bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Turbulent Viscosity Prescription in Accretion Discs
Authors: Godon Patrick
Published: July 2016

The validity of the standard α viscosity prescription in turbulent accretion discs is analyzed. It is found that the α viscosity prescription is no longer valid when the disc is not Keplerian. The analysis is based on simple scaling arguments for fully developed turbulences in accretion discs. An analytical treatment is carried out for geometrically thin, non-Keplerian discs in vertical hydrostatic equilibrium, and is compared with the standard values of the viscosity in the boundary layer region and with the viscosity prescription derived from a general causal equation for the evolution of the stress tensor.
Mass and Angular Momentum Flows in Magnetic CVs
Authors: King A. R.
Published: July 2016

I review recent progress in understanding the accretion geometry and angular momentum flows in magnetic CVs. The recent discovery that AE Aqr is an ejector demonstrates that the criterion for disc formation depends on the spin rate of the white dwarf, in addition to the strength of its magnetic field. It seems likely that AE Aqr represents one phase of a cyclic evolution followed by magnetic CVs. An important consequence is that an observed white dwarf spin rate is not uniquely determined by current properties of the system (e.g. magnetic field and instantaneous accretion rate), but also by its history.
Spin-Resolved Hα Spectroscopy and Photometry of the Intermediate Polar RXJ0558+5353
Authors: Duck S. R. , Still M. D. , Allan A. , Horne K. , Hilditch R. W.
Published: July 2016

RXJ0558+5353 was discovered and classified as an intermediate polar during the ROSAT all-sky survey and subsequent optical follow up programme (Haberl et al. 1994). A further pointed ROSAT observation revealed a spin periodicity of 272.74 s and a soft X-ray component well represented by an absorbed 57 eV blackbody, the spin modulation being due principally to intensity variations of the component (rather than variable absorption). Optical spectroscopy showed the orbital period to be 4.15 h. In this paper we show the true spin period to be 545.4555(8) s (Allan, Horne & Hilditch 1995), twice the published X-ray period, and also discuss preliminary results of the first spin-resolved spectroscopy of RXJ0558+5353.
Asynchronous Rotation in By Cam: It’S Got a Good Beat and You Can Dance to it (Very Slowly)
Authors: Silber A. D.
Published: July 2016

Since its discovery, BY Cam was known to be an atypical AM Her type CV (Remillard et al. 1986). Observations showed the orbital and white-dwarf spin periods differ by about 1% (Silber et al. 1992). As the white dwarf rotates relative to the secondary, the accretion stream encounters different magnetic geometries, and hence follows different accretion paths to the white dwarf. The magnetic geometry seen by the accretion stream repeats at the beat period (1/Pbeat = 1/Pspin − 1/Porb), which is 7 to 20 d (the range is due to the uncertainty in the measured periods). The shape of the light curve changes from night to night, which can be explained by the changing geometry of the highly-beamed cyclotron emission. Even if the asynchronous rotation is the underlying cause of the changing light curve, the light curve could differ at similar beat phases if the threading process is chaotic. Previous attempts to study the beat period using IUE (Zucker et al. 1995) and optical data (Mason & Chanmugam 1992) have been inconclusive.
The Possible Contribution from the Accretion Disk During the Quiescence of VW Hyi
Authors: Huang M. , Sion E. M. , Hubeny I. , Cheng F. H. , Szkody P.
Published: July 2016

We have re-analyzed UV spectra of the dwarf nova VW Hyi during its quiescence, obtained with the Faint Object Spectrograph (FOS) on Hubble Space Telescope (HST), by considering the possible contribution from the accretion disk, which was not included in the previous analysis.
VW Hyi: A Rapidly Cooling White Dwarf?
Authors: Gänsicke Boris T. , Beuermann Klaus
Published: July 2016

We estimate the post-outburst cooling time-scale of the white dwarf in VW Hyi, using the available quiescent IUE spectra. The determination of the white-dwarf temperature close to the outburst is hampered because disc emission still contributes to the SWP flux.
Classical Nova Evolution: Clues from Soft X-Ray Emission
Authors: MacDonald James
Published: July 2016

Multi-wavelength observations have shown that, after optical decline, the stellar remnants of classical nova outbursts evolve at constant, near-Eddington, bolometric luminosity to high effective temperature (> 2 105 K), before turning off. Here we briefly review the observations of classical novae in this phase of evolution, and discuss what the soft X-ray observations tell us about the mass of the underlying white dwarf and the rate of mass change due to stellar winds and accretion from the stellar companion.
Accretion Disk Dynamics of Her X-1
Authors: Vrtilek S. D. , Cheng F. H.
Published: July 2016

The Her X-1/HZ Her system consists of a neutron star with a rotation period of 1.24s orbiting a ‘normal’ stellar companion every 1.7d. Variation in optical and ultraviolet magnitude is attributed to X-ray heating on the side facing the active neutron star with some contribution from X-ray heating of the disk. The system also has a 35-day period in which the X-ray emission displays so-called main and short ‘on’ states separated by relative X-ray quiescence. The 1.7-day optical flux variations continue throughout the 35-day period. No clear consensus exists as to the origin of the 35-day period; a popular interpretation is that of occultation of the compact X-ray source by a tilted, precessing, accretion disk.
Accreting White Dwarfs and type Ia Supernovae
Authors: Livio Mario , Branch David , Yungelson L. R. , Boffi Francesca , Baron E.
Published: July 2016

