bluuebunny/crossref_metadata_2025 huggingface dataset:
Deep Imaging of SNRs at Low Frequencies Using the GMRT
Authors: Bhatnagar Sanjay
Published: July 2016

Radio observations of large Supernova Remnants (SNRs) in the Galaxy are plagued with the problems of confusion and limitations of synthesis telescopes in imaging the emission at large angular scales. Since most SNRs are brighter at low radio frequencies, and the contamination due to thermal emission is reduced, deep and high resolution imaging of Galactic SNRs at meterwave lengths is most useful in their detection and classification. Relatively high resolution and sensitivity over a large range of angular scales provided by the GMRT at meterwave lengths makes it an ideal instrument for detailed multi-frequency imaging of Galactic SNRs.
Carbon Recombination Lines at 34.5 MHz from the Galactic Plane
Authors: Kantharia N.G. , Anantharamaiah K.R.
Published: July 2016

We report the detection of carbon radio recombination lines (CRRLs) near 34.5 MHz (n ∼ 575) and near 328 MHz (n ∼ 270) from 6 positions with l < 17°, b = 0°. Modelling the data shows that the observed CRRLs can arise under a range of physical conditions which are found in atomic HI, molecular and photo-dissociation regions (PDRs) in the galactic disk.
Pulsars: An Observational Overview
Authors: Manchester R.N.
Published: July 2016

Pulsars are among the most exciting and interesting objects in the Universe. They typically have very steep radio spectra, so they are most easily observed at relatively low radio frequencies. In this review, I summarise some recent important observational results and describe recent searches for pulsars, including the very successful Parkes multibeam survey.
Low-frequency Profiles of the Crab Pulsar
Authors: Kuzmin Arkady
Published: July 2016

Integrated profiles of the Crab pulsar at frequencies 102, 111, 127, 147, and 196 MHz compensated for the interstellar scattering are presented. Observed profiles were compensated for interstellar scattering and intrinsic pulsar profiles were restored. The component structure and their frequency evolution was analyzed. The main pulse is two-component and a so-called precursor is its first component. The interpulse have two components too.
A WSRT Search for Millisecond Pulsars
Authors: Tian W.W. , Strom R.G. , Stappers B.W. , Zhang X.Z. , Wu X.J. , Ramachandran R.
Published: July 2016

Based on our examination of the characteristics of about 280 known pulsars and 40 millisecond pulsars (MSPs), we have derived selection criteria for MSP candidates: steep spectrum, highly linearly polarized point sources. The first sample of 14 candidates from the NVSS at 1.4 GHz and the WENSS at 325 MHz has been observed by the WSRT using PuMa at both 92 and 21 cm in May 1999. We have finished processing all data and find no evidence for MSPs for a dispersion measure range of 0 —- 200 cm−3 pc in this first sample.
Interpretation of James' Experiments in Plasma Theory of Solar Radar Echoes
Authors: Mel'nik V.N.
Published: July 2016

In the framework of the plasma theory of solar radar echoes results of the known James' experiments such as the values of effective cross-sections, the anisotropy of reflections, the spectrum of reflected signals, the heights of radar scattering and others are explained. In particular in this theory reflection of radar signal with high effective cross-sections (σ = (10 − 100)πR2⊙) occur in processes t + l ⇌ t + l on the Langmuir turbulance generated by Type III electrons at altitudes (1.4—1.6)-R⊙ when electron streams propagate towards the Earth. If the electrons move away from the Earth then the scattering cross-sections due to process t + l ⇌ t + l are small (σ < πR2⊙). Reflections from the heights up to 5R⊙ can occur at scattering of radar wave on the ion-sound turbulance (processes t + s ⇌ t) accompanied the Langmuir turbulance.
Low Frequency Science with the Square Kilometre Array
Authors: Taylor A.R.
Published: July 2016

Over the past several years an international community of scientists and engineers has emerged with a common goal to solve the technical challenge required to construct a giant radio telescope with a collecting area of one square kilometre. The Square Kilometre Array (SKA) will have a hundred times more collecting area than our most powerful existing radio telescopes, providing sensitivity of a few tens of nanoJy in the centimetre/decimetre wavelength continuum. With a spatial resolution better than the Hubble Space Telescope, a field of view larger than the full moon, and the ability to simultaneously image a wide range of red shift, the SKA will be the worlds premier spectroscopic imaging telescope at any waveband.

At long wavelengths the SKA will be able to detect emission from atomic hydrogen gas at extreme redshifts, allowing study of the “Dark Ages” of the Universe, before, and during, the transition phase when the initial stars formed and reionization occurred. The combination of sensitivity, wide field of view and high angular resolution, will allow high resolution imaging of the interstellar media and magnetic field of a vast number of galaxies to high redshift. Measurements of atomic hydrogen emission and continuum emission will trace the star formation history of the Universe from primordial galaxies to the present.
Existence and Energy Balance of the Solar Dynamo
Authors: van Geffen J.H.G.M.
Published: July 2016

The idea behind the use of ensemble averaging and the finite magnetic energy method of van Geffen and Hoyng (1992) is briefly discussed. Applying this method to the solar dynamo shows that the turbulence — an essential ingredient of traditional mean field dynamo theory — poses grave problems: the turbulence makes the magnetic field so unstable that it becomes impossible to recognize any period.
Storage of Magnetic Flux in the Overshoot Region
Authors: Moreno-Insertis F. , Schüssler M. , Ferriz-Mas A.
Published: July 2016

