bluuebunny/crossref_metadata_2025_split huggingface dataset:
AGN Properties and Their Contribution to the Cosmic X-Ray Background
Authors: Matsuoka M. 
Published: July 2016

AbstractWe have investigated the characteristics of AGN using data from ASCA X-ray observations and considered their contribution to the CXB. There are mainly four specific topics that need to be considered: (1) the absorption edges due to warm gas, (2) the complex spectra of Seyfert 2 galaxies, (3) the broad iron emission line, and (4) the soft X-ray excess.The CXB can be explained by superposing AGN spectra according to cosmological distance, but so far the distant quasars (z > 1) that have been observed show spectra in the 2–10 keV band that are steeper than the spectrum of the CXB. Recent observations have been more clearly defining the properties of the AGN one by one. We have more than 80 high-quality AGN spectra, but their properties are not well-balanced due to poor sampling of low-luminosity AGN. A large number of lowluminosity AGN might be the main contributors to the CXB.
Millisecond pulsar observation system using AOS
Authors: Hanado Y. , Imae M. , Sekido M. 
Published: July 2016

Communications Research Laboratory (CRL) developed a new millisecond pulsar observation system which used an Acousto-Optic Spectrometer (A0S). An AOS is simple and effective at dividing a wide band signal into many channels simultaneously. Using this system, we started preliminary observations of PSR1937+21 for the purpose of precise measurements of millisecond pulsar’s pulse timing.Fig. 1 shows a block diagram of our observation system using the 34m antenna of CRL. This antenna has several receivers (1.5, 2, 5, 8, 10, 15, 22, 43 GHz) with selective polarizer. We use 1.5GHz or 2GHz band for pulsar observations. An IF signal with 50MHz bandwidth is divided to 200kHz × 256ch by the AOS. The speed of data transporting rate from the camera is about 13μs which limits a time resolution. We get 100 bins per one period for PSR1937+21. The video averaging processor works as two 8bits A/D converters and an averager which allows 224pulses’ addition in each channel. The averaged data of each channel are combined after de-dispersion processing which is carried out in 1/1000 steps of the pulsar period. ¿From this final profile, the peak phase is defined as arrival pulse timing. Host#2 calculates thea prioripulse period by TEMPO program, and supplies it in real time to the synthesizer which controls the averaging trigger clock of the timing signal generator. The reference clock of this system is synchronized with UTC (CRL) via the GPS satellites. The difference between the reference clock and the internal clock of the timing signal generator is monitored using a time interval counter.
Neutron Star Population Dynamics
Authors: Cordes James M. , Chernoff David , Arzoumanian Zaven 
Published: July 2016

AbstractWe summarize our efforts at understanding the galactic neutron star (NS) population using likelihood and bayesian analyses. These include determination of the velocity distribution of young, high-magnetic field objects; the spatial, velocity, period and luminosity distributions of millisecond pulsars; and a full analysis of high-field objects including modeling of pulsars’ radio beams with the implicit assumption that such objects, for fixed period and period derivative, are standard candles.
Precision Pulsar Timing in the Presence of Interstellar Weather – PSR B1937+21 and the Crab Pulsar
Authors: Backer D. C. , Wong T. 
Published: July 2016

AbstractWe report on six months of dual-frequency, precision timing of PSR B1937+21 and the Crab pulsar. Variations in the column density of electrons – interstellar weather – are studied. The column is not unique in the presence of frequency-dependent multipath scattering, and this may explain the non-square law dependence of systematic timing residuals on B1937+21. The electron column density variations of the Crab pulsar are summarized in a structure function that ranges from 1012cm to 1015cm. These density fluctuations are located in the thermal shell surrounding the synchrotron nebula.
The death line of millisecond pulsars
Authors: Björnsson Claes-Ingvar 
Published: July 2016

AbstractThe distribution of millisecond pulsars, just as normal pulsars, is affected by a death line. Since a large fraction of millisecond pulsars lie close to the derived death line, a significant number of neutron stars may exist which are not observed as millisecond pulsars. This makes the birth rate discrepancy between millisecond pulsars and their assumed low mass x-ray binary progenitors more acute.
Numerical study of the radio microstructure associated with the plasma turbulence emission model
Authors: Weatherall James C. 
Published: July 2016

