bluuebunny/crossref_metadata_2025_split huggingface dataset:
Testing the Strong Equivalence Principle in strong field regimes
Authors: Wex Norbert 
Published: July 2016

A possible functional dependence of the ratio of ‘gravitational’ massmGand ‘inertial’ massmIon the gravitational self-energyEG,is called aviolation of the Strong Equivalence Principle (SEP).Weakly self-gravitating bodies are found in the solar system where lunarlaser-ranging data restrict the Nordtvedt parameter η to absolute values smaller than 0.001, (Dickey et al. 1994, Müller et al. 1995). To test higher order contributions one needs to consider strongly self-gravitating bodies such as neutron-stars.Small-eccentricity binary-star systems consisting of a neutron star (|EG|/mc2~ 0.15) and a white dwarf (|EG|/mc2~ 10−4) are excellent ‘laboratories’ to test the SEP in a strong-field regime. As shown by Damour and Schäfer (1991) a violation of the SEP would lead to a periodic change in the eccentricity of the orbit of the binary pulsar caused by the galactic acceleration. Thus the observation of old small-eccentricity long-orbital-period neutron-star white-dwarf binary systems put (with a certain confidence level) a limit on the violation of the SEP.
Pulsar Timing Limits on Very Low Frequency Stochastic Gravitational Radiation
Authors: Dewey Rachel J. , Thorsett Stephen E. 
Published: July 2016

AbstractA low-frequency, stochastic gravitational radiation background can be detected through the irregularities it induces in pulsar arrival times. In this poster we re-examine pulsar timing data presented in Kaspi, Taylor and Ryba (1994) [Ap.J.,428, p. 713] and present an optimal statistical framework for using timing data from a single pulsar to constrain the energy density in a gravitational wave background. Observations of PSRB1855+09 yield an upper limit (95% confidence) 1.0 × 10−8or (90% confidence) 4.8 × 10−9of the closure density at frequency 4.4 × 10−9Hz. This result probably rules out cosmological models that use cosmic strings as seeds for galaxy formation. Using combined observations of the orbital decay of four binary pulsars we also derive weaker limits at frequencies as low as 10−12Hz.
Whence the pulses?
Authors: Melrose D.B. 
Published: July 2016

AbstractRadio emission mechanisms for pulsars are reviewed with emphasis on five possible sites for the emission: the pair production front (PPF), two regions in the relativistically outflowing plasma (denoted ROP1 and ROP2) between the PPF and the light cylinder (LC), and two sited near the LC. Several maser emission mechanism are viable for ROP1, where radius-to-frequency mapping applies. Suggested Schott radiation from outside the LC is discussed critically.
Are Giant Pulses Evidence of Self-Organized Criticality?
Authors: Young Matthew D. T. , Kenny Brian G. 
Published: July 2016

The statistical distributions of certain giant pulse (GP) properties appear to be well described by power laws. This suggests that the emission mechanism that produces giant pulses is a scale-invariant one. In turn this may indicate that the source of the GPs is in a state of self-organized criticality (SOC). For a recent discussion of SOC see Sornetteet al. (1995).Prior to this conference, the only pulsars reported to exhibit GPs were the Crab pulsar, PSR B0531+21 (Lundgrenet al. 1995), and the millisecond pulsar PSR B1937+21 (Cognardet al. 1996). However, at the conference it was reported that giantmicropulseshad recently been observed from PSR J0437–4715 (Ables and McConnell, this volume). In all cases the statistical distributions of observed GP heights and/or fluxes are found to be well described by simple power laws. The arguments in this note apply to all these pulsars.
Mosaic structure of the emission region of pulsar PSR 0329+54
Authors: Kuzmin A.D. , Izvekova V.A. 
Published: July 2016

