bluuebunny/crossref_metadata_2025 huggingface dataset:
An Explanation for Pulsar Mode Changing Phenomenon
Authors: Zhang B. , Qiao G.J. , Lin W.P. , Han J.L.
Published: July 2016

There are three mechanisms to cause pulsar inner gap breakdown: the inverse Compton scattering (ICS) of the high energy particles off the thermal-peak photons, off the resonant-frequency photons and the curvature radiation (CR). The pulsar mode-changing phenomenon can be interpreted as a switching effect between theresonant ICS sparking modeand thethermal ICS sparking mode.
A Geometrical origin of the Pulsar Core and Conal Emissions
Authors: Kapoor R.C. , Shukre C.S.
Published: July 2016

We have analysed the dipole magnetic field geometry for the general case of an oblique rotator and have found that open field lines which define the polar cap divide into two branches (Kapoor and Shukre 1996) which appear naturally relevant for distinguishing the core and conal emissions. The polar cap shape is actually determined by a quadratic equation having two roots leading to two values of the polar angle,θ+andθ−with respect to the magnetic axis for a given azimuth φ. For the north pole bothθ+andθ−branches are shown as polar plots in Fig. 1 for various inclination angles α and a typical pulsar period. The discussion of pulsar polar caps hitherto (e.g. Biggs 1990) had not distinguished between theθ+and theθ−solutions. The region defined by theθ+solution is completely contained inside the polar cap. It has a peculiar triangular shape whose lowest vertex is always on the magnetic axis. This naturally suggests an identification of theθ+and theθ−regions with the core and conal emission zones.
Pulse profiles of millisecond pulsars
Authors: Jayawardhana Ray , Grindlay Jonathan E.
Published: July 2016

We present a comparison between the average radio pulse profiles of millisecond pulsars (MSPs) in the field and in globular clusters. Our sample consists of 20 field MSPs and 25 cluster MSPs for which observations exist at 400 - 600 MHz.

We find that 6 of the 20 field MSPs, or about 30%, have a comparable interpulse at a phase offset of 180 ±30 degrees. None of the cluster objects shows this feature. Here we define a ‘comparable interpulse’ as one whose intensity is at least 10% of the primary pulse. This lower limit is well above the noise level of all the profiles in our sample. While the cluster MSPs have much more poorly resolved profiles at present than field MSPs, it is unlikely that a strong interpulse near 180 degrees could be ‘hidden’ within the primary peak.
Monitoring Millisecond Pulsars in Full Polarization
Authors: Xilouris Kiriaki M. , Kramer Michael
Published: July 2016

Over a two year period the polarization properties of the largest sample of millisecond pulsars yet observed have been regularly monitored with the Effelsberg 100-m radiotelescope at λ21cm. A comparison of the observed emission properties with those of the population of long period pulsars is presented here. Most of the sources exhibit wide, often multiple-component profiles, with complex polarization features, not easily interpretable in the context of the well established phenomenological models used to describe the properties of long period pulsars. While both groups share common emission features suggesting similar emission processes, the implied field structures as revealed from polarization information appear substantially different from a dipolar structure. Generally, short period pulsars exhibit a relatively large percentage of circularly polarized emission while at λ21cm they tend to be less polarized than long period pulsars.
Birefringence as a Mechanism for the Broadening and Depolarization of Pulsar Average Profiles
Authors: McKinnon M. M.
Published: July 2016

Shortly after orthogonal modes of polarization were observed in pulsar radio emission (Manchester et al. 1975), a series of theoretical papers (Cocke & Pacholczyk 1976, Melrose & Stoneham 1977, Melrose 1979) were quick to point out that these abrupt, 90 degree transitions in polarization position angle could be explained by a propagation effect. More specifically, the plasma above pulsar polar caps may be birefringent. The orthogonal modes separate because they have different indices of refraction. So, as Allen & Melrose (1982) point out, the plasma is somewhat analogous to a terrestrial birefringent crystal, at least in the way it affects the ray paths of the modes. With very sensitive observations of individual pulse polarization, Stinebring et al. (1984) concluded that orthogonal modes are superposed, meaning they occur simultaneously. This observation is consistent with the birefringence hypothesis. Stinebring et al. also suggested that pulsars depolarize at high radio frequency via the superposed modes. Barnard & Arons (1986) expanded on the earlier theoretical work, and proposed that, in addition to orthogonal modes, birefringence could account for the broadening of pulsar average profiles at low radio frequency and their depolarization at high frequency. The purpose of this paper is to further investigate the suggestions of Stinebring et al. and Barnard & Arons.
Multifrequency Radio Properties of the Crab Pulsar
Authors: Moffett David A. , Hankins Timothy H.
Published: July 2016

During a single Arecibo observation in 1981 of the Crab pulsar, a profile at 4.7 GHz was recorded which appeared to contain additional components and an interpulse (IP) shifted to earlier phase. The experiment was continued at the VLA, taking advantage of its phased array mode to form a synthesized beam, which resolves out the bright Crab Nebula background. Observations were conducted between February 9 and May 27, 1994, at 0.33, 1.4, 4.9, and 8.4 GHz. Additional radio profiles presented here were recorded at Arecibo (0.43, 0.6, and 4.7GHz) and Effelsberg (2.7GHz) by Hankins & Fowler (unpublished).

