bluuebunny/crossref_metadata_2025 huggingface dataset:
The Unification of Active Galaxies: Observations
Authors: Goodrich R.W.
Published: July 2016

Unification theories have been central to much of our recent progress in the study of active galactic nuclei (AGN). These theories often explain the differences between some observationally defined classes of objects as due to what might be considered ‘uninteresting’ or nonfundamental parameters, such as viewing angle. In this presentation, I discuss not only such orientation-dependent unification theories, but also expand the concept to unification through other means, such as evolutionary effects.
HUT Observations of the Lyman Limit in AGN: Implications for Unified Models
Authors: Kriss G. , Krolik J. , Grimes J. , Tsvetanov Z. , Espey B. , Zheng W. , Davidsen A.
Published: July 2016

We observed a total of 13 low-redshift AGN with the Hopkins Ultraviolet Telescope (HUT) during the course of the Astro-1 and Astro-2 missions. Of these, 4 show intrinsic Lyman-limit absorption — NGC 1068, NGC 4151, NGC 3516 and NGC 3227. AU galaxies with optically thick Lyman limits have extended narrow-line regions with bi-polar morphologies. All AGN with no absorption are Seyfert Is with compact NLRs. These observations support geometrical shadowing as the means for collimating the ionizing radiation in unified models of AGN, most likely in a photoionized atmosphere above the obscuring torus.
ROSAT Observations of Radio Quasars: Unification of Flat and Steep-Spectrum Sources?
Authors: Yuan W. , Brinkmann W. , Siebert J.
Published: July 2016

We have studied the dependence of X-ray spectral and luminosity properties on radio morphology using ROSAT data, for a sample of radio quasars. The results support the unified schemes for FS and SS quasars.
The Nature of the Energy Source in LINERs
Authors: Colina L. , Koratkar A.
Published: July 2016

LINERs are found in ~30% of all bright galaxies, including luminous infrared galaxies. They form a heterogeneous class powered by a variety of ionizing mechanisms such as low-luminosity AGNs, starbursts, shocks, or any combination of these.

In early-type spirals, LINERs are powered by a low-luminosity AGN, or by an AGN surrounded by circumnuclear star-forming regions. In luminous infrared galaxies, LINERs are powered by starbursts with associated wind-related extended shocks, and an AGN may play a minor role, if any. LINERs in some FR I radio galaxies show a strong evidence for the presence of a massive central black hole, and there are indications for the existence of shocks in the nuclear disks of these galaxies. Yet, the dominant ionizing mechanism for LINERs in radio-quiet ellipticals and FR I host galaxies is still unclear.

Multifrequency high spatial resolution imaging and spectroscopy are essential to discriminate among the different ionizing mechanisms present in LINERs.
Design of (2+1+2)D FFT for Interferometric Pulsar Survey
Authors: Daishido T. , Tanaka N. , Sudo S. , Suzuki M. , Saito Y. , Agehama R. , Adachi M. , Watanabe N.
Published: July 2016

The Following design of a Pulsar Survey System with a Huge Interferometric Array is discussed. (1) A Huge Array of 320m × 320m with 256(= 16 × 16) spherical dishes of 20m in diameter, (2) RF is 1.4 GHz, (3) Receivers are frequency modified GPS(1.57542, 1.2276GHz) ones, (4) Phase and Delay Tracking, (5) Phase Calibration using Differential GPS(GPS signal × 2 → CW), (6) (2+1+2)D FFT /256 pixel Imaging + 256 ch Filtering + Dispersion Removal and Period finding(17M point floating 2DFFT by DSP), (8) Observing time required for the same sensitivity to Arecibo τ/τA: 0.88(Timing), 0.003(Survey).
The Case for no field decay from improved pulsar population studies
Authors: Hartman J.W. , Verbunt F. , Bhattacharya D. , Wijers R.
Published: July 2016

We perform radio pulsar population synthesis to study the evolution of the pulsar population. In doing this, we continue our earlier work on this subject (Bhattacharya et al. 1992). We have extended our work by 1) calculating orbits in the whole galaxy (the simulation of the observations however is still limited to the solar neighborhood), 2) using the high birth velocities of radio pulsars from Lyne & Lorimer (1994) and 3) implementing the new model by Taylor & Cordes (1993) of the distribution of free electrons in the galaxy. A full report of this work will be given in Hartman et al. (1996).
Further Observations of the Planets Pulsar
Authors: Wolszczan A.
Published: July 2016

Recent results of timing observations of the planets pulsar, PSR B1257+12, are discussed. The current timing model includes significant contributions from the second and the third–order period derivatives. If these contributions are related to dynamical effects induced by a fourth distant planet, it would be a Saturn–mass object in a ~170 year orbit around the pulsar.
14 Years of Daily Timing Observations of the Vela Pulsar
Authors: McCulloch P M
Published: July 2016

Daily timing observations of the Vela pulsar have been made over the last 14 years. During this time there has been seven large period jumps, or glitches, four of these have been observed as they occurred. We examine the time scale of these glitches and several other events which appear to be mini-glitches.
VLBI Position Determinations for the Millisecond Pulsar B1937+21
Authors: Bartel N. , Chandler J.F. , Ratner M.I. , Shapiro I.I.
Published: July 2016

