bluuebunny/crossref_metadata_2025 huggingface dataset:
The Origin of Continuum Emission in Active Galactic Nuclei
Authors: Bregman Joel N.
Published: July 2016

The general understanding of the continuum emission from AGN has changed from the picture where nonthermal processes were responsible for all of the emission. The current body of observation indicates that there are two types of objects, one being the blazar class (or blazar component), where nearly all of the emission is nonthermal, due primarily to synchrotron and inverse Compton emission. Variability studies indicate that the emitting region decreases with size from the radio through the X-ray region, where the size of the X-ray region is of order a light hour. More than two dozen of these radio-loud AGNs have been detected at GeV energies (one source at TeV energies), for which the radiation mechanism may be inverse Compton mechanism.

In the other class, the radio-quiet AGN (component), the emission is almost entirely thermal, with radiation from dust dominating the near infrared to submillimeter region. The optical to soft X-ray emission is often ascribed to black body emission from an opaque accretion disk, but variability studies may not be consistent with expectations. Another attractive model has free-free emission being responsible for the optical to soft X-ray emission. The highest frequencies at which these AGN are detected is the MeV range, and these data should help to determine if this emission is produced in a scattering atmosphere, such as that around an accretion disk, or by another model involving an opaque pair plasma.
Misdirected Quasars in Distant Radio Galaxies
Authors: di Serego Alighieri Sperello , Cimatti Andrea
Published: July 2016

We present the results of recent spectro–polarimetry and imaging–polarimetry of distant radio galaxies which show: (1) broad polarized permitted emission lines, (2) narrow unpolarized forbidden emission lines, (3) a flat (in fλ) polarized UV continuum and (4) an absorption feature, probably interstellar. The direction of the E vector of polarization is always perpendicular to the optical/radio axis. These observations are strong evidence that these objects harbour a quasar, which is visible only through scattering by the interstellar medium of the galaxy. The continuum polarization drops to the red of the 4000Å break, suggesting dilution by an evolved stellar population. A two-component model made of a dust scattered quasar and an evolved stellar population reproduces well the polarization and the spectral energy distribution, including the IR data.
ROSAT Observations of Active Galactic Nuclei
Authors: Brinkmann W.
Published: July 2016

The large number of Active Galactive Nuclei detected for the first time through their X-ray emission in the ROSAT All Sky Survey as well as the first measurements of the X-ray emission of many previously known AGN provide a new unprecedented large basis for the statistical and morphological exploration of these objects.

The soft energy range of the X-Ray Telescope, the good energy resolution of the PSPC detector, and the high sensitivity of the instrument further allows an investigation of the spectral properties of sources in this energetically important energy band.

A short overview is given of the actual ongoing research concentrating on the study of the soft X-ray class properties of the various types of AGN.
Review of GRANAT Observations of AGNs
Authors: Churazov E. , Gilfanov M. , Finoguenov A. , Sunyaev R. , Chernyakova M. , Apalkov Yu. , Grebenev S. , Lagunov I. , Jourdain E. , Roques J.P. , Mandrou P. , Bouchet L. , Ballet J. , Claret A. , Laurent P. , Lebrun F.
Published: July 2016

Brief review of AGNs observations in the X-ray / soft gamma-ray bands with the orbital observatory GRANAT is presented.

For three well known bright objects (3C273, NGC4151 and Cen A) broad band (3 keV–few hundreds keV) spectra have been obtained. Imaging capabilities allowed accurate (several arcminutes) identification of these objects with sources of hard X-rays.

The spectrum of NGC4151 above ≈ 50 keV was found to be much steeper than that in most of the previous observations, while in standard X-ray band the spectrum agrees with observed previously. The comparison of the observed spectra with that of the X-Ray Background (XRB) indicates that sources similar to NGC4151 could reproduce the shape of XRB spectrum in 3–60 keV band.

Cen A was observed in the very low state during most of observations in 1990–1993, except for two observations in 1991. The variability of the hard X-ray flux has been detected on the time scales of several days.
On the Broad Band Energy Distribution of Blazars
Authors: Maraschi Laura , Ghisellini Gabriele , Celotti Annalisa
Published: July 2016

The broad band energy distributions of blazars are revisited with particular emphasis on the sources detected in γ-rays by the Compton Observatory (GRO). The observed distributions can be broken down into two main components, corresponding to two broad peaks in the vFv representation. The first occurs in the FIR-optical range, the second in the MeV-GeV region. In the case of MKN 421, which may be representative of X-ray selected BL Lacs, the first peak is shifted to higher frequency (≃ 1016 Hz) and the γ-ray spectrum extends to TeV energies. There is general agreement that the first spectral component is due to synchrotron radiation from a relativistic jet, although some problems remain in deriving the spectrum and location of the emitting relativistic electrons. The second component, which in most objects extends from the X-ray to the γ-ray range, can be naturally interpreted as inverse Compton scattering by the same electrons producing the synchrotron photons, either on the synchrotron photons themselves (SSC) or on photons external to the jet. It is argued that multifrequency studies of these sources including γ-rays will allow to test Inverse Compton models and to distinguish between different sources of photons.
Near IR - Observations of the Jet in M87
Authors: Neumann M. , Meisenheimer K. , Röser H.-J. , Stickel M.
Published: July 2016

The central region of M87 in the K′ (2.1 μm) - band was imaged using the 2.2m telescope on Calar Alto, Spain. In addition to the jet our K′ exposure (Fig. 1) shows an arclike structure ∼ 24 arcsec southeast of the nucleus. This is the IR counterpart to the feature detected by Stiavelli et al. (1992) in the optical and to the brightness maximum of the southeastern radiolobe designated as “theta” (Hines et al. 1989). Its radio to IR spectral index is α = −0.88 ±0.01 (Sv ∞ vα), consistent with the radio spectral index of α = −0.84 ± 0.07 (Salter et al. 1989) of the whole radio lobe measured between 5 GHz and 230 GHz.
The Origin of AGN-IR Emission
Authors: Stenholm L. G.
Published: July 2016

Advanced multi dimension radiative transfer calculations for an AGN source with a dust disk shows that the AGN-IR emission can be due to reradiation from heated dust in a thick disk. The models produces a weak silicate feature for a wide range of physical conditions, in agreement with the observations.
The Soft X-ray Excesses Observed by ROSAT
Authors: Walter R. , Fink H.H.
Published: July 2016

The properties of the soft X-ray excesses of bright Seyfert 1 galaxies and Quasars are described using the observations obtained with the PSPC (0.1–2.4 keV) detector of the XRT telescope aboard ROSAT during the ROSAT all sky survey (RASS). The sample consists of 58 Seyfert 1 type AGN detected with more than 300 counts during the RASS and observed at least once with IUE.

The soft X-ray photon indices of our sample members range from 1.6 to 3.4 in a wide distribution (< Γ > = 2.50, σ = 0.48). The width of the distribution is considerably larger than the mean statistical uncertainty on the individual spectral slopes (σ = 0.33). Excepting for IC 4329A and Mrk 766, the mean contribution of absorbing cold matter intrinsic to the Seyfert galaxies of our sample to the absorbing column density is less than 1020cm−2. In IC 4329A and Mrk 766 intrinsic absorbtion is observed at soft X-ray. Both sources are also strongly reddened by dust.

An excess of soft X-ray flux is detected in 90% of the sources above the exptrapolation of the hard X-ray power law. It can be shown that the PSPC spectral slope is a measure of the strength of the soft X-ray excess. If the reddened sources are excluded, a correlation appears between the strength of the ultraviolet blue bump and the soft X-ray photon index (figure 1). The ratio of the ultraviolet to infrared fluxes and the ultraviolet spectral slope are also related to the strength of the blue bump. The observations are compatible with a model where most of the spectral variations arising among the sources studied are driven by the strength of the bump component, which varies by a factor of 100 from object to object. A bump model consisting of a power law with a high energy cutoff at 80 eV can fit most of the sources. In any case, the spectral energy distribution of the ultraviolet to soft X-ray bump is characterised by vFv(1375 Å) = (1–5) ∫ε > 150eVFεdε.
The Structure of Relativistic MHD Jets
Authors: Appl Stefan , Camenzind Max
Published: July 2016

An analytic model for a stationary force-free relativistic magnetized jet is presented. In those models a poloidal current provides the tension that balances the internal pressure. Our ignorance of the detailed conditions in the collimation zone is accounted for by specifying the current distribution as an (essentially free) function of the flux surfaces. The asymptotically cylindrical Grad-Schlüter-Shafranov (GSS) equation is solved for a nonlinear current distribution, I(Ψ) = c(1 – exp(−bΨ)) which covers both diffuse (b 《 1) and sharp (b 》 1) pinches, and weak (small c) and strong (large c) currents.
ROSAT X-ray Observations of Pair Mrk474/NGC 5682
Authors: Bi Hongguang
Published: July 2016

Like radio and optical observations of AGN/Galaxy pairs (e.g. Carilli, C & van Gorkom, J. 1992, ApJ, 399, 373), X-ray observations of the pairs can reveal absorption at high energy band, and also, possible galactic gaseous X-ray emissions that are very useful in constructing halo models. ROSAT/PSPC X-ray spectra of 4 AGNs in the well-known pairs 3C232/NGC 3067, 3C275.1/NGC 4651, 3C309.1/NGC 5832 and Mrk474/NGC 5682 are reported here. Especially, we have detected an extragalactic HI of NGC 5862 in the Mrk474 spectrum.
ROSAT Spectra of Quasars
Authors: Bühler P. , Courvoisier T.J.-L. , Staubert R. , Brunner H. , Lamer G.
Published: July 2016

X–ray observations of AGN with Einstein, EXOSAT and Ginga have shown, that the spectra of quasars in the energy range 2 to 10 keV can be approximately described by a single power law model with a photon index of 1.7 to 2.0. They also suggested that a soft X-ray excess component (below ≈ 1 keV) is a common feature in many quasars. In order to investigate whether a soft excess is characteristic for a certain class of objects we analysed the data of the pointed ROSAT PSPC observations of the six radio-loud quasars PG0007+106, PKS0135-247, QSO0537-286, QSO0923+392, PG1225+317, 3C273 and the radio-quiet quasar PG0804+761. In a first step the observed spectra were fitted with an absorbed single power law model. The hydrogen column density was fixed to its galactic value and the normalisation at 1 keV and the spectral index α were the free fit parameters. In order to decide whether a soft component is present in a source, the resulting power law index was compared with the hard X-ray power law index (2–10 keV) determined in the past with other instruments. A steep ROSAT PSPC spectrum indicates the presence of an additional soft X–ray component. In four cases (PKS0135-247, PG0804+761, QSO0923+392, 3C273) we find that the spectra in the PSPC band are considerably steeper than the spectra above 2 keV and therefore suggest the presence of a soft excess. In order to quantify the contribution of the soft excess these spectra were successively fitted with a model containing a hard power law component and an additional soft component described either by a power law, thermal bremsstrahlung or black body model. For the other three members of our sample (0007+106, 0537-286, 1225+317) the fitted power law index is not enhanced. This means that no soft component has been detected, but not necessarily that it does not exist. There are two effects which render more difficult the detection of a soft component in ROSAT spectra, the absorption of photons by interstellar material and the shift of the spectra towards lower energies due to the redshift. Both processes have first an effect on the soft part of the observed spectrum and it is therefore evident, that this leads to a decrease of the sensitivity for soft X–rays of the emitted spectrum. For the three quasars in our sample, where no soft excess has been detected, either the column density (0007+106) or the redshift (0537-286, 1225+317) is especially large and therefore an eventually present soft component could have remained undetected. In these cases we calculated upper limits for the strength of such a soft component (P. Bühler et al., to be published in A&A.)
ROSAT Selected Interacting Galaxies with Narrow Emission Lines
Authors: Engels D. , Bade N. , Studt J. , Fink H.
Published: July 2016