The combined action of the subadiabatic ambient stratification in the overshoot region below the convection zone and the inertial forces associated with the solar rotation is shown to lead to the suppression of the escape of magnetic flux in the form of toroidal flux tubes both toward the surface and toward higher latitudes. We show that a flux ring initially in thermal equilibrium with its environment and rotating with the ambient angular velocity moves radially and latitudinally towards an equilibrium configuration of lower internal temperature and larger internal rotation rate with respect to the surrounding, field-free gas. We conclude that flux rings with B≲ 105 G can be kept within the overshoot region if the superadiabaticity is sufficiently negative, i.e. δ = ▿ – ▿ad≲–10−5; below that field strength the poleward drift is also reduced to a latitudinal oscillation of moderate amplitude, δθ ≲ 20 deg. Flux rings with significantly larger field strength cannot be kept in the equatorial parts of the overshoot region: their equilibrium configuration is located at high latitudes far outside the solar activity belts and, at any rate, requires unrealistic values of δ.
Solar and Auroral Activities During the 17th Century
Authors: Legrand J.P. , Le Goff M. , Mazaudier C. , Schröder W.
Published: July 2016

The dark spots on the solar disk, some of them are visible with the naked eye, and the aurorae, especially those strectching down to the tropics, are the best visible manifestations of the solar activity. Since more than one century, we know that this activity follows a regular periodic cycle of 11-years (Heinrich Schwabe 1844), but with an intensity, which is sufficiently variable, to speak of “small” and “large” solar cycles.
Rossby Number or Rotation Period?
Authors: Stȩpień K.
Published: July 2016

It is shown that the scaling of rotation periods by a color-dependent parameter (turnover time) improves substantially the observed activity-period relations only for single, main sequence, solar type stars with 0.5 ≲ B – V ≲ 0.8. For other single main sequence stars and for single giants activity indices correlate equally well with rotation period and the Rossby number, or show no correlation with either parameter.
Long-Term Spot Photometry and Differential Rotation of the Spotted Flare Stars Ev Lac and by Dra
Authors: Panov K.P.
Published: July 2016

Ev Lac = Gliese 873 (dM4.5e) is a well-known flare star with hydrogen Balmer lines as well as with Ca II lines in emission. Rotational modulation by starspots has been discovered by Pettersen (1980) who determined the photometric (rotational) period P = 4.378 d. Spot photometry of EV Lac was obtained with the 60 cm telescope of the Bulgarian National Astronomical Observatory in the years 1983–87 and 1989–91. For these years (except for 1989 and 1990) light curves are available in the V and B bands. From the BNAO-data and the data published by Pettersen (1980) a new ephemerishas been derived which shows a slight revision of the period.
Dynamo–Action in Accretion Disks
Authors: Deinzer W.
Published: July 2016

Accretion disks are approximated by thin tori and the generation of magnetic fields by torus–dynamos is investigated. Solutions for the general α2ω–dynamo embedded into vacuum and into an ideally conducting medium are presented. Whereas the former solutions are qualitatively similar to those obtained for thin disks, there is a mode for the latter peculiar to torus–geometry. Excitation conditions for torus–dynamos are compared to those realized in accretion disks in cataclysmic variables, around T Tauri stars and in AGN's.
Accretion Disk Flares in Energetic Radiation Fields
Authors: Van Oss R.F. , Van Den Oord G.H.J. , Kuperus M.
Published: July 2016

We consider the physics of magnetic flares in the energetic radiation field of an accretion disk corona (ADC). The X-ray emission from these flares is thought to be responsable for the observed hard powerlaw component in the X-ray spectra of galactic black hole candidates in their ‘high’ spectral state. During the flare event (inverse Compton) scattering of soft photons from the underlying disk into hard photons occurs on accelerated electrons in current sheets. The electrons are decelerated by the radiation drag force that results from the up-scattering. This friction-like effect of the intense background radiation field on the motion of the electrons in the sheet can be considered as a form of resistivity in the magnetohydrodynamical picture of the current sheet: Compton resistivity. A spectrum is derived for the up-scattered radiation from current sheets in the ADC and it is found that this spectrum mimics a powerlaw above a critical photon energy.
Radio Astronomy Techniques of Observing Magnetic Fields: The Galaxy
Authors: Wielebinski Richard
Published: July 2016

Optical techniques were first used to detect magnetic fields in cosmic objects. Hale used the Zeeman effect to detect solar magnetic fields in 1908. Babcock extended the Zeeman technique to show the existence of magnetic fields in Ap stars in 1946. Optical polarization observations were made as early as 1920 by W.F. Meyer who observed the Hubble variable nebula NGC 2261. Polarization observations of the Andromeda nebula were made by Öhman in 1942. However at first the interpretation of these optical polarization observations was in terms of scattered light only. The theoretical work of Davis and Greenstein suggested that optical polarization could also be due to dust grains aligned in magnetic fields. Observations of Hiltner and Hall supported this interpretation. Extensive surveys of starlight polarization were made by many observers giving information about nearby magnetic fields in the Galaxy. Optical polarization observations of galaxies gave some information on the Magellanic Clouds and other nearby objects but due to lack of sensitivity progress was slow.
The Galactic Dynamo: Modes and Models
Authors: Rüdiger G. , Elstner D. , Schultz M.
Published: July 2016

The hitherto known essentials of the present-day dynamo theory of the galactic magnetic fields are reported. The vertical stratification of the interstellar turbulence is exclusively considered as the source of the α-effect. New expressions for this tensorial effect and its quenching by the field are applied. Although its anisotropy and the influence of the halo easily yield the excitation of non-axisymmetric magnetic configurations of diverse equatorial symmetry, the galactic differential rotation finally leads to axisymmetric and quadrupolar solutions. The magnetic strength of the dynamo fields slightly exceeds the equipartition value while its angular momentum transport (into the intergalactic space) is very small.

For increasingly steep vertical gradients of the turbulence intensity a saturation of the field strength is found since the eddy diffusivity grows with the α-effect. Only beyond the maximum of the field the equatorial symmetry changes to an equatorial antisymmetry,i.e.to dipolar solutions.

In order to produce the observed values of the pitch angles one has only to choose correlation times of the turbulence slightly exceeding the usually accepted 107yrs.
Nonlinear Interaction Between Magnetic Fields and Spiral Arms
Authors: Chiba M.
Published: July 2016

The evolution of galactic magnetic fields under the influence of spiral arms is investigated numerically by 2-dimensional simulation. We compute several models, especially when the swing-excitation mechanism works. We consider also the modification of the mean velocity fields driven by the Lorentz force of the growing magnetic fields. The characteristic structure of magnetic fields around the arm in each model is compared with the observations.
Galactic Dynamics and Magnetic Field Amplification
Authors: Lesch Harald
Published: July 2016

Stimulated by recent high frequency radio polarization measurements of M83 and M51, we consider the influence of non-axisymmetric features (bars, spiral arms, etc…) on galactic magnetic fields. The time scale for the field amplification due to the non-axisymmetric velocity field is related to the time scale of angular momentum transport in the disk by the non-axisymmetric features. Due to its dissipational character (cooling and angular momentum transport) the gas plays a major role for the excitation of non-axisymmetric instabilities. Since it is the gaseous component of the interstellar gas in which magnetic field amplification takes place we consider the interplay of gasdynamical processes triggered by gravitational instabilities and magnetic fields. A comparison with the time scale for dynamo action in a disk from numerical models for disk dynamos gives the result that field amplification by non-axisymmetric features is faster in galaxies like M83 (strong bar) and M51 (compagnion and very distinct spiral structure), than amplification by an axisymmetric dynamo. Furthermore, we propose that axisymmetric gravitational instabilities may provide the turbulent magnetic diffusivity ηT. Based on standard galaxy models we obtain a radially dependent diffusivity whose numerical value rises from 1025cm2s−1 to 1027cm2s−1, declining for large radii.
Statistical Method for Astrophysical Turbulence Investigation
Authors: Lazarian A.
Published: July 2016

Present-day galactic dynamo theories widely use a concept of the ISM turbulence. In the present paper a statistical method of MHD turbulence study is discussed. The method is based on the solution of the inverse problem for the observational data. It is shown that in many important cases the inverse problem has a unique analytical solution. Examples, including the study of a random density field and a random magnetic field, are discussed.
The Geodynamo
Authors: Roberts P.H.
Published: July 2016

A comparison is made of the differences and similarities between the solar dynamo and the geodynamo. Special attention is paid to the energetics, the dynamics, the role of turbulence, and the α- and ω-sources in these dynamos.
Time Evolution of the Solution in Model Z
Authors: Anufriev A.P. , Cupal I. , Hejda P.
Published: July 2016

Time evolution of the solution of model Z is considered simply as an aid to obtain the steady state solution. Balance equations of the energy of the azimuthal field EB showes that excluding several beginning time steps the solution exposes the time behaviour with a physical sense.
The UV-Optical-Near-IR Emission of BL Lacertae Objects
Authors: Falomo R. , Pian E. , Scarpa R. , Treves A.
Published: July 2016

Results from UV, optical and near-IR simultaneous observations for 11 BL Lac objects are reported. We find that for all but one source the spectral flux distribution can be described by a single power law (fv ∞ v−α) plus, where relevant, the contribution of the host galaxy. The comparison of the optical-near-IR and UV spectral indices for two samples of BL Lacs suggests the same picture for a larger sample of objects.
Extreme Quasars: Observations and Constraints
Authors: Elvis Martin
Published: July 2016

The range of continuum shape the quasar phenomenon covers is larger than is usually thought, and is limited by observational sensitivity, between 1/3 and 1/2 of all quasars are “extreme” in at least one band. We have embarked on a program of observations to explore extreme spectral shapes, and to push to high redshift/luminosity. This paper presents X-ray and multi-wavelength SEDs for 12 z∼3 quasars.
Hubble Space Telescope Observations of AGN
Authors: Macchetto F.
Published: July 2016

Only little more than three years have passed since the launch of the Hubble Space Telescope (HST) and the wealth of results produced by astronomers using it, have already made fundamental contributions to our understanding of a variety of astrophysical processes. A considerable number of investigations have been, and are being, devoted to the study of the whole gamut of problems associated with activity in galaxies. These range from the very largest scales, namely those applicable to the study of the optical jets and galaxy mergers (10–100 kpc) to the smallest scales (1–10 pc) relevant to investigate the broad-line regions and the very center of the active galaxies. In all cases, the high-spatial resolutions, extended dynamic range and ultraviolet response, has made possible the study of a number of objects with a detail impossible without the HST.
The X-ray Emission of Quasars as Observed by Ginga
Authors: Lawson A.J. , Turner M.J.L.
Published: July 2016