In Figure 1 we have plotted a summary of normalized profiles from several radio frequencies and infrared. The VLA profiles are time aligned, while the rest are aligned to the main pulse (MP). A new component (labeled LFC) appears 36° ahead of the MP between 0.6 and 4.9 GHz, not coincident with the position of the precursor, and with a spectral index similar to that of the MP. The MP disappears at 8.4 GHz, probably due to spectral effects. The IP appears to undergo a transition in phase and flux, disappearing at 2.7 GHz and reappearing 10° earlier at 4.7 GHz with a radically different spectral index. Two high radio frequency components (labeled HFC1 and HFC2) appear at 4.9 and 8.4 GHz, and possibly at the noise level at 1.4 GHz. They have flatter spectral indices than the MP and IP and their centroid phase changes with respect to the MP – moving to later phase with increasing frequency. The infrared profile exhibits a “bump”, or third component near the same phase as HFC1 and HFC2.
Pulsar radio beams and emission altitudes
Authors: Kijak Jaroslaw , Gil Janusz A.
Published: July 2016

We verify the relationship proposed by Kijak and Gil (1996) for the pulsar radio emission altitudes

(see also Eq.3 in Gil & Krawczyk, 1996), using the pulse-profile Effelsberg raw data at 1.41 GHz. We measured profile pulse-widths at the lowest intensity level corresponding to 0.01% of the maximum intensity (Fig. 1b), using the polarlog-scale technique (Hankins and Fowler, 1986). We calculated opening angles (Fig. 1a) and emission altitudes (Fig. 1c) assuming that:i) pulsar radiation is narrow-band with radius-to-frequency mapping operating in the emission region,ii) pulsar emission is beamed tangentially to the dipolar magnetic field lines,iii) the extreme profile wings originate near or at the last open field lines.
ASCA X-Ray Observations of the Vela Pulsar Jet
Authors: Ögelman Hakki , Markwardt Craig
Published: July 2016

An X-ray jet-like outflow, beginning at the Vela pulsar and extending about seven parsecs along the pulsar spin axis direction has recently been discovered (Markwardt & Ögelman 1995). We present data obtained by the X-ray ASCA satellite which confirms the enhanced X-ray emission at the jet head and discuss the allowable spectral models. The jet parameters are updated according to the combined ROSAT and ASCA results.
Origin of High Velocity Pulsar and Soft Gamma Ray Repeaters
Authors: Hanami Hitoshi
Published: July 2016

We consider a close binary system with separation ≃ 0.2 R⊙which consists of a (C+O) star of mass ≃ 4 M⊙and a neutron star as a progenitor of soft gamma-ray repeater (SGR) and a high velocity pulsar. After the event of the supernova explosion, both new and old neutron stars have high relative velocity of ≃ 1000km s−1to the center of mass of the ejecta. SGR activities can be induced by the episodic accretion of the supernova ejecta onto the old neutron star or the strange high rotating pulsar of the new neutron star. Future observations with fine positional resolution can clarify the position ambiguity between the gamma ray and X-ray sources.
Pulsar/Supernova Remnant Associations
Authors: Kaspi Victoria M.
Published: July 2016

We review proposed pulsar/supernova remnant associations, summarize recent highlights, including searches for young pulsars, searches for remnants, studies of previously proposed associations, and attempts at pulsar/remnant association syntheses. We argue that most proposed associations require additional investigation before they can be considered secure. Existing evidence from secure associations implies pulsars are born with large magnetic fields and short periods, but do not necessarily have particularly large radio luminosities. We argue that the evidence for large space velocities from associations is ambiguous.
The Pulsar Magnetosphere – A Stationary Self-Consistent Solution
Authors: Hofmann Bernhard , Herold Heinz , Ruder Hanns
Published: July 2016

Using fundamental equations of physics we determine with a simple model a globally self-consistent state of a pulsar magnetosphere.
Pulsar Flux Monitoring and Refractive Scintillation
Authors: Stinebring Daniel R. , Smirnova Tatiana V. , Hovis Jennifer , Kempner Joshua C. , Myers Edward B. , Hankins Timothy H. , Kaspi Victoria M. , Nice David J.
Published: July 2016

We have monitored the 610 MHz flux density of 21 pulsars on a daily basis for five years. The flux density time series for these pulsars range from nearly constant for the most distant and heavily scattered pulsars to rapidly varying, saturated time series for more nearby pulsars. The measured stability of the flux density from the most distant pulsars (variations less than 5%) implies that the average radio emission from pulsars, before it has been affected by propagation through the ISM, is constant in strength over five years. The flux variations for 12 of the pulsars are consistent with a Kolmogorov turbulence spectrum over a range of more than three orders of magnitude in scattering strength, with no detectable presence of an inner scale (si≥ 107cm). The flux variations are greater than predicted by this model for five pulsars – including the Crab and Vela – but this group is consistent with a Kolmogorov spectrum and an inner scale of ∼ 1010cm.
Resolving Pulsar Magnetospheres Using Interstellar Scintillation
Authors: Smirnova T. V. , Shishov V. I. , Malofeev V. M.
Published: July 2016

Pulsars are very small objects and to resolve a pulsar magnetosphere you would need an interferometer with a baseline of 14 AU at a frequency 100 MHz. If the angular size of the diffraction pattern at the Earth is less than the angular size of pulsar:θc<θLCthen emission regions separated by alight-cylinder radius will produce scintillations that are independent. The interstellar scintillation method presents a unique oppotunity for measuring the angular size of sources with a resolution up to 10−8arcsec at meter wavelengths.