In the context of an identification program of sources from the ROSAT All-Sky Survey (RASS) on Schmidt objective prism plates (Bade et al. 1992a, b) we discovered two galaxy pairs, which contain a narrow-line Seyfert 1 component with an X-ray luminosity of Lx ∼ 1044 erg s−1 and an HII–region galaxy. Apparently they are interacting. Their redshifts are 0.1 < z < 0.3 and their brightnesses 17.5 < B < 19.5. A third one was found among EINSTEIN sources. Typical separations between the components are 10″. Near the pairs other galaxies were found, and although their physical association is not confirmed spectroscopically it is quite probable that they form a small cluster of galaxies. ROSAT HRI observations indicate that the X-ray emission is not extended and originate from the AGN alone. It is remarkable that the AGN in all physical pairs identified so far have rather narrow permitted emission lines with linewidths ≤ 1500 km s−1.
X-ray Detection of the Nuclear Source in the Cygnus a Galaxy
Authors: Harris D.E. , Perley R.A. , Carilli C.L.
Published: July 2016

From a ROSAT HRI observation of Cygnus A (42 ksec), we detect x-ray emission from the galaxy identified with the radio source. This was accomplished by subtracting a modified King model: (Surface brightness ∝ to [1+(r/a)2](0.5–3β)) in order to study residual features once the main body of emission from diffuse gas had been deleted. The central source was present for all acceptable values of the core radius, a, and exponent, β. Details of the image processing, an evaluation of emission from the radio hotspots, and a study of the effect of the radio lobes on the gas distribution will be presented elsewhere.
Connection Between Optical and High Frequency Radio Variability in AGN
Authors: Tornikoski M. , Valtaoja E. , Smith A.G. , Nair A.D.
Published: July 2016

We have been searching for correlated optical and radio variability in large temporal data sets of 22 extragalactic radio sources. The optical data were obtained with the 76-cm reflector at the Rosemary Hill Observatory in Florida, USA. The radio data were obtained at two different sites: 22, 37 and some of the 90 GHz data at the Metsähovi Radio Research Station, Finland, and 90 and 230 GHz data at the Swedish-ESO Submillimetre Telescope (SEST) on La Silla, Chile. Because the SEST data unfortunately reaches only back to 1988, the 90 and 230 GHz data were complemented by the IRAM data from Steppe et al. (A&AS 75, 1988 and A&AS 96, 1992).
Optical Microvariability in Radio Quiet Quasars
Authors: Wiita Paul J. , Krishna Gopal , Sagar Ram
Published: July 2016

We have observed 11 radio quiet QSOs (RQQSOs) to see if they exhibit intranight variability in the optical. The detection of such microvariability would support models in which fluctuations on accretion disks are dominant, while if it is never present, models based on relativistic jets would be favored. Although several of these RQQSOs show hints of microvariability, we cannot claim to have discovered this phenomenon in this class of objects. Several of the comparison stars have clearly shown rapid variability.
An Eight-Month Monitoring Campaign on a Sample of AGN
Authors: Winge Cláudia , Peterson Bradley M. , Pastoriza M.G. , Storchi-Bergmann T. , Baldwin J.
Published: July 2016

We present the preliminary results of an 8-month monitoring campaign carried out on 6 AGN during the period December 1991 – July 1992. All but one of our targets showed continuum and/or line variability. The data were obtained using the 2D-Prutti + Cassegrain spectrograph at the CTIO 1.0-m telescope, and reduced following standard procedures. The slit width was 5″ and the nuclear spectra were extracted in a 10″ aperture. The wavelength coverage is 3500–7200Å, with 8Å resolution. The data were flux calibrated using standard stars and then normalized using the [O III] λ5007Å line flux for each object. NGC 6814: our spectra reveal that this object is still in a low state of activity and within the S/N ratio of our data, no variability was observed during this campaign. The stellar population is dominant in the nuclear spectrum and a synthesis using the star cluster library of Bica (1988) indicates a mainly old (∼ 86% of the continuum flux at 5870Å due to a population with age ≥ 10 Gyr), [Z/Z⊙] ≥ 0.3 stellar content, with an intrinsic reddening of E(B–V)=0.20. NGC 3227: using an off-nuclear spectrum corresponding to the two 5″×10″ regions 20.4″ E/W of the nucleus, we obtained also a mainly old (77% at 5870Å with age ≥ 10 Gyr), [Z/Z⊙]=0.3) synthetic stellar population, which contributes ∼ 43% of the nuclear light at 5600Å. The cross correlation of the 4245Å continuum and Hβ light curves results in a 18±3 -day lag. IC 4329A: our data show evidence of variability as a slow and constant increase in both continuum and lines fluxes, but no isolated event was detected. ESO141-G55: the light curves show small variations in the continuum, but no noticeable line variability. Akn 120 and Fairall 9: the data consists of two sets of spectra, separated by ∼ 6 months. Within each set little or no variability was detected, but strong line and continuum variations occurred between them.
VLBI Morphology of GHz-Peaked Spectrum Radio Galaxies
Authors: Dallacasa D. , Fanti C. , Fanti R.
Published: July 2016

