bluuebunny/crossref_metadata_2025_split huggingface dataset:
The nuclear properties of early-type galaxies in the Virgo and Fornax clusters
Authors: Côté Patrick 
Published: May 2007

AbstractWe summarize findings from imaging surveys of 143 early-type galaxies in the Virgo and Fornax Clusters. Using deep HST images in the F475W (g) and F850LP (z) band-passes obtained with the Advanced Camera for Surveys (ACS), we have examined the central structure of the program galaxies, finding clear evidence for a compact stellar nucleus in ∼ 75% of the sample. The formation of early-type galaxies of low- and intermediate-mass is often – but not always – accompanied by the formation of a compact stellar nucleus.
Accreting corona model of the X-ray variability in soft state GBH and AGN
Authors: Czerny Bożena , Janiuk Agnieszka 
Published: May 2007

AbstractWe develop a two-flow model of accretion onto a black hole which incorporates the effect of the local magneto-rotational instability. The flow consists of an accretion disk and an accreting corona, and the local dynamo affects the disk/corona mass exchange. The model is aimed to explain the power spectra of the sources in their soft, disk-dominated states. The local perturbations of the magnetic field in the disk are described as in King et al. (2004) and Mayer & Pringle (2006), but the time-dependent local magnetic field is assumed to affect the local supply of the material to the corona. The accreting corona model can reproduce the broad power spectra of Soft State X-ray binaries and AGN. The model, however, predicts that (i) sources undergoing radiation pressure instability (GRS 1915+105) should have systematically steeper power spectra than other sources, (ii) AGN should have systematically steeper power spectra than GBH. More measurements of power spectra of Soft State sources are clearly needed.
Supermassive black holes in BCGs
Authors: Bontà E. Dalla , Ferrarese L. , Miralda-Escudé J. , Coccato L. , Corsini E. M. , Pizzella A. 
Published: May 2007

AbstractWe observed a sample of three Brightest Cluster Galaxies (BCGs), Abell 1836-BCG, Abell 2052-BCG, and Abell 3565-BCG, with the Advanced Camera for Surveys (ACS) and the Imaging Spectrograph (STIS) on board the Space Telescope. For each target galaxy we obtained high-resolution spectroscopy of the Hα and [N II] λ6583 emission lines at three slit positions, to measure the central ionized-gas kinematics. ACS images in three different filters (F435W, F625W, and FR656N) have been used to determine the optical depth of the dust, stellar mass distribution near the nucleus, and intensity map. We present supermassive black hole (SBH) mass estimates for two galaxies which show regular rotation curves and strong central velocity gradients, and an upper limit on the SBH mass of the third one. For the SBHs of Abell 1836-BCG and Abell 3565-BCG, we derived M• = 4.8+0.8−0.7 × 109 M⊙ and M• = 1.3+0.3−0.4 × 109 M⊙ at 1 σ confidence level, respectively. For the SBH of Abell 2052-BCG, we found M• ≤ 7.3 × 109 M⊙.
The VSOP Survey: final aggregate results
Authors: Dodson R. , Horiuchi S. , Scott W. , Fomalont E. , Paragi Z. , Frey S. , Wiik K. , Hirabayashi H. , Edwards P. , Murata Y. , Moellenbrock G , Gurvits L. , Shen Z. , Lovell J. 
Published: May 2007

AbstractIn February 1997 the Japanese radio astronomy satellite HALCA was launched to provide the space-borne element for the VSOP mission. HALCA provided linear baselines three-times greater than that of ground arrays, thus providing higher resolution and higher AGN brightness temperature measurements and limits. Twenty-five percent of the scientific time of the mission was devoted to the “VSOP survey” of bright, compact, extra-galactic radio sources at 5 GHz. A complete list of 294 survey targets were selected from pre-launch surveys, 91% of which were observed during the satellite's lifetime.The major goals of the VSOP Survey are statistical in nature: to determine the brightness temperature and approximate structure, to provide a source list for use with future space VLBI missions, and to compare radio properties with other data throughout the electro-magnetic spectrum. All the data collected have now been analysed and is being prepared for the final image Survey paper. In this paper we present details of the mission, and some statistics of the images and brightness temperatures.
Generation of shocked hot regions in black hole magnetosphere
Authors: Fukumura Keigo , Takahashi Masaaki , Tsuruta Sachiko 
Published: May 2007