We determined with VLBI the coordinates of PSR B1937+21 and compare them with other determinations obtained with interferometry and timing. All the position estimates agree within one combined standard error, after the timing positions have each been rotated to the IERS extragalactic reference frame.
Relativistic effect of gravitational deflection of light in binary pulsars
Authors: Doroshenko Oleg V. , Kopeikin Sergei M.
Published: July 2016

Timing formula for data processing of observations of binary pulsars that accounts for the relativistic deflection of light in the gravitational field of the pulsar’s companion is presented, and the measurability of this effect along with its variance estimates is discussed. The deflection of the pulsar’s pulse trajectory in the gravitational field of its companion leads to variation in the pulsar’s rotational phase. This variation appears as a narrow sharp growth of the magnitude of the post-fit residuals in the vicinity of the moment of the superior conjunction of the pulsar with its companion. In contrast to the relativistic Shapiro effect, the amplitude of the effect of gravitational deflection of the pulsar radio beam has two peaks with opposite signs, which become sharper as the inclinationiof the pulsar’s orbit approaches to the right angle. The effect under consideration influences the estimation of parameters of the relativistic Shapiro effect in the binary pulsars with nearly edgewise orbits. Its inclusion in the fitting procedure provides a more careful measurement of the sine of the orbital inclinationi, as well as the masses of the pulsar and its companion. This permits an improved testing of alternative theories of gravity in the strong field regime. The effect of the gravitational deflection of light has been numerically investigated for binary pulsars with nearly edgewise orbits. It is shown that the effect is observed in general only when cosi is less than 0.003. This estimate becomes less restrictive as the pulsar’s spin axis approaches the line of sight.
Plasma Instabilities: Sources for Coherent Radio Emission
Authors: Asseo Estelle
Published: July 2016

The mechanism for the generation of pulsar radio emission has not yet been identified. Several coherent emission processes, linked to the motion of relativistic particles in the extremely strong pulsar magnetic field, have been proposed as possible candidates. Essential improvements, based on fundamental concepts of plasma physics, prove that collective plasma effects can provide the necessary degree of coherence. Progress in the 1990s, which is reported here, relates to curvature maser emission processes and relativistic plasma emission mechanisms.
Separation of integrated pulse shapes into unique sub-components
Authors: Kramer Michael
Published: July 2016

Average pulse profiles are generally separable into several components whereas individual components can be described by a Gaussian shape. One generally distinguishes betweencoreandconalcomponents, although it is yet unclear whether core and conal components originate from the same (Lyne & Manchester 1988) or a different emission mechanism (Rankin 1983). Investigating this problem, we studied the behaviour of individual components observed in about 200 profiles of 18 pulsars measured at three different frequencies, i.e. at 1.4 GHz, 4.75 GHz and 10.55 GHz. We unambiguously determined the number, location, width, flux density and spectral index of individual components using a special technique (Kramer et al. 1994). The applied method ensures that only intrinsic features of the pulse profiles are fitted by comparing off-pulse noise statistics and post-fit residuals as a goodness-of-fit estimator. As a first result, we note that all high S/N pulsar profiles can be accurately described by using only a small number (usually ≤ 5) of gaussian components, although we also find an example of a seven component pulse shape (B0740–28). Fitted components determined for different observations of the same pulsar were averaged, producing a grand mean profile which is completely noise-free and thus suitable for a reliable flux density measurement of individual components, for an accurate determination of the pulse width to calculate opening angles, ρ, of the emission cone, or for use as a template for obtaining pulse arrival times.
A study of polarisation modes in PSR 0823+26
Authors: Rankin Joanna M. , Rathnasree N.
Published: July 2016

We explore the detailed polarisation behaviour of pulsar 0823+26 using the technique of constructing partial “mode-separated” profiles corresponding to the primary and secondary polarisation modes. The characteristics of the two polarisation modes in this pulsar are particularly interesting, both because they are anything but orthogonal (Backer & Rankin 1980), and because the secondary mode exhibits structure seen neither in the primary mode nor in the total profile.

Using the model-angle method of polarisation-mode deconstruction (Rankinet. al. 1989; Cordeset. al. 1978), we can take the following representation of the single-vector model to define the respective primary and secondary-mode PA traverses

where χ is the PA,ϕthe longitude,the maximum PA sweep rate, andAa constant which can be computed from the total PA traverse, χcbetween reference longitudes ±ϕcas

and which is formally equal to sin ζ/ tan α, where α and ζ are the angles that the magnetic axis and the sight line make with the rotation axis, respectively.
On polarisation of high intensity pulses in radio pulsars
Authors: Rathnasree N. , Rankin Joanna M.
Published: July 2016

A marked anti-correlation between the degree of linear polarisationdLand the intensityI, has been reported for some pulsars (Manchester, Taylor & Huguenin 1975; Xilouriset. al.1994). A detailed investigation of the variation in the total polarisation of single pulses for some pulsars has been done, with proper statistical correction applied to the linearly polarised power. This study, then, reveals very different behaviour as well as some remarkable correlations in many pulsars, which reflect directly on the nature of pulsar radio emission.