The question of the possible progenitors of supernovae Type la (SNe la) is examined. It is argued that SNe la are thermonuclear explosions of accreting C-O white dwarfs. The existing observational evidence favors somewhat models in which the exploding star ignites carbon upon reaching the Chandrasekhar mass. A careful examination of all the potential progenitor classes reveals that when realization frequencies are combined with a variety of observational charcteristics, no single class emerges as containing the obvious progenitors. It is argued that coalescing white dwarfs or supersoft X-ray sources are the most likely progenitor systems. A few critical observations which could help identify the progenitors unambiguously are discussed.
The Extended Dust Emission around GK Per
Authors: Dougherty S. M. , Waters L. B. F. M. , Bode M. F. , Lloyd H. M. , Kester D. J. M. , Bontekoe TJ. R.
Published: July 2016

GK Per, a classical nova system that erupted in 1901, is one of the more unusual examples of its type. It has the longest known orbital period for a classical nova (1.997d; Crampton, Cowley & Fisher 1986); and it contains a white dwarf primary with an evolved K2 sub-giant secondary. Most remarkably, the IRAS Sky Survey (1991) reveals that GK Per exhibits far-IR dust emission extending ~ 17′ to the NW and SE of the nova (Bode et al. 1987; Seaquist et al. 1989). We have re-analysed the IRAS data using maximum entropy reconstruction (Bontekoe et al. 1991; Bontekoe, Koper & Kester 1994) to resolve structures at a spatial resolution approaching the diffraction limit of IRAS, which is 1′ at 60 μm and 1.7′ at 100/μm.
Relativistic Iron Kα Emission in Seyfert Galaxies
Authors: Nandra K.
Published: July 2016

Evidence is presented for widespread relativistic effects in the central regions of active galactic nuclei (AGN). A sample of 18 Seyfert 1 galaxies observed by ASCA show iron Kα emission which is resolved, with mean full width at half maximum (FWHM) ~ 50,000 km s−1 for a Gaussian profile. However, many of the line profiles are asymmetric. A strong red wing is indicative of gravitational redshifts close to a central black hole, and accretion-disk models provide an excellent description of the data. Such observations probe the innermost regions of AGN, and arguably provide the best evidence yet obtained for the existence of supermassive black holes in the centers of active galaxies.
On Shock Conditions in Black-Hole Accretion
Authors: Yuan Feng , Lu Ju-Fu
Published: July 2016

We study the effects of different shock conditions upon shock properties, such as their location and strength. We find that it is very important to include the effects of radiative energy loss in the shock front.
Rapid Continuum Variability in NGC 4151
Authors: Edelson Rick
Published: July 2016

The bright Seyfert 1 galaxy NGC 4151 was monitored intensively by IUE, ROSAT, ASCA, CGRO, and ground-based telescopes for 10 days in 1993 December. The source, which was near its peak historical brightness, showed strong, correlated variability at X-ray, ultraviolet, and optical wavelengths (see Fig. la). The strongest variations were seen in medium energy (~1.5keV) X-rays, with a normalized variability amplitude (NVA) of 24%. Weaker (NVA = 6%) variations, uncorrelated with those at lower energies, were seen at soft γ-ray energies of ~100keV. No significant variability was seen in softer (0.1–1 keV) X-ray bands. In the ultraviolet/optical regime, the NVA decreased within increasing wavelength, from 9% to 1% between 1275 Å and 6900 Å.
The HST Sample of Radio-Loud Quasars: Emission Lines from Lyα to Hβ
Authors: Wills Beverley J. , Brotherton M.S. , Wills D. , Thompson K.L. , Baldwin J. A. , Carswell R. F. , Browne I.W.A. , Netzer H. , Francis P.J.
Published: July 2016

We have obtained HST and ground-based spectrophotometry of a sample of ~61 radio-loud quasars from shortward of Lyα to longward of Hβ. The aim was to investigate the dependence of quasar properties on orientation of the central engine axis to the observer’s line of sight. As an approximate measure of inclination we use the radio core-dominance, i.e., the ratio of beamed radiocore emission to the emission in the extended lobes at 5 GHz rest frequency. About half the radio sources have core-dominance greater than unity (jet or axis pointed close to our line of sight). Quasar pairs were matched in radio lobe luminosity and redshift to reduce bias caused by strong dependences on intrinsic luminosity.

Observation and reduction techniques were standard, and the spectral resolution is equivalent to 230–400 km s−1 (Wills et al. 1993). We have performed correlation analyses among emission-line and continuum parameters, as well as spectral principal-component analyses (SPCA, Francis et al. 1992).
Complete Atlases of Recalibrated Archival HST FOS Spectra of Quasars and AGN
Authors: Pesto S. , Koratkar A. , Blitz E. , Evans I. N.
Published: July 2016

The ionization structures of AGNs are determined by the specific ionization mechanisms and the shapes of the ionizing continua. The technique of using emission-line intensity ratios to classify objects and investigate their ionization mechanisms is enhanced significantly by combining high-quality UV and optical spectrophotometry. The HST archive is an excellent source of such data.

The FOS spectra are recalibrated using the latest ‘average inverse sensitivity’ (AIS) calibration. This new method for flux calibrating FOS data (1) normalizes count data from all apertures to the 4”.3 aperture to account for changes of aperture throughput as a function of the Optical Telescope Assembly focus; (2) corrects the data for time-dependent detector sensitivity degradation; and (3) scales the data to the white-dwarf reference scale. The AIS calibration method has been developed over a period of several years, with improvements applied progressively based on observed deficiencies and/or discrepancies of the existing calibrations. Indeed, the final AIS calibration incorporates corrections in the wavelength overlap regions of adjacent gratings derived based on inconsistencies discovered as a result of this study of over 1000 FOS spectra.
First Results of Optical Monitoring of 3C 390.3
Authors: Dietrich M. , O’Brien P.T. , Leighly K. M.
Published: July 2016

In late autumn 1994, the International AGN Watch started a multiwavelength monitoring campaign on 3C 390.3, the first radio-loud AGN to be selected for high temporal-resolution monitoring from the radio domain to X-ray energies. This AGN is is of particular interest since significant variations have been observed on both short and long time scales in both the line fluxes and line profiles (Barr et al. 1980, Veilleux & Zheng 1991).