We present preliminary results on a spectal analysis of quasars observed by the X-ray observatory Ginga. Simple power-law models with fixed Galactic absorbtion provide an adequate description of the spectra for most of the sources in the 2–18 keV band. A small number of sources show evidence for a feature at 6.4 keV (in the source rest frame) due to Fe line emission. Maximum likelihood and Spearman rank tests were used to investigate the relationship between radio loudness and X-ray spectral index in this class of object. These tests showed, respectively, that the mean X-ray spectral index of radio quiet quasars (RQQs) is significantly different from that of flat spectrum radio loud quasars (FRSQs) at the >99% level, and that the dominant relationship with spectral index is radio loudness (not X-ray luminosity or redshift) at >99% significance. This last result has not previously been demonstrated in this band, but agrees with findings in the lower energy Einstein band (0.5–3.5 keV). These results are discussed in the context of current unified models.
X-ray Emission and Reflection in AGNs
Authors: Netzer Hagai
Published: July 2016

X-ray spectra of many AGNs are dominated by strong absorption-like features at low (0.5–1 keV) energies. Recent progress in modeling AGNs indicate that pure X-ray absorption is unlikely to be observed and the contribution of emission and reflection must be significant. Several such models are shown and compared with what is likely to be observed by two X-ray experiments, ROSAT and ASCA. It is argued that X-ray colors may be useful diagnostic tools in analyzing such spectra.
Modeling Bent Radio Jets: Another Probe of the Central Engine
Authors: Hughes P.A. , Aller M.F. , Aller H.D.
Published: July 2016

We present a model for curved parsec-scale jets that includes most of the key radiation physics and relativity, but which is simple enough to allow an exploration of diverse geometries and flow parameters.
EUVE Observations of NGC 5548
Authors: Kaastra J.S. , Mewe R. , Heise J. , Alkemade F.J.M. , Schrijver C.J. , Carone T.
Published: July 2016

The first extreme ultraviolet spectrum of NGC 5548 obtained by EUVE is presented.
Instantaneous Flux Spectra Measurements of the about 100 AGNs at 6 Frequencies from 1 GHz to 22 GHz
Authors: Nizelski N.A. , Kovalev Yu.A. , Berlin A.B.
Published: July 2016

Preliminary spectral results are presented for the 100 objects, selected from a VLBI-servey at 6–7 wave lengths of 31 cm, 13 cm, 8.2 cm, 7.6 cm, 3.9 cm, 2.7 cm, and, for the declinations greater than +13 degrees, at 1.38 cm. The most of presented spectra may be resulted by the emission of a halo-jet structure of AGNs.
The Nature of the NIR Emission from Seyfert 1 Galaxies: NGC 4051
Authors: Salvati M. , Calamai G. , Hunt L.K. , Del Zanna G. , Giannuzzo E. , Mannucci F. , Stanga R.M. , Kidger M. , Wamsteker W.
Published: July 2016

The near infrared emission (NIR) of radio quiet active galactic nuclei is commonly attributed to dust, absorbing and re-emitting some of the nuclear UV radiation. The dust can survive only at distances larger than a few light months, and any rapid variation of the nuclear radiation, on timescales of a day or less, will be completely smeared out.
Anisotropic Effects in Thomson Cascade Models of Active Galactic Nuclei
Authors: Baring Matthew G.
Published: July 2016

CGRO observations of high energy γ-rays from active galactic nuclei (AGN) suggest that beaming may be prevalent in these sources. Anisotropic effects in AGN continuum spectra produced by the inverse Compton scattering mechanism are outlined, in particular the resulting spectral breaks and modification of spectral indices that depend strongly on the electron anisotropy and the observational viewing perspective.
Free-free Emission and the Big Blue Bump
Authors: Barvainis Richard
Published: July 2016

Optically thin thermal emission may be a viable alternative to optically thick accretion disks for the origin of the optical/UV Big Blue Bump. In this contribution I summarize a number of points favoring the optically thin, or free-free, hypothesis. The free-free model is consistent with the most stringent quasar size and luminosity constraints provided sources are composed of a large number of very small and dense cloudlets or filaments.
A Study of Gamma Spectral Break in AGN
Authors: Marcowith A. , Henri G. , Pelletier G.
Published: July 2016

Since its launch, CGRO has detected more than 20 γ-ray emitting AGN, most of them associated with powerful, radio-loud, flat-spectrum objects, exhibiting VLBI superluminal motions. In the case of 3C279, the huge value of the apparent luminosity (∼ 1048erg.s−1) and the variability time-scale of a few days (Hartmann et al., 1992) gives a very large compacity lapp ≃ 200, that is, the medium should be completely thick to γ-rays. This contradiction can be explained if the γ-rays originate from a relativistic jet pointing at a small angle with respect to the line of sight (Maraschi et al., 1992). However, the still large value of compacity suggests the existence of an inner, more compact region where pair production can take place efficiently (Henri et al., 1993). This supports the so-called “two-flow” model, where the superluminal motion is attributed to the expansion of a relativistic pair plasma heated by a MHD jet from an accretion disk (Sol et al., 1989). Hence we propose to interpret the spectral break observed in many objects around a few MeV (Lichti et al., 1993) by an opacity effect due to photon-photon absorption by pair production.
The Emission Spectra of Radioweak Quasars. I. The Fir Emission
Authors: Niemeyer Martina , Biermann Peter L.
Published: July 2016