AbstractRecent observational data of short time-scale fluctuations in the radio emission of pulsars offer the opportunity for new tests of proposed emission models. For this purpose, the existing models must be developed to make predictions regarding the temporal characteristics of the emission. A computer solution of the time evolution of plasma wave turbulence details the properties of the nonlinear plasma emission mechanism. As a consequence of ponderomotive nonlinearity in the plasma medium, two-stream growing modes develop modulational instability, leading to the onset of strong, two-dimensional plasma turbulence. The turbulence exhibits explosive spatial collapse of regions of high electric field, and the escape of bursts of radiation.
Polarimetric Observations of PSR J0437–4715
Authors: Navarro José , Manchester R. N. 
Published: July 2016

To date there have been few polarimetric observations of millisecond pulsars, mainly due to the instrumental challenge of simultaneous high time resolution and large bandwidth. Such observations provide our most direct clues to the structure of the magnetic fields around pulsars, and are especially important in the case of millisecond pulsars, where radio emission necessarily originates very close to the neutron star surface.We have observed the bright millisecond pulsar J0437–4715 at the Parkes Radiotelescope with the Caltech Fast Pulsar Timing Machine, at several radio frequencies and in full polarimetric mode. Our analyses show significant deviations from the standard dipole field geometry.
Pulsar Radio Spectra
Authors: Malofeev Valerij M. 
Published: July 2016

AbstractA review of simultaneous and compiled spectra is presented, and a catalog of radio spectra for 340 pulsars reported. Pulsars with flux density measurements at three and more frequencies are included. Statistics of spectral indices and frequencies of the energy maximum and the break are presented, as well as the correlations with other pulsar parameters. The classification of 127 rich pulsar spectra has been made. Three main types of spectra are identified.
Very High Energy Emission from Pulsars
Authors: Kifune Tadashi 
Published: July 2016

AbstractObservations of gamma rays around 1012eV (= 1 TeV) from pulsars are reviewed and the results are discussed and compared with emission at other wavelengths. Very high energy gamma rays do not appear to be modulated with the pulsar period, which suggests that a major part of the VHE emission is not from the pulsar magnetosphere.
Variability of CGRO/EGRET Gamma Ray Sources
Authors: McLaughlin M. A. , Mattox J. R. , Cordes J. M. , Thompson D. J. 
Published: July 2016

We have developed a method for quantifying the flux variabilities of high energy gamma ray sources. We have applied this method to 128 sources listed in the second catalog of sources detected with the Energetic Gamma Ray Experiment Telescope (EGRET) (Thompson et. al. 1995). These sources include the Large Magellanic Cloud, 5 pulsars, 41 active galactic nuclei (AGN), and 81 sources not yet identified with known objects.Our data include photon maps (E &gt; 100 MeV) from 134 EGRET viewing periods spanning a roughly 3year period. Each source was observed in 3-20 viewing periods ranging from a few days to 3 weeks in length. For each observation, a source flux was calculated using the method of maximum likelihood (Mattoxet al. 1996) which simultaneously estimates the strength of the Galactic and isotropic diffuse emission, and that of a point source distributed as the EGRET point spread function.
Gamma Ray Bursts as Death of Magnetized Neutron Stars
Authors: Hanami Hitoshi 
Published: July 2016

AbstractWe propose magnetic cannon ball mechanism in which the collapse of a magnetosphere onto a black hole can generate strong outward Poynting flux which can drive a baryon-free fireball. This process can occur at the final collapsing phase of a neutron star with strong magnetic field. The magnetic cannon ball can drive a relativistic outflow without the rotation of the central object. This baryon-free process can explain gamma-ray bursts as the final phase of dead pulsars.
Pulsar Wind Nebulae
Authors: Cordes James M. 
Published: July 2016

AbstractI discuss pulsar wind nebulae for which ram pressure from the neutron star’s motion is a key element of the morphology. These PWN are tools for determining the pulsar distance, radial velocity component, and interaction of pulsar winds with surrounding media. The Guitar Nebula pulsar (B2224+65) also represents a ‘smoking gun’ for velocity kicks from asymmetric supernovae or other rocket effects. The detectability of wind nebulae from pulsars and from as-yet unknown neutron stars is discussed.
Distorted Dipole Magnetic Fields
Authors: Burman Ron 
Published: July 2016