In the optical, spectroscopic data and broad-band flux measurements in B, V, R, and I were obtained. The brightness of 3C 390.3 was calculated relative to the stars in the field. The R magnitudes are based on observations recorded at Calar Alto, Spain, in 1994 December. Generally, AGN spectra are intercalibrated using narrow forbidden emission lines since these lines can be taken as constant on time scales of decades (Peterson 1993). Since the [O III] λλ4959, 5007 flux is variable on time scales of several months (Zheng et al. 1995), these lines were studied in detail. We found that they were constant within ~2% during 1995 (Dietrich et al. 1996). The spectra were therefore intercalibrated by using the narrow forbidden emission lines. 3C 390.3 was also observed with IUE for 14 months (O’Brien et al. 1996) and with ROSAT for nine months in 1995 (Leighly et al. 1996). Radio data were also obtained during a 3-month MERLIN campaign.
C IV λ1549 Emission-Line Profile Variations in AGN
Authors: Türler Marc , Courvoisier Thierry J.-L.
Published: July 2016

We study the C IV λ1549 emission-line profile variations in 18 Seyfert 1-type objects observed with the IUE satellite from 1978 to 1991. The core and the two wings of the line are integrated separately in order to study differences between the wings and the core and between the blue and the red wings. A principal component analysis is applied to spectra of each object. The results suggest the presence of a significant infall component in the line-emitting region of several AGN.
A New Luminosity Effect in QSO Spectra
Authors: Corbin Michael R. , Boroson Todd A.
Published: July 2016

Comparison of the emission-line and continuum parameters of 48 low-redshift QSOs reveals the asymmetry of the C IV λ1549 broad emission line to be strongly correlated with ultraviolet continuum luminosity, such that increasing luminosity produces increasing redward asymmetry. A similar correlation has been found for broad Hβ. Redward profile asymmetries can be modeled as the result of the gravitational redshift of line photons from the very broad-line region (VBLR) by 109–1010M⊙ black holes, but blueward profile asymmetries require a competing effect such as electron scattering.
Coronal Lines from the BLR, NLR, and ENLR
Authors: Wagne Stefan J.
Published: July 2016

We discuss kinematical evidence that highly ionized (‘coronal’) lines are emitted from gas sharing the same velocity field as the BLR, NLR, and extended NLR. A close correlation between ionization potential and line width and blueshift with respect to systemic velocity suggests a hot outflow being responsible for the emission of coronal lines. This outflow is probably connected to the warm absorber observed in X-rays and the outflowing radio plasma. The high degree of ionization is dominantly due to photons from the blue bump but contributions from shocks are indicated in at least some of the sources observed.
Near-Infrared Imaging Spectroscopy of the Seyfert Nucleus of the Circinus Galaxy
Authors: Maiolino R. , Thatte N. , Kroker H. , Gallimore J.F. , Genzel R.
Published: July 2016

The Circinus galaxy is a nearby (4 Mpc) spiral that hosts a Seyfert nucleus as deduced by the emission of intense coronal lines (Oliva et al. 1994) and by the prominent ionization cone observed in [O III] images (Marconi et al. 1994).

We present K-band imaging spectroscopy of the nucleus of this galaxy obtained by means of 3D, the MPE imaging spectrometer (Weitzel et al. 1996), and ROGUE, a first-order adaptive-optics system (Thatte et al. 1995), mounted on the 2.2-m ESO telescope. The spectral resolution is 1000 and the average optical seeing was about 0”.6 (= 12 pc at the source).
Bidimensional [O III] λλ4959, 5007 Spectroscopy in the Circumnuclear Region of the Active Galaxy NGC 1068
Authors: García-Lorenzo B. , Arribas S. , Mediavilla E. , del Burgo C.
Published: July 2016

We present preliminary results about the velocity field of the ionized gas in the central region of NGC 1068, inferred from the [O III] λλ4959, 5007 emission lines. The data, 570 spectra in the inner 23″ × 18″ of this galaxy, were obtained with an optical fiber system which allows 2-D spectroscopy. The velocity field for the ionized gas inferred from the [O III] lines is in good agreement with recent results based on the Hα+[N II] lines.
An Objective-Prism Survey of Emission-Line Galaxies
Authors: Kim Chulhee
Published: July 2016

In order to discover emission-line galaxy (ELG) candidates towards the Hydra Void, an objective-prism survey was undertaken. As a first step, five fields were observed with the UK Schmidt Telescope, and we discovered a total of 33 candidates on a single prism plate through the [O III] λλ4959, 5007 emission feature.
Low-Luminosity Seyfert Nuclei
Authors: Ho Luis C. , Filippenko Alexei V. , Sargent Wallace L.W.
Published: July 2016

We describe a new sample of Seyfert nuclei discovered during the course of an optical spectroscopic survey of nearby galaxies. The majority of the objects, many recognized as AGNs for the first time, have luminosities much lower than those of classical Seyferts and populate the faint end of the AGN luminosity function. A significant fraction of the nuclei emit broad Hα emission qualitatively similar to the broad lines seen in classical Seyfert 1 nuclei and QSOs.
Spectral Properties of Parkes Flat-Spectrum Radio Sources
Authors: Drinkwater Michael J. , Francis Paul J. , Webster Rachel L.
Published: July 2016

