bluuebunny/crossref_metadata_2025 huggingface dataset:
Accretion Disks and Line Emission in AGN
Authors: Rokak E.
Published: July 2016

Irradiated accretion disks around massive black holes are expected to produce part of the line spectrum of AGN, but most of the disk emission must be thermal, observed at UV wavelengths. The two emission components, lines and continuum, are fitted by a unique accretion-disk model that gives the mass of the black hole and the inclination of the disk. The distribution of the disk inclination in a complete sample of Seyfert 1 galaxies suggests that their nuclei are orientation-selected, affected by strong absorption at low disk latitudes. The black-hole masses in the same sample confirm the long-standing non-linearity between M and L for AGN and the non-causal relationship between nearby Seyfert 1 galaxies and distant quasars (i.e., pure luminosity evolution is ruled out).

Irradiated accretion disks are also combined with the relativistic jet model in order to constrain the orientation and the Lorentz factor of 14 superluminal radio sources. At least for a few objects, the line and the radio data are inconsistent with both models, unless a new parameter (jet bending, a second emission-line component, etc.), is also involved. Despite this inconsistency and the ambiguous evidence for combined disk and jet fits in the remaining superluminal sources, a successful merger of these two models might address questions about the nature of AGN and also constrain the Hubble constant.
The HST Sample of Radio-Loud Quasars: Fe II and Other Correlations
Authors: Wills D. , Thompson K.L. , Brotherton M.S. , Wills Beverley J. , Baldwin J. A. , Carswell R. F. , Browne I. W.A. , Netzer H.
Published: July 2016

We are analyzing the emission lines and continuum spectra of a sample of ~61 radio-loud quasars to investigate dependences amongst various spectral, radio, and X-ray parameters, in particular to look for dependences of spectral properties on inclination of the the radio-jet axis (Wills et al. 1997).

We have carried out conventional correlation analyses, as well as spectral principal-component analyses (SPCA) as described in the previous paper (Wills et al. 1997). We found that the single largest contribution to the spectrum-tospectrum variations was from a component — the ‘first principal component’ (PC1) — that has a more UV (or less red) continuum than the mean spectrum, and a weaker narrow-line (NLR) spectrum. The ‘second principal component’ (PC2) accounts for only 8–12% of the spectrum-to-spectrum variation, contributing a weaker UV, and stronger red continuum, and showing stronger narrow emission lines. There is also a tendency for the broad (BLR) lines in the second principal component spectrum to be narrower (note the sharper He II λ1640 and [O III] λ1663 features redward of the stronger C IV λ1549 emission line, and perhaps a narrow component of the N V λ1240 line redward of Lyα).
A Detailed Comparison of HST FOS and IUE UV Spectra of Selected Seyfert Nuclei
Authors: Koratkar A. , Pesto S. , Evans I.N.
Published: July 2016

Significant improvements in our understanding of the physical conditions in active galaxies requires the development of sophisticated models that can predict in detail the emission from the nucleus. Accurate measurements of both the UV continua and the many weak diagnostic UV lines provide critical calibrations for such models.

Rigorous comparisons of the HST FOS and IUE UV flux calibrations have so far been performed using spectrophotometric standard star spectra. These calibration observations have precision acquisition sequences and the spectra have very high S/N. Such data are not representative of typical FOS observations of an AGN, which often cannot be acquired with the same precision as standard stars, especially for pre-COSTAR data. Furthermore, the UV flux from a typical AGN is several magnitudes fainter than from a spectrophotometric standard star, and is more representative of typical non-stellar fluxes. Flux-dependent effects (in either FOS or IUE) may need to be considered at these lower flux levels.
Spectral Monitoring of NGC 4151 and 3C 390.3 at the 6-m Telescope
Authors: Shapovalova A.I. , Burenkov A.N. , Bochkarev N.G.
Published: July 2016

Since 1986, we have carried out spectral monitoring of several Seyfert galaxies with the 6-m telescope of SAO RAS to study the structure and kinematics of the broad-line regions (BLR). Here we present the observational results for NGC 4151 and 3C 390.3.