The far-infrared (FIR) spectra of radioweak quasars show a steep rise from the mm to the FIR wavelengths with an spectral index often α ≥ 2.5, and a slow decrease beyond the FIR with α ≃ −1. A comparison of the FIR luminosity with both radio and X-ray emission demonstrates, that only the active nuclei can provide the energy to heat the dust. We propose that the heating is due to the central engine via relativistic particles. These particles originate from a putative source on the symmetry axis close to the central engine and diffuse through a tenuous galactic halo to heat dusty molecular clouds in a disk configuration. We demonstrate that this mechanism can produce the FIR spectra with reasonable assumptions, and compare them with observations (Chini et al. 1989). We examine the diffusion through the halo and the energy deposition in the disk for two types of source (pointsource, line source, intensity decrease with z−β) and a diffusion coefficient, dependent on the spherical radius r (D ∞ rγ). We obtain the total energy deposition in the disk as a function of the disk radius. For the calculation of the FIR spectra, one must determine the dust temperature. We construct a heat balance that takes into account the absorbed and emitted emission of energy. The calculated dust temperature distribution depends on two parameter: the radial dependence of the diffusion coefficient and the z-dependence of the line source. Then we calculate the FIR spectra of a disk in the wavelength range 10 to 1300 μm. We determine the luminosity of a finite disk, where the limits are determined by the maximal and minimal temperature (TD,max = 1500K given by the dust destruction, TD,min = 20K given by a transition to dust heating from young stars in the extended disk).
Dust Distribution in IRAS Seyfert Galaxies
Authors: Pastoriza M. G. , Bonatto Charles , Bica Eduardo , Storchi-Bergmann T.
Published: July 2016

Observational evidences of dust in the nuclear region of AGNs are substantial (Rudy 1984, ApJ, 284, 33; Jones et al. 1984, PASP, 96, 692). The ionization cones observed in several Seyfert galaxies has been interpreted as shadowing effects by a dust obscuring torus which hides the broad emission line region (BLR) and the central source (Wilson 1992; Storchi-Bergmann, Mulchaey and Wilson 1992, ApJ 395, L73). A large sample of optical and far-IR data for IRAS Seyfert galaxies has been analysed together with dust emission models (Bonatto and Pastoriza 1993), where it has been concluded that the same dust emission model can be applied to both Seyfert types. In order to further study the effects of dust in the spectra of active galactic nuclei, we have obtained spectrophotometry of 21 IRAS Seyfert galaxies in the range 3500–7200 Å and analyse them in conjuction with their IRAS fluxes. The stellar population type is derived from comparisons with normal galaxy templates using dilution effects in the K CaII line as discriminator. For 55% of the sample the population is of late type. For the rest, blue continua due to recent star formation and/or power-law may amount up to 30% at 4000Å. We conclude that the bulge stellar populations of IRAS Seyfert galaxies are similar to those of normal spirals, except that they are more reddened by E(B-V)i ∼ 0.20. Population-subtracted emission line ratios indicate on average stronger reddening for the narrow-line region (E(B-V)l ∼ 0.8. From photoionization models a power-law index for the ionizing continuum α=1.5, and a metallicity larger than solar are obtained. The most luminous IRAS galaxy of the sample (IRAS555) is discuss in detail: in order to be compatible with the observed IRAS fluxes and the optical stellar continuum, the ionizing continuum must be reddened by AV > 10 magnitudes. Consequently a dust structure in this galaxy appears to be increasingly affecting stars and gas towards the galaxy center.
Do Fluid Waves Propagate in Mildly Relativistic Thermal Pair Plasmas?
Authors: Pietrini P. , Krolik J.H.
Published: July 2016

Relativistic pair plasmas are implicated in the physics of the central regions of AGNs, and the observed variability of these sources can be related to the dynamics and changes in structure of these plasmas. To this respect a study of the behaviour of waves to which the pair plasma reacts as a fluid is quite relevant. We analyze the linear response to perturbations of a simple thermal mildly relativistic pair plasma system.
Acceleration Efficiency in Nonthermal Sources and the Soft Gamma-rays from NGC 4151 Observed by OSSE and SIGMA
Authors: Maciołek-Niedźwiecki Andrzej , Zdziarski Andrzej A. , Lightman Alan P.
Published: July 2016

We show that the recent observations of the Seyfert galaxy NGC 4151 in hard X-rays and soft γ-rays by the OSSE and SIGMA detectors onboard CGRO and GRANAT, respectively, are well explained by a nonthermal model with acceleration of relativistic electrons at an efficiency of ≲50% and with the remaining power dissipated thermally in the source (the standard nonthermal e± pair model assumed 100% efficiency). Such an acceleration efficiency is generally expected on physical grounds. The resulting model unifies previously proposed purely thermal and purely nonthermal models. The pure nonthermal model for NGC 4151 appears to be ruled out. The pure thermal model gives a worse fit to the data than our hybrid nonthermal/thermal model. Our results are presented in Zdziarski, Lightman, & Maciołek-Niedźwiecki (1993).
Spectral Variability of 3C 273 at soft X-rays
Authors: Staubert R. , Courvoisier T.J.-L. , Fink H. , Ulrich M.-H. , Brunner H. , Friedrich S. , Otterbein K.
Published: July 2016