There were different attempts to resolve pulsar magnetospheres by the scintillation method (Cordes, Weisberg and Boriakoff, 1983, Wolszcan and Cordes, 1987; Smirnova and Shishov, 1989; Smirnova, 1992). Here we present new observations of 4 pulsars: PSR 0834+06, 1133+16, 1237+25 and 1919+21 at a frequency 102 MHz from which we can see evident decorrelation of the pulsar spectrum with increasing space separation between sources in the pulsar magnetosphere.
Kinematic distances for southern pulsars: Gum & Carina
Authors: Koribalski Bärbel , Johnston Simon , Weisberg Joel
Published: July 2016

We have observed 21-cm absorption and emission spectra in the direction of about 20 southern pulsars with the Parkes telescope to derive their kinematic distances and to study the interstellar medium. In each case we thoroughly investigated the environment of each pulsar as well as sources along the line of sight which may contribute to the pulsars’ dispersion measure (DM).

Some of the results, which are published in Koribalski et al. (1995) and Johnston et al. (1996), are included in the compilation of Hi absorption measurements by Joel Weisberg in this volume. In the following we present a detailed discussion on pulsars toward 1) the Gum Nebula and 2) the Carina Arm.
Rotational and Orbital Fluctuations of Eclipsing Binary Pulsar PSR B1744-24A
Authors: Nice David J. , Thorsett Stephen E.
Published: July 2016

Eclipsing binary pulsars systems highlight an important stage in the evolution of isolated millisecond pulsars. In these systems, the pulsar’s companion is losing mass due to Roche lobe overflow and/or a stellar wind induced by intercepted energy from the pulsar flux. Eventual evaporation of the companions could yield isolated millisecond puslars. PSR B1744-24A was the second eclipsing millisecond pulsar to be discovered (Lyneet al. 1990). It is in a 1.8 hr orbit with a ∼ 0.1 M⊙companion. Its eclipses show some variability, and the pulsar is undetectable at about 25% of observing epochs, presumably because it is completely enveloped by the companion’s outflow (Nice & Thorsett 1992).
Non-Stationary Accretion in Her X–1–like Systems
Authors: Geppert U. , Urpin V.
Published: July 2016

Accretion heats the neutron star crust thereby decreasing the electric conductivity in the solid region. This leads to a rapid field decay when the currents supporting the field are concentrated in the solid crust (Geppert & Urpin 1994, Urpin & Geppert 1995). Depending on the duration of the accretion phase and on the total mass accreted the field can be decreased by 3 − 4 orders of magnitude after 106− 107years. This mechanism explains the low magnetic fields of many pulsars entering binary systems.

However, there exist both low–mass (e.g. Her X–1, 4U 1626–67) and high–mass (e.g. Cen X–3, SMC X–1) systems, where the neutron star deserves strong accretion and the magnetic field is still large.
Intermediate-Mass Binary Pulsars: a New Class of Objects?
Authors: Camilo F.
Published: July 2016

Approximately 4/5 of the ∼ 35 millisecond pulsars known in the disk of the Galaxy are in binary systems. The vast majority of these binary pulsars have (presumed) helium white dwarf companions with massesm2< 0.45 M⊙, spin periodsP< 10 ms, and all are in extremely circular orbits (Fig. 1). In a search for millisecond pulsars with the Arecibo radio telescope, we have recently discovered PSR J1022+1001, a 16.45 ms pulsar in a 7.8 d orbit with a companion that is at least 0.73 M⊙, and is more likely as massive as 0.8−1.0M⊙; and PSR J0621+1002, a 28.85 ms pulsar in an 8.3 d orbit with a companion at least 0.45 M⊙, and more likely withm2≈ 0.54 M⊙. One other system, PSR J2145–0750, hasP= 16.05 ms, orbital periodPb= 6.8 d, andm2≈ 0.50 M⊙(see Table 1).
A Super-Eddington Wind Model for GRO J1655–40
Authors: Meier David L.
Published: July 2016

A model for GRO J1655–40 is described in which the hard X/γ-ray behavior, and long delay between the X/γ and radio outbursts, are explained by processes which occur when the accretion rate approaches and exceeds the Eddington limit. The principal feature of the model is a dense, optically thick, super-Eddington wind ejected from the center of the accretion disk. The wind is responsible for determining the luminosity and spectral evolution of the object and for suppressing the formation of a fast, relativistic jet while the accretion rate is above the Eddington limit.

Our model makes use of the “magnetic switch” mechanism we recently discovered with MHD simulations of jet production in magnetized accretion disk coronae. A fast jet can be turned on (or off) by increasing (or decreasing) the Alfvén velocity in the corona relative to a critical value. Examination of models of sub- and super-Eddington disks shows that VA remains below the critical value while the wind is present, but could exceed it when the wind disappears and a hot, optically thin corona forms.
Accretion Disks with Convective Viscosity
Authors: Smak J.
Published: July 2016

Models of vertical structure are calculated for a range of parameters applicable to dwarf novae with two types of viscosity being included: the standard α-disk viscosity and the additional turbulent viscosity in the convective regions. The resulting surface density (∑) υs. effective temperature (Te) relations, compared to those without convective viscosity, show larger separation between the two critical points of the ∑ – Te relation, ∑min and ∑max. This could suggest that with such a modification the dwarf nova outbursts could be reproduced with a single value of α. (Note that in the standard α approach two different α’s are needed on the hot and cool branch of the ∑ – Te relation, with αcool ≈ αhot/4). It turns out, however, that this is not the case. This is due to the fact that additional convective viscosity makes also ∑max smaller than in the pure α case.
Three-Dimensional Simulations of Accretion Disks
Authors: Hawley John F. , Balbus Steven A.
Published: July 2016

