ismailis and the destruction of their state centered at Alamut. Misled by the writings of Hulagu's courtier Juwayni, many of the Persian historians and later Western authors believed that the community had indeed been annihilated. While the continued survival of the Ismailis has now become clear, what has hitherto remained largely underestimated — if not completely unnoticed — is the persistence of their activities in the South Caspian regions of Gilan, Daylam, and Mazandaran, including at the fort of Alamut itself in the wake of the Mongol invasions.
Veiling the Sun
Authors: Virani Shafique N. 
Published: May 2007

AbstractTaqiyya, precautionary dissimulation, is a significant feature of Islam, and particularly of Shi'i Islam. For the Ismaili Shi'a — a minority within a minority whose creed emphasized the paramount importance of the esoteric dimension of the revelation — this need was even more pronounced. The destruction of their network of fortresses ushered in a period in which, more than ever, dissimulation was required for survival. Ismaili tradition maintains that when Alamut was vanquished, the Imam Shams al-Din Muhammad was smuggled away to safety. This chapter is about the life of this Imam and that of one of his disciples, the poet Nizari Quhistani, whose life and writings shed light on the practice of taqiyya.
The Way of the Seeker
Authors: Virani Shafique N. 
Published: May 2007

AbstractThe celebrated Iranian poet, philosopher, and traveler Nasir-i Khusraw was moved by a dream to abandon his carefree ways and search for truth. His quest led him to swear his allegiance to al-Mustansir bi'llah, the Ismaili Imam and sovereign of a mighty empire. Centuries later, a Muslim scholar by the name of Bu Ishaq Quhistani had a similar crisis of faith, which led him to pledge his fealty to the Ismaili Imam of his time, coincidentally also named Mustansir bi'llah, who, however, was in concealment. This chapter follows the spiritual pilgrimage of Bu Ishaq, explores the conduct of the da'wa in this period, and explores the concept and context of taqiyya in greater depth. It also reassesses the relationship between Sufism and Ismailism in the wake of the Mongol invasions.
Ordinary Mind as the Way
Authors: Poceski Mario 
Published: May 2007

Abstract
Under the leadership of Mazu Daoyi (709-788) and his numerous disciples, the Hongzhou School emerged as the dominant tradition of Chan (Zen) Buddhism in China during the middle part of the Tang dynasty (618-907). This book offers an examination of the Hongzhou School's momentous growth and rise to pre-eminence as the bearer of Chan orthodoxy, and analyzes its doctrines against the backdrop of the intellectual and religious milieus of Tang China. It demonstrates that the Hongzhou School represented the first emergence of an empire-wide Chan tradition that had strongholds throughout China and replaced the various fragmented Schools of early Chan with an inclusive orthodoxy. The study is based on the earliest strata of permanent sources, rather than on the later apocryphal “encounter dialogue” stories regularly used to construe widely-accepted but historically unwarranted interpretations about the nature of Chan in the Tang dynasty. The book challenges the traditional and popularly-accepted view of the Hongzhou School as a revolutionary movement that rejected mainstream mores and teachings, charting a new path for Chan's independent growth as a unique Buddhist tradition. This view, the book argues, rests on a misreading of key elements of the Hongzhou School's history. Rather than acting as an unorthodox movement, the Hongzhou School's success was actually based largely on its ability to mediate tensions between traditionalist and iconoclastic tendencies. The book shows that there was much greater continuity between early and classical Chan — and between the Hongzhou School and the rest of Tang Buddhism — than previously thought.
3 Care Theory and Economic Justice
Authors: Engster Daniel 
Published: May 2007

AbstractPolitical and economic theorists have generally ignored caring practices in outlining accounts of economic justice. Building upon the work of recent feminist theorists, this chapter develops a theory of economic justice organized around caring practices. The first section outlines the basic concepts and normative orientation of a caring economic theory. The second section discusses Virginia Held's and Nancy Folbre's important accounts of care and economic justice. While Held and Folbre identify some of the central tenets of a caring economic theory, they focus primarily on supporting and regulating direct care services within the economy. The book's own approach is broader and more far‐reaching, asking how we can best organize our general economic institutions and policies to provide all individuals with a real opportunity to give and receive adequate care. The third section takes up this subject by exploring the economic system (communism, market socialism, market capitalism, etc.) most conducive to caring values. In the fourth section, it formulates six general principles for establishing and maintaining a caring economic order, and describes in some detail the economic policies following from them. The final section briefly explores the viability of a caring economic order in the context of globalization.
4 Care Theory and International Relations
Authors: Engster Daniel 
Published: May 2007

AbstractThis chapter explores the question: What does it mean to care for others in international relations? Sara Ruddick, Fiona Robinson, and others have outlined international relations theories based upon care ethics, but their accounts are fairly general and say little about the rights and policies necessary for establishing caring relations among people across the world. The first half of this chapter develops a human rights framework based upon human beings' universal duty to care for others. The chapter argues that this framework avoids the central shortcomings of other international rights frameworks, and more generally provides a standard of justice that should be reasonably acceptable to people from diverse cultural and religious backgrounds. The second half of the chapter outlines some specific strategies and policies for enforcing human rights abroad and caring for distant others. In the last section, the chapter discusses the conditions under which care theory might justify the use of military force, especially for the sake of intervening into other countries for humanitarian purposes.