Mestel et al. (1985; MRΩ2) introduced an axisymmetric pulsar magnetosphere model in which electrons leave the star with non-negligible speeds and flow with moderate acceleration, and with poloidal motion that is closely tied to poloidal magnetic field lines, before reachingSL, a limiting surface near which rapid acceleration occurs. As well as these Class I flows, there exist Class II flows which do not encounter a region of rapid acceleration (Burman 1984, 1985b). The formalism introduced by MRΩ2to describe the moderately accelerated flows can be interpreted in terms of a plasma drift across the magnetic field, following injection along it (Burman 1985a).The MRΩ2formalism fully incorporates the toroidal magnetic field generated by the poloidal flow. The general formalism leaves the poloidal magnetic field unspecified, but, in the detailed development of MRΩ2, and in my papers, that field was taken to be the dipolar field of the star.Numerical work by Fitzpatrick &amp; Mestel (1988a,b) suggested that the dipole approximation is inadequate. They developed a numerical technique for incorporating the modification to the poloidal magnetic field that is generated by the toroidal motions throughout the magnetosphere. They based their treatment on the hypothesis that those motions are such as to cancel the dipole field of the star, leaving a sextupole poloidal magnetic field at large distances.
Multiple Imaging of Pulsars by the ISM
Authors: Gupta Yashwant 
Published: July 2016

AbstractRefraction of pulsar radiation by electron density irregularities in the interstellar medium can sometimes produce multiple imaging of pulsars. Such events can be used as tools to resolve the emission regions in pulsar magnetospheres. Results from recent observations of a double imaging event for PSR B1133+16 are described. Significant fringe phase variations are seen across the pulse. The minimum value for the transverse separation of the emitting regions at the two edges of the pulse is inferred to be ≈ 5 × 105m. These results are compared with earlier values reported in literature and the implications are discussed.
Aspects of Mass Transfer in X-ray Binaries
Authors: Tauris Thomas M. 
Published: July 2016

The final stage of mass transfer in a compact binary system is very important for calculating the orbital parameters of the resulting system. We demonstrate how simple ‘bifurcation mechanisms‘ may lead to the existence of three classes of binary millisecond pulsars and a possible gap in the orbital period distribution. Recent discoveries indicate that such a gap could exist (see Fig. 2).Furthermore, we demonstrate that the expected theoretical correlation (e.g. Joss et al. 1987, Rappaport et al. 1995) between orbital periods and white dwarf companion masses does not seem to fit observations of wide-orbit lowmass binary pulsars (LMBPs). It is interesting to notice that the five LMBPs with Porb&gt; 100dall have companion masses which are lighter (at the ∼80 % confidence level on average) than expected from the theoretical core-mass period relation.
Accretion Discs around Black Holes
Authors: Wehrse Rainer 
Published: July 2016

AbstractThe structure of accretion discs around (super-)massive black holes is discussed in this contribution with special emphasis on the radiation fields. These are of crucial importance for the understanding of these objects since photons control in most cases not only the temperature distributions but also the pressures and shapes. Recent progress in the modelling of photon fields now provides the means for a much improved understanding of the consequences of the multidimensional structure of the discs as well as of the effects of the strong space time curvature and of the high velocities involved. However, the simultaneous inclusion of the NLTE level populations and of many spectral lines is still a major problem. It is also demonstrated that special and general relativity effects strongly distort the apparent brightness distributions and spectra such accretion discs so that a solution of the inverse problem will be very difficult.
Boundary Layers in Cataclysmic Variables and Pre-Main-Sequence Stars
Authors: Popham Robert 
Published: July 2016

AbstractThe boundary layer region, where the accretion disk meets the accreting star, is crucial to understanding the spectra and evolution of accretion disk systems. Recent numerical modeling of the flow of the accreting material and radiation in the boundary layer has provided a better understanding of this region. I will describe the “standard” boundary layer structure predicted by the models for the case where the boundary layer is optically thick and geometrically thin in the vertical direction. Large variations in this structure can occur when the boundary layer becomes optically thin or geometrically thick. Boundary layer models have been applied to cataclysmic variables and accreting pre-main-sequence stars. I will discuss the boundary layer spectra predicted by the models and how well they agree with observations of these objects. The boundary layer also controls the transfer of angular momentum and energy between the disk and star. This can have important effects upon pre-main-sequence stellar evolution.
Neutron Star Mergers, Disks Around Black Holes, and Gamma-Ray Bursts
Authors: Janka H.-Th. , Ruffert M. 
Published: July 2016