The transport of angular momentum is the central issue in accretion disk dynamics. We review recent three-dimensional simulations that investigate possible transport mechanisms. Purely hydrodynamic local instabilities and turbulence are ruled out; global spiral waves remain a possibility. MHD turbulence, arising from a local MHD instability, has been shown effective in transporting angular momentum at dynamically important rates. These results establish the basic picture of accretion disk transport.
A Magnetic Alternative to the Standard Viscous Accretion Disc
Authors: Campbell C.G.
Published: July 2016

A magnetic alternative to the standard viscous accretion disc is presented. The magnetic field is generated and maintained in the disc by a dynamo mechanism. Magnetic stresses dominate in the advection of angular momentum, and only weak turbulence is needed to generate the required field.
Interaction Of A Stellar Magnetic Field With A Turbulent Accretion Disk
Authors: Bardou Anne , Heyvaerts Jean
Published: July 2016

Magnetized objects surrounded by a turbulent and keplerian accretion disk are considered. In such systems, magnetic field lines are embedded into the disk. The magnetic field of the central object is assumed to be dipolar in the absence of the accretion disk. In the presence of a turbulent accretion disk, it is shown that the interaction with the disk stretches magnetic field lines along the disk and that most of the non-magnetospheric magnetic flux is expelled outside the disk.
Disc Accretion Onto Magnetic Stars: Slow Rotator And Propeller
Authors: Li Jianke , Wickramasinghe Dayal T.
Published: July 2016

We study two magnetised accretion – outflow problems: the slow rotator and the propeller. In the former case, we show that the funnel flow does not result in the accretion of a significant amount of matter angular momentum, contrary to what is assumed in the standard Ghosh and Lamb model. Implications of this finding are investigated, particularly in relation to the fastness parameter. We also argue that magnetospheric mass ejection (the magnetospheric streamer model) is a viable mechanism for the ejection of mass and angular momentum from a magnetic star-disc system in the propeller regime.
On the Dramatic Spin-Up/Spin-Down Torque Reversals in BATSE Observations of Accretion Powered Pulsars
Authors: Nelson Robert W. , Vaughan Brian A. , Bildsten Lars , Chakrabarty Deepto , Koh Danny T. , Prince Thomas A. , Finger Mark H. , Wilson Robert B. , Rubin Bradley C.
Published: July 2016

X-ray pulsars are the only accreting magnetic stars where rotation torques induced by accretion are large enough to be measured on short timescales ~ days. They are thus unique laboratories for studying the interaction between an accretion disk and a stellar magnetosphere. We describe 5 years of continuous pulsar timing observations by the BATSE instrument on GRO which paint a strikingly different picture of pulsar spin behavior than understood from the previous 20 years of sparse observations. In particular, we find that more than half of the persistent pulsars we observe undergo dramatic torque reversals, switching suddenly between extended periods of steady spin-up and steady spin-down. Moreover, variations in pulsed flux are anticorrelated with torque in at least one system undergoing secular spin-down, GX1+4. This behavior contradicts standard accretion torque theory (Ghosh and Lamb 1979). A simple – albeit unconventional – hypothesis which naturally explains these observations is that the disks in these systems somehow alternate between epochs of prograde and retrograde rotation.
A Model for WZ Sge with “Standard” Values of α
Authors: Hameury J.M. , Huré J.M. , Lasota J.P.
Published: July 2016

We present a model for the dwarf nova WZ Sge which does not imply an unusually – and unexplained – low value of the viscosity during low states. We propose that the inner parts of the accretion disc are disrupted by either a magnetic field or evaporation, so that the disc is stable (or very close to being stable) in quiescence, as the mass transfer rate is very low, and the disc can sit on the cool, lower branch of the thermal equilibrium curve. Outbursts are triggered by an increase of mass transfer, causing a standard disc instability, and are strongly enhanced by illumination effects. Both the recurrence time, and the characteristics of the light curve in outburst can be accounted for.
Radiation-Driven Warping: The Origin of Warps and Precession in Accretion Disks
Authors: Maloney Philip R. , Begelman Mitchell C.
Published: July 2016

A geometrically thin, optically thick, warped accretion disk with a central source of luminosity is subject to non-axisymmetric forces due to radiation pressure; the resulting torque acts to modify the warp. Initially planar accretion disks are unstable to warping driven by radiation torque, as shown in a local analysis by Pringle (1996) and a global analysis of the stable and unstable modes by Maloney, Begelman, & Pringle (1996). In general, the warp also precesses.