We report on the results of three observations of 3C 273 by ROSAT (Staubert et al. 1993).
NGC 4151: An Accurate Upper Limit to the Dimensions of the Central Continuum Source?
Authors: Solomos Nicolaos H.
Published: July 2016

Simultaneous (5672 Å and 3400–3900 Å)) optical continuum photometric observations of the Seyfert galaxy NGC4151, were carried out within ≤4 week periods, down to a time resolution of < 1hr. A new active phase (1990) is detected with onset and slope captured in 1989. Implications of the variability record from 1983, to 1990 (Fig-1), are discussed.
Variability of NGC 3783: First Results from an Intensive Ground-Based Monitoring Campaign
Authors: Stirpe Giovanna M.
Published: July 2016

The International AGN Watch collaboration undertook an intensive monitoring campaign of the bright Seyfert 1 galaxy NGC 3783 between December 1991 and August 1992, in order to study the variations of the continuum and broad emission lines. Spectroscopic and photometric observations took place at several ground-based observatories and formed the optical/IR counterpart to the UV observations conducted with the IUE (Reichert et al. 1993).
OJ 287: A Blazar with Everything
Authors: Takalo L.O.
Published: July 2016

We have collected all the observations available to us of blazar OJ 287. Here we will present preliminary results from our investigation of these data. The photometric light curves show large outbursts occuring (quasi)simultaneously in all frequences. The largest outbursts occured during 1972 and 1983. The B-band light curve can be extended to the year 1894. This being the longest available observational data set of all blazars. Polarization light curves in optical show random variations in all timescales. In the radio bands the polarization observations show well defined structure in the light curves. Light curves and simple correlation analysis based on the light curves on different frequences will be presented.
Relativistic Jets with Stellar Wind Entrainment
Authors: Bowman Mark
Published: July 2016

Observations suggest that the flow speeds in extragalactic radio jets are relativistic on parsec scales. This evidence includes rapid variability, brightness temperatures in excess of the inverse Compton limit and even the motion of individual features with apparent superluminal velocities. In contrast, FR–1 flow speeds appear to be non–relativistic on kiloparsec scales (the case is not clear for FR–2 sources); consequently, the possibility of jet deceleration has been explored.
High Resolution HI Observations of NGC 1068
Authors: Brinks Elias , Skillman Evan D. , Terlevich Roberto J. , Terlevich Elena
Published: July 2016

Surprisingly few Seyfert galaxies have been mapped at near optical resolution in the 21–cm line of neutral atomic hydrogen, despite the fact that studies of the gaseous component hold out the possibility of identifying the cause of infall of gas to or outflow from the central region. We therefore decided to observe the Seyfert 2 galaxy NGC 1068 with the NRAO–Very Large Array. The spatial resolution of the final images is about 8 ″ or 700 parsec at a distance of 18 Mpc; the velocity resolution is 5.2 km s−1.
Astrophysical Results from Geodetic VLBI Campaigns
Authors: Britzen S. , Witzel A. , Gontier A.-M. , Schalinski C.J. , Campbell J.
Published: July 2016

Geodetic VLBI observations of extragalactic radio sources –designed to measure earth orientation parameters– are performed regularly since more than 10 years now. In different campaigns about 20 Quasars and BL Lacs are being monitored at 2.3 and 8.4 GHz. The high duty-cycle of these observations (every month for IRIS-S) and the resulting enormous data base allow to study the milliarcsecond structures and their variations simultaneously at two frequencies on short timescales. Since the accuracy of baseline determination and measurement of earth rotation parameters has reached a limit where source structure contributions become significant, there is substantial interest to monitor and correct for the source structure “effects”. Therefore we perform a regular analysis of sources selected from IRIS-S (high north-south resolution and almost circular beam for low declination sources) and EUROPE (high sensitivity due to large telescopes) campaigns covering a maximum time base of 10 years (1983–1993). The (undesired) structure of the sources leads to an occasional updating of the source catalogue in order to have “pointlike” sources which are observed 10–15 times for three to seven minutes during 24 hours. Meanwhile about 50 sources have been observed in geodetic campaigns. The comparatively poor data quality requires careful calibration with a source whose structure is well–known from high dynamic range observations (e.g. the blazar 1803+784). The dynamic range of these maps is limited to 1:50. The merit of this database lies obviously in the monthly persecution of structural changes in extragalactic radio sources over at best 10 years time and the filling of the gaps between high dynamic range observations. Sources which are presently of particular interest to us, include 1803+784, 4C39.25, 0528+134, 3C454.3 and OJ287.
Type Transitions in Starbursts Powered AGN
Authors: Aretxaga Itziar , Terlevich Roberto
Published: July 2016

There is mounting evidence that type transitions are a common property among Active Galactic Nuclei: the broad lines in, at least, eleven Seyfert galaxies have ocassionaly appeared and subsequently disappeared leading to the reclasification of their nuclei from type 1–1.5 to type 1.8–2 or viceversa.
Spectroscopic Studies of Emission Line Galaxies
Authors: Chun M. S. , Sung E. C. , Moon H. K. , Byun Y. I.
Published: July 2016

Spectroscopic Observations were made to study 42 emission line objects. The analysis of these long slit spectra shows that 15 out of 42 galaxies are blue compact galaxies (BCGs). 21 of them are starforming or HII galaxies and 3 were found to be normal galaxies.
High Spatial Resolution 2D Spectrography of ENLR in Seyfert Galaxies
Authors: Pecontal E. , Ferruit P.
Published: July 2016

Three active nuclei environments have been observed with the integral field spectrograph TIGER operating in the visible domain : Mkn 34, NGC 5929 and M 51. These three objects exhibit linear radio-sources evocating expulsion of plasmons from the nucleus. Long-slit or Pérot-Fabry observations showed that the gas of the galaxies is interacting with the radio-emitter, and models of this interaction have been proposed. These new observations combines the two spatial dimensions of integral field spectrography (with 0.7″ FWHM) with the rather large spectral domain of classical spectrography.
Nuclear Activity in the Seyfert Galaxy NGC 1365
Authors: Hjelm M. , Lindblad P.O. , Jörsäter S.
Published: July 2016

NGC 1365 is a barred Seyfert 1.5 galaxy. Fig 1a is a contour plot of an [OIII]λ5007 image (Jörsäter & Lindblad 1989), showing a plume-like structure pointing towards SE in the direction of the minor axis of the galaxy, which also is the direction of the steepest velocity gradient in [OIII]λ5007. The plume is roughly aligned with a radio feature in the 6 and 20 cm continuum (see Sandqvist et al., this volume). The [OIII]-emission on the NW side is weaker. This plume-like structure is not seen in Hα.
Optical, HST, and ROSAT Observations of BAL QSOs
Authors: Kopko Michael , Turnshek David A. , Espey Brian R.
Published: July 2016

We consider multiwavelength observations of Broad Absorption Line (BAL) QSOs which include optical spectrophotometry supplemented by HST-FOS UV spectrophotometry and/or ROSAT-PSPC x-ray observations. For moderate to high redshift objects, increasing the wavelength coverage into the UV permits observation of BALs due to different ions of the same element for several different elements for the first time. By employing appropriate assumptions, ionic column densities as a function of outflow velocity can be derived from these observations, resulting in constraints on the level of ionization and chemical composition of the BAL region (BALR) gas and the photoionization model itself.
Influence of the Gravitational Field on the Shape of Spectral Lines in Spectra of Seyfert Galaxies and Quasars
Authors: Popović L. Č. , Vince I. , Kubičela A.
Published: July 2016

On the basis of preliminary examination of the model of Seyfert galaxies and quasars we have concluded that their gravitational field may have an important influence on the shape of spectral lines when the emission cloud is in gravitational field of massive nuclei (mass about 107–108 M⊙ for Seyfert galaxies, see e.g. Padovani et al. 1990), and the emission cloud is large enough (for example about 1014–1015 m for Broad Line Region (BLR) of NGC 7469 (Bonatto & Pastoriza 1990) or about 1021 m for quasar 3C 257 (Forbes et al. 1990)), so that the emitters are in very different gravitational field along the line of sight.
Star-Formation and Nuclear Activity in Three Galaxies with Nuclear Rings
Authors: Storchi–Bergmann Thaisa , Wilson Andrew S. , Baldwin Jack A.
Published: July 2016

We investigate two current problems in active galactic nuclei – the mode of fueling the putative black hole, and the question whether the circumnuclear regions have experienced unusual chemical processing – by studying the kinematics and chemical abundance of the gas in the nuclear region of galaxies with sites of ongoing star formation near the active nucleus. We discuss the results for three galaxies with nuclear rings: NGC1097 – for which we recently discovered broad double peaked Hα and Hβ emission from its LINER nucleus (Storchi-Bergmann, Baldwin & Wilson 1993, ApJ 410, L11); NGC1672, which also presents a LINER nucleus; and NGC5248, a galaxy with a ring but no nuclear activity, used as a comparison. Narrow–band images obtained with the CTIO 1.5m telescope were used to map the emitting gas. Longslit spectroscopy obtained with the 4m telescope at high spectral resolution (at several positions over the nuclear region) was used to obtain the gas velocity field. In the two galaxies with LINER nucleus, the starforming rings are located in the turnover of the rotation curves, which show that the gas is rotating faster at the rings than farther out. We conclude that the rings are associated with inner Lindblad ressonances, which may be particularly effective in forcing gas inwards and fuelling the black hole (Wilson et al. 1986, ApJ 310, 121). From the emission line ratios the gas excitation is maped, and it is found that even in NGC5248, the nucleus presents a different excitation, suggesting a very mild LINER activity. Low-dispersion spectroscopy was also obtained in order to calculate the chemical abundances and compare the values obtained for the nuclear gas with those obtained for the HII regions in the ring and beyond the ring (when present). The goal is to check the results of recent studies (Storchi-Bergmann & Pastoriza 1989, ApJ 347, 195; 1990, PASP 102, 1359), based on spectroscopy of the nucleus, which indicate an enhanced abundance of nitrogen, up to 5 times solar for the gas of the narrow line region of LINER and Seyfert 2 nuclei.
Internal Faraday Rotation in Compact Radio Sources (CRS)
Authors: Björnsson Claes-Ingvar
Published: July 2016

Standard inhomogeneous synchrotron models can explain the polarization properties of CRS if proper account is taken for internal Faraday rotation; neither depolarization due to synchrotron self-absorption nor a tangled magnetic field plays an important rôle. The effects of inhomogeneities are important; the polarization properties of flux escaping from a Faraday thick region are quite different from those coming from a homogeneous source. The observed polarization of strong lined CRS indicates (i) a jet with constant opening angle, (ii) a large scale magnetic field whose main component is along the jet axis and (iii) the density of Faraday rotating electrons scales with radial distance in the same way as does the density of synchrotron emitting ones. Furthermore, the preferred values of both the degree of polarization and the polarization angle, as well as their approximate frequency independence, are consistent with the assumption that the Faraday rotating electrons and the synchrotron emitting electrons belong to the same energy distribution; the former being the non/semi-relativistic end of the latter. The source properties of weak lined CRS (BL Lac objects) are harder to infer, mainly because much of the polarized flux remains unresolved even at the VLBI-scale. The weak polarization structure in BL Lac objects might be due to shocks and no Faraday rotation but it can also be accounted for with a jet structure similar to the one inferred for the strong lined CRS. Although an efficient Fermi-type acceleration mechanism can not be excluded, the polarization characteristics of Faraday thick shocks in a jet make them unlikely as acceleration sites.

The polarization properties of the VLBI-core are not those expected from the unresolved inner parts of the jet structure deduced from the resolved emission. Instead it seems likely that the VLBI-core consists of two components; in addition to the inner part of the jet, there is a component which is directly related to the optical blazar emission region. Time variations and the properties of the circular polarization imply that the latter, blazar component, is characterized both by a large scale magnetic field and large Doppler factors. Relativistic streaming in the blazar component is important; for example, the gross features of the initial phases of radio outbursts can be explained in a scenario where the streaming electrons are pitch angle scattered.
The Vertical Structures of Accretion Disks in AGN
Authors: Riffert H. , Dörrer T. , Staubert R. , Ruder H.
Published: July 2016

Radiation emitted from an accretion disk around a central black hole is the widely accepted model for the observed optical to UV emission from AGN. We have calculated the properties of a standard α-accretion disk (Shakura and Sunyaev, 1973). We present a fully self-consistent model of the structure and the spectrum of such a disk, i.e. the internal vertical density and temperature profiles are calculated simultaneously with the local spectra. Constant density models have been presented by (Ross et al., 1992). The central object is assumed to be a Kerr black hole (BH); relativistic corrections are included. The local energy production is assumed to be entirely due to turbulence. The radiative transfer equation is solved using the Eddington approximation. Inelastic Compton scattering is treated approximately by the Kompaneets equation, and the absorption cross section contains free-free and bound-free processes for hydrogen. The energy transport includes radiation and convection, and the convective flux is calculated in the mixing length theory, taking into account the heating and cooling of the rising elements. Although the convective flux is energetically negligible it has a strong influence on the vertical density structure. We performed several calculations for different parameters such as Ṁ and α. In regions, where the surface radiation flux is large, we get a strong density inversion because the radiation force per unit mass overcomes the gravitational force. Such a density profile, however, is unstable against convection. Including the convective flux then leads to a monotonic density profile. Figures 1 and 2 show the structure and integrated spectrum for two different disk models.
The Nuclear Disk of NGC4261: HST Images and WHT Spectra
Authors: Ferrarese Laura , Ford Holland C. , Jaffe Walter , van den Bosch Frank , O'Connell Robert W.
Published: July 2016

The properties of the nuclear region of the elliptical galaxy NGC4261 (=3C270), the second brightest radio source in the Virgo cluster, have been studied using high resolution HST images and La Palma WHT spectra.
Reprocessing of Uv and Line Emission in AGN Accretion Discs
Authors: Rokaki Evlabia , Boisson Catherine
Published: July 2016

It is commonly admitted that AGN contain a massive black hole fuelled most likely by an accretion disc. Several spectral features of the AGN, as the continuum excess in the UV and the broad line spectrum, involving different physical processes of emission (thermal for the UV continuum, photoionisation for the line spectrum) have been proposed as signatures of the disc. Physical parameters of the nucleus (as the mass of the black hole, M, the disc inclination, i, and accretion rate, Ṁ) are better determined when these two spectral features are modelled simultaneously. Here, we present results from the disc modelling (see) of the UV and broad Hβ emission of the 22 Seyfert 1 galaxies in a complete AGN sample selected in a hard X-ray survey.
Some Peculiarities of Variable Optical Spectra of 11 Low-Redshift Quasars
Authors: Pronik I.I.
Published: July 2016

The flux of narrow 5007 Å [OIII] forbidden line during last 20 years is accepted as a bench-mark for calibration of the continuum and broad-lines fluxes in AGN. But one can not get away from the problem of the forbidden lines variability in these objects. The first report were published by Bardin et al. (1967). Some of the results are revieved by V. Pronik, I. Pronik (1988, 1992). There were 4 years monitoring of [OIII] fluxes variability in the Seyfert galaxy NGC 1275 nucleus (Pronik et al., 1990). Now we reexamine the published data of W. Zheng et al. (1986, 1987, 1988), discussed earlier in supposition of forbidden lines constant in spectra of 11 low-redshifted QSOs. Maximal calibration coefficients adopted by W. Zheng et al. in supposition of [OIII] lines constant were in the interval 2.0–3.6. On the other hand the fluxes errors are about 15%. Disagreement is very high. This is one of the arguments in the forbidden lines variability Tightness.
II. The Galaxy
Authors: Larsson-Leander G.
Published: July 2016

In connexion with the importance of present views on stellar evolution for discussions of the evolution of the Galaxy, the sessions dealing with galactic problems were preceded by a review of items relating the evolution of stars with that of the Galactic System. The following represents with only few modifications the introductory paper on this subject as presented by J. H. Oort.