AbstractWe performed the multifrequency time aligned measurements and the component structure analysis of the integrated profile of PSR 0329+54 in frequency range from 0.1 to 10 GHz. The result is that a commonly adopted five-component structure of the integrated profile does not provide a good match to the observed profiles. Only a six-component structure fits observations well. This result calls into question the validity of the two conal and core zones emission model. We suggest that the emission region inside of the cone of the open magnetic field lines represents a mosaic bunch of the discrete outflows of relativistic charges along magnetic field lines, injected by mosaic group of localized sparks in the polar cap. Our suggestion is based on the Rutherman and Sutherland belief that the polar gap discharges through a group of localized sparks, spaced at distances nearly equal to the height of the polar gap.Mode changing may be produced by the change of an activity of some sparks pattern without rearranging the structure of the emission region.
Single pulse profiles and the Lorentz factor of emitting particles in pulsar magnetospheres
Authors: Rathnasree N. 
Published: July 2016

If each significant component in a single pulse from a radio pulsar represents emission from a single site and the intensity at longitudes other than the peak arises from the forward beaming of this emission, the angular distribution of intensity within a component is given by (Zheleznyakov, &amp; Shaposhnikov 1972),Here,, with ν the velocity of the emitting particles at the emission site, α is the spectral index of emission in the rest frame of the emitting particles, and is also the spectral index as seen by the observer, ν is the observed frequency of the radiation.Kναis the intensity in the rest frame of the emitting particles. ϕ0is the angular co-ordinate corresponding to the direction of motion of the emitting particles, and ϕ is the angular co-ordinate at different regions in a single component.
Individual Pulse Polarization of Pulsars at Low Frequencies
Authors: Suleymanova S.A. , Izvekova V.A. , Pugachev V.D. 
Published: July 2016

AbstractThis paper presents the results of the measurements of linear polarization characteristics of individual pulses at frequencies 40, 60 and 103 MHz for 10 strong pulsars. We have measured total intensity, linear polarization percentage and angle along the pulse window and obtained distribution displays for these data.Two orthogonal polarization modes are common features in the radiation of pulsars at low frequency. The energy ratio of these two modes can change significantly between different frequencies. The linear polarisation percentage has a general tendency to increase at low frequencies, but by very different factors for different components of the integrated intensity profile. The relationship between the polarization properties of PSR 0943+10 and its mode changing behaviour was studied. It is shown that the energy ratio and the frequency of occurence of two polarization modes change simultaneously with changes in the integrated intensity profile.
Pulsar Electrodynamics — Pulsars and Puzzlers —
Authors: Shibata Shinpei 
Published: July 2016

AbstractA gedanken experiment presented here provides basic understanding of how the pulsar magnetosphere operates. We discuss current issues about the electric-field acceleration along magnetic field lines and subsequent pair creation, and also about the pulsar wind problem. It is stressed that any local model, such as the inner gap model, the outer gap model and the pulsar wind model, must have free parameters to link it to other part of the magnetosphere.
Wave Propagation in Pulsar Magnetospheres and Interstellar Interferometric Observations
Authors: Gallant Yves A. 
Published: July 2016

Using a refractive scintillation event of PSR 1237+25, Wolszczan &amp; Cordes (1987) inferred a projected displacement of the emission region of order 108cm across the pulse. Gupta (these proceedings) inferred a lower separation limit of a few times 107cm from a similar event for PSR 1133+16. In both cases the projected displacement was also a nonmonotonic function of pulse phase.Neither these large separations nor the nonmonotonic behavior can be explained in a simple model which assumes that the emission originates parallel to the field lines of a magnetic dipole, at a fixed altitude across the open field zone, and propagates in a straight line to the observer. There is considerable circumstantial evidence for dipolar fields from polarization sweep and pulse morphological studies. Time delays due to different emission altitudes could produce asymmetries in pulse profiles and projected displacements, but cannot explain the large separations if the emission originates well within the light cylinder.
Magnetic field amplification in newly-born neutron stars
Authors: Wiebicke H.-J. , Geppert U. 
Published: July 2016