We have constructed composite spectra of a large sample of flat-spectrum radio sources. The spectra are all very similar over a wide range of radio and optical properties, and are also similar to a composite of optically selected QSOs. We find, however, that the forbidden lines of the very reddest objects are anomalously strong.
Determination of the Gravitational Potential of Seyfert Cores from High-Resolution Spatial and Spectral Data
Authors: Wittkowski M.
Published: July 2016

We summarize the current state of our project to determine the gravitational potential in the innermost few hundred parsecs of Seyfert cores from observed line-of-sight velocities of molecular clouds. Therefore we distinguish between the observational part on the one hand and the theoretical aspects on the other. On the theoretical side the problem is lack of knowledge of the flow pattern and the spatial distribution of the clouds. We analyze the possibility of distinguishing between the different flow patterns and determining the mass distribution. On the observational side the problem is obtaining sufficiently high spatial and spectral resolution.
Macho Detection by Pulsar Timing Observation
Authors: Ohnishi Kouji , Hosokawa Mizuhiko , Fukushima Toshio , Takeuti Mine
Published: July 2016

The magnitudes of some general relativistic effects depend on the mass of gravitating objects; therefore, these effects can be used for the stellar mass measurement. Several methods have been proposed; for example, the microlensing effect (Paczyński 1986), and the parallactic variation of gravitational deflection of the light from the source (Hosokawa et al. 1993).

Recently some candidates for MACHOs – a kind of dark matter candidates in the Galactic halo – have been discovered by their microlensing effect, and their masses were estimated to be of the order of 0.1Mʘ, under many assumptions. Actual measurement of MACHO masses are important in specifying what kind of object the MACHO is.
To explain Crab pulsar emission by ICS Model
Authors: Han J.L. , Zhang B. , Giao G.J. , Xu R.X.
Published: July 2016

Primary results of our recent work show that radio, infrared and optical, X-ray andγ-ray emission of Crab pulsar might be explained by Inverse Compton Scattering (ICS) mechanism.
On the pulsar radiation mechanism
Authors: Gangadhara R. T.
Published: July 2016

Pulsars have typical magnetic field strengths between 108and 1012G. Therefore, even if the particles are produced with nonzero perpendicular component of velocity at the pole, they radiate out this component quickly due to synchrotron radiation. Therefore, the motion of a particle along a field line becomes one dimensional in regions where filed lines are straight. However, when they move along the curved magnetic field lines, they get accelerated due to the centrifugal force. They gain again the perpendicular energy at the expense of parallel energy, but can not gyrate in the curved field lines and hence do not experience any curvature or gradient drifts.
Wide Beams from Young Pulsars (or One Pole for All)
Authors: Manchester R. N.
Published: July 2016

Polarization observations show the existence of a well-defined group of young pulsars with highly linearly polarized mean pulse profiles. Many of these pulsars have interpulses. I suggest that both the main pulse and the interpulse in these pulsars are part of a very wide conal beam emitted along field lines emanating from a single magnetic pole. Such wide beams may be responsible for all interpulse emission.
Pulsar Polarization, Emission, and Beaming
Authors: Rankin Joanna M.
Published: July 2016

This paper discusses observational and analytical questions pertaining to the pulsar emission problem. A short outline of the area is given for those new to the subject. Some of the literature pertinent to pulsar polarization, emission and beaming, which has appeared over about the last five years is mentioned. There is a short discussion of efforts to carry out polarimetric observations of higher quality, and finally, there is a short discussion of recent work by the author and her colleagues.
Multi-Frequency Pulsar Polarimetry at High Frequencies
Authors: von Hoensbroech A. , Xilouris K. M.
Published: July 2016

A sample of 62 pulsar profiles has been studied with full polarization information at high radio frequencies, aiming at studying the dependency of emission altitude at the deepest layers of pulsar magnetospheres. The emission is consistent with heights ranging between 1-2% of the light-cylinder-radius, while a slight radius-to-frequency mapping is evident.
Gamma-Ray Pulsar Emission Models
Authors: Harding Alice K.
Published: July 2016

With the increased sensitivity of gamma-ray detectors on the Compton Gamma-Ray Observatory (CGRO) the number of presently known gamma-ray pulsars has grown. The new detections are beginning to provide clues to the origin of the high-energy radiation in the form of emerging patterns and correlations among observed quantities such as gamma-ray efficiency and spectral index vs. age. But there are still many questions about the location of the emission and its relation to the radio, optical and X-ray pulses. This paper will review models for gamma-ray emission from pulsars and will examine how well the detailed predictions of these models account for the existing observations.
The Problem of Energy Transfer in the Crab Nebula
Authors: Machabeli G. , Mchedlishvili G. , Shapakidze D.
Published: July 2016

The possibility of Langmuir wave generation in electronpositron plasma is considered. As a result of induced scattering, these waves find themselves in the superluminal region. Thereby such waves can transfer energy to the Crab Nebula essentially without loss, where the remaining plasma creates condition of collapse of Langmuir waves. As a result, the tail of thee±distribution function stretchs out to Lorentz factors of the order of γ±≤ 109. Via synchrotron emission, particles of these energies can radiate X and γ - radiation.
The Galactic Electron Density Distribution
Authors: Weisberg Joel M.
Published: July 2016

Pulsars are excellent probes of the galactic free electron layer. Interstellar dispersion and scattering measurably affect the observed pulsar signals, thereby providing information on the distribution and density of the free electrons causing these phenomena.

Primary calibration of galactic electron density models is achieved through adjusting their parameters to fit the observed dispersion of pulsars having independently measured distances. The distances are determined via kinematic analyses of HI absorption spectra, through angular or timing parallax measurements, and from associations with other objects of known distances.

The models have become steadily more refined as the body of data upon which they are based has grown. Independent distance measurements continue to accrue. The discovery of pulsars in globular clusters provided high latitude lines of sight for probing the z-distribution (Reynolds 1989). Additional calibration has been provided through incorporation of interstellar scattering measurements into the modelling process (Cordeset al. 1991). Individual spiral arms are now explicitly modelled (Taylor & Cordes 1993).

While great progress has been achieved with these models, there are still uncertainties in modelling the electron density of the local region and the inner Galaxy, and in the z–distribution of the electron layer. Currently anticipated observations will help to resolve some of these issues.
Investigation of pulsar diffractive scintillation at 4.75 and 10.55 GHz
Authors: Malofeev V. , Shishov V. , Sieber W. , Jessner A. , Kramer M. , Wielebinski R.
Published: July 2016

Many papers were in the past devoted to the investigation of the interstellar medium (ISM) with the help of pulsars, most of them studying the time and frequency structure of pulsar flux variations in the strong scintillation regime. Weak scintillation is typically found at cm- and dcm-wavelengths, but depends on distance so that the critical frequency (νc) increases with distance. Pulsar intensities weaken, however, at high frequencies, since as a rule pulsar spectra have spectral indices steeper than −1.5. This explains why there are practically no measurements of pulsars in the weak scintillation regime.

We report in this paper on first measurements of the correlation function of pulsar intensity fluctuations, of the decorrelation timeτdand of the scintillation indexmdat high frequencies, i.e. at 4.75 and 10.55 GHz in the weak scintillation regime. The detail data analysis, theoretical relations and comparison with theory will presented by Malofeev et al. (1996).
On Galactic magnetic field derived from RMs of pulsars
Authors: Han J.L. , Qiao G.J.
Published: July 2016

RMs of all 262 pulsars are used to see the large scale magnetic field of our Galaxy. We find that: (1). RMs of 91 pulsars at high galactic latitude (|b| > 8.6°) show two toroidal magnetic rings antisymmetric with respect to galactic plane. These data shouldn’t be used for modelling the large scale field in Galactic disk; (2). pulsars at low galactic latitude are concentrated on the spiral arms; (3). the directions of fields have a similar pitch angle to that of spiral arms.
Observations of Disks and Outflows from Young Stars
Authors: Bally John
Published: July 2016

I review recent observations and accretions disks and jets powered by young stellar objects.
Dynamical and Microphysical Constraints on Accreting Magnetospheric Clouds in Active Galactic Nuclei
Authors: Kuncic Zdenka
Published: July 2016

The range of microphysical and dynamical timescales at the centres of Active Galactic Nuclei (AGN) is sufficiently wide to permit multiphase structure. In particular, very dense, cool clouds can coexist with a hot, magnetically-dominated plasma. The strong dynamical forces in this central magnetosphere can give rise to clouds so small that microphysical processes determine whether they can survive for long enough to produce potentially observable spectral signatures due to thermal reprocessing. Specific physical constraints on the scale sizes of such reprocessing clouds are examined. It is found that there exists a parameter subspace in the extreme high density regime for which gas can sustain cool temperatures whilst maintaining pressure equilibrium with the ambient magnetosphere.
Hydrodynamic Simulations of Wind-Accretion with Gradients
Authors: Ruffert M.
Published: July 2016

I investigate the hydrodynamics of three-dimensional Bondi-Hoyle-Lyttleton accretion including velocity and density gradients in the incoming flow and determine how much angular momentum is accreted. A medium taken to be an ideal gas with an adiabatic index of 5/3 or 4/3 moves at supersonic speeds (Mach 3 and 10) past a totally absorbing sphere with a radius of 0.1 or 0.02 accretion radii. The velocity within the medium is given a gradient of 3% or 20% (over one accretion radius). I find that a substantial amount (0.1 to 0.7) of the specific angular momentum available within one accretion radius in the upstream flow actually is accreted. The amount is smaller for smaller accretor sizes. The flow is roughly just as unstable as in the previous models without gradients. The unstable flow is best seen in animated sequences.
Kilohertz QPO in Low Mass X-Ray Binaries: an Overview
Authors: van der Klis M.
Published: July 2016

I review the current status of the investigations of the kilohertz quasi-periodic oscillations that have been discovered in low-mass Xray binaries (LMXBs) with NASA’s Rossi X-ray Timing Explorer (RXTE) since February 1996. Seven sources have now shown this new phenomenon, one Z source (Sco X–l) and 6 atoll sources (all X-ray bursters), and some patterns are beginning to emerge. The frequencies of the oscillations are between 500 and 1200 Hz. They can be coherent for more than 102 cycles, but a more typical coherence is several 101. Amplitudes are between 0.5 and 16% (rms) of the total flux. Most sources show double kHz peaks separated by a few 102 Hz, which move up and down in frequency together. In Sco X–l the peak frequencies systematically increase, and the peak separation systematically decreases, with Ṁ. In 4U 1728–34 a third oscillation is seen at a frequency equal to the difference frequency of the two kHz peaks, but only during X-ray bursts. A simple interpretation in terms of a beat-frequency model with the difference frequency being the neutron star’s spin, as suggested by this result, is inconsistent with the fact that in Sco X–l the peak separation varies.
X-Ray Observations Of SS 433 With ASCA
Authors: Kotani T. , Kawai N. , Matsuoka M. , Brinkmann W.
Published: July 2016

