bluuebunny/crossref_metadata_2025_split huggingface dataset:
Radiation Hydrodynamics and Soft X-Ray Emission of Accreting Magnetic White Dwarfs
Authors: Beuermann K. , Fischer A. , Rousseau Th. 
Published: July 2016

AbstractObserved cyclotron spectra of AM Herculis binaries imply a large range of mass flow rates in the accretion spot on the white dwarf. We derive this ṁ–distribution for the case of UZ For. For AM Her stars with different field strength B, such a distribution is shifted in ṁ proportional to B. This fact can account for the observed dominance of bremsstrahlung at low B and of quasi-blackbody emission at high B values.
Hydrodynamical Models of Line-Driven Accretion Disk Winds
Authors: Kallman Timothy , Pereyra Nicolas A. , Blondin John M. 
Published: July 2016

The existence of winds from cataclysmic variables (CVs) has been known for some time, there are a variety of unresolved questions surrounding this phenomenon. These include: the origin of the apparent polar nature of the winds; the rate of mass loss in the winds and the associated driving mechanism; the origin for the characteristic shapes of the UV resonance line profiles, particularly the absorption component; and the apparent association between outburst state and the wind existence. Resolution of all these issues depends on understanding the dynamics of the wind. In this paper we describe one and two dimensional models for disk wind dynamics.Using 1D analytic models we have explore the physical conditions necessary for the existence of a disk wind, and study the dependence of wind speed and mass loss rate on radius. This leads to a criterion which must be satisfied by the rate of increase in the radiation field with height above the disk surface and by the parameters describing the line radiation pressure force (c.f. Castor, Abbott and Klein, 1976).
The Dynamics and Radiative Properties of Clouds in Magnetized Accretion Disk Outflows in AGNs
Authors: Kartje John F. , Königl Arieh 
Published: July 2016

AbstractWe have embarked on a general analysis of multi-component outflows from magnetized accretion disks in AGNs. In this scenario, dense diamagnetic clouds are embedded in a centrifugally driven wind and are uplifted from the disk surface by the dynamical drag of the wind as well as by the “melon seed” magnetic pressure gradient force. We follow the motion of the clouds above the disc surface, taking account of the radiation pressure force exerted by the central continuum for different spectral energy distributions and emission patterns. We study the evolution of the clouds as they accelerate through the wind, considering possible sources of confinement and estimating the cloud lifetimes against various disruptive processes. We then examine the spectral signatures of accelerated clouds in the context of this dynamical scheme and compute absorption line profiles as a function of viewing angle through the wind. We apply our results to the interpretation of the observed optical/UV spectra from BALQSOs and of the broad EUV and X-ray absorption features detected in a number of BL Lac objects, as well as to other AGNs in which radiative acceleration of clouds has been inferred (e.g., “warm absorbers”).
Below the Lyman Edge: UV Polarimetry of Quasars
Authors: Koratkar Anuradha , Goodrich Robert , Antonucci Robert 
Published: July 2016

AbstractThe Lyman edge at 912Å is an important diagnostic region for studying quasi-stellar objects (QSOs). In particular, it reveals a great deal about the physical conditions within the atmospheres of accretion disks, a ubiquitous component of QSO theories. Observations of the Lyman edge regions of QSOs have shown scant evidence for the predicted features – few QSOs show the broad, partial Lyman edges expected to be common according to most theories. The FOS in its polarimetry mode has been instrumental in studying the Lyman edge region in QSOs. One of the most exciting discoveries is that the polarization rises, not at wavelengths longward of the Lyman edge, but at wavelengths well below it! Here we present the status of polarimetry observations at the Lyman edge and discuss their implications to accretions disks
Dissipation of Turbulent Magnetic Fields in Accreting Black Holes
Authors: Kowalenko Victor , Melia Fulvio 
Published: July 2016

AbstractCalculations of the spectrum resulting from accretion onto a massive black hole often make use of the “equipartition assumption” in order to estimate the magnetic field intensity. Thus, the mechanism for the dissipation of the magnetic field and the resulting dynamical influence on the gas have not been treated quantitatively, nor self-consistently. Here, we introduce an alternative approach for modelling the magnetic field dissipation from basic principles, using current ideas about turbulent fields and tearing mode instabilities.
On the Origin of Iron Kα and Hɪ Balmer Lines in AGN
Authors: Marziani P. , Calvani M. , Sulentic J. W. , Romano P. , Zwitter T. , Dultzin-Hacyan D. 
Published: July 2016