The most important correction to be applied to linear polarisation data arises from the differences in the statistical properties of the Stokes parametersQandU, defining the linear polarisation, and the linearly polarised powerThe measured value of the linearly polarised power is larger than the true value, with the difference being, where σ is the measured standard deviation in the off-pulse region in any of the Stokes parameters (Rankin, Campbell & Spangler 1975).
Unusual frequency dependence of the integrated profile of the millisecond pulsar PSR J2145-0705
Authors: Kuzmin A.D. , Losovski B.Ya.
Published: July 2016

We report on observations and frequency dependence analysis of the integrated profile of the millisecond pulsar PSR J2145-0705. Observations were performed at 102 MHz with the BSA radio telescope in Pushchino.

To analyze the frequency dependence of the integrated profile we supplemented our data with high frequency measurements by Bailes et al. (unpublished). For frequency dependence analysis we used the Gaussian fit separation method of presentation the integrated pulse profile as a superposition of Gaussian-shaped individual components (Wu, Xu and Rankin 1992; Foster, Fairhead and Backer 1991). A good fit is provided by four component structure, suggested by Bailes et al. 1994.
Optical Observations of Pulsars
Authors: Gouiffes Christian , Ögelman Hakki
Published: July 2016

In the course of a programme to study optical pulsars, we have observed at different occasions PSR0540-69, the 50 msec pulsar in the LMC. Like the Crab pulsar, it has been detected at X-rays, optical and radio and its braking index (∼2) determined. In this communication we report some results obtained on this pulsar, in particular the presence of narrow features in the pulse profile and compare it with a nearly simultaneous X-ray observation.

The observations were carried out at the 3.6m telescope at La. Silla observatory, Chile. The instrument consisted on a single channel photometer coupled with a. photomultiplier (GaAs photocathode). The sampling frequency was 10 kHz and the output of the photon counting system was recorded sequentially on magnetic tape. A set of filters and diaphragms were available. A standard analysis was then performed. After corrections to the solar system barycenter, the data were analyzed and the best period determined using thetest (Buccheri et al, 1983).
High Energy Pulsars: Pulses and Populations
Authors: Romani Roger W.
Published: July 2016

Recent X-ray and γ-ray observations have detected a number of isolated spin-powered pulsars. Studies of the pulse profiles of these objects are providing a useful guide to the site of the high energy emission. The γ-ray pulses, which are closely tied to the primary population of radiating particles, seem to be an especially useful discriminant between pulsar models. With an understanding of how the pulsar luminosity and beaming factors evolve with spin parameters, pulsar population syntheses can also be used to check the predictions of high energy emission models. In turn, comparison with γ-ray sky surveys constrains the properties of the young pulsar population.
Energy Transport in a Rotation-Modulated Pulsar Wind
Authors: Melatos A. , Melrose D. B.
Published: July 2016

The structure and energetics of a rotation-modulated pulsar wind are examined. It is shown that the displacement current in the wind asymptotically dominates the conduction current, creating an outer radiation zone whose inner boundary lies well inside the wind termination shock. A self-consistent nonlinear-plasma-wave model of the radiation zone predicts that the ratio of Poynting flux to kinetic-energy flux at the termination shock is small (~ 10−3for the Crab), in agreement with independent observational estimates.
Interstellar Scattering: Observations and Interpretations
Authors: Rickett Barney
Published: July 2016

The successful theory for radio propagation through the interstellar plasma is reviewed, where the density spectrum follows the Kolmogorov model. However, there are also several observations indicating more refraction than expected. A particular model of enhanced refraction is proposed in which isolated regions of the warm ionized medium support filaments of enhanced density on a scale of 1 AU, which do not couple to a turbulent cascade.
Interstellar Fringes from PSR B0834+06
Authors: Rickett Barney , Lyne Andrew , Gupta Yashwant
Published: July 2016

The spectra of radio flux from pulsars show deep modulations, over a typical time scale Δtdand frequency scale Δfd. These random diffractive interstellar scintillations are caused by inhomogeneities in the interstellar plasma on scales of 105m to 106m; on occasion there are also refractive modulations caused by very much larger scales. We report here an episode of periodic modulations of the dynamic spectrum of PSR B0834+06 seen in the sequence of observations centered at 408 MHz reported by Gupta et al. (1994 - GRL). There were 12 observations of about 2 hours covering 5 MHz spaced over 14 months. An episode of very fine periodic fringes was detected, though the period 45 kHz in frequency was barely resolved by the 19.5 kHz channel bandwiths; the period in time was about 5 minutes and was fully resolved. The normal Δfdwas about 4 MHz (GRL) - ≈90 times the fringe period.
Scintillation Studies of the Pulsar PSR B0329+54
Authors: Stinebring Daniel R. , Faison Michael D. , McKinnon Mark M.
Published: July 2016

Refractive and diffractive scintillation are thought to be two related effects of scattering in the interstellar medium. The predicted modulation of diffractive scintillation parameters by refractive effects has not been thoroughly tested, however. We report 24 days of scintillation observations of the radio pulsar PSR B0329+54 from September 1993 to June 1994 with a 26-m telescope operating at 610 MHz. Dynamic spectra were obtained on each day, from which the characteristic bandwidth and time scale of the diffractive scintillation pattern were determined. A relative flux value for the pulsar was also obtained on each day. The cross-correlation coefficient for each unique pair of the observables — flux,δF, bandwidth,δνand time scale,δt— was formed from these data. The observed values of these coefficients and their 67% confidenceintervals are:CδFδν= −0.4 ± 0.2,CδFδt= −0.7 ± 0.1, andCδνδt= 0.5 ± 0.2. Theoretical expectations are thatCδFδν= −0.8,CδFδt= −0.6, andCδνδt= 0.8. We conclude that we have detected the expected modulation of diffractive parameters by refractive scintillation. This adds confidence to the interpretation that diffractive and refractive scintillation of compact radio sources are caused by the same underlying scattering process.
The Distribution of Fractional Linear Polarization and the Random Component of Polarization Position Angle
Authors: McKinnon M. M. , Stinebring D. R.
Published: July 2016

One of the most fascinating features of the polarization of pulsar radio emission is the occurrence of orthogonal modes of polarization. The origin of the modes is not clear, but, whatever their underlying nature, the modes will affect observables such as the instantaneous linear polarization. We derive an idealized distribution of fractional linear polarization assuming that the modes are superposed and compare our result with observations. We discuss how superposed modes may affect the position angle distributions.

Consider a subpulse composed of superposed modes of orthogonal polarization. We assume that each mode is completely linearly-polarized with no dispersion in position angle. If the flux densities of the individual modes are represented by the independent random variablesX1andX2, then the linear polarization of the subpulse is related toX=X1−X2and its total intensity isY=X1+X2. We denote the means of the mode distributions byμ1andμ2and their standard deviations byσ1andσ2. The means are generally not the same because observed distributions of position angle (e.g. Stinebring et al. 1984) show that the modes generally do not occur with equal frequency. If the individual modes are normally-distributed with identical standard deviations,XandYare also normally-distributed, independent random variables. In this ideal case, the distribution of fractional polarization,Z=|X/Y|, is
Classical Spin-Orbit Coupling and Periastron Advance in PSR J0045–7319
Authors: Kaspi Victoria M.
Published: July 2016

Radio timing observations of the SMC binary pulsar PSR J0045–7319 show, for the first time in a binary pulsar, that classical spin-orbit coupling and periastron advance are occurring. From the observations, the angle θ between the B star spin axis and the orbital angular momentum is constrained to be 25° < θ < 41° (Kaspi et al. 1996b). Under the conventional assumption that the pre-supernova angular momenta were aligned, this provides direct evidence for an asymmetric supernova explosion. In addition, a large, unexpected orbital decay is observed in the system.
The Origin of Millisecond Pulsars
Authors: Bhattacharya Dipankar
Published: July 2016

According to the standard model, millisecond pulsars are the descendants of low-mass X-ray binaries (LMXB). The importance of this formation route has, however, been questioned by several authors on different grounds. This paper critically reviews the arguments and assumptions underlying the standard model. The kinematic properties of the LMXB and millisecond pulsar populations are compared, and are found to be compatible. This provides an additional argument in favour of the standard model.
Tomography of Accretion Flows in Binary Stars and Active Galactic Nuclei
Authors: Horne Keith
Published: July 2016

Astrotomography resolves accretion flows with micro-arcsecond angular resolution. Eclipses by a binary companion star slice up a disk surface, giving monochromatic maps of the disk, or spectra from any region of its surface. Doppler tomography maps emission-line regions from the changing velocity profile as the binary rotates, revealing radial and azimuthal structure, gas streams, irradiated companion stars, magnetic flows, and slingshot prominences. Echo mapping exploits time delays between the hard radiation from near the compact object at the focus of the flow, and softer emission generated by irradiation of regions farther out. The maximum entropy techniques for fitting intensity maps to data are currently being extended by incorporating local physics and mapping physical parameters such as temperature, density, surface density, and velocity dispersion.
Imaging Relativistic Radio Jets and the X-ray-Radio Connection in X-ray Transients
Authors: Hjellming R. M.
Published: July 2016

The superluminal radio jets produced by GRO J1655–40 during a series of X-ray outbursts in 1994 were the first indications of a delayed form of relativistic outflows from black hole accretion disk environments. In this paper we review the relation between the radio jets and changes in the X-ray environment for the 1994 events in GRO J1655–40 and compare this behavior with similar X-ray-radio correlations that have since been found in GRS 1716–249, GRS 1739–278, and the 1996 recurrence of another correlated event in GRO 1655–40. We also discuss newly found radio-X-ray correlations in a galactic X-ray binary, Cyg X–3.
New Radio and Optical Data for GRO J1655–40
Authors: Hunstead Richard W. , Wu Kinwah , Campbell-Wilson Duncan
Published: July 2016

MOST 843 MHz flux densities are presented for the May 1996 outburst from GRO J1655—40. A deep radio image of the field reveals extended emission regions which may be associated with the radio jets. The optical spectrum during the 1994 outburst shows remarkable similarities to that of a Wolf-Rayet WN star.
Instability, Turbulence, and Enhanced Transport in Accretion Disks
Authors: Balbus Steven A. , Hawley John F.
Published: July 2016

The nature of MHD and hydrodynamical turbulence in accretion disks is discussed. Comparison is made with planar Couette flow, a classical system prone to nonlinear shear instability resulting in enhanced turbulent transport. Both Keplerian and non-Keplerian hydrodynamical disks are studied, and it is found that only constant angular momentum disks are unstable to nonlinear disturbances and develop enhanced turbulent transport. Convective instabilities do not lead to enhanced turbulent transport. Hydrodynamical Keplerian disks are quite stable to nonlinear disturbances. Several lines of argument are presented which all lead to this conclusion, but the key to disk turbulence is the interaction between the stress tensor and the mean flow gradients. The nature of this coupling is found to determine completely the stability properties of disks (hydrodynamics and magnetic), and the nature of turbulent transport. The weak field MHD instability, which is of great astrophysical importance, displays the same type of stress tensor – mean flow coupling that all classical local shear instabilities exhibit. Hydrodynamical Keplerian disks, on the other hand, do not. Accretion disk turbulence is MHD turbulence.
Probing Accretion Disks in AGN with Water Masers
Authors: Maloney Philip R.
Published: July 2016

Extremely luminous extragalactic water masers – the so-called “megamasers”, with isotropic luminosities of tens to hundreds of solar luminosities – appear to be uniquely associated with active galactic nuclei. The recent survey of Braatz et al. indicates that 20% of Seyfert 2 galaxies have detectable water maser emission. Although originally suggested to arise in shocks, it now seems likely that the masers arise from the irradiation of high-pressure molecular gas by X-rays from the AGN. Quantitative modelling shows that the observed megamaser luminosities can plausibly be produced in this fashion. Both observational limits on the size scales and the high gas pressures required indicate that the water maser emission arises on very small scales, either in a circumnuclear “torus” or the accretion disk itself. In the best-studied case, NCG 4258, the masers are produced in a geometrically thin, warped accretion disk. The maser models can be used to derive quantitative information about the physical conditions in the disk, namely, the mass accretion rate, and therefore the radiative efficiency. I discuss the implications of water maser observations and models for the study of accretion disks and circumnuclear tori in AGN.
X-ray Observations of Accretion Disks
Authors: White Nicholas E.
Published: July 2016

The properties of accretion disks in low mass X-ray binaries (LMXRB) are reviewed in the context of recent results from the ASCA observatory.
Magnetohydrodynamic Turbulence in Accretion Discs: Towards More Realistic Models
Authors: Torkelsson Ulf , Brandenburg Axel , Nordlund Åke , Stein Robert F.
Published: July 2016

The shearing box has rapidly become the accepted way to investigate turbulence in Keplerian shear flows. In this paper we discuss to what extent and in which way the outcome of the shearing box is affected by the adopted boundary conditions, and how the shearing box can be modified to capture more of the physics of an accretion disc. The original shearing box model is too symmetric to generate a net accretion flow, but the symmetry can be broken by including the main effects of the cylindrical geometry of the real disc. However the quantitative change in the resulting angular momentum transport is small.
Magnetic Accretors in Binaries
Authors: King A.R.
Published: July 2016

I consider the angular momentum balance in binaries where the accretor has a significant magnetic field. The ejector AE Aqr provides a counterexample to most simple ideas. In particular it shows that the criterion for disc formation must involve the spin rate of the accretor, and that this rate may be subject to cycles, rather than settling to an equilibrium characterized by the magnetic fieldstrength. Angular momentum loss via magnetized disc winds can never be strong enough to affect the binary evolution significantly, but spinup of the accretor can have a marked effect. Although there is strong spin-orbit coupling in the AM Her systems, this cannot produce the orbital expansion needed to explain the low accretion rate states of these systems. Instead a mechanism intrinsic to the secondary star (such as starspots) probably interrupts mass transfer in all short-period CVs: the results are seen directly in AM Her systems, but masked by the presence of an accretion disc in most other cases.
Instabilities in Accretion Disks of Cataclysmic Variables: A Unification Model for Dwarf Nova Outburst
Authors: Osaki Yoji
Published: July 2016

Instabilities of accretion disks in cataclysmic variable stars are reviewed in relation to dwarf nova outbursts. Two different kinds of instabilities of accretion disks are now known: the thermal instability and the tidal instability. The thermal instability is produced by hydrogen ionization-recombination transition, which gives rises to a thermal limit-cycle oscillation in accretion disks and it is thought to be responsible for outbursts of U Gem-type dwarf novae. The tidal instability is produced by the tidal effects of the secondary star on accretion disks, by which the disk is deformed to eccentric form and it slowly precesses in the inertial frame of reference. The tidal instability is thought to be responsible for the superhump phenomenon observed during superoutbursts of SU UMa-type dwarf novae. There is a rich variety in outburst behaviors of non-magnetic cataclysmic variables, starting from non-outbursting nova-like stars to various sub-classes of dwarf novae. A unification model for dwarf nova outbursts is then proposed based on these two instabilities. In this model, the non-magnetic cataclysmic variables are classified in the orbital-period versus mass-transfer-rate diagram into four regions depending on different combination to these two instabilities, and their observed outburst behaviors are basically understood on this diagram.
Mass Transfer in Low Mass Close Binaries
Authors: Wu Kinwah
Published: July 2016

The mass transfer process in low mass close binaries is reviewed. The driving mechanisms and the stability properties are discussed by means of general, simple formulations. A model in terms of mass transfer instabilities is suggested to explain the outbursts of GRO J1655–40 in 1994.
The Nature and Evolutionary Status of GRO J1744–28
Authors: Joss P. C. , Rappaport S.
Published: July 2016

GRO J1744–28 is the first known X-ray source to display both bursts and periodic pulsations. This source may thus provide crucial clues that will lead to an understanding of the differences in the nature of the X-ray variability among accreting neutron stars. We deduce that the magnetic field of the neutron star is relatively weak (~ 8 × 1010G) but, nevertheless, sufficiently strong to funnel the accretion flow onto the magnetic polar caps and suppress the thermonuclear flashes that would otherwise give rise to type I X-ray bursts. We also present a series of interrelated arguments which demonstrate that the observed bursts are of type II and probably result from an instability associated with the interaction of the neutron-star magnetic field with the inner edge of the accretion disk. From these results, we infer that X-ray pulsars, GRO J1744–28, the Rapid Burster, and the type I X-ray bursters may form a sequence of possible behaviors among accreting neutron stars, with the strength of the magnetic field serving as the crucial parameter that determines the mode of X-ray variability. The companion star in the GRO J1744–28 binary system is probably a very low-mass (~ 0.2M⊙) giant that is in the final stages of losing its hydrogen-rich envelope. We have carried out binary evolution calculations which show that (1) if the mass of the giant was ~ 1M⊙when mass transfer onto the neutron star commenced, then the orbital period and the core mass of the giant have increased from ~ 1 to ~ 11.8 days and from ~ 0.15 to ~ 0.21M⊙, respectively, during the mass-transfer epoch, which has lasted for ~ 8 × 108yr, (2) the present long-term average X-ray luminosity is ~ 4 × 1036ergs s−1, which is at least two orders of magnitude lower than the luminosity at the peak of the transient outburst, and (3) the predicted long-term equilibrium rotation rate of the neutron star is remarkably close to the observed pulse rate. The transient nature of GRO J1744–28 may well be related to the final stages of dissipation of the envelope of the giant companion.
Cygnus X–1: A Case for a Magnetic Accretion Disk?
Authors: Nowak Michael A. , Vaughan B. A. , Dove J. , Wilms J.
Published: July 2016

With the advent of RXTE, which is capable of broad spectral coverage and fast timing, as well as other instruments which are increasingly being used in multi-wavelength campaigns (via both space-based and ground-based observations), we must demand more of our theoretical models. No current model mimics all facets of a system as complex as an x-ray binary. However, a modern theory should qualitatively reproduce — or at the very least not fundamentally disagree with – all of Cygnus X–1’s most basic average properties: energy spectrum (viewed within a broader framework of black hole candidate spectral behavior), power spectrum (PSD), and time delays and coherence between variability in different energy bands. Below we discuss each of these basic properties in turn, and we assess the health of one of the currently popular theories: Comptonization of photons from a cold disk. We find that the data pose substantial challenges for this theory, as well as all other currently discussed models.
UBV-Photometry and 35–day Cycle Model for X-ray Binary HZ Her/Her X–l
Authors: Shakura N. I. , Smirnov A. V. , Ketsaris N. A.
Published: July 2016

Based on the detailed analysis of UBV–photometry of HZ Her obtained in 1972–1994, a model of 35–day cycle is proposed in which both forced precession of a tilted accretion disk and free precession of the neutron star are present.
HST Eclipse Studies of Magnetic CVs: Resolving the UV Hot Spot and Accretion Stream
Authors: Stockman H.S.
Published: July 2016

Time-resolved photometry and spectroscopy of cataclysmic variables (CV) are powerful tools for clarifying the physical size, placement, and conditions of emission regions in these compact systems. We present HST time resolved UV spectroscopic data for one self-eclipsing mCV system, ST LMi, and two secondary eclipsing systems, DP Leo and UZ For. These observations clearly show the relative contributions of three emission components: the white dwarf, a hotter region surrounding the accretion shock, and the photoionized accretion stream. UZ For was observed in an unusually active state by both HST and EUVE. These data provide strong evidence that the accretion stream is “clumpy”, with overdensities 100–1000 times the average density. Using photoionization codes such as XSTAR and CLOUDY, we find that steady, supersonic, and homogenous flow in the UZ For accretion stream is unstable to compression heating. As a consequence, we propose a two-phase model for the stream and obtain density enhancements comparable to those deduced from the strengths of the UV emission lines and EUVE absorption features. Similar behavior may be expected from active, asynchronous magnetic CVs with coupling radii greater than several white dwarf radii.
Spectropolarimetry of CV’s; Signatures of Magnetic Fields in Accretion Flows
Authors: Steeghs Danny , Horne Keith
Published: July 2016

We present preliminary results of spectropolarimetric observations of several cataclysmic variables using the ISIS spectropolarimeter on the 4.2m William Hershell Telescope at La Palma. Our aim is to look for Zeeman signatures of magnetic fields in cataclysmic variables. This would provide a direct measurement of magnetic fields in the accretion flows of CVs. Our current dataset allows us to set upper limits to the presence of magnetic fields and constrain the field geometry in different types of cataclysmic variables.
Unified Accretion Disk Models Around Black Holes and Neutron Stars and Their Spectral Properties
Authors: Chakrabarti S. K.
Published: July 2016

We review the current understanding of accretion flows around compact objects with a special emphasis on advective disks. We discuss the influence of the centrifugal pressure supported high density region around compact objects (where shocks may also form) on the emitted spectra. We show that the stationary and non-stationary spectral properties (such as, low and high states, transition of states, quasi-periodic oscillations, quiescent and rising phases of X-ray novae, etc.) of both low mass and supermassive black hole candidates could be satisfactorily explained within the framework of the analytical solution of the advective disks without invoking any ad hoc components such as Compton clouds or magnetic corona.
Evidence for Radiative Acceleration in Quasars
Authors: Arav Nahum
Published: July 2016

I give an overview of a promising signature for radiative acceleration in quasars “the ghost of Lyα,” which is seen in the spectra of a few broad absorption line (BAL) QSOs. The ghost appears as an absorption hump in the C IV λ1549 BAL and is centered around 5,900 km s−1 to the blue of the corresponding broad emission line (BEL). This velocity separation is the same as the velocity separation between the N V λ1240 and Lyα lines. Thus, when the N V BAL and the C IV BAL are plotted as a function of velocity (where zero velocity corresponds to the peaks of these BELs), the hump in the C IV BAL appears at the same velocity as the Lyα BEL and qualitatively resembles it. The best examples and model fits are shown and the radiative dynamics explained.
High Energy Neutrinos from Blazars
Authors: Protheroe R.J.
Published: July 2016

I describe a model of energetic gamma ray and neutrino emission in blazars which is consistent with most of the gamma-ray observations, and use this model to estimate the diffuse intensity of high energy neutrinos from blazars.
The Disk Wind Model of the Broad Line Region of Active Galactic Nuclei
Authors: Chiang J. , Murray N.
Published: July 2016

In a fashion similar to winds in O stars, the AGN disk winds may be responsible for the broad, blue-shifted absorption of resonance lines which characterize the Broad Absorption Line QSOs. The dynamical features of the disk wind may also account for many of the properties of the broad emission lines of AGN. Although the velocity field of the material responsible for the line emission is primarily that of the accretion disk, the presence of an accelerated radial wind influences the line formation so that single-peaked profiles are generic. Further, the recent reverberation mapping response of NGC 5548 is also qualitatively explained by these same radiative transfer effects.
ASCA observation of 4U1624–49
Authors: Angelini Lorella , Parmar Arvind , White Nicholas
Published: July 2016

ASCA observations of the LMXRB 4U1624–49 reveal the presence of extended emission surrounding the X-ray source probably due to a dust scattered halo. The halo spectrum can account for the low energy excess seen in the dip spectrum.
Radio, Infrared and X-Ray Observations of GRS 1915+105
Authors: Fender R.P. , Pooley G.G. , Robinson C.R. , Harmon B.A. , Zhang S.N. , Canosa C.
Published: July 2016

We present multiwavelength observations of the superluminal jet source GRS 1915+105 in 1996 April–May, over which period a variety of phenomena, including radio QPO, strong infrared emission lines and rapid X-ray flickering and outbursts were observed.
Optical and IR Observations of Aql X-1
Authors: Garcia Michael R. , Callanan Paul J.
Published: July 2016

We have obtained optical spectra and IR photometry in an attempt to determine the orbital parameters of the Aql X-1 system. Spectra from the MMT in October 1995 appear to detect the secondary, but are not sufficient to measure the mass function. IR photometry in and out of mini-outburst find K ~ 15.4, and may indicate that the disk contributionat K is modest during the mini-outburst.
The Spin-Resolved He ɪɪ Profile of RX J0558+53
Authors: Harlaftis E.T. , Horne K.
Published: July 2016

We observed the new intermediate polar RX J0558+53 withthe 4.2m WHT in March 1995. We detect 2–3%% pulsations of the He ɪɪ emission line on the 545s spin period. The spin-resolved Hell spectrogram shows a complex structure with two roughly anti-phased components moving from red to blue (double pulse). This is most likely produced by non-axisymmetric gas flow in the rotating magnetosphere of the white dwarf.
X-Ray Flares and Outflows Driven by Magnetic Interaction Between a Protostar and its Surrounding Disk
Authors: Hayashi Mitsuru , Shibata Kazunari , Matsumoto Ryoji
Published: July 2016

Here we present a model of hard X-ray flares and hot plasma outflows (optical jets) observed in protostars. Assuming that the dipole magnetic field of a protostar threads the protostellar disk, we carried out 2.5-dimensional magnetohydrodynamic (MHD) simulations of the diskstar interaction. The closed magnetic loops connecting the central star and the disk are twisted by the rotation of the disk. In the presence of resistivity, magnetic reconnection takes place in the current sheet formed inside the expanding loops. Hot, outgoing plasmoid and post flare loops are formed as a result of the reconnection. Numerical results are consistent with the observed plasma temperature (107 – 108K), the length of the flaring loop (1011 – 1012cm), and the speed of optical jets (200 – 400 km s−1 ).
Dust Evolution in Protoplanetary Accretion Disks
Authors: Henning Th. , Schmitt W. , Mucha R.
Published: July 2016

We have numerically investigated the dust evolution in a protoplanetary accretion disk which is described by a time-dependent one-dimensional (radial) α-model. The coagulation of particles due to cohesive collisions is calculated by solving the non-linear Smoluchowski equation. The feedback of the dust evolution and the related opacity changes to the disk evolution is explicitly treated. Three different regimes during the evolution of the grain population can be identified.
Clues and Modelling for Missing Boundary Layer in Cataclysmic Variables
Authors: Huang M. , Sparks W.M. , Sion E.M.
Published: July 2016

Recently, it has become observationally evident that during a dwarf nova (DN) outburst, a significant portion of the gravitational energy accreted onto the white dwarf (WD) may not be radiated away instantly from a narrow boundary layer as predicted by the standard disk theory. Instead, it may be stored in the WD through various mechanisms and the radiative area may be much larger; thus the long-puzzling missing boundary layer may be accounted for when the response of the WD to the accretion is considered. The results from our group and collaborators on this aspect are outlined in the first part. A progress report on the development of a new numerical model forms the second.
A Self-Similar Model for Extragalactic Jets and the FRI/FRII Divide
Authors: Kaiser C.R. , Alexander P.
Published: July 2016

We present a model for the large scale structure of FRIItype extragalactic radio sources. The sources are shown to grow selfsimilar and the dependence of the length of the source and the pressure inside the cocoon on the life time are calculated. The stability of the jets in such sources is investigated and the jet power at which FRII sources turn into FRIs is found to be in good agreement with observations.
Water Maser Emission from Dusty Clouds in AGNs
Authors: Kartje John F. , Königl Arieh , Elitzur Moshe
Published: July 2016

A natural site for water maser emission in AGNs is provided by dusty gas with properties characteristic of broad line region (BLR) clouds. Radiation shielding by dust in the clouds is critical for allowing molecular gas to exist ≤ 1 pc from the central engine. Thus, the innermost radius at which such masers appear should correspond to the grain sublimation radius rsub. We suggest a dynamical model in which the masing clouds are embedded within a magnetized accretion disk wind.
Spiral Shocks in Accretion Disks with SPH
Authors: Murray James Rhys
Published: July 2016

Smoothed Particle Hydrodynamics (SPH) is now seen as a numerical scheme well suited to the study of accretion disks. SPH simulations have been conducted of cataclysmic variable disks (Lubow 1991, Murray 1996, Armitage and Livio 1996), galactic disks (Artymowicz and Lubow 1989), and protostellar disks (Artymowicz and Lubow 1994). It is therefore important to test the technique against theory and other numerical results to obtain an estimate of the accuracy and reliability of SPH in this context. Previously SPH has been tested against standard stationary and time-dependent results of viscous thin disk theory (Murray 1996). Strictly these tests relate to disks where ‘viscous’ terms dominate pressure terms in the equations of motion.

In this paper we describe tests of the code more appropriate for hot disks where pressure forces are relatively more important than viscosity. Specifically we consider the form of the spiral density waves that can be excited in a disk by a perturbing gravitational potential. Very low mass perturbing bodies excite linear spiral waves which redistribute angular momentum in the disk. For increasingly massive perturbers, the disk response becomes nonlinear and eventually shocks form. In the standard formulation of SPH, an artificial viscosity term is added to the SPH equations to improve shock capture. This is equivalent to introducing a fixed ratio of shear to bulk viscosity into the equations of motion. In Eulerian schemes, artificial viscosity has been discarded in favour of other more accurate, less dissipative schemes for resolving shocks. The continued use of artificial viscosity in SPH has become a source of ‘friction’ between numericists. The simulations described here demonstrate the scheme’s ability to resolve spiral shocks, and show that SPH is a valuable tool for probing the structure of tidally perturbed accretion disks.
A Model of Hybrid Magnetospheric Structure Filled with Cylindrical Polar Jet and Conical Wind Envelope
Authors: Nitta Shin-ya
Published: July 2016

Non force-free cylindrical equilibrium of the magnetically driven relativistic MHD flows is investigated as a model of astrophysical jets/winds. This work is a generalization of the previous work Nitta (1995). We consider the situation that the magnetic field lines emanated from the central object are rotating, and the frozen plasmas are magnetically accelerated outward and construct a self-organized magnetosphere due to the Lorentz force and the inertial force. Recent observations revealed that many objects have a hybrid structure of collimated jet and non-collimated wind regardless with species of the central object, e.g. YSO’s, stars, pulsars or AGN’s. In order to explain these structures, we present a model that the magnetosphere has a hybrid asymptotic structure: the cylindrical jet and the conical wind fill the infinitely distant polar region and the lower latitude region, respectively. The asymptotically conical wind was investigated in the previous paper (Nitta 1994). Here we investigate the asymptotically cylindrical jet at ‘finite cylindrical radius’ from the rotational axis. In this case, the inertial force is important for the force balance because a fraction of the flows having finite angular momentum converges to finite cylindrical radius.
Stellar Winds of Classical T Tauri Stars
Authors: Paatz Gemot , Camenzind Max
Published: July 2016

We present calculations of the structure of magnetized winds of classical T Tauri stars (TTSs) in an axisymmetric, stationary, polytropic approximation in a given magnetosphere (i.e. we do not selfconsistently take into account the influence of the flow dynamics on the structure of the underlying magnetosphere). According to the widely accepted model of CTTSs the magnetosphere is dominated by a strong stellar magnetic field (B* ≃ 1 kG) which may be of dipolar type. The behaviour of the magnetic flux-tube function yields valuable constraints on the wind solutions.
Simultaneous optical and EUVE Observations of the IP PQ Gem
Authors: Ramsay Gavin , Howell Steve , Sirk Martin , Cropper Mark , Potter Stephen , Rosen Simon
Published: July 2016

The CV PQ Gem is thought by many to be the first truly ‘Intermediate’ Polar in that it displays characteristics typical of the synchronous and high magnetic field strength (B ~10–230MG) AM Her systems as well as those of the asynchronous (and much weaker magnetic field strength) Intermediate Polar systems. Here we present the results of quasi-simultaneous optical photopolarimetric and EUVE observations.