SS 433 has been observed with ASCA for three years since the launch in 1993. The excellent energy resolution of ASCA revealed the Doppler-shifted emission lines from the both jets, though it had been generally accepted that the X-ray emitting region of the receding jet is hidden behind the accretion disk. Thus the estimation on the properties of the X-ray jet, such as length, temperature, and mass outflow rate, should be revised in accordance with the ASCA data. Modeling the jet as a radiating ballistic plasma, we determined these quantities. It is also tried to determine the mass of the system from a data covering an eclipse.
White Dwarf Masses in magnetic CVs: Multi-temperature Fits to Ginga data
Authors: Cropper Mark , Ramsay Gavin , Wu Kinwah
Published: July 2016

We have used the hard X-ray spectrum obtained from Ginga to determine the mass of the white dwarf primary star in 13 magnetic CV systems. Our model for the spectral fit includes the temperature and density structure in the post-shock accretion flow, taking into account the additional cooling of the cyclotron radiation. We obtain good fits to the data, and we compare our derived masses to those determined by other means.
Numerical Simulations of MHD Winds from Accretion Disks
Authors: Stone James M.
Published: July 2016

The contributions that time-dependent multidimensional numerical simulations have made to our understanding of MHD winds from accretion disks are reviewed. Current simulations can be divided into four categories: (1) axisymmetric global models, (2) axisymmetric simulations of the wind only, (3) three-dimensional local models, and (4) threedimensional global models. Results from each category are discussed. Current results indicate that weakly magnetized disks are turbulent, and that this turbulence is responsible for dynamo action which amplifies the disk field. These effects may have important consequences for the production of MHD winds. We discuss the feasibility of fully three-dimensional global models that can capture these effects in the future.
Infrared Jets from Protostars: The case of HH212
Authors: Zinnecker Hans , McCaughrean Mark J.
Published: July 2016

We describe the appearance and significance of HH212, the most symmetric two-sided molecular hydrogen jet/counterjet system yet discovered. This prototype embedded protostellar H2jet emanates from a low-luminosity isolated protostar in Orion. It exhibits matched pairs of knots and bow-shocks interpreted as arising from a time-variable source, which we take to indicate that protostellar accretion through the encircling disk is non-steady and pulsed.
Optical/Ultraviolet Continuum Polarization of AGN Accretion Disks
Authors: Blaes Omer , Agol Eric
Published: July 2016

We show how the effects of Faraday rotation and a detailed treatment of the radiative transfer can address various aspects of the polarization problem of AGN accretion disks. In particular, we show how accretion disks might explain the rises in polarization observed blueward of the Lyman edge in several quasars.
General Relativistic Simulation of Jet Formation from Magnetized Accretion Disk
Authors: Koide Shinji , Shibata Kazunari , Kudoh Takahiro
Published: July 2016

Recently, superluminal motions are observed not only from active galactic nuclei but also in our Galaxy. These phenomena are explained as relativistic jets propagating almost toward us with Lorentz factor more than 2. For the formation of such a relativistic jet, magnetically driven mechanism around a black hole is most promising. We have extended the 2.5D Newtonian MHD jet model (Shibata & Uchida 1986) to general relativistic regime. For this purpose, we have developed a general relativistic magnetohydrodynamic (GRMHD) numerical code and applied it to the simulation of the magnetized accretion disk around a black hole. We have found the formation of magnetically driven jets with 86 percent of light velocity (i.e. Lorentz factor ~ 2.0).
Outflow Angles and Bulk Lorentz Factors for Different Categories of AGN
Authors: Guerra Erick. J. , Daly Ruth A.
Published: July 2016

Relativistic outflows from AGN can be parameterized by θ, the angle subtended by the direction of the outflow and the line of sight to the observer, and γ, the bulk Lorentz factor of the outflow. The Doppler factor, δ, and the apparent speed in the plane of the sky, βapp, are combinations of θ and γ. The Doppler factor can be estimated using either the equipartition Doppler factor, δeq (Readhead 1994), or the inverse Compton Doppler factor, δIC. These Doppler factor estimates are combined with observed βapp to solve for θ and γ for different categories of AGN.

Ghisellini et al. (1993) compute δIC for 105 compact radio sources, and Güijosa & Daly (1996) compute δeq for the same sample. Daly, Guerra, & Güijosa (1996) estimate θ and γ for the 43 sources that have βapp listed by Vermeulen & Cohen (1994) and δeq computed by Güijosa & Daly (1996).

Solutions and errors for θ and γ are presented in Figures 1 and 2 using δeq and δIC respectively. Guerra & Daly (1996) discuss these estimates and errors in greater detail. These AGN fall into the following categories: BL Lacertae objects (BL Lacs), core-dominated high-polarization quasars (CDHPQ), core-dominated low-polarization quasars (CDLPQ), core-dominated quasars with no polarization information (CDQ(NPI)), lobe-dominated quasars (LDQ), and radio galaxies (RG).
Accretion Disks in the SW Sex Stars
Authors: Hoard D. W. , Szkody Paula
Published: July 2016

We present recent results of time-resolved optical spectroscopy on two SW Sex stars, PG 0859+415 and BH Lyncis.
Discovery of an X-Ray Off-State in the Supersoft Source CAL 83
Authors: Kahabka P.
Published: July 2016