In 1986–96, about 150 spectra of the NGC 4151 nucleus were obtained with SP124+TV scanner and 24 spectra with a long-slit (UAGS+CCD) or a multipupil field spectrograph (MPFS + CCD). About 20 spectra of 3C 390.3 were obtained in 1995–96 with the UAGS + CCD and with MPFS + CCD. More detailed information about observations, data processing and results will appear in Shapovalova et al. (1996).
A Search for Optical Line Variability in Narrow-Line Seyfert 1 Galaxies
Authors: Giannuzzo M. Ester , Stirpe Giovanna M.
Published: July 2016

We present the results of a variability study of ‘narrow-line Seyfert 1 galaxies’: in 10 objects out of 12 the optical line flux changed in one year, with no statistical differences in variability with respect to ‘normal’ Seyfert 1s. We discuss how models for NLSls are affected.
Thermal Instability and Alfvén Waves in the Formation of Quasar Clouds
Authors: Gonçalves D.R. , Jatenco-Pereira V. , Opher R.
Published: July 2016

We use thermal instability as a condensation mechanism to form the characteristic clouds of the BLR of quasars. We include in the total heat-loss function the influence of the heating caused by the damping of Alfvén waves. We study the damping mechanisms: nonlinear, resonance surface, and turbulent. From this analysis, we show that this heating mechanism plays an important role in the formation of these clouds.
Disk Emission Lines
Authors: Murray N. , Chiang J.
Published: July 2016

A thin disk illuminated by a central source will produce single-peaked broad emission lines if there is a wind emerging from the disk. The velocity gradient in the wind produces an anisotropic optical depth. For optically thick lines, the emission is strongest along directions perpendicular to the Keplerian velocity of the disk. The resulting line profiles are single peaked even though the emitting gas moves on essentially circular orbits. We argue that the broad emission lines seen in quasars, Seyferts, and luminous cataclysmic variables arise in disk winds.
Čerenkov Line Radiation: An Important Line Mechanism in the Broad-Line Region
Authors: Shi Jian-rong , Wu Hao , you Jun-han
Published: July 2016

Observations (Espey et al. 1989, Carswell et al. 1991, Marziani et al. 1996) at high resolution have shown relative shifts between the Balmer lines and the C iv line in a number of QSOs. In this paper, we suggest that in the BLR there are many cloudlets with dense gas that is optically thick, and the BLR is not only illuminated by UV-X radiation, but also by relativistic electrons. Therefore the Čerenkov line radiation has to be taken into consideration, and we calculate the Čerenkov line redshifts and the profiles.
A Link Between Seyfert Emission-Line Widths and X-Ray Continuum Slopes
Authors: Boile Th. , Brandt W.N.
Published: July 2016

This paper reports on AGN with extremely soft X-ray spectra observed with ROSAT. From their optical emission lines, these objects are classified as narrow-line Seyfert 1 galaxies (NLSl), almost all with extremely large Fe II/Hβ flux ratios and relatively narrow optical lines of hydrogen. NLSl have generally steeper soft X-ray continuum slopes than normal Seyfert 1s, and there may exist an anticorrelation between 0.1–2.4 keV continuum slope and the FWHM of the Hβ line. Objects with steep 0.1–2.4 keV continuum slopes and Hβ FWHM > 3000 km s−1 are clearly discriminated against by nature. When simple power-law models are fit to the data, photon indices reach values up to about 5, much higher than is usually seen in Seyfert 1s. Models with smaller-mass black holes and/or higher accretion rates show some promise to explain the relation between the FWHM of the Hβ line and the X-ray continuum slope. We further report evidence for persistent giant and rapid variability in the ultrasoft narrow-line Seyfert 1 galaxy IRAS 13224–3809.
Extended Emission-Line Regions Around AGN
Authors: Robinson A.
Published: July 2016