AbstractThe idea that a significant fraction of line emission in AGN comes directly from an accretion disk is attractive for several reasons – not least the obvious one of establishing the black hole paradigm. We performed a few consistency tests for the hypothesis that both FE Kα and Hα are emitted by an accretion disk.The main results of this preliminary investigation are as follows. FE Kα is systematically much broader than Hα at FWHM, but the widths of the two lines are not correlated. For each of the 9 objects with FE Kα profile most consistent with disk emission, we computed the possible disk contribution on the basis of a weak field model. Although the Hα profiles are not consistent with disk model emission, rotational motion could still be the main broadening mechanism. We then compared disk inclinations deduced from FE Kα model profile fitting to the ones we derived from model fits of Hα. The inclination values are consistent. Finally, we found that a simple illumination model can produce both disk FE Kα and Hα emission, if a small fraction of continuum is scattered toward the disk to yield ionization parameter ξ > 10−2 ergs s−1 cm.We conclude that the bulk FE Kα cannot be associated to the Broad Line Region. Albeit several radio-quiet Seyfert 1 objects show FE Kα profiles consistent with emission from the inner part of an illuminated accretion disk, the general situation remains unclear, as fits to line profiles require an unsatisfactory large range in model parameters like emissivity and inner and outer radii.
Three Dimensional MHD Simulations of Parker Instability in Differentially Rotating Disk
Authors: Matsuzaki T. , Matsumoto R. , Tajima T. , Shibata K. 
Published: July 2016

AbstractNonlinear growth of the Parker instability (PI) and the Balbus & Hawley instability (BHI) in accretion disks have been studied by local three-dimensional magnetohydrodynamic (MHD) simulations. In high-β disks (β = Pgas/Pmag > 1), the PI has only minor effects on the saturation level of BHI. In low β disks (β ≤ 1), the disk stays in a low-β state because magnetic flux cannot escape fast enough to convert the disk into a high-β state. We found that even in low-β disk the BHI generates fluctuating magnetic fields. The effective magnetic viscosity αB(= –⟨BrBΦ/4πP0⟩) is O(0.1) when β ~ 1.
3-D Hydro dynamic Simulation of Accretion Disk Formation in LMC-X4
Authors: Owen Michael P. , Blondin John M. 
Published: July 2016

We present preliminary results of a time-dependent, three-dimensional hydrodynamic simulation of LMC-X4, an HMXB known to be undergoing RLOF. The simulation is initialized with the collapsed companion embedded in the undisturbed primary wind. The primary is in contact with the Roche surface, although no tidal stream or accretion disk is initialed; they are allowed to form independently.Several features of general interest to disk-fed HMXBs are apparent in the simulation. First, the primary immediately develops a compressed-wind disk in the orbital plane. This may be a natural result in most disk-fed HMXBs. Fora circularized system in an orbit close enough for RLOF to take place, we may expect the primary to be in corotation. The surface velocity may then be a significant fraction of the breakup velocity, leading to a compressed-wind disk.
High-Speed Optical Spectroscopy of a Cataclysmic Variable Wind: BZ Cam (0623+71)
Authors: Ringwald F. A. , Naylor T. 
Published: July 2016

The nova-like variable BZ Cam (also called 0623+71) is an unusual cataclysmic variable star in that it resides in a nebula, discovered by Ellis, Grayson, & Bond (1984) and designated EGB 4. It is more unusual in that its optical spectrum reveals a wind from its accretion disk. This was discovered serendipitously during a radial velocity study to find orbital period by Thorstensen, Thomas, & Patterson (1993; see also Patterson et al. 1996), who found intermittent P Cygni profiles in the He I λ 5876 Å and Hα emission lines.The 4.2-m William Herschel Telescope and its ISIS spectrograph were used to obtain time-resolved spectra of these lines with 0.4 Å/pixel dispersion and 30-second time resolution. These new spectra have about 5 times the spectral resolution and 24 times the time resolution of those of Thorstensen et al. (1993). These observations were obtained on the nights of 1995 February 6 – 8 UT. The blue arm of ISIS was centered on the He I λ 5876 Å; the red arm covered Hα. Typical signal-to-noise ratio was 18 per resolution element.
Super-Eddington Accretion in the Formation of Low-Mass X-ray Binaries and Millisecond Pulsars
Authors: Webbink R. F. , Kalogera V. 
Published: July 2016

AbstractConsiderations of donor star stability, age, and mass transfer rate show that low-mass X-ray binaries and binary millisecond pulsars with orbital periods longer than a few days must have survived an initial phase of super-Eddington mass transfer. We review the physical arguments leading to this conclusion, and examine its implications for the apparent discrepancy between the death rate for low-mass X-ray binaries and the birth rate of binary millisecond pulsars.
Two New T Tauri stars and a Candidate FU Orionis Star associated with Bok Globules
Authors: Yun J. L. , Moreira M. 
Published: July 2016