An X-ray off state of CAL 83 has been observed in April 1996 with the ROSAT HRI three weeks after a normal on state. An upper limit for a linear decline time of the observed flux of ~20 days (and of an efolding decline time of ~6 days) is deduced. This decline may be due to the response of the white dwarf envelope to a temporary increased mass accretion rate giving rise to an envelope expansion. CAL 83 may resemble the recurrent supersoft LMC transient RX J0513.9–6951 with episodes of disappearance in X-rays.
Mass Flux and Toroidal Magnetic Field in Magnetically Driven Jets from Accretion Disks: Steady Solutions and Application to Jet/Wind in YSO
Authors: Kudoh T. , Shibata K.
Published: July 2016

We solved one-dimensional steady and axisymmetric magnetohydrodynamical (MHD) equations to study basic properties of astrophysical jets from accretion disks. We found that the mass flux of the jets depends on the poloidal magnetic field strength of the disk. The mass loss rates observed in T Tauri winds will constrain the physical quantities in the accretion disks.
Infrared Emission Around Cyg X-3
Authors: Ogley R.N. , Bell Burnell S.J. , Fender R.P.
Published: July 2016

We present UKIRT infrared images of the X-ray binary Cygnus X-3. We address the possibility of extended infrared emission and show that it could be either warm circumstellar material or a star near the binary’s line of sight.
Mid-infrared Observations of Magnetic Fields in the Disks of Bi-Polar Outflow Sources
Authors: Smith Craig H. , Wright Christopher M. , Aitken David K. , Roche Patrick F.
Published: July 2016

We present the results from mid-infrared spectro-polarimetric observations of a number of bi-polar outflow sources. The specto-polarimetric data provides information on the polarization mechanism and the magnetic field direction. The field direction in the disks of the observed sources is most often normal to the ambient field direction and lies in the plane of the disk, indicating a toroidal rather than poloidal field configuration.
Optical Signatures of Reprocessing from Hercules X-l
Authors: Still M. D. , Reynolds A. P. , Quaintrell H. , Roche P. , Chakrabarty D. , Levine S. E.
Published: July 2016

The mechanism providing the 35-day period found in optical and X-ray light curves of the eclipsing low-mass X-ray binary Her X-l is considered to be the precession of a tilted and twisted accretion disc about the neutron star. We have obtained spectrophotometric observations of this system. The majority of line absorption and emission originates on or near the mass-losing primary, with distributions over the inner face of the star consistent with irradiation from the environs of the compact object. After suitable corrections for heating, the neutron star is found have a mass of 1.6±0.3M⊙, in contrast to the last radial velocity study which found a value less than 1.0 M⊙ . Rotational velocity measurements, while insufficiently precise to reject the older mass estimate, suggest that the rotational period of HZ Her differs from the synchronous rate by no more than 20%. Using a recently determined figure for the effective temperature of the unheated face, the distance to Her X-l is estimated at 6.7±0.4kpc, higher than prior estimates. The systemic velocity is found to be –69±6km s−1. In order to to determine the plausibility of the twisted disc model we reconstruct the expected shadow of the disc across the heated inner face of the donor star to compare with observation. Large scale emission structure is reproduced, but the model fails to synthesize finer observational details. HeII λ4686 Å emission is detected and found to be distributed closely about the neutron star, and is a likely tracer of the accretion flow.
Wind Accretion in Separated Binaries
Authors: Walder R.
Published: July 2016

In the framework of Euler flows, I present simulations of wind accretion in well separated binaries for three different cases: Cygnus X-3, a high mass X-ray binary (see e.g. Schmutz et al. 1996), ζ Aurigae, a system showing strong atmospheric eclipse effects (see e.g. Griffin et al. 1990), and the generic barium star model of Theuns and Jorissen (1993), which is recomputed here with a different numerical method (a MUSCL-type integrator, incorporated in our AMRCART code). These simulations represent a first, small sample out of the large parameter space of wind accretion in separated binaries (see Table 1).

On the orbital scale, the vorticity of the flow is due to the orbital motion of the stars. It is particularly large for the case where the wind velocity is comparable to the orbital speed of the stars (see Fig. 1). In the vicinity of the accreting star, the vorticity is determined by the accretion process. With two strong vortices above and below the accretor (with respect to the orbital plane), the flow resembles the flow out of a bath tub. On a smaller scale, one finds even more vorticity: The flow is highly turbulent. Such turbulence and the shear flows in the large scale vortices cannot be well captured by an Euler flow model. A next step of improvement would be the use of an appropriate MHD turbulence model.
Stimulating Simulating
Authors: Whitehurst Rob
Published: July 2016

The difficulties associated with numerical simulation of accretion discs are outlined along with a potential treatment, FLAME. This technique bridges the gap between existing finite difference codes and particle methods in modern computational fluid dynamics (CFD).
Multi-Frequency VLBA+Effelsberg Observations of 1038+528 A/B
Authors: Rioja M. J. , Porcas R. W.
Published: July 2016

We made a November 1995 observation of the close (33 arc sec) pair 1038+528 A,B using the VLBA+Effelsberg at 2.3 and 8.4 GHz, and the VLBA alone at 15 GHz. Our analysis of the precise astrometric separation between the core peak in A and a component ~ 1.8 mas from the core in B sheds new light on the observed changes with time and frequency.
Rotation-Measure Mapping of 3C 119
Authors: Flatters C.
Published: July 2016

The compact steep-spectrum source 3C 119 has been mapped using the VLBA at four frequencies spread over the 5 GHz observing band. The high rotation-measure reported at short wavelengths is found to continue unbroken beyond the depolarization wavelength indicating that 3C 119 is depolarized by an external medium.
Magnetic Field Configuration in 4C 39.25
Authors: Alberdi A. , Lara L. , Gómez J.L. , Marcaide J.M. , Pérez-Torres M.A. , Kemball A. , Leppänen K. , Marscher A.P. , Patnaik A. , Porcas R.
Published: July 2016