AbstractWe have performed three-dimensional hydrodynamical simulations of the coalescence of binary neutron stars taking into account the emission and backreaction of gravitational waves in the Newtonian code based on the “Piecewise Parabolic Method”. The use of the physical equation of state (EOS) of Lattimer & Swesty (1991) allowed us to calculate the production of neutrinos. We evaluated our models for the efficiency of v⊽ annihilation in the surroundings of the coalescing neutron stars. The corresponding energy deposition prior to and during merging turned out to be 2–3 orders of magnitude too small to power a typical γ-ray burst (GRB) with an energy output of ~ (1051/4π) erg/sterad at cosmological distances. Analytical estimates of the subsequent evolution of the disk which possibly surrounds the central black hole showed that even under the most favorable conditions the energy provided by v⊽ → e−e+ → γγ falls short by at least an order of magnitude. We discuss the implications of our results and speculate about possibilities how v⊽ annihilation might still be a viable energy source for GRBs.
Eclipsing AM Herculis Binaries
Authors: Bailey Jeremy 
Published: July 2016

AbstractAM Herculis Binaries (or Polars) are a subclass of the Cataclysmic Variables in which the accreting white dwarf has a strong magnetic field giving rise to highly polarized cyclotron radiation from the shock heated accretion region. A number of AM Herculis binaries are now known in which the white dwarf is eclipsed by the companion star. High time resolution observations of these eclipses allow a particularly detailed study of the process of accretion onto the magnetic white dwarf. Results on a number of systems will be presented and used to derive information on the accretion structure as well as on the fundamental properties of the binaries.
Properties of Magnetic Accretion Curtains: Magnetic CVs and T Tauri Stars
Authors: Ferrario Lilia 
Published: July 2016

AbstractIn this paper, I present a review on the properties of accretion curtains in magnetic Cataclysmic Variables and T Tauri stars. In particular, I will show that magnetically confined accretion curtains that are heated by hard, soft x-rays or UV radiation originating from the accretion shocks at the surface of the accreting star can give rise to the observed complex emission line profiles.
Modelling the Polarization from Accretion Disks
Authors: Dittmann O. J. 
Published: July 2016

AbstractThe 3D transfer equation for polarized radiation is solved for several different model configurations. In the case of Rayleigh scattering the phasematrix is decomposed into a sum of matrix products to allow the use of operator splitting iteration schemes. For 30 slabs with constant extinction matrix and constant emission the emerging polarized fiuxe are calculated. We find that the optical depth and the scattering parameter can be fixed from observations even if only the fluxes are known. Specifying the extinction matrix our models can be applied to the inner regions of active galactic nuclei.
Constraints of Winds from Accretion Disks
Authors: Idan I. , Shaviv G. 
Published: July 2016

AbstractThe structure of an accretion disk illuminated by X-rays is investigated. For high values of X-ray heating no static disk solution was found, while for low values of heating a corona was formed above the disk. In the high X-ray illumination case the only possible wind solution is the supersonic solution meaning the evaporation of the disk. Only a very narrow range of X- ray heating and critical point height yield the proper wind solution that agrees with the disk solution. Finally, a self-consistent model of accretion disk and a wind is presented.
Dynamics of Self-Accreting Disks in Be Stars
Authors: Kroll P. , Hanuschik R.W. 
Published: July 2016

AbstractBe star disks are formed by ejection of stellar matter from the surface of a B star rotating at almost critical velocity. In SPH simulations we find that most of the ejected particles fall back on the stellar surface but those with sufficient angular momentum are able to feed a disk-like structure. Owing to viscous interaction some particles are lifted to larger radii where they carry high angular momentum. Viscous forces also cause a thinning of the initially geometrically thick disk and the final accretion of most of the disk material. Different simulations show how the formation and the extension of the decretion disk depend on the ejection velocity, the viscous parameter α and on how long the source is active. After the outburst the disk thins out more and more, over a timescale much longer than the outburst time.The simulations are compared to Hα observations of the Be star µ Cen.
Direct Imaging of Circumstellar Disks in the Orion Nebula
Authors: McCaughrean Mark J. 
Published: July 2016