GHz-Peaked Spectrum (GPS) radio sources are intrinsically small (< 1 kpc) and unbeamed objects. The galaxies considered here (0316+161, 0404+768, 0428+205, 1323+321, 1358+624, 1819+39, 1829+29) have been selected from the Peacock and Wall (1981) catalogue, and belong to a complete sample of Compact Steep-Spectrum (CSS) radio sources (Fanti et al., 1990). Their radio spectra show a turnover which could be explained in terms of synchrotron self-absorption. It occurs at frequencies ranging from about 100 MHz to 5 GHz and for this reason they do not appear in the 3CR catalogue.
Directivity Pattern Simulation of the Jet Radio Emission
Authors: Kovalev Y.Y.
Published: July 2016

Recently the 1.5 years flux observations of a quasar 0235+16 at 8 frequencies have been explained by the emission of a jet in a strong radial magnetic field of an AGN (in according with the Hedgehog model, suggested by N.S. Kardashev in 1969; see poster by Kovalev Y.Y. and Larionov G.M. to this Symposium).
Kinematics of the BLR Clouds in AGNs and Quasars
Authors: Gondhalekar P M
Published: July 2016

The Lyα and the C IV line profiles in the spectra of quasars and Seyfert 1 galaxies can be described by a combination of a narrow and a broad component. Over four orders of magnitude in luminosity the profiles of Lyα and C IV lines in the quasar spectra are very similar but a change is observed in the C IV profile in the spectra of Seyfert 1 galaxies which cover a smaller luminosity range. The correlation of the FWHM of Lyα, C IV and Hβ lines suggests that the Lyα and C IV lines are emitted from clouds in a similar kinematic enviornment but part of C IV line may also be emitted from clouds which emit the Hβ line.
The Nuclear Region of the Sbc Spiral Galaxy NGC 5055: A Mildly Active Nucleus
Authors: Pişmiş P. , Manteiga M. , Mampaso A. , Recillas-Cruz E. , Cruz-Gonzàlez G.
Published: July 2016

NGC 5055 is one of a list of nearby large spiral galaxies we have selected for a morphological and kinematic study of their bulges. CCD images are obtained at various spectral bands and in the Hα line using the 2.1 m reflector at San Pedro Martir observatory in México, while long-slit spectra at four different PA's are secured with the IDS spectrograph of the Isaac Newton Telescope of the observatory Roque de los Muchachos at La Palma, Spain. Some of the galaxies on our list for which observations are already performed are, aside from NGC 5055, NGC 3351, 4314, 5383 and 5915. These galaxies are not known to have active nuclei. However, we believe that activity may be a common phenomenon spanning a wide range of energetics, from the most active quasars and radio-galaxies (with jets) down to the mildest cases like our Galaxy or M31. The latter may be designated as MAGN (mildly active galactic nuclei). These ideas are treated in a review by Pişmiş (1987, Rev. Mex. Astron. Astrof. 14). The MAGN are usually nearby, and hence offer the possibility to study them in sufficient detail. It is reasonable to expect that the physical phenomenon underlying activity in galactic nuclei is one and the same, and it is essentially the global parameters such as energy at the nucleus that give rise to the different classes of AGN. Thus by studying the nearby mildly active galaxies one can construct a physically acceptable model supported by observation; such model, based on firmer grounds, can then be applied to all AGN.

NGC 5055 (Sbc) with an adopted distance of 8.2 Mpc has a very bright bulge with a tenuous multiple arm structure around it, extending to 8 arcmin. Our velocity field and morphology of NGC 5055 lead to the following conclusions.

1. The galaxy presents a north-south asymmetry; the southern approaching side has its isophotes closer together than at the farther side. We adopt PA 101° for the line of nodes. Our long-slit spectra cover the position angles: 58°, 101°, 112° and 155°.

2. The rotation curve shows a linear region around the nucleus. At PA 101°, the line of nodes, the amplitude is 270 km s−1 between points ±5 arcsec on either side of the nucleus.

3. There is high concentration of mass at the nuclear region (the bulge of the galaxy). An estimate of the mass for the region where the rotation curve is linear ±5 arcsec, is 1.5 × 108 M⊙. Burbidge et al. (1960) give a total mass of 7.6 × 1010 M⊙. The bulge density is thus found to be 500 times the average density of this galaxy.