We discuss the nature of this instability, and its possible implications for accretion disks in X-ray binaries and active galactic nuclei. Specifically, we argue that this effect provides a plausible explanation for the misalignment and precession of the accretion disks in X-ray binaries such as SS 433 and Her X–l; the same mechanism explains why the maser disk in NGC 4258 is warped.
On Modelling the Lightcurves of Binary X-ray Sources
Authors: Hessman F.V. , van Teeseling A. , Beuermann K.
Published: July 2016

The lightcurves of non-magnetic X-ray binaries are usually modelled using standard techniques developed for ordinary double stars plus some assumptions about the geometry and temperature distribution of the accretion disk. The analyses of the observed optical lightcurves of systems suggest that the disks must have extremely large rims (H/R ~ 0.3) in order to produce the variable obscuration needed to reproduce the often asymmetric lightcurves. However, even models with large rims have problems explaining the X-ray absorption seen in systems with smaller inclinations. We discuss two phenomena which show that non-standard effects in X-ray binaries can play major roles in the determination of the lightcurves: the “spray” caused by the passage of the accretion stream through the “bow-shock” at the outer rim of the disk; and the effects of soft X-ray illumination of the secondary star.
HST GHRS Observations of the Herbig Ae Star HD104237: First UV Observations of a Hot Disk Wind from a Pre-Main Sequence Star
Authors: Brown Alexander , Djie H.R.E. Tjin A , Blondel P.F.C. , Harper G.M. , Bennett P.D. , Skinner S.L.
Published: July 2016

We have obtained ultraviolet spectra of the Herbig Ae star HD104237 using the Goddard High Resolution Spectrograph (GHRS) on HST. The high temperature emission and absorption lines show remarkable outflow absorption features, which have very similar profiles that are essentially independent of formation temperature. The profiles are not those expected from a spherically-symmetric stellar wind but have optically-thick absorption to −280 km s−1 and a high velocity plateau extending to −375 km s−1. The profile shape is a manifestation of the nonspherical geometry of the flow. The observed UV emission is too strong to be associated with the hot X–ray emitting plasma seen by ASCA and probably is generated by the interaction of the innermost part of an accretion disk with the corotating outermost magnetospheric field. The outflow is almost certainly the inner part of a biconical disk wind.
Do Herbig Ae/Be Stars Have Disks?
Authors: Ray T.P. , Corcoran M.
Published: July 2016

The Herbig Ae/Be stars are optically visible pre-main sequence stars of intermediate mass (M* ≈ 3−8M⊙) and are thought to be the higher mass analogues of the T Tauri stars. While there is no doubt that classical T Tauri stars, i.e. those with EW(Hα) ≳ 10 Å, are surrounded by disks, it remains controversial as to whether this is the case with the equivalent Herbig Ae/Be stars. It has even been questioned whether the powerful winds that are ejected by Herbig Ae/Be stars are driven by accretion. To address these problems we have examined a large sample of these stars with the idea of using their forbidden line emission as an indirect diagnostic for the presence of disks. Striking similarities with the classical T Tauri stars are found. For example we have discovered evidence not only for a strong correlation between near-infrared colours and the equivalent width of the forbidden line emission but also that the forbidden line emission normally arises in a blueshifted outflow component. It has already been shown in the case of the classical T Tauri stars that the correlation of near-infrared colour with forbidden line equivalent width is due to a link between the accretion rate and the outflow rate. The virtually identical relationship seen in the case of the Herbig Ae/Be stars must then also have a similar origin. Our finding that the forbidden line emission in Herbig Ae/Be stars is normally blueshifted shows not only that it arises in an outflow but, as in the classical T Tauri stars, such an asymmetry in the velocity centre of the line must be caused by the obscuring effects of a disk. We find that the correlation seen in the classical T Tauri stars between the mass-loss rate and infrared excess can be extended, when we include the Herbig Ae/Be stars, to cover almost 5 orders of magnitude in stellar luminosity. Our observations therefore broaden the findings of earlier observers for low mass young stars and indicate the presence of circumstellar disks around the majority of Herbig Ae/Be stars with forbidden line emission. A corollary of our results is that the same outflow mechanism must operate in both the classical T Tauri stars and the Herbig Ae/Be stars with forbidden line emission.
HST Observations of the HH 47 and HH 111 Stellar Jets
Authors: Hartigan Patrick
Published: July 2016

The superb spatial resolution made possible by the WFPC2 imager on the Hubble Space Telescope has opened a new era in the study of shocks in stellar jets. This paper summarizes the results of imaging surveys of two of the brightest and best resolved stellar jets, HH 111 and HH 47. The new HST images show that the jets appear quite different in the Ha and [S II] lines; Ha concentrates in distinctive filaments while [S II] tends to be clumpier and more widespread. Filamentary Hα emission should trace the location of the shock fronts if the preshock gas is neutral, because a significant fraction of the incident H gas becomes excited collisionally before becoming ionized in moderate velocity shocks.

Both HH 111 and HH 47 exhibit multiple bow shocks along the channel of the jet, and in some cases we observe the classical double shock structure of a bow shock/Mach disk expected within the working surface of a jet. The jet material is considerably denser than that of the ambient gas. Ejection angles vary a few degrees with time, giving some jets a ‘wiggling’ appearance. However, motion along the jet appears to be radial; there is no convincing evidence for azimuthal motion in the radial velocity data. Multiple bow shocks observed along the jets probably arise from unsteady accretion of a protostellar disk onto the central object.
Magnetized Accretion Disks and the Origin of Bipolar Outflows
Authors: Königl Arieh
Published: July 2016