AbstractWe present a scenario of magnetic field (MF) evolution of newly-born neutron stars (NSs). Numerical calculations show that in the hot phase of young NSs the MF can be amplified by thermoelectric effects, starting from a moderately strong seed-field. Therefore, there is no need to assume a 1012G dipole field immediately after the gravitational collapse of the supernova (SN) event. The widely accepted scenario for such a field to be produced by flux conservation during the collapse is critically discussed. Instead, it can be generated by amplification and selection effects in the first 104yrs, and by the subsequent fast ohmic decay of higher multipole components, when the NS cools down.
An AU-Aperture Lens to Resolve the Vela Pulsar’s Radio Emission Region
Authors: Gwinn C.R. , Ojeda M.J. , Britton M.C. , Reynolds J.E. , Jauncey D.L. , King E.A. , Flanagan C.S. , Smits D.P. , Preston R.A. , Jones D.L. 
Published: July 2016

AbstractWe use radio-wave scattering in the Vela supernova remnant, surrounding the Vela pulsar, as an AU-scale lens to study the Vela pulsar’s emission region.
Characterization of Multiple Refractive Scintillation Events in the Directions of Two Millisecond Pulsars
Authors: Cognard I. , Lestrade J.-F. 
Published: July 2016

High-precision timing of the millisecond pulsars PSR B1937+21 and PSR B1821-24 are conducted at 1.4 and 1.7 GHz with the high rate of observations of 10-15 times per month at Nançay. Time Of Arrival (TOA) and pulsar flux density are both measured. The rms of the daily post-fit TOA residuals are at the level of 0.5μs and 3.0μs, respectively. A characterization of refractive scintillation events produced by the Ionized Interstellar Medium (IISM) both in the TOA residuals and flux density variations is discussed.Timing at Nan^ay is conducted with a pre-detection dedispersion system. The analysis of the TOAs was done with our software AnTiOPE solving for the classical pulsar parameters. The flux densities of the pulsars are averaged over ~30 or ~70 minutes. Calibration of the system temperature and efficiency of the telescope is good at the 10% level and diffrative scintillation limits this calibration to a comparable level (~35 scintels for PSR B1937+21 over 30 minutes and 7.5 MHz).
The White Dwarf Companions of Recycled Pulsars
Authors: van Kerkwijk M. H. 
Published: July 2016

AbstractI review what properties of the white-dwarf companions of recycled pulsars can be inferred from optical observations, and discuss how these can help us understand the characteristics and evolution of these binaries. I focus on spectroscopic observations, describing results obtained recently, and looking forward to what may come.
Hubble Space Telescope Observations of Millisecond Pulsar Companions: Constraints on Evolution
Authors: Lundgren S. C. , Foster R. S. , Camilo F. 
Published: July 2016

AbstractIn observations of six binary millisecond pulsars with the Hubble Space Telescope, we have discovered white dwarf companions to PSRs J0034-0534, J1022+1001, J1713+0747, and J2019+2425 and improved photometry on PSRs J1640+2224 and J2145-0750. Three of the white dwarfs are among the coolest and oldest known. We have determined that the masses for the helium companions are consistent with the expectation based on the core mass of a progenitor that filled its Roche lobe. The cooling times for many of the white dwarfs are much less than the characteristic spin-down times, implying that the spin period at the end of the accretion stage was close to the current period. The initial spin periods calculated are used to place limits on the accretion rate at the end of the low-mass X-ray binary phase. The accretion rates are found to be over an order of magnitude less than the Eddington rate.
Tidal Interactions in Pulsar Binaries
Authors: Mardling Rosemary 
Published: July 2016

AbstractThe value of using pulse timing to measure orbital variations in eccentric pulsar binaries which are close enough at periastron to interact tidally is discussed. We briefly review a model for dynamical tidal evolution which shows that chaotic orbital evolution is possible, and list several applications to real systems. The system PSR J0045-7319 is then discussed, and a possible explanation for its decreasing orbital period is suggested.
Advective Disks
Authors: Narayan R. 
Published: July 2016