AbstractWe study magnetohydrodynamic (MHD) standing shocks in ingoing plasmas in a black hole (BH) magnetosphere. We find that low or mid latitude (non-equatorial) standing MHD shocks are both physically possible, creating very hot and/or magnetized plasma regions close to the event horizon. We also investigate the effects of the poloidal magnetic field and the BH spin on the properties of shocks and show that both effects can quantitatively affect the MHD shock solutions. MHD shock formation can be a plausible mechanism for creating high energy radiation region above an accretion disk in AGNs.
Evidence for the AGN nature of LINERs
Authors: González-Martín O. , Masegosa J. , Márquez I. , Jiménez-Bailón E. 
Published: May 2007

AbstractWe report the analysis of the X-ray data for a sample of 48 LINER nuclei with available X-ray Chandra imaging. In González-Martín et al. 2006 21 objects had enough count rate to make the spectral analysis. Here we enlarge the sample performing the spectral analysis of the XMM-Newton observations of 7 additional galaxies. Our aim is to investigate the physical mechanisms which power the nuclear activity of LINERs. The use of multiwavelength information at radio, UV, optical HST and X-ray lead us to conclude that at least 60% of the LINERs are hosting a low luminosity AGN in their nuclei.
The entropy increase during the black hole formation
Authors: Hara Tetsuya , Sakai Keita , Kunitomo Shuhei , Kajiura Daigo 
Published: May 2007

AbstractThe entropy increases enormously when a star collapses into a black hole. For the radiation dominated star, the temperature has decreased from the almost gravitational equilibrium one to the so-called black hole temperature. If we interpret this temperature decrease as the volume increase of the black hole, the entropy increase could be understood as the free expansion of radiation throughthe increased volume. The expected volume size is tentatively estimated. Under this interpretation, it is derived that the entropy is proportional to the horizon surface area and the microscopic states of the black hole entropy could be understood as the statistical states of the enlarged phase space.
Observational manifestations of accretion onto isolated black holes of different masses
Authors: Karpov Sergey , Beskin Gregory 
Published: May 2007

AbstractThe process of accretion onto the isolated black holes under the various conditions of the ISM and its observational manifestations are discussed. For the majority of the Galaxy volume the accretion rate is as low as 10−6–10−9 of Eddington one, and the accretion is spherically-symmetric. Such objects manifest itself as a weak optical and x-ray sources with featureless spectra and the significant variability of the emission.For the BH located inside the dense molecular cloud the regime of accretion depends on its massand velocity. A massive (100–1000M⊙) BH born in the cloud or having low relative velocity, may manifest itself as a ultra-luminous x-ray source (ULX).
AGN types as different states of massive black holes
Authors: Komberg Boris V. 
Published: May 2007

AbstractAfter discovering microquasars – active stellar systems with relativistic outflows (Mirabel et al. 1992) – many papers bringing the observational arguments on similar nature of accreting systems with different BH masses (from stellar to galactic nuclei) have appeared. It became clear that a level of activity in such systems could depend on few parameters: BH mass and angular momentum; accretion rate and magnetization parameter of accretion disk (AD); relative orientation of BH and AD angular momentum. The bolometric luminosity and characteristic variation time in such systems is proportional to BH masses, which span an interval in 5–8 decades.
Relativistic jets and non-thermal radiation from collapse of stars to black holes
Authors: Kryvdyk V. , Agapitov A. 
Published: May 2007