Centrifugally driven winds from the surfaces of magnetized accretion disks are an attractive mechanism for removing the angular momentum of the accreted matter and of producing bipolar outflows and jets in compact astronomical objects. In this contribution, I first review steady–state disk–wind models that have been constructed for the different density regimes of circumstellar disks and comment on their expected stability. I then consider several nonsteady effects, including disk formation in molecular cloud-core collapse, magnetic flux transport through the disk, and the role of magnetic fields in the FU Orionis outburst phenomenon. I conclude with a discussion of some of the unique observational properties of disk-driven outflows in young stellar objects and in active galactic nuclei. These characteristics are a consequence of the highly stratified density and velocity structures of centrifugally driven outflows, their large momentum discharges (which result in the efficient uplifting of dust from the disk), and, in the case of molecular disks around lowluminosity objects, their comparatively low initial degrees of ionization (which can lead to rapid heating by ambipolar diffusion).
Magnetically-Driven Winds from Protostellar Disks
Authors: Wardle Mark
Published: July 2016

Angular momentum transport in protostellar disks can be achieved by the action of a large scale magnetic field that runs vertically through the disk. The magnetic field centrifugally drives material from the disk surfaces into a wind, initiating a bipolar outflow. One apparent difficulty for this model is that the conductivity of the disk is extremely low in the inner 0.1–10 AU of the disk, where grains are the dominant charge carriers. Near the midplane, charged grains are unable to drift through the neutral gas and there is negligible coupling between the magnetic field and the disk material.

However, the removal of angular momentum and acceleration of a wind by a magnetic field can still take place in the surface layers of the disk where the gas conductivity increases dramatically. Solutions to the multifluid MHD equations for the vertical structure of a disk at a particular radius are presented. Most of the disk material sits in hydrostatic equilibrium and does not interact with the magnetic field running vertically through it. Near the disk surfaces, the coupling between the magnetic field and disk material is sufficient to initiate an outflow from the disk surface.
Inside the Bullets of Orion
Authors: Burton Michael G.
Published: July 2016

This paper discusses how high spatial and spectral resolution observations of bow-shock ‘bullets’ in Orion are challenging our understanding of molecular shock physics.
The Dark Mass Concentration at the Galactic Center
Authors: Melia F.
Published: July 2016

Stellar kinematic studies indicate the presence of a concentrated central mass at just under 2 × 106M⊙, in close agreement with the mass deduced from gas velocities measured with the [Ne II] line. Although this mass is most likely a black hole, it may be dominated by a tightly concentrated cluster of stellar remnants. If Sgr A*, a point radio source coincident with this central mass, is a massive black hole embedded in a region with strong gaseous outflows, as suggested by the observation of He I, Brα and Brγ line emission, it is accreting from its environment via the Bondi-Hoyle process. We discuss the consequences of this activity, including the expected mass and angular momentum accretion rate onto the black hole, and the resulting observable characteristics. The latest infrared images of this region appear to rule out the possibility that this large scale flow settles down into a standard α-disk at small radii. We discuss some possible scenarios that might account for this, including strong advection in the disk or the presence of a massive, fossilized disk. Not all of the gas affected in this way by Sgr A*’s strong gravitational field becomes bound. Some of it is redirected into a focused flow that in turn interacts with other coherent gas structures near the black hole. We suggest that the mini-cavity (to the south-west of Sgr A*) may be formed as a result of this activity, and argue that the characteristics of the mini-cavity lend some observational support for the presence of a concentrated mass near Sgr A*. We show, however, that as far as the mini-cavity is concerned, this concentrated mass need not be in the form of a point mass, but may instead be a highly concentrated cluster of stellar remnants.
HZ Puppis: an Old Nova and Intermediate Polar
Authors: Abbott T. M. C. , Shafter Allen W.
Published: July 2016

We present observations of the old nova HZ Pup (Nova Pup 1963 No. 1) showing it to be an intermediate polar with an exceptionally rich selection of photometric periodicities arising from spin and orbital variations and beating between these two.
Periodical Instabilities in the Blackhole Candidate GX339–4 Accretion Disk
Authors: Durouchoux Philippe
Published: July 2016

GX339-4, a black hole candidate, has been monitored since more than 30 years by X and gamma-ray spectrometers on board a dozen of satellites. One of the main characteristics of this source is its bimodal behaviour (high and low states). These states, apparently driven by accretion of matter from a companion onto a compact object, appear to be periodic, with a 14.5 month repetitivity, and an approximative 4 month duration. We discuss, in this paper, on periodic instabilities in the accretion disk surrounding GX339–4 to explain this bimodal behaviour.
Nonlinear Outcome of Gravitational Instability in Optically Thick Disks
Authors: Gammie Charles F.
Published: July 2016

In the outer parts of disks in active galactic nuclei and around young stellar objects (YSOs) the internal sources of heat may be too weak to prevent gravitational instability. We are thus motivated to examine the nonlinear outcome of gravitational instability in an optically thick disk. We use height-integrated, two-dimensional numerical simulations that include pressure (the gas has a polytropic equation of state), self-gravity, and cooling. The cooling function is calculated using a one-zone model and is characterized by a single dimensionless parameter τcool, which is the ratio of the cooling time to the orbital period. The simulations are done in the context of a local model of the disk (the “shearing sheet”). We also include the possibility of an effective “viscosity” characterized by a dimensionless parameter α.