AbstractWe present observations of the Orion Nebula made with the Hubble Space Telescope in which a number of stars are seen surrounded by dark silhouettes seen projected against the bright background HII region. We find a variety of morphologies, all consistent with thin circumstellar disks spanning a range of diameters (50 to 1000 AU) and inclination angles (0 to > 80 degrees). The silhouette intensity profiles cannot be fit by standard disk models in which the surface density follows a radial power law with an exponent in the range −0.75 to −1.5. Rather, the data are best fit by opaque inner disks with exponential edges, and we discuss possible physical origins of this apparent truncation. Masses in the range 6 × l026−4 × 1030 g (i.e., up to 0.002 M⊙) are determined for the disks by assuming that the faint light measured from them is background light transmitted through the disk. However, these are strict lower limits on the true disk masses, as most of this light can be accounted for by PSF blurring and scattering in the HST optical train; the present observations are in fact consistent with completely opaque disks. Central stars are seen directly in five of the silhouettes, while the presence of a star is inferred in the sixth, where small reflection nebulae are seen above and below the plane of the near edge-on disk. Optical and near-infrared stellar photometry is consistent with young (~ 1 Myr) low-mass (0.3−1.5 M⊙) stars, with several showing evidence for excess near-infrared emission from the disk inner edge. These direct imaging observations are discussed in the wider context of circumstellar disks in the Orion Nebula and Trapezium Cluster, additionally revealed as compact ionized nebulae (so-called “proplyds”) in the vicinity of the central OB stars, and via infrared (>2µm) excesses in stellar photometry. Overall, disks are found to be common in the cluster (>50% of all stars), implying that they can survive the rigours of life near massive stars.
A Two Dimensional Photoionization Front Model for YSO Envelopes in the Orion Nebula
Authors: Sutherland Ralph S. 
Published: July 2016

AbstractA simplified axi-symmetric 2.5D radiative transfer model of a YSO envelope (HST-1, 177–341, O’Dell & Wen 1994) in the Orion Nebula (NGC1976) is computed assuming only a spherical distribution of gas with a powerlaw density function. The model fits recent Hubble Space Telescope data (Bally et al. 1996) very well on 1015 cm scales, suggesting that the morphology of the ‘proplyd’ objects is due to photoionization on this scale rather than a direct wind-wind interaction (Henney et al. 1996). The fact that a simple spherical distribution of gas fits the ionization observations so well also implies that somewhere between the scale of the YSO accretion disk and the observed ionization front radius the gas distribution has changed.
Nuclear Stellar Disks in E/S0 Galaxies
Authors: Jaffe Walter , van den Bosch Frank 
Published: July 2016

AbstractNew HST images and spectra of the nuclear disks in two Virgo Cluster E/S0 galaxies reveal that they were probably formed together with their parent galaxies. The two galaxies show very different color gradients. This is most likely caused by the escape of high metallicity gas from early stars in the lower mass galaxy. One galaxy shows strong kinematic evidence for a massive central black hole.
Optical Polarization and Line Variability in Quasars with Associated Absorption
Authors: Aldcroft T. , Bechtold J. , Smith P. , Foltz C. , Schmidt G. 
Published: July 2016

AbstractThe physical origin of associated absorption lines (zabs ≈ zqso) which are observed in radio-loud quasar is generally not well understood. Two observable properties, line variability and quasar optical polarization, can serve to constrain the possibilities. To this end, we have obtained high-resolution spectra (1 Å) and broad-band optical polarizations for over 30 radio-loud quasars with known CIV associated absorption. The quasars are at redshifts between about 1 and 2, and were previously observed spectroscopically at similar resolution between 1985 – 1986 by Foltz et al (1987). The associated CIV absorption systems include a variety of velocity profiles from weak single lines to very complex multi-component systems to the BAL-like profile of PHL 1157+0128. In this poster we show the first strong evidence for line variability in z > 1 radio-loud quasars. We find that in general the variability is less than ~ 30%. The optical polarization of CIV absorbed quasars is consistent with all radio-loud quasars.