Analysis of the general velocity field based on four long-slit spectra shows an asymmetry between the East and West sides, ±5 arcsec around the nucleus of NGC 5055, suggestive of the existence of non-circular motion. Indeed evidence is found of an outflow on the west side of the Galaxy within a cone emanating from the center towards the NW with a projected radial velocity of around 80 km s−1. Thus this galaxy shows activity at its center and is a candidate for the MAGN group.
Subarcsecond-Scale Optical and Radio Structure Correlations in Seyfert Galaxies
Authors: Pogge R.W. , Derobertis M.M.
Published: July 2016

An unanswered question in the study of Seyferts is the nature of the relationship between the extended radio-continuum and optical emission-line gas. Detailed comparison is difficult as most Seyferts have radio structure on sub-arcsecond scales, while most optical imaging is on 1–2″ scales. Despite this, some basic features have emerged. Extended radio and optical emission regions are generally aligned in projection, but the overall optical emission extends to much greater galactocentric radii. Pedlar et al. (1989) and Whittle et al. (1986) have reported a tendency for optical emission knots to lie behind the radio lobes, interpreted in terms of the “cooling length” of gas heated by a radiative bowshock driven into the ISM by a jet. In NGC 1068 (Cecil et al. 1990) and M51 (Cecil 1988), however, ambient gas appears to be piling up ahead of a radio lobe at the terminus of the radio jet.
Multifrequency Polarimetry of CSS Sources
Authors: Lüdke Everton , Akujor Chidi E. , Garrington Simon T.
Published: July 2016

Compact Steep Spectrum Sources (CSS) have projected linear sizes < 20 kpc and overall steep spectrum (5 ∼ v−α, α ≥ 0.6). Interactions with a dense interstellar medium may confine the CSSs and produce the high amounts of Faraday rotation that some distorted sources present. The first results of a detailed study of the multifrequency polarization properties of a sample of CSS sources with MERLIN and the VLA are presented.
Frequency-Dependent Polarization in Comptonization Models for AGN
Authors: Poutanen Juri
Published: July 2016

The angular distribution and the polarization of radiation as a function of the angle and frequency for the two-phase model of accretion disks in AGN are found. The results depend strongly on the temperature of the hot corona.
Physics of Magnetized Accretion Disks in AGN
Authors: Field George , Rogers Robert
Published: July 2016

Field and Rogers (1993) proposed that the accretion disks in moderate - L AGN (≲ 1044 erg sec−1) are dominated by magnetic stress rather than gas or radiation pressure. A magnetic field parallel to the disk forms loops above and below it where reconnection accelerates electrons to relativistic energies. The nonthermal radiation observed is the synchrotron emission and inverse-Compton scattering by these electrons.
Structure and Emission Line Spectrum of an X-ray Heated Accretion Disk in AGN
Authors: Ko Yuan-Kuen , Kallman Timothy R.
Published: July 2016

We investigate the structure of an X-ray heated accretion disk in active galactic nuclei. It is found that X-ray heating can prevent the disk to be disrupted by its self-gravity under sufficient X-ray heating. The disk size can be two orders of magnitute larger than that limited by self-gravity of the disk without X-ray heating. An accretion disk corona will be formed by X-ray heating and can be a site for line emission. We present such emission line spectra which range from optical to hard X-ray energies and compare with the observational data.
K-Correction Biases and the Quasar Luminosity Function
Authors: Baker A. C. , Hewett P. C.
Published: July 2016

By characterising the range of quasar UV-optical spectral indices and any correlation with it e.g. luminosity or line parameters, we hope to remove one more bias from the quasar luminosity function (QLF).
On the Unification of Radio Galaxies and Quasars
Authors: Chyzy Krzysztof T.
Published: July 2016

A comparison of the projected linear size evolution of extended quasars and radio galaxies are often used as a test of the radio galaxy - quasar unification schemes. If both the mentioned categories of radio sources differ to an observer only due to the various viewing directions, then their radio linear sizes are expected to evolve with redshift in the same way (Gopal-Krishna & Kulkarni, 1992). However, apart from the simplest linear size parameter L we can still determine two independent parameters assessing the asymmetry of the radio structure: Q - the arm lengths ratio; M - misalignment, which measures the apparent bending, and defined as the ratio of the displacement of the core from the source axis to the linear size. The asymmetry parameters Q and M can also be a powerful tool in the consistency test for the orientation based unification scheme as their evolutionary patterns should be the same for radio galaxies and quasars. Contrary to the linear size, they are not sensitive to the simple homological rescaling of the whole structure and hence to the age or expansion velocity of the structure.
Optical Differences Between Radio-Loud and Radio-Quiet QSOs
Authors: Francis Paul J.
Published: July 2016

We analyse the rest-frame UV spectra of a complete sample of optically selected radio-loud and radio-quiet QSOs. Our results are:

1:

Broad absorption-line QSOs (BALQSOs) are all radio quiet, but they are strongly clustered toward the top end of the radio-quiet population in radio power.

2:

Radio-loud QSOs have higher equivalent-width, narrower high ionisation emission-lines than radio-quiet QSOs.