AbstractWe present photometric and spectroscopic evidence of two new T Tauri stars formed in the conditions of isolated small Bok globules. The spectral energy distributions of these objects display excess infrared emission, they are associated with optical reflection nebulae, and their optical spectra reveal Balmer emission lines and the Li I λ6707 Å absorption line. Additionnally, we report the discovery of what is likely to be a new FU Orionis star seen towards Bok globule CB34. The star is about 4 magnitudes brighter than it appears on the Palomar plates and is associated with the aggregate of young stellar objects forming in Bok globule CB34.
The Blazar Paradigm: Synchro-Compton Emission from Relativistic Jets
Authors: Marscher Alan P. 
Published: July 2016

AbstractI review the current paradigm for nonthermal emission from jets in blazars. The evidence for relativistically flowing jets seems to be more compelling than the case for incoherent synchrotron and self-Compton emission in these objects. I discuss some of the important aspects of current observations of rapid variability at radio frequencies, and stress that one must be careful when calculating the Doppler factor that saves us from the inverse Compton “catastrophe.” I discuss the possibilities for the nature of the VLBI components and present evidence that, at high frequencies, the core is a standing shock wave (Mach disk), while the superluminal components are propagating shocks. I expect that high-frequency and space VLBI will resolve many of the major outstanding issues.
Structure and Properties of AGN Cores from VLBI and Total Flux Density Variations
Authors: Valtaoja Esko 
Published: July 2016

AbstractBy combining VLBI and total flux density data it is possible to get an indirect “look” at the innermost, unresolved core regions of AGN and to estimate physical parameters such as the intrinsic brightness temperatures, Lorentz factors and viewing angles, unobtainable by either VLBI or multi-frequency flux monitoring alone.
Relativistic Numerical Simulations of Superluminal Sources
Authors: Gómez J.L. , Martí J. Mª. , Marscher A.P. , Ibáñez J. Mª. , Alberdi A. 
Published: July 2016

AbstractWe study the generation and evolution of superluminal components in relativistic jets through relativistic hydrodynamical and emission simulations of a square-wave perturbation in the jet velocity.
The Magnetic Switch as the Origin of the FR I/FR II Break
Authors: Meier D.L. , Godon P. , Edgington S. , Payne D.G. , Lind K.R. 
Published: July 2016

AbstractWe propose that the Fanaroff & Riley division between class I and class II radio sources has its origins in the coronae of magnetized accretion disks around black holes. The “magnetic switch”, an effect that critically controls the speed of jets produced by such disks, can explain both qualitative and quantitative differences in the properties of the two classes. These include why morphology and jet speed are functions of radio power and why the division between the two classes is a strong function of galaxy optical luminosity.
Symmetric Parsec-Scale Radio Jets in NGC 4261
Authors: Jones Dayton L. , Wehrle Ann E. 
Published: July 2016

AbstractVLBA observations of NGC 4261 (3C 270) reveal highly symmetric radio structures at both 1.6 and 8.4 GHz. There is little evidence for free-free absorption in the inner few pc, despite the fact that HST imaging shows this galaxy to contain a nearly edge-on disk of gas and dust in its nucleus. However, at our highest resolution we find a narrow gap in emission just east of the radio core which we interpret as evidence for a small (sub-parsec) nearly edge-on accretion disk which is obscuring the base of the counterjet. The position angle of the pc-scale radio axis agrees with the position angle of the VLA-scale jets, which differs from the apparent rotation axis of the nuclear disk seen by HST.
S5 0836+710 A Kelvin-Helmholtz Unstable Jet on Parsec Scales?
Authors: Otterbein K. , Krichbaum T.P. , Kraus A. , Witzel A. , Hummel C.A. , Zensus J.A. 
Published: July 2016

AbstractThe highly redshifted quasar S5 0836+710 (z = 2.172) displays an outstanding one sided jet with complex morphology. The continuous jet shows several remarkable lateral displacements (kinks) of its ridgeline on various length scales. Despite the strength of these distortions the jet is not destroyed by them and remains well collimated. We investigated the possibility to explain the displacements by Kelvin-Helmholtz instabilities.
First VLBA Images of the Nuclei in 3CR Lobe-dominated Quasars
Authors: Hough D.H. , Vermeulen R.C. , Readhead A.C.S. 
Published: July 2016