We find that the gravitational instability in thin, Keplerian disks leads to sustained angular momentum transport that is essentially local in character. Instability drives Q toward 1.7, and provides an angular momentum flux αeff ≃ 0.4/τcool. The disk breaks up when the cooling time is shorter than the dynamical time, which is equivalent to saying that αeff < 1. We conclude that gravitational instability can raise the angular momentum transport rate in the outer parts of AGN and YSO disks (although YSO disks may be too thick for our local approach to be strictly applicable). This can occur over a factor of a few in radius. The gravitationally dominated region is bounded on the inside by that radius where other heating processes (e.g. MHD turbulence driven by the Balbus-Hawley instability) make Q > 1. It is bounded on the outside by that radius where the cooling time is shorter than the dynamical time, or the disk is optically thin so that the equation of state is soft. At larger radius the disk will be clumpy.
Periodic Changes of the Accretion Geometry in the Nearly-Synchronous Polar RX J1940.1–1025
Authors: Geckeler Ralf D. , Staubert Rüdiger
Published: July 2016

RX J1940.1-1025 is a newly discovered magnetic Cataclysmic Variable and one of only three known polars with a slightly non-synchronous (< 3 %) rotation of the white dwarf primary. The accretion geometry between the infalling accretion stream and the magnetic field of the WD thus changes periodically with the beat period of 50.0 d between the orbital and the spin period of the WD. The accretion thus occurs along different field lines, depending on the beat phase.

For the first time we have observed this effect as a periodic shift in the timings of the absorption troughs in the optical and X-ray pulse profiles of RX J1940.1-1025 with phase of the beat period. There is evidence for a secular decrease of the spin period of RX J1940.1-1025 with a synchronization time scale of the order of 102y.
The Intrinsic UV/Soft X-Ray Spectrum of Quasars
Authors: Haardt Francesco , Madau Piero
Published: July 2016

The detection of a Hell absorption trough in the spectra of three high-redshift quasars provides new constraints on the spectral shape of the UV extragalactic background. The relative strengths of the observed flux decrements at the rest-frame wavelengths of 1216 and 304 Å require a relatively soft radiation field at 4 ryd compared to 1 ryd. If the ionizing metagalactic flux is dominated by the integrated light from QSOs, and the Hell reionization of the universe was completed well before z ~ 3, then the UV/soft X-ray spectrum of individual quasars at these epochs must, once the cosmological “filtering” through material along the line of sight is taken into account, satisfy similar constraints on the average. We model the propagation of AGN-like ionizing radiation through the intergalactic medium using CUBA, a numerical code developed in our prior work. We show that, in order to explain the reported Hell absorption, any thermal component responsible for the “soft X-ray excess” observed in the spectra of AGNs at z ≲ 0.3 must, at z ~ 3, have a typical temperature ≳ 80 eV, and a luminosity not exceeding ≈ 20% of that of the “UV bump”.
The Atmospheric Variations of the Peculiar B[e] Star HD 45677 (FS CMa)
Authors: Israelian G. , Friedjung M. , Graham J. , Muratorio G. , Rossi C. , de Winter D.
Published: July 2016

We have studied spectra of the peculiar B[e] star HD 45677. Examination of the Balmer wings enabled us to determine a value of log g = 3.9 indicating a possibly luminosity class V. The weak Heɪ lines togetherwith the Si ɪɪ 4128 and 4130 Å doublet indicate a low rotation velocity in the order of 70 km s−1, which is much lower than the previously claimed value of 200 km s−1 by Swings & Allen (1971). We have examined high-resolution profiles of the strong He I line at 5876 Å and found on one hand that we can explain the variation of the profile by the motions of clouds, some of which accreted. The Balmer lines on the other hand show the presence of an accelerated wind plus absorption by a disk seen edge-on
Southern Hemisphere VLBI Observations of the Expansion of GRO J1655–40
Authors: King E.A. , Jauncey D.L. , Reynolds J.E. , Tzioumis A.K. , McKay D.J. , Kesteven M.J. , Gough R. , Migenes V. , Sinclair M.W. , Tingay S.J. , Preston R.A. , Meier D.L. , Murphy D.W. , Jones D.L. , Lovell J.E.J. , Ellingsen S.P. , McCulloch P.M. , Campbell-Wilson D. , Hunstead R.W. , Quick J. , Smits D.
Published: July 2016

We present high-resolution radio observations of the second Galactic superluminal radio source GRO1655-40, which was detected as an X-ray transient on 1994 July 27. Our radio radio images reveal two components moving away from each other at an angular speed of 65±5 mas/day, corresponding to superluminal motion (υ/c = 1.4 ± 0.4) at the estimated distance of 3–5 kpc. The 12-day delay between the X-ray and radio outbursts suggests that the ejection of material at relativistic speeds occurs during a stable phase of accretion onto a black hole, which follows an unstable phase with a high accretion rate. A complete description and discussion of these observations can be found in Tingay et al 1995 (Nature, 374, pp 141–143).
Magnetically Driven Jets from Accretion Disks: Comparison Between 2.5D Nonsteady Simulations and 1.5D Nonsteady/Steady Solutions
Authors: Kudoh T. , Matsumoto R. , Shibata K.
Published: July 2016