3:

Further Reading

See Francis, Hooper & Impey, 1993, Astronomical Journal 106, 417 and references therein for more details and discussion.
Spectrophotometrical Models for AGN
Authors: Suran Doru Marian , Popescu Nedelia Antonia
Published: July 2016

We compare the observational colour diagrams with the position of the lensed quasars, mean cluster memberships for z < 1 and galactic evolutive tracks in order to determine the influence of these effects in AGN evolution.
II. The Galaxy
Authors: Larsson-Leander G.
Published: July 2016

The objects from which the structure of the galactic halo may be derived by optical means are the extreme population II objects such as RR Lyrae variables with periods longer than 0-4 days, the sub-dwarfs, globular clusters, stars similar to those found in globular clusters such as the bright red giants, and the blue stars found in the galactic polar regions. The longperiod variables with periods shorter than 200 days and the ordinary highvelocity stars are now regarded as belonging to an intermediate population II, somewhat younger than the halo population II proper.
The symmetry of the time and latitude problems
Authors: Murray C.A.
Published: July 2016

The general problem of time and latitude may be said to be the determination of the three components of the vector representing the small rotation of a conventional coordinate system fixed in the Earth, relative to a rotating system defined by the celestial pole, a system of star places, and a standard clock (or time signal). Two components of this vector are the coordinates of the pole of rotation in the conventional system, and the third is essentially the difference between U. T. (strictly U. T. 1.) and the time by the clock.
Definition du Centre de la Lune et D'une Surface De Reference
Authors: Weimer Th.
Published: July 2016

Chaque profil du bord lunaire est en général rapporté au cercle qui passe au mieux par une quarantaine de points situés sur ce bord. Le centre de ce cercle, et aussi son rayon, si nous ne connaissons pas l'échelle des clichés utilises, est done défini d'une façon un peu arbitraire. Les différents cercles de référence risquent de ne pas faire partie d'une même sphère et, pour l'observateur, leurs centres ne se projettent pas nécessairement sur le centre de la sphère.
The Origin of the Moon and its Relationship to the Origin of the Solar System
Authors: Urey Harold C.
Published: July 2016

During the last 10 years, the writer has presented evidence indicating that the Moon was captured by the Earth and that the large collisions with its surface occurred within a surprisingly short period of time. These observations have been a continuous preoccupation during the past years and some explanation that seemed physically possible and reasonably probable has been sought.
Thermal History of the Moon
Authors: Levin B. J.
Published: July 2016

According to contemporary concepts, the Moon was formed by accumulation of cold solids, and was cold itself at the beginning. Later on, the accumulation of radiogenic heat in the Moon's interior caused its heating and melting (total or partial, depending on the content of radioactive elements), which was followed by its physico-chemical and gravitational differentiation.
Spectroscopic Proofs for Existence of Volcanic Processes on the Moon
Authors: Kozyrev N. A.
Published: July 2016

A concept of the Moon devoid of internal energy, sufficient for volcanic and mountain-forming processes, is widely accepted at the present time. Therefore, it is generally assumed that the relief formation of the Moon is due to external actions on its surface. However, such a viewpoint is not sufficiently substantiated. In fact, the history of Earth's relief shows that the period of telescopic observations of the Moon is too short to enable us to observe changes in whole sections of the crust. Catastrophic changes, apart from actions of water and atmosphere, occur on the Earth only in a very restricted area, and the size does not exceed a few kilometres. Therefore, we must not expect on the Moon any sudden changes over an area exceeding appreciably one square second. The reality of such minute effects in the relief could hardly be established on the basis of available cartographic data.
Microphotometric Analysis of the Emission Flare in the Region of the Central Peak of the Crater Alphonsus on 3 November 1958
Authors: Kalinyak A. A. , Kamionko L. A.
Published: July 2016

A microphotometric analysis of the spectrum of the emission flare in the region of the central peak of the crater Alphonus, obtained by N. A. Kozyrev and V. I. Ezersky on 3 November 1958, leads to a conclusion that the escape of gas from the depths of the Moon had a purely fluorescent character. By the character of the intensity distribution, the spectrum of the flare is similar to the emission spectra observed in the heads of comets. Some maxima of the intensity of curve can be identified with the Swan molecular bands of C2. No continuous radiation of thermal character was observed.
Some Systematic Visual Lunar Observations
Authors: Arthur D. W. G.
Published: July 2016

Since the visual observer obtains a resolution some three times that obtained photographically with the same telescope, justification of this method of getting data on the lunar surface is quite unnecessary. Visual observations have the well-known drawbacks of subjectivity and selectivity and are also positionally inaccurate. These defects can be controlled and their effects reduced by repetition and by appropriate observation routines.
The extreme Ultraviolet emission from the Sun between the Lyman-alpha lines of H I and C VI
Authors: Tousey R. , Austin W. E. , Purcell J. D. , Widing K. G.
Published: July 2016

As a result of research carried out with rocket-borne grating spectrographs, the nature of the extreme ultraviolet spectrum of the Sun is now known to a short wavelength limit of 33.7 Å, the Lyman-alpha line of C VI. Most of the emission lines of wavelengths greater than 400 Å have been identified, as have those from 80 Å to 33.7 Å. Between 149 Å and 400 Å, however there are many intense emission lines whose identity has not as yet been established. Twenty or more have been proved to be from iron, since they appear in spectra obtained from high temperature plasmas into which iron has been introduced, but the stages of ionization have not yet been established. Lines from the elements most abundant in the Sun, H, He, O, N, O, Ne, Mg, Al, Si, S and Fe, in most of the stages of ionization requiring 500 eV or less for production have been found. The outstanding exceptions are the lines in the fluorine and neon sequences.