We have performed simultaneous multi-frequency polarization VLBA observations of the compact radio sources 3C 395 and 4C 39.25 which show both stationary and superluminal components in their parsec-scale structures. Those of 3C 395 have been reported elsewhere. Here we report on high resolution maps of the total intensity and polarized radio emission of 4C 39.25, trace the magnetic field configuration along the jet, and explore different possibilities for the nature of the components within the framework of the bent shocked relativistic jet model.
Detection of Parsec-Scale Circular Polarization with the VLBA
Authors: Homan D. C. , Wardle J. F.C. , Ojha R. , Roberts D. H.
Published: July 2016

Circular polarization has been detected in 3C 279 and 3C 84 at multiple epochs, using the VLBA at 15 GHz. This is the first detection of circular polarization in a compact radio source at VLBI resolution. In the case of 3C 279 the polarization is most likely produced by the conversion of linear to circular polarization by low energy relativistic electrons in the emitting region. If this is so, the absence of Faraday rotation by the same electrons suggests that the jet consists of an electron-positron plasma.
Millimeter Continuum Monitoring of Extragalactic Radio Sources with the IRAM 30M Telescope
Authors: Ungerechts H. , Kramer C. , Lefloch B. , Leon S. , Masset F. , Moreno R. , Paubert G. , Reynaud D. , Sievers A. , Wild W.
Published: July 2016

We continue to determine flux densities at 3mm, 2mm, and 1.3mm wavelength for selected extragalactic sources. Light-curves for some sources now cover nearly 12 years.
The Rosat-Green Bank Sample of Intermediate BL Lac Objects
Authors: Laurent-Muehleisen S. A. , Kollgaard R. I. , Feigelson E. D.
Published: July 2016

The Rosat-Green Bank BL Lac sample consists of 119 objects and smoothly bridges the gap between the previously disparate subclasses of radio- and X-ray-selected objects. Further study of this sample should provide useful constraints to the unified scheme and help determine if modifications are necessary.
Very Long Baseline Polarimetry of BL Lac
Authors: Denn G. R. , Mutel R. L.
Published: July 2016

We have made polarization sensitive maps of BL Lac with the VLBA at 15, 22, and 43 GHz at seven epochs from 1995.42 to 1997.16. Three new superluminal components (S8, S9, and S10) have been identified, each having a unique signature in trajectory and polarization characteristics.
Low-luminosity BL Lac Objects and Flat-spectrum Radio Galaxies
Authors: Bondi M. , Dallacasa D. , Marchã M. J. M. , Stanghellini C.
Published: July 2016

We present first results from a new sample of low radio luminosity flat spectrum radio galaxies.
A Spectral Analysis of 3C 67 and 3C 190
Authors: Katz-Stone D. M. , Rudnick L.
Published: July 2016

Using new high resolution VLA and VLBA data and existing MERLIN data of 3C 67 and 3C 190, we find both sources have a complex spectral structure similar to larger Fanaroff-Riley type II sources. Our analysis of 3C 190 predicts either an unusually steep injection index of −0.8 and a young age, or a superposition of different age spectral components.
CTD 93—The Not-So-Simple Double
Authors: Shaffer David B. , Kellermann K. I.
Published: July 2016

A VLBA map of CTD 93 at 2 cm shows the morphology to be better described as a core-jet configuration than as a symmetric compact double structure.
Maser Radiation from a Turbulent Keplerian Disk: NGC 4258
Authors: Watson W. D. , Wallin B. K. , Wyld H. W.
Published: July 2016

Calculations are summarized for the spectral and spatial distribution of maser radiation that emerges from a turbulent Keplerian disk when viewed nearly edge-on. A close comparison is made with the refined observational data about the masing accretion disk around the presumed massive black hole at the nucleus of the galaxy NGC 4258.
SiO and H2O Masers in the Central Parsec of the Galaxy
Authors: Menten Karl M. , Reid Mark J.
Published: July 2016

We have discovered maser emission from SiO and H2O molecules toward a number of evolved stars within the central parsec of our Galaxy. The maser positions can be registered with milliarcsecond precision relative to the radio continuum emission of the nonthermal Galactic center source Sgr A*. Since the masing stars are prominent infrared sources, our data can be used to locate the position of Sgr A* on infrared images of the Galactic center region. Using VLBA observations it will be possible to measure proper motions of the maser stars, which can be used to put constraints on the mass distribution in the central parsec.
Multi-Frequency Monitoring of a Sample of Extragalactic Radio Sources
Authors: Mingaliev M. , Botashev A. , Stolyarov V.
Published: July 2016

The preliminary results of monitoring of simultaneous spectra of a sample of extragalactic sources are given. Eight sets of observations were done at the RATAN-600 radio telescope in 1995-1996 at six frequencies (0.96, 2.3, 3.9, 7.7, 11.2, and 22 GHz). The light curves as well as the variability parameters are given
An Image of a Highly Relativistic Jet from a Large Flare in the X-Ray Binary Cyg X-3
Authors: Mioduszewski A. J. , Hjellming R. M. , Rupen M. P. , Waltman E. B. , Pooley G. G. , Ghigo F. D. , Fender R. P.
Published: July 2016

A VLBA image of the X-ray binary Cyg X-3 made two days after a 10 Jy radio flare shows a one-sided, curved jet with a size scale of ≈60 mas. This seems to indicate a jet with a velocity of ≥0.89c with a inclination of a few degrees to the line of site, and indicates that some of events where Cyg X-3 flares above 3 Jy may come from highly relativistic jets close to the line of sight.