AbstractWe report the first VLBA images of the nuclei in eight objects from the 3CR complete sample of 25 lobe-dominated quasars (LDQs): 3C 207, 3C 208, 3C 212, 3C 245, 3C 249.1, 3C 263, 3C 270.1, and 3C 275.1. These images reveal core-jet structures of considerable extent and complexity. In combination with earlier VLBI work on the 3CR LDQ sample, the partial distribution of apparent parsec-scale jet speeds for ten objects is relatively flat up to ~ 5h−1c, or perhaps even ~ 10h−1c. While this is not inconsistent with simple beaming models and quasar-FR II radio galaxy unification, it is crucial to obtain the complete speed distribution for truly definitive tests. Work is in progress on multi-frequency, dual-polarization, and phasereferencing VLBA observations on selected objects in the sample.
VLBA Studies of Molecular Gas toward Centaurus A
Authors: van Langevelde Huib Jan , Beasley Anthony 
Published: July 2016

AbstractWe observed the four OH 18 cm transitions against the Cen A VLBI source. With high spatial resolution we detect the same molecular absorption as previously seen with ATCA. Both the excitation and VLBI absorption suggest a cloud size of ≲ 1 pc.
Probing the Accretion Region of NGC 1275 with VLBI
Authors: Walker R.C. , Kellermann K.I. , Dhawan V. , Romney J. D. , Benson J. M. , Vermeulen R. C. , Alef W. 
Published: July 2016

AbstractMulti-frequency VLBA observations were used to study the magnitude and radial dependence of free-free absorption of the radio emission from the counterjet in 3C 84.
VLBA Imaging of a Large Sample of Blazars
Authors: Attridge J. M. , Roberts D. H. , Wardle J. F.C. 
Published: July 2016

AbstractAs part of our continuing study of parsec-scale magnetic fields in active galactic nuclei we have obtained deep polarization-sensitive images of the blazar 1055+018 with the VLBA at 5 GHz. These dramatic images reveal a magnetized layer of material on the outer surfaces of the jet, distinct from the bulk of the jet. This morphology suggests interaction of the jet with the surrounding medium, the resulting shear stretching the magnetic field lines in the direction of the flow. Further multi-frequency polarization-sensitive observations of 1055+018 offer the opportunity to study radio jet-ambient medium interactions in detail.
VLBA Monitoring of Three Gamma-Ray Bright Blazars: AO 0235+164, 1633+382 (4C 38.41), & 2230+114 (CTA 102)
Authors: Xu W. , Wehrle A. E. , Marscher A. P. 
Published: July 2016

AbstractWe have been monitoring gamma-ray blazars with the NRAO VLBA at 22 and 43 GHz since late 1993. We present results on three sources: AO 0235+164, 1633+382 (4C 38.41), and 2230+114 (CTA 102).
Variability of the Radio Nucleus of the Galaxy M81
Authors: Bietenholz M. F. , Bartel N. , Rupen M. P. 
Published: July 2016

AbstractWe report on VLA and VLBI observations of the nucleus of the nearby spiral galaxy M81. The VLA observations show the flux density of the nucleus to be variable by 50%. The VLBI observations indicate that the structure of the nucleus of M81 is somewhat variable on timescales of weeks.
VLBI Observations of Central Region in NGC 3079
Authors: Satoh Satoko , Inoue M. , Nakai N. , Shibata K. M. , Kameno S. , Migenes V. , Diamond P. J. 
Published: July 2016

AbstractWe present multi-frequency observations towards the nucleus of NGC 3079 using both Japan VLBI Network (J-Net) and the VLBA including phased VLA and Effelsberg. We detected two continuum components at 1.4 and 8.4 GHz, and determined the spectral indices for each component. Further, we found several H ɪ absorption features towards the continuum components whose velocity gradient is opposite to the galaxy rotation. Assuming rotation, the central mass is estimated to be 3 × 106M⊙. The water maser distribution extends in North-South direction along the galactic disk, while no clear indication of a Keplerian rotating disk was found.
Proper Motions and the Distance to a Water Vapor Maser in the Galaxy M33
Authors: Argon A. L. , Greenhill L. J. , Moran J. M. , Reid M. J. , Menten K. M. 
Published: July 2016

AbstractThe relative proper motions of water vapor maser features in the H ɪɪ region IC 133 have been used to determine a distance to the galaxy M33 that is independent of the usual calibrations associated with extragalactic distance estimates, e.g., extinction and metallicity.
Imaging the Surface of a Star: VLBA Monitoring of the SiO Masers around U Herculis
Authors: Diamond P. J. , Kemball A. J. 
Published: July 2016