High-excitation extended emission-line nebulae around active galactic nuclei probably result either from photoionization of the interstellar medium by beamed continuum radiation, or dynamical interactions between radio sources and the ambient gas, or both. Here I discuss the models based on these mechanisms, and their relative importance in radio-quiet and radio-loud active galaxies.
Near-Infrared Emission Lines in AGNs
Authors: Krabbe A.
Published: July 2016

Near-infrared high-resolution imaging and spectroscopic observations of NGC 7469, Mrk 231, IRAS F10214+4724, and Circinus are presented. They indicate the presence of extended star-forming activity in the vicinity of the active nuclei of these galaxies on scales between 10 pc and 1 kpc from the nuclei. The very different distance scales covered by these objects show that the coexistence of AGN and star-formation activity is a common phenomenon. A first-order evolving star-cluster model calculation shows that we are beginning to understand the history and evolution of these circumnuclear star-forming regions.
Shocking Outflows in Seyfert Galaxies: An Imaging Perspective
Authors: Pogge Richard W.
Published: July 2016

Representative results of a search for structures suggestive of shocked gas in the circumnuclear regions of Seyfert galaxies are presented. At issue is whether we can identify regions that appear to be shocked by outflows from the active nucleus. Such regions will be good targets for future spectrophotometric studies to determine what role shocks play in the physics of the AGN/host-galaxy interaction.
How Strong Should an Emission Line Be for BL Lac Classification?
Authors: Marchã M.J.M.
Published: July 2016

An equivalent-width limit EW < 5 Å has been imposed as a selection criterion for BL Lac objects. However, such sharp cutoff has no physical meaning, and it is likely to be biasing BL Lac samples. This result is suggested by the analysis of a sample of low-luminosity, flat radiospectrum sources selected for the purpose of investigating the limits of BL Lac phenomena. In this work it is proposed that, instead of imposing sharp limits on the quantities observed, we should look for clear breaks occurring in the distributions of the observed properties for each sample.
AGN Properties and Their Contribution to the Cosmic X-Ray Background
Authors: Matsuoka M.
Published: July 2016

We 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.
Emission Lines in Active Galaxies: Outlook for the Future
Authors: Peterson Bradely M.
Published: July 2016

I briefly outline some of the unanswered questions that have emerged as recurring themes at this conference and offer some speculation about how these will be addressed with new techniques and facilities of the future.
Searching for Pulsars in the WENSS
Authors: Kouwenhoven Marco , Berger Michiel , Deich Will , Bruyn Ger de
Published: July 2016

The Westerbork Northern Sky Survey is an imaging survey carried out at 325 MHz by the Westerbork Synthesis Array Telescope (de Bruyn, 1996). It covers the northern sky above declination 30° with a resolution of 54” and a limiting flux density (5σ) of circa 15 mJy/beam. The WENSS also provides polarization maps of this part of the sky. About one fourth of the WENSS-325 area will also be covered at 608 MHz to the same limiting flux density. Table 1 gives the parameters of these surveys. It also contains the parameters of the FIRST (Faint Images of the Radio Sky at Twenty-cm, Becker et al. 1995), which is a high resolution survey carried out at 1500 MHz.
Mark IV: A Phase Coherent Observing System for Pulsars
Authors: Shrauner J. A. , Stairs I. H. , Dewey R. J. , Krumholz M. , Taylor H. E. , Taylor J. H. , Thorsett S. E.
Published: July 2016

We have built a new radio astronomical receiving system designed specifically for very high precision timing and polarimetry of fast pulsars. Unlike most detectors currently used to study pulsars, this intrument does not square the received signal at the time of observation. Instead, voltages proportional to the instantaneous electric vectors of incoming signals are digitized, time-tagged, and recorded on high speed magnetic media. We have tested the system using a 5 MHz bandwidth signal with 2-bit digitization at the Greenbank 140 foot telescope. Full polarization information was obtained with a 0.2μs time resolution. We have used this system to study the giant pulses emitted by PSR B0531+21 and PSR B1937+21, to determine high precision dispersion measures, and to perform high precision timing and polarimetry.
A Wide-Bandwidth Digital Filterbank
Authors: Foster R. S. , Ray P. S. , Lundgren S. C. , Backer D. C. , Dexter M. R. , Zepka A.
Published: July 2016