We have performed 1D(1.5D) and 2D(2.5D) nonsteady MHD numerical simulations of astrophysical jets which are magnetically driven from Keplerian disks, in order to clarify the origin and structure of jets ejected from protostars and active galactic nuclei. The initial and boundary conditions are similar to those of 2D(2.5D) nonsteady MHD simulations of Shibata and Uchida (1986) and Matsumoto et al. (1996); there is initially a Keplerian disk with a nonrotating corona outside, both of which are penetrated by vertical magnetic fields. The subsequent interaction between the disk/corona and the vertical fields are studied as an initial value problem. Against the current belief that this kind of simulations show simply a transient jet caused by nonsteady interaction between the disk/corona and the magnetic field, we have found that the jets ejected from the disk in this way have the same properties of the steady magnetically driven jets that were investigated by using ID steady wind solution (Kudoh & Shibata 1995), even if the jets are not exactly in steady state.
Toroidal Fields: a Driving Mechanism for Protostellar Jets
Authors: Liffman Kurt , Siora Anna
Published: July 2016

We propose that a toroidal magnetic field is the main driving component of a protostellar jet. We discuss how the ram pressure of the jet may damp a Parker-like instability and provide a stable environment for a jet flow.
“Red Blazars”: Evidence Against A Synchrotron Origin
Authors: Masci Frank J. , Webster Rachel L.
Published: July 2016

Recently, a substantial population of Blazar-like sources exhibiting sharp near-infrared cutoffs and hence exceedingly reddened optical to near-infrared colours (Bj – K ≿ 6) have been discovered in a complete sample of flat spectrum radio sources (Drinkwater et al. 1996). We argue that such “red” colours cannot be due to a synchrotron radiation mechanism alone.
Radiation driven winds from CV accretion disks
Authors: Proga Daniel , Drew Janet E. , Stone James M.
Published: July 2016

We present some initial results of our numerical, 2D hydrodynamical models of line driven flows from the accretion disk in cataclysmic variables. We assume the disk radiation pressure pushes out the isothermal material from a flat, geometrically thin, Keplerian disk.

We calculate the disk radiation field using the surface brightness of a standard “α disk” (Shakura & Sunyaev 1973). We do not include a bright boundary layer in the calculations. We approximate the total radiative line acceleration, adopting the formalism due to Castor, Abbott, & Klein (1975). We use our generalized 2D version of their force multiplier. The multiplier is still described by two parameters representing the number of lines and the ratio of optically thin to optically thick lines. The main modification of the original CAK force multiplier is in the depth parameter, which is now a function of the gradients of two velocity components instead of the single velocity gradient as in the ID case.

We investigate how the disk structure and mass loss rate depend on the disk and central star luminosity, and boundary conditions such as the disk density.

We find that transonic flows from disks do not relax toward steady states. However, their time averaged properties become constant after some time. Our models show that most of mass loss originates from close to the central star – a few stellar radii. Models without a central star radiation field produce flows more vertical than models in which one is present. However, other global, time averaged properties of flows such as the total wind mass, the wind mass loss rate, and velocity are similar. The ratio between the wind mass loss and disk accretion rate increases rapidly with the accrection rate.
Hydro dynamical Evolution of Circumbinary Accretion Disks
Authors: Różyczka M. , Laughlin G.
Published: July 2016

SPH simulations of circumbinary accretion disks are verified with the help of a grid-based Eulerian code. The phenomenon of pulsed accretion flow through the central gap is confirmed.
Uncovering Flickering in Time-Resolved Spectroscopy for the Nova-like Variable UX Ursa Majoris
Authors: White James C.
Published: July 2016

The flickering phenomenon in cataclysmic variables (CVs) is manifest photometrically as variations in system brightness with amplitudes up to about 1 mag and on timescales from seconds to tens of minutes. Although a pronounced characteristic of CVs, flickering has been studied, in general, only tangentially and in the context of overall CV photometric properties. It is usually uncovered in CV photometry, yet my Doppler tomographic analysis of data collected on the KPNO 2.1-meter telescope in 1982 by Schlegel, Honeycutt, and Kaitchuck (1983) for the nova-like variable UX Ursa Majoris suggests that flickering also exists in this system’s spectroscopy.

Using the integrated continuum flux from the UX UMa observations and Bruch’s (1992) methodology for classifying high- and low-flicker data, I constructed two data subsets corresponding to high- and low-flicker states. I generated Doppler tomograms of these high- and low-flicker states and interpret differences between the tomograms as spectroscopic signatures of flickering in the system.

In UX UMa’s Hβ Doppler tomograms, a small, faint, incomplete ring of emission is visible for both flickering states. Dominating ring emission is strong emission in the (+Vx,+Vy) quadrant. The usual location for Swave emission, in the (−Vx,+Vy) quadrant, is here the region of faintest emission. Differenced Doppler tomograms, produced by subtracting from the tomograms the symmetric ring-emission component, show clear differences between the high- and low-flicker states. Further, these early results suggest Doppler tomography may be a useful technique for studying the secondary stars in CVs imaged in this manner. Enhanced chromospheric activity of the red dwarf companion is clearly visible in the high-flickering state tomogram at (0, Krd) and may, therefore, afford investigators the opportunity to estimate the chromospheric flux and radial velocity of the secondary star.
The VSOP Mission—A New Era for VLBI
Authors: Hirabayashi H.
Published: July 2016

The first VSOP satellite, HALCA, was successfully launched on 12 February 1997, ushering in a new era for VLBI astronomy. This paper will give a brief overview of the mission, satellite and the on-going In-Orbit Checkout of the mission elements.
The Identification of EGRET Sources with Flat-Spectrum Radio Sources
Authors: Mattox J.R.
Published: July 2016

We provide a table of 42 blazars which we expect to be robust identifications of EGRET sources. The table includes the lensed source, PKS 1830–211 which we identify with a previously unidentified EGRET source.