AbstractThe formation of the relativistic jets and a non-thermal emission from the collapsing magnetized stars with dipole magnetic fields and the heterogeneous particles distribution are investigated. These polar jets are formed when the stellar magnetosphere compress during collapse its magnetic field increases considerable. The electric field is produced in magnetosphere, which the charged particles will be accelerated. As follow from the calculation, the jets can be formed from collapsing stars already the explosion of supernova stars without shock waves. These jets will generate the non-thermal radiation. The radiation flux depends on the distance to the star, its magnetic field and the particle spectrum in the magnetosphere. This flux can be observed near Earth by means of modern telescopes in the form of the radiation pulse with duration equal to time collapse.
Rotation curves, dark matter and general relativity
Authors: Letelier Patricio S. 
Published: May 2007

AbstractWe study the possibility of pure general relativistic models without exotic matter to describe the observed flattening of the rotation curves for stars moving in circular orbits in a galaxy disk. In particular we consider the dragging of inertial frames (rotation of the source) and the presence of a Taub–NUT (Newman–Unti–Tamburino) “charge”, the gravitational equivalent to a magnetic monopole in electrodynamics.
The orbiting spot model gives constraints on the parameters of the supermassive black hole in the Galactic Center
Authors: Meyer Leonhard , Eckart Andreas , Schödel Rainer , Dovčiak Michal , Karas Vladimír , Duschl Wolfgang J. 
Published: May 2007

AbstractWe report on recent polarimetric observations of the 18± 3 min quasi-periodicity present in near-infrared flares from Sagittarius A*. Observations in the K-band allow us a detailed investigation of the flares and their interpretation within the hot spot model. The interplay of relativistic effects plays a major role. By simultaneous fitting of the lightcurve fluctuations and the time-variable polarization angle, we give constraints to the parameters of the hot spot model, in particular, the dimensionless spin parameter of the black hole and its inclination. We consider all general relativistic effects that influence the polarization lightcurves. The synchrotron mechanism is most likely responsible for the intrinsic polarization. We consider two different magnetic field configurations as approximations to the complex structure of the magnetic field in the accretion flow. Considering the quality of the fit, we suggest that the spot model is a good description of the origin for the QPOs in NIR flares.
Two-dimensional MHD simulations of accretion disk evaporation
Authors: Nakamura Kenji E. 
Published: May 2007

AbstractWe simulate the accretion disk evaporation to study the changes of accretion disk structure during the state transition from the soft state to the hard state. We performed 2 dimensional MHD simulations by including the heat conduction process. We assume the axisymmetric accretion and put a cold rotating gas torus in a hot halo in hydrostatic equilibrium initially. Weak magnetic fields are threaded vertically. Heat conduction equation and MHD equations are solved separately according to the time splitting method. We obtained the result that accretion disk is heated by the hot corona and the hot gas evaporates from the accretion disk surface. We found that magnetic fields lines bended by disk rotation restrict the energy transport vertically and make disk evaporation ineffective.
Steady models of optically thin, magnetically supported two-temperature accretion disks around a black hole
Authors: Oda H. , Nakamura K. E. , Machida M. , Matsumoto R. 
Published: May 2007

AbstractWe obtained steady solutions of optically thin two-temperature magnetized accretion disks around a black hole. We included relativistic bremsstrahlung cooling, synchrotron cooling and inverse Compton effects and assumed that the disk is threaded by toroidal magnetic field. We found that a magnetic pressure dominated new branch, which we call a ‘low-β branch’, appears in the thermal equilibrium curves. The luminosity of the optically thin, magnetically supported disk can exceed 10% of the Eddington luminosity (0.1 LEdd).
Power spectra from spotted accretion discs
Authors: Pecháček Tomáš , Dovčiak Michal , Karas Vladimír 
Published: May 2007

AbstractSome aspects of power-spectral densities (PSD) of active galactic nuclei are similar to those of galactic black hole X-ray binary systems (McHardy et al. 2005). The signal originates near a black hole and its modulation by general-relativistic effects should be taken into account (Życki & Nedźwiecki 2005). We modified the previous calculations of these effects, assuming a model of spots which occur on the disc surface and decay with a certain lifetime.
Brownian motion of black holes in stellar systems with non-Maxwellian distribution of the field stars
Authors: Pedron Isabel Tamara , Coimbra-Araújo Carlos H. 
Published: May 2007