The Navy/Berkeley Pulsar Processor (NBPP) is a digital filterbank which is based on the successful Digital Filter Boards constructed for the University of California Coherent Dispersion Removal Processor (CDRP). One 9U VME crate holds a complete system with 96 channels × 2 polarizations. Running at maximum speed, the full crate will cover 1.8 MHz/channel = 172 MHz total bandwidth. Narrower bandwidths are available by running the system clock slower. The digitization has 4 bits of precision for good dynamic range and minimal quantization effects. The output data has variable time resolution; typically 50-100μs for search mode, and 2.4μs for timing mode. A flexible analog mixer/filter front end provides variable width filters, programmable attenuators, and input power level measurements, along with IF-to-baseband mixing and amplification capability. Data acquisition software running on a Sun Sparcstation-20 is based on software developed for controlling the Penn State Pulsar Machine (PSPM).
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

We 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.
The Next Five Years of Pulsar Timing
Authors: Taylor J. H.
Published: July 2016

Timing measurements of pulsars have yielded a number of important results over the years, and their value is generally a strong function of measurement accuracy. I briefly summarize the present state of affairs in pulsar timing, and then offer some judgments about what may help to produce the best results in coming years.
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

We 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

The 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

Recent 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.
Geometry of emission in PSR 1929+10
Authors: Rankin Joanna M. , Rathnasree N.
Published: July 2016

Rankin (1990) attempted to distinguish between one- and two-pole interpulse models for PSR 1929+10, and, despite the evidence to the contrary (Lyne & Manchester 1988; Phillips 1990), argued that it was probably a two-pole interpulsar on the basis of its narrow components.Ifit is a two-pole interpulsar, its interpulse has just the right width to be a core component—that is,, the angular width of the polar cap. However, PSR 1929+10 was virtually the only well studied pulsar of any profile class which could not be comfortably fitted into the quantitative description of the conal emission geometry as discussed by Rankin (1993 a,b). The problem arose due to the narrow dimensions of the conal component pair in this pulsar, which do not fit well with the inner and outer cone properties followed by many pulsars. In order to explore this issue further, we use the technique of constructing partial ‘mode-separated’ profiles corresponding to the primary and secondary polarisation modes.
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

A 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.
Physical processes in pulsar magnetospheres and non-thermal high-frequency emission
Authors: Usov Vladimir V.
Published: July 2016

The energy source of a pulsar’s non-thermal emission is the rotational energy loss of the neutron star. The rotational energy of the neutron star is transformed into the pulsar radiation by a long sequence of processes. The processes of this sequence are discussed.
Very High Energy Emission from Pulsars
Authors: Kifune Tadashi
Published: July 2016

Observations 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 > 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

We 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

I 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 & 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

Refraction 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.
Simultaneous Observations of Large Enhancement In the Flux of PSR 0950+08 Over a 200 km Baseline at 103 MHz
Authors: Bobra A.D. , Chandra Harish , Vats Hari Om , Janardhan P. , Vyas G.D. , Deshpande M.R.
Published: July 2016

Interplanetary Scintillation (IPS) is a diffraction phenomenon in which coherent electro-magnetic radiation, from a distant radio source, passes through the solar wind, which is a turbulent refracting medium, and suffers scattering. This results in random temporal variations of the signal intensity (scintillation) at the Earth. IPS observations to monitor the interplanetary medium (IPM), to measure solar wind velocities in the directions of a number of compact extra-galactic radio sources and to estimate the angular diameters of their compact components have been carried out for many years at 103 MHz using the IPS facility (Alurkar et al. 1989) of the Physical Research Laboratory (PRL), Ahmedabad, India. Over a period of approximately 10 years of such observations, it has been seen that PSR 0950+08 has always remained well within the noise level. We observed a sudden enhancement in its flux (Deshpande et al. 1994) on 29 July, 1992. The ionospheric observations which are being carried out on a regular basis at PRL using an ionosonde also recorded a steep increase in the absorption index Fmin, which is an indicator of the excess ionization produced due to X-rays. During this period, the Sun was exceptionally quiet, thereby raising the question about the origin of the X-ray flux responsible for the observed steep rise in Fminduring the transit of PSR 0950+08.
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> 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 in Cataclysmic Variable Stars
Authors: Warner B.
Published: July 2016