AbstractWe report on 4 epochs of VLBA polarization observations of the 43 GHz, v=1, J=1–0 SiO masers in the circumstellar envelope around the Mira variable U Herculis.
Four Southern Intraday Variable Radio Sources
Authors: Kedziora-Chudczer L. L. , Jauncey D. L. , Wieringa M. H. , Reynolds J. E. , Tzioumis A. K. 
Published: July 2016

AbstractThis is a progress report on the ATCA IDV survey of compact, flat or inverted spectrum radio sources. We found that four sources: PKS 0405–385, PKS 1034–293, PKS 1144–397, and PKS 1519–273 out of the sample of 125 show high flux density variability on the daily timescale. The characteristics of observed IDV are discussed and we reflect on its possible origin.
Polarization Properties of Intraday Variable Blazars
Authors: Kraus A. , Krichbaum T. P. , Witzel A. 
Published: July 2016

AbstractIntraday variability (IDV) is a common phenomenon within blazars, and is seen in about 30 % of all sources in this class. Here we report on IDV observations carried out with the 100m telescope of the MPIfR, especially focusing on variations of the linear polarization.
Towards an Understanding of the Galactic Distribution of Electron-Density Fluctuations
Authors: Salgado J. F. , Salter C. J. , Ghosh T. , Junor W. , Manoharan P. K. 
Published: July 2016

AbstractVLBA observations of 32 compact sources within 30° ≤ ᶩ ≤ 75°, | b | < 3° are being used to test whether the galactic electron-density fluctuations contain a spiral component.
The Evolution of Compact Steep-Spectrum Sources
Authors: Jeyakumar S. , Saikia D. J. 
Published: July 2016

AbstractWe used our high-resolution radio images made with VLA of a large number of compact steep-spectrum (CSS) sources selected from well-defined samples of radio sources and the radio data of these samples to explore the evolution of CSSs with time. We suggest that the majority of CSSs are likely to be young sources advancing outwards through an asymmetric inhomogeneous environment to form the larger ones. We examine the symmetry parameters of both CSSs and larger sources and compare these with both analytical and numerical estimates of propagation of jets through an asymmetric environment. We also examine the consistency of CSSs with the unified scheme for radio galaxies and quasars.
Survey of Milliarcsec Structure in Eight Seyfert Galaxies: Results on NGC 1068 and NGC 4151
Authors: Roy A. L. , Ulvestad J. S. , Colbert E. J. M. , Wilson A. S. , Norris R. P. 
Published: July 2016

AbstractWe are surveying eight nearby Seyfert galaxies (four Sy1s and four Sy2s) that have compact radio cores, using the VLBA. We are interested in parsec-scale morphology and low-frequency absorption effects, and so are observing four frequencies (1.6, 4.8, 8.4 and 15 GHz) to get spectral-index diagnostics. In this paper, we present results on two galaxies, NGC 1068 and NGC 4151. NGC 4151 shows a curved radio jet on the sub-parsec scale, with the smallest scale structure misaligned by 55° from the jet on scales of parsecs to hundreds of parsecs. NGC 1068 contains several components in the inner tens of parsecs, with those components showing a variety of absorption and resolution effects.
Scintillation and the Vela Pulsar’s Magnetosphere
Authors: Gwinn C. R. , Britton M. C. , Reynolds J. E. , Jauncey D. L. , King E. A. , McCulloch P. M. , Lovell J. E. J. , Flanagan C. S. , Smits D. P. , Preston R. A. , Jones D. L. 
Published: July 2016

AbstractRadio-wave scattering in the Vela supernova remnant acts as an imperfect lens to resolve the pulsar’s radio emission region. We use this lens to measure the pulsar’s emission region. We suggest that refraction of radiation within the pulsar’s magnetosphere is responsible for the observed size.
GRS 1915+105: Flares, QPOs and Other Events at 15 GHz
Authors: Pooley G. G. , Fender R. P. 
Published: July 2016

AbstractMonitoring with the Ryle Telescope at 15 GHz of the Galactic X-ray transient source GRS 1915+105 has revealed a remarkable range of rapid and extended flares which appear to be related to the X-ray emission as recorded by the RXTE all-sky monitor. Quasiperiodic oscillations in the range 20–40 min have been found and are probably related to oscillations in the soft X-ray flux.
New Radio Observations of Circinus X-1: A Summary
Authors: Fender R. P. 
Published: July 2016

AbstractNew radio observations from the Australia Telescope Compact Array of the radio jet X-ray binary Circinus X-1 are summarized. Radio flux density monitoring around nearly an entire orbit is presented, confirming continued radio flaring around phase 0.1 (near periastron passage) as well as a lesser enhancement half an orbit later.