AbstractA massive black hole at the center of a dense stellar system, such as a globular cluster or a galactic nucleus, is subject to a random walk due gravitational encounters with nearby stars. It behaves as a Brownian particle, since it is much more massive than the surrounding stars and moves much more slowly than they do. If the distribution function for the stellar velocities is Maxwellian, there is a exact equipartition of kinetic energy between the black hole and the stars in the stationary state. However, if the distribution function deviates from a Maxwellian form, the strict equipartition cannot be achieved.The deviation from equipartition is quantified in this work by applying the Tsallis q-distribution for the stellar velocities in a q-isothermal stellar system and in a generalized King model.
Detection of IMBHs from microlensing in globular clusters
Authors: Safonova Margarita , Rahvar Sohrab 
Published: May 2007

AbstractGlobular clusters have been long predicted to host intermediate-mass black holes (IMBHs) in their centres. The growing evidence that some/all Galactic globular clusters (GCs) could harbour middle range (102 – 104M⊙) black holes, just as galaxies do, stimulates the searches and the development of new methods for proving their existence. Here we propose another method of detection – the microlensing of the cluster stars by the central BH.
Color variations of gravitationally lensed quasars as a tool for accretion disk size estimation
Authors: Shalyapin V. N. 
Published: May 2007

AbstractSince the amplitude of microlensing variability depends on a source size the monitoring of gravitationally lensed quasars can produce the valuable information about the accretion disk size. Comparison of standard deviations in two wavebands yields useful constraints from quite moderate number of multicolor observations.Existing optical VRI monitoring data for the quadruple gravitationally lensed quasar Q2237+ 0305 allow to obtain the source size ratio in two bands, V and R or V and I, as a function of size in the V band. Agreement with the standard accretion disk theory which predicts the dependency of a source size on wavelength ∼ λ4/3 can be achieved only if the quasar size in V band is comparable with the Einstein radius (≃ 1017 cm).
An f(R) gravitation for galactic environments
Authors: Sobouti Yousef 
Published: May 2007

AbstractWe propose an action-based f(R) modification of Einstein's gravity which admits of a modified Schwarzschild-deSitter metric. In the weak field limit this amounts to adding a small logarithmic correction to the Newtonian potential. A test star moving in such a spacetime acquires a constant asymptotic speed at large distances. This speed turns out to be proportional to the fourth root of the mass of the central body in compliance with the Tully-Fisher relation. A variance of MOND's gravity emerges as an inevitable consequence of the proposed formalism.
Peculiar outbursts of a black hole X-ray transient, V4641 Sgr
Authors: Uemura M. , Kato T. , Nogami D. , Imada A. , Ishioka R. 
Published: May 2007

AbstractWe have kept optical monitoring of a peculiar black hole X-ray binary, V4641 Sgr. Based on our observations, we show that its unprecedented activity can be divided into 5 phases. In this paper, we report their observational properties.
Self-gravitating warped disks around nuclear black holes
Authors: Ulubay-Siddiki Ayse , Gerhard Ortwin , Arnaboldi Magda 
Published: May 2007

AbstractMany galactic nuclei contain disks of gas and possibly stars surrounding a supermassive black hole. These disks may play a key role in the evolution of galactic centers. Here we address the problem of finding stable warped equilibrium configurations for such disks, considering the attraction by the black hole and the disk self-gravity as the only acting forces. We model these disks as a collection of concentric, circular rings.We find the equilibria of such systems of rings, and determine how they scale with the ring parameters and the mass of the central black hole. We show that in some cases these disk equilibria may be highly warped. We then analyze the stability of these disks, using both direct time integration and linear stability analysis. This shows that the warped disks are stable for a range of disk-to-black hole mass ratios, when the rings extend over a limited range of radii.
The modelling of the line-locking effect in broad absorption line QSOs
Authors: Vilkoviskij Emmanuil Y. , Yefimov Sergey N. 
Published: May 2007

