Science.gov

Sample records for pulsars progress problems

  1. Towards solving the pulsar timing sampling problem

    NASA Astrophysics Data System (ADS)

    van Haasteren, Rutger; Ellis, Justin; Vallisneri, Michele; Nanograv Collaboration

    2016-03-01

    Bayesian data analysis of Pulsar Timing Array (PTA) has proved to be a computationally challenging problem, with scaling relations that are super-linear in both the number of pulsars and the number of model parameters. Thus far, our best models cannot be used when analyzing full (international) pulsar timing array datasets in the search for gravitational waves, and shortcuts always need to be made. A promising approach in the literature, based on Hamiltonian sampling techniques, has been shown to be infeasible in realistic datasets due to phase transition behavior of the likelihood. We have introduced a coordinate transformation that mitigates this phase transition behavior, and makes Hamiltonian sampling efficient. This makes a full (stochastic) gravitational-wave search in pulsar timing data feasible with our most up-to-date models. This method scales almost linearly with the number of pulsars. Supported by NASA through Einstein fellowship PF3-140116.

  2. Solution to the Sigma Problem of Pulsar Wind Nebulae

    NASA Astrophysics Data System (ADS)

    Porth, Oliver; Komissarov, Serguei S.; Keppens, