bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractWe 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

AbstractWe 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

AbstractLINERs 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

AbstractThe 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).
Further Observations of the Planets Pulsar
Authors: Wolszczan A. 
Published: July 2016

AbstractRecent 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

AbstractDaily 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

AbstractWe 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.
Plasma Instabilities: Sources for Coherent Radio Emission
Authors: Asseo Estelle 
Published: July 2016

AbstractThe 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.
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 &amp; 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 traverseswhere 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 ±ϕcasand 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 &amp; 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 &amp; 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

AbstractRecent 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

AbstractThe 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

AbstractThe 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.
Scintillation Studies of the Pulsar PSR B0329+54
Authors: Stinebring Daniel R. , Faison Michael D. , McKinnon Mark M. 
Published: July 2016

AbstractRefractive 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

AbstractRadio 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° &lt; θ &lt; 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

AbstractAccording 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

AbstractAstrotomography 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

AbstractThe 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

AbstractMOST 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

AbstractThe 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

AbstractExtremely 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.
Magnetohydrodynamic Turbulence in Accretion Discs: Towards More Realistic Models
Authors: Torkelsson Ulf , Brandenburg Axel , Nordlund Åke , Stein Robert F. 
Published: July 2016

AbstractThe 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

AbstractI 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

AbstractInstabilities 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.