Spectroheliograms, photographed with normal incidence spectrographs, show that the emission lines Fe XV 284 Å, Fe XVI 335, 361 Å, originate principally from active regions, in contrast to He II 304 Å, which is emitted with great intensity from the disc also. Continuum emission, in the wavelength range 170–300 Å, has been recorded from intense centers of activity.
The Laboratory production of solar iron lines in the vacuum Ultraviolet
Authors: House Lewis L.
Published: July 2016

The Scylla plasma which is contained in a ceramic discharge tube has been purposely contaminated with known impurities. The spectrum of the discharge with Fe (CO)5 added shows most of the solar lines in the 150–220 Å region. Some of these strong lines may be produced by iron in intermediate stages of ionization (Fe X to Fe XIV).
Comments on X-rays emitted by the sun
Authors: Lindsay John C.
Published: July 2016

Observations from the first Orbiting Solar Observatory have set an upper limit of 3.40 ± 0.95 photons/cm2.s for the 20–100 keV X-ray flux from the “quiet” Sun. Eight impulsive and short-lived 20–100 keV X-ray bursts were observed which were associated with optical flares and cm radio bursts. The 2–8 Å X-ray flux from the “quiet” Sun was observed to be associated with plage groups on the Sun. The intensity for this 2–8 Å X-radiation was found to be quite variable, changes of 5% being observed almost hourly.
An observation of jupiter in the Ultraviolet
Authors: Stecher Theodore P.
Published: July 2016

A single photoelectric spectral scan of Jupiter in the ultraviolet is presented in the form of a geometric reflectivity. The reflectivity is then assumed to be due to Rayleigh scattering by molecular hydrogen. An upper limit to the amount of molecular hydrogen above the cloud layer of a 11 km atm. is derived.
Cosmic gamma rays — experimental
Authors: Kraushaar W. L.
Published: July 2016

As yet no experiment, satellite-borne, balloon-borne or earth-based has provided compelling evidence for more than upper limits to the intensity of cosmic gamma rays of more than a few MeV energy. Even these upper limits have been useful in blocking in some of the large scale properties of energetic particles in interstellar and intergalactic space. Nevertheless, the smallest upper limit set on the intensity of diffuse gamma rays 3.10−4 cm−2 s−1 sterad−1 (from the satellite experiment in Explorer XI) is a factor of about 20 above the intensity prediction which can be made with rather good confidence for gamma rays made in cosmic ray collisions with interstellar atomic hydrogen.

Predictions of the gamma ray flux from the various discrete-source emitters of synchrotron radio noise are model-sensitive and in general appreciably smaller than existing upper limits. These upper limits are in the 3.10−4 cm−2 s−1 region for gamma rays of E > 5.107 eV and in the 5.10−11 cm−2 s−1 region for gamma rays of E > 5.1012 eV.
Upper limits to the flux of high energy γ-rays from selected quasi-stellar and other sources, using the Cerenkov technique
Authors: Long C. D. , Porter N. A. , Weekes T. C. , Fruin J. F. , Jelley J. V.
Published: July 2016

Upper flux limits at the earth for γ rays of energy greater than about 5 × 1012 eV, have been established for the quasi-stellar sources 3C 147, 3C 196, 3C 273, the Crab Nebula, and the magnetic variable 53 Cam. They are all of the order 10-10 photons cm-2. s-1. Corresponding upper energy limits at emission are of the order 5 × 1047 ergs s-1 for the quasi-stellar sources, and 5 × 1035 ergs s-1 for the Crab Nebula, if γ-ray absorption is assumed negligible. Possible absorption mechanisms are discussed.
Coronascope II observation of the white light corona from a stratospheric balloon
Authors: Newkirk Gordon , Bohlin J. David
Published: July 2016

By use of an apodized occulting dish before the objective lens of a coronagraph the instrumentally scattered light can be reduced to about 10-9 B⊙. Observation of the streamers of the solar corona from 1.8 to 5.25 R⊙ outside of eclipse from a balloon at 30 km altitude are described. A solar streamer complex present at the west limb on 5 March 1964 was apparently the origin of the particles causing the recurrent geomagnetic storms of late 1963 and early 1964.
Ionospheric focussing
Authors: Daniell G. J.
Published: July 2016

A radio antenna within the ionosphere can receive extraterrestrial radiation incident only within a limited cone of directions. A brief review is presented of the theoretical calculations, using various models, of the size and shape of the cone, and the magnitude of the received signal, both from a uniformly bright sky and from a single point source. The approximations of ray theory are discussed and the effects of the curvature of the earth and the inclusion of the terrestial magnetic field are mentioned.
A satellite system for radio astronomical measurements at low frequencies
Authors: Alexander J. K. , Stone R. G.
Published: July 2016

A study program was initiated at the Goddard Space Flight Center in 1962 to survey the astronomical observations most readily and profitably performed by an orbiting radio observatory, to analyze the antenna configurations most appropriate for such a mission and to develop the radiometers and other supporting instrumentation required for a radio astronomy satellite. This study has culminated in the conceptual design of a spacecraft intended solely for radio astronomical observations at wavelengths beyond the ionospheric cut-off. By utilizing long (250 m) antenna elements with a terminating resistance placed an odd number of quarter-wavelengths from the end, a V-antenna can be formed having a beamwidth less than 30° and an 18 db front-to-back ratio over a band of frequencies near 5 MHz. Proper combinations of four such long elements in a double-V or X configuration, furthermore can be made to yield some gain over a, dipole for observations as low as 0.3 MHz. A step-frequency, Ryle-Vonberg radiometer which employs an all solid-state-component comparison noise source has been developed to perform over a 70 db dynamic range with a relative accuracy of ± 0.5 db. A simple, precise instrument to measure both the resistive and reactive components of antenna impedance has also been developed for satellite use. Observations with this system from a gravity-gradient stabilized spacecraft in a 6000 km orbit would afford significant contributions to galactic studies, solar physics, and planetary astronomy by extending radio observations to frequencies in the range 0 3 to 10 MHz.
Optical Systems
Authors: Fehrenbach Ch.
Published: July 2016