An overview is given of the spatial and time-dependent properties of the accretion discs in cataclysmic variable stars.
Accretion Discs around Black Holes
Authors: Wehrse Rainer
Published: July 2016

The 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

The 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.
The Quasi-Coherent Oscillations of SS Cygni
Authors: Mauche Christopher W.
Published: July 2016

Properties of the quasi-coherent oscillations in the extreme ultraviolet flux of the dwarf nova SS Cygni are described.
Neutron Star Mergers, Disks Around Black Holes, and Gamma-Ray Bursts
Authors: Janka H.-Th. , Ruffert M.
Published: July 2016

We 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

AM 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

In 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

The 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

The 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

Be 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.
Magnetospheric Accretion in T Tauri Stars
Authors: Armitage Philip J.
Published: July 2016

Many, perhaps most, accreting T Tauri stars show evidence for magnetically dominated accretion flows near the stellar surface. I discuss the implications of this for the rotation rates and long-term photometric variability of T Tauri stars.
Direct Imaging of Circumstellar Disks in the Orion Nebula
Authors: McCaughrean Mark J.
Published: July 2016

We 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

A 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

New 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

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

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

The existence of winds from cataclysmic variables (CVs) has been known for some time, there are a variety of unresolved questions surrounding this phenomenon. These include: the origin of the apparent polar nature of the winds; the rate of mass loss in the winds and the associated driving mechanism; the origin for the characteristic shapes of the UV resonance line profiles, particularly the absorption component; and the apparent association between outburst state and the wind existence. Resolution of all these issues depends on understanding the dynamics of the wind. In this paper we describe one and two dimensional models for disk wind dynamics.

Using 1D analytic models we have explore the physical conditions necessary for the existence of a disk wind, and study the dependence of wind speed and mass loss rate on radius. This leads to a criterion which must be satisfied by the rate of increase in the radiation field with height above the disk surface and by the parameters describing the line radiation pressure force (c.f. Castor, Abbott and Klein, 1976).
The Dynamics and Radiative Properties of Clouds in Magnetized Accretion Disk Outflows in AGNs
Authors: Kartje John F. , Königl Arieh
Published: July 2016

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

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

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

The idea that a significant fraction of line emission in AGN comes directly from an accretion disk is attractive for several reasons – not least the obvious one of establishing the black hole paradigm. We performed a few consistency tests for the hypothesis that both FE Kα and Hα are emitted by an accretion disk.

The main results of this preliminary investigation are as follows. FE Kα is systematically much broader than Hα at FWHM, but the widths of the two lines are not correlated. For each of the 9 objects with FE Kα profile most consistent with disk emission, we computed the possible disk contribution on the basis of a weak field model. Although the Hα profiles are not consistent with disk model emission, rotational motion could still be the main broadening mechanism. We then compared disk inclinations deduced from FE Kα model profile fitting to the ones we derived from model fits of Hα. The inclination values are consistent. Finally, we found that a simple illumination model can produce both disk FE Kα and Hα emission, if a small fraction of continuum is scattered toward the disk to yield ionization parameter ξ > 10−2 ergs s−1 cm.

We conclude that the bulk FE Kα cannot be associated to the Broad Line Region. Albeit several radio-quiet Seyfert 1 objects show FE Kα profiles consistent with emission from the inner part of an illuminated accretion disk, the general situation remains unclear, as fits to line profiles require an unsatisfactory large range in model parameters like emissivity and inner and outer radii.