AbstractRecent work on advection-dominated accretion flows (ADAFs) is reviewed. The article concentrates on an optically thin branch of ADAFs which is present at mass accretion rates below a critical value ~ (10−2– 10−1) the Eddington rate. Models based on this branch have been quite successful at explaining a number of low-luminosity X-ray binaries and galactic nuclei, and some brighter systems. Some progress has also been made toward understanding the various spectral states of accreting black holes. It is argued that ADAFs may provide one of the best techniques for demonstrating the reality of event horizons in black holes.
Relativistic Diskoseismology
Authors: Wagoner Robert V. 
Published: July 2016

AbstractWe will summarize results of relativistic calculations of the eigenfunctions and eigenfrequencies of modes of oscillation trapped within the inner region of thin accretion disks by non-Newtonian gravitational properties of a black hole (or a compact, weakly-magnetized neutron star). The focus will be on the most observable, robust, and best-studied class: the analogue of (internal) gravity modes in stars. The frequencies of the corresponding peaks in the power spectrum of the resulting luminosity modulations depend almost entirely upon only the mass and angular momentum of the black hole. The frequency width also depends upon the viscosity parameter of the disk. Searches for such features are being carried out by the RXTE satellite.
Planetary Formation in Protostellar Disks
Authors: Lin D.N.C. 
Published: July 2016

AbstractRecent discoveries of planets around other stars suggest that planets are ubiquitous and their dynamical properties are diverse. We reviewed the formation mechanism for protoplanets and the post-formation planet-disk tidal interaction which may have led the short-period planets to their present configuration. We suggest that these planets may be the survivors of a populations of similar planets which have plunged into and contaminated the stellar convection zone. In the context of the solar system, the mass of the giant planets and the present distribution of the minor planets may be used to infer the structure and evolution for the primordial solar nebula. The large eccentricity of 70 Vir and HD 114762 may be due to cohesive collisions in planetary systems which become unstable during their long term orbital evolution.
Recent Observations of Flickering in CVs and AGN
Authors: Welsh W. F. , Wood Janet H. , Horne Keith 
Published: July 2016

AbstractFlickering is a phenomenon associated with all known accretion powered processes. Yet despite its energetic importance and universality, our understanding of flickering remains elementary. Only recently has the flickering itself become a topic of serious investigation. This paper briefly addresses two fundamental observational questions: “Where is the flickering coming from?” and “What is the spectrum of the flickering?”.
Modeling Tidal Effects in Accretion Discs
Authors: Godon Patrick 
Published: July 2016

AbstractA two-dimensional time-dependent spectral code is used for the study of tidal effects in accretion discs. A cool disc around a white dwarf (characteristic of CV systems) is modeled under the assumption of a polytropic equation of state and a standard alpha viscosity prescription. For a mass ratio q < 0.1 (considered here) and under the assumption of a reflective inner boundary, tidal effects induce an eccentric (m=l azimuthal) mode in the disc together with an elliptic (m=2 azimuthal) mode in the inner disc.
Breaking the 100 MG Barrier: The First High Field Magnetic CV
Authors: Szkody Paula , Schmidt Gary D. , Smith Paul S. , Silber Andrew , Hoard D.W. , Tovmassian Gaghik , Gänsicke B.T. , de Martino D. 
Published: July 2016

AbstractWe present results from IUE and optical spectra, optical photometry and circular polarimetry during high and low states of the highly luminous soft X-ray cataclysmic variable AR UMa that identifies the primary in this system as a white dwarf with a magnetic field of 230 MG. The high magnetic field likely threads accretion blobs all the way from the secondary to below the surface of the white dwarf, resulting in a lack of polarised cyclotron emission and an extreme soft-X-ray luminosity during the high state.
Discless Accretion in Intermediate Polars?
Authors: Buckley David A.H. 
Published: July 2016