FEHRENBACH : It's a great honour for me to be the chairman of the first session of the IAU's 27th Symposium, on The Construction of Large Telescopes. In such high circles of astronomical research here in the western states, we, as Europeans, are extremely satisfied to have the opportunity to compare our methods with yours. Personally, this is the third time I have visited Tucson and the Kitt Peak National Observatory, and I am still impressed by the important means the American people have at their disposal. In Europe, unfortunately, we do not yet have such material facilities, and this is why we are particularly happy to be here; we feel that the mutual exchange of views and information between the representatives of the different groups all over the world will be highly beneficial, especially for us who are presently involved in the construction of large telescopes.
Anisotropic Heat Transfer Inside Rotating Neutron Stars
Authors: Hui C. Y. , Cheng K. S.
Published: July 2016

We have developed the anisotropic heat transport equation for rotating neutron stars. With a simple model of neutron star, we also model the propagation of heat pulses resulting from transient energy releases inside the star. Even in the slow rotation limit, the results with rotational effects involved could differ significantly from those obtained with a spherically symmetric metric in the timescale of the thermal afterglow.
Heavy Neutron Stars? A Status Report on Arecibo Timing of Four Pulsar – White Dwarf Systems
Authors: Nice David J. , Splaver Eric M. , Stairs Ingrid H.
Published: July 2016

Relativistic phenomena (orbital precession, Shapiro delay, and/or orbital decay) have been measured in Arecibo timing observations of four pulsar-white dwarf binaries, leading to constraints on the neutron star masses. We have detected the decay of the PSR J0751+1807 orbit due to gravitational radiation emission, the first such measurement in a binary with a low mass ratio (m2/m1 ≪ 1). Timing data constrains the mass of this pulsar to bet between 1.6 and 2.8 M⊙. Masses of the other pulsars are in marginal agreement with the canonical pulsar mass of 1.35 M⊙, but higher values are preferred.
Pulsar Wind Nebulae and Their Supernovae
Authors: Chevalier Roger A.
Published: July 2016

Young supernova remnants that contain pulsar wind nebulae provide diagnostics for both the inner part of the supernova and the interaction with the surrounding medium, providing an opportunity to relate these objects to supernova types. Among observed young nebulae, there is evidence for a range of supernova types, including Type IIP (Crab Nebula and SN 1054) and Type IIb/IIn/IIL (G292.0+1.8).
The Termination Shock in a Striped Pulsar Wind
Authors: Lyubarsky Yury
Published: July 2016

Toroidal stripes of opposite magnetic polarity are formed in the equatorial belt of the wind emanating from an obliquely rotating pulsar magnetosphere. Such a striped wind transfers most of its spindown energy because the angular distribution of the energy flux in the pulsar wind is maximum at the equator. The alternating field annihilates either in the pulsar wind or at the termination shock so that the flow in the equatorial belt downstream of the termination shock is weakly magnetized. At high latitudes, the magnetization of the flow is higher than in the equatorial belt whereas the total energy flux is smaller. At such a distribution of the energy flux and magnetization, the downstream flow separates into an equatorial disk and a magnetically collimated polar jet. Particle acceleration at the termination shock in a striped wind is discussed. It is argued that the radio emitting electrons are accelerated by driven reconnection of the alternating field at the shock whereas the Fermi acceleration of electrons preaccelerated in the reconnection process results in a high energy tail responsible for the X- and γ-ray emission.
The σ Problem of the Crab Pulsar Wind
Authors: Kirk J. G. , Skjæraasen O.
Published: July 2016

The conversion of the Crab pulsar wind from one dominated by Poynting flux close to the star to one dominated by particle-borne energy at the termination shock is considered. The idea put forth by Coroniti (1990) and criticized by Lyubarsky & Kirk (2001) that reconnection in a striped wind is responsible, is generalized to include faster prescriptions for the a priori unknown dissipation rate. Strong acceleration of the wind is confirmed, and the higher dissipation rates imply complete conversion of Poynting flux into particle-borne flux within the unshocked wind.
X-ray Studies of the Pulsar Wind Nebula Around PSR B0540-69
Authors: Petre R. , Hwang U. , Holt S. S. , Williams R. M.
Published: July 2016

The pulsar wind nebula (PWN) surrounding the 50-ms pulsar B0540-69 in the Large Magellanic Cloud shares many properties with the Crab Nebula, the canonical Galactic PWN. We have used the ACIS instrument on the Chandra X-ray Observatory to perform spatially resolved spectroscopy of the PWN. The spectrum of the inner 10″ is characterized by a simple power law, with a spectral index that steepens strongly with radius. Outside the central 10″ the spectra also require a thermal component. This diameter corresponds to a shell detected in [OIII], suggesting that this shell represents a skin around the PWN, in analogy to the Crab. We infer the value of several key PWN parameters, including σ, the average ratio of electromagnetic to particle flux.
Spatially Resolved Spectrum of the Vela PWN
Authors: Kargaltsev Oleg , Pavlov George
Published: July 2016

A series of 13 Chandra observations has provided the deepest images of the Vela PWN yet available. In addition to the fine structure of the inner PWN features, a much larger and fainter asymmetric X-ray nebula emerges in the summed images. The shape of this outer PWN is similar to that of the radio PWN. We also present the spectral map of the Vela PWN that reveals a shell of soft emission surrounding the inner PWN and an extended region of harder emission south-west of the pulsar. This may indicate that the outer jet is supplying particles to this region.