AbstractWe present a unification model of the matter outflow from AGN. The model includes calculations of the hot gas dynamics, the dynamics of the cold clouds in the hot gas flow, and the radiation transfer in this two-phase medium. We used the model for calculation of the ultraviolet spectrum of the quasar q1303+308. The spectrum of this object is a well-know example of the line-locking effect. Our model calculations permits for the first time to obtain some thin details seen in the observed absorption spectrum, which confirms the validity of the main issues of our theory and model.
The relation between the properties of the NLR in narrow-line Seyfert 1 galaxies and the accretion rate
Authors: Xu Dawei , Komossa Stefanie 
Published: May 2007

AbstractWe present a systematic study of the properties of the narrow-line region (NLR) of narrow-line Seyfert 1 galaxies (NLS1s) using Sloan Digital Sky Survey (SDSS) spectroscopy. Various correlations between the observed parameters and physical properties of NLS1s and broad-line Seyfert 1 galaxies (BLS1s) are detected. We search for possible origins of these trends by employing correlation analyses. We further investigate the relationship between black hole mass, Eddington ratio (L/LEdd) and physical parameters of the NLR.
Doppler boosting and de-boosting effects in relativistic jets of AGNs and GRBs
Authors: Zhou Jianfeng , Su Yan 
Published: May 2007

AbstractIt is widely accepted that the Doppler de-boosting effects exist in counter relativistic jets. However, people often neglect another important fact that both Doppler boosting and de-boosting effects could happen in forward relativistic jets. Such effects might be used to explain some strange phenomena, such as the invisible gaps between the inner and outer jets of AGNs, and the rapid initial decays and re-brightening bumps in the light curves of GRBs.
Climate change already altering Earth, IPCC Says
Authors: Zielinski Sarah 
Published: May 2007

The Intergovernmental Panel on Climate Change has confirmed what many scientists had suspected: anthropogenic climate change is already altering the Earth. Ice is melting, water patterns are changing, and a host of organisms are being affected in a variety of ways. More changes are expected as temperatures rise, and the world's poor will be affected the most.The report from IPCC Working Group II, I “Climate Change 2007: Impacts, Adaptation and Vulnerability,” is the second of three parts of the IPCC Fourth Assessment Report (see Eos 88(6) and 88(7), 2007). The full 1572‐page report, which will be published in book format in September, was compiled over the last few years by 174 lead authors and 222 contributing authors and included the participation of 1183 experts. A 23‐page Summary for Policymakers, which was negotiated by government representatives during a plenary held in Brussels, Belgium, was finalized and released on 6 April (see http://www.ipcc.ch).
Harrison receives 2006 William Gilbert Award
Authors: McEnroe Suzanne A. , Harrison Richard J. 
Published: May 2007

Richard J. Harrison received the William Gilbert Award at the 2006 AGU Fall Meeting. The award recognizes outstanding and unselfish work in magnetism of Earth materials and of the Earth and planets.This year the Gilbert Award is given to an outstanding young scientist under the age of 35. Richard Harrison easily fulfills the first criterion and just makes the second. He is now 34. As I reviewed Richard's accomplishments, I was once again impressed with his scope and level of research. He has 50 papers published, or in press, and all of them are of the same high scientific caliber. Many of you know Richard's cutting‐edge research with electron holography showing magnetic interactions across magnetite‐ulvospinel intergrowths, and are familiar with his groundbreaking research on lamellar magnetism. His TEM observations, combined with extensive Monte Carlo simulations of atomic interactions in hematite‐ilmenite interfaces, which took both electrostatic and magnetic interactions into consideration, have developed the idea of contact layers as a magnetic substructure of defect moments at the interfaces. This was followed by work that showed that contact layers reduce charge imbalance at the interfaces.