AbstractI review the evidence for disc and discless accretion in the asynchronous magnetic CVs, the intermediate polars (IPs). The presence and relative amplitudes of the spin and synodic (beat) X-ray periods, and related orbital sidebands, are very model dependent, and support disc accretion dominating in all the well-studied IPs. A component of non-disc accretion is sometimes observed, a result of stream overflow penetrating to the magnetosphere, and is responsible for the synodic period. The recently discovered polarized IP, RX J1712.6–2414, is a prime candidate (the first) for purely discless, stream-fed accretion in such a system. While the polarisation varies at the spin period, the X-ray variations occur at the synodic period, a result of the modulation in the mass transfer rate for a discless accretor.
Young Binary Star/Disk Interactions
Authors: Lubow Stephen H. , Artymowicz Pawel 
Published: July 2016

AbstractYoung binary star systems have associated gaseous disks that affect their evolution. Strong tidal forces of a binary give rise to gaps that separate circumstellar (CS) disks from the circumbinary (CB) disk. We discuss two important processes that involve binary/disk interactions. The first is eccentricity evolution of a binary embedded in a disk. The second is accretion of gas across the gap that separates CS and CB disks. These results may also have implications for the recently discovered planets.
Theory and Simulation of Asymmetrically Perturbed Radiatively Cooled Jets
Authors: Hardee P. E. , Stone J. M. , Xu J. 
Published: July 2016

AbstractResults of a spatial stability analysis and of numerical simulations of a “slab” jet in which optically thin radiative cooling is dynamically important are presented. Two different cooling curves are used. Unstable Kelvin-Helmholtz modes are significantly different from the adiabatic limit, and the form of the cooling function strongly affects the results. The numerical simulations are in excellent agreement with the linear stability analysis. In the non-linear regime growth of the surface wave at low frequencies results in sinusoidal oscillation which can disrupt the jet, while non-linear body waves produce low amplitude wiggles within the jet that can result in shocks within the jet. In cooling jets, these shocks can produce dense knots and filaments of cooling gas within the jet, and weak shock “spurs” in the ambient gas. Acceleration of ambient gas can be produced by these “spurs”, or by rapid entrainment if the jet is disrupted. For parameters typical of protostellar jets perturbations with a period of < 100 yrs should excite body waves which produce internal shocks and small amplitude wiggles. The lack of large amplitude wiggles in most observed systems is consistent with the suggestion that jets arise from the inner regions (r < 1 AU) of accretion disks.
Parameters of Disks from VLBI Observations
Authors: Walker R. C. 
Published: July 2016

AbstractVLBI provides the only direct imaging technique currently available that is able to resolve even the outer parts of accretion disks. Recent observations of water masers in NGC 4258 and of free-free absorption of counterjet radiation in NGC 1275 are the best examples of where VLBI has provided important data on the parameters of disks. Other observations are now being made of similar sources. In addition, recent VLBI observations of HI absorption promise to add yet more constraints on the outer disk regions.
Order and Chaos in Accretion Disks of Active Galactic Nuclei
Authors: Chian Abraham C.-L. 
Published: July 2016

AbstractLangmuir turbulence plays an important role in electron heating and generation of plasma emission in accretion disks of active galactic nuclei. The nonlinear dynamical behavior of Langmuir turbulence and its relevance in the interpretation of AGN variability is discussed. In particular, we study nonlinear saturation of the Langmuir stimulated modulational instability, for which the low-frequency mode is a resonant ion-acoustic wave. The nonlinear system of coupled wave equations is shown to undergo transition from order to chaos via the route of quasiperiodicity. The periodic, quasiperiodic and chaotic variabilities in AGN emissions may be the electromagnetic signatures of the ordered and chaotic states of Langmuir turbulence in accretion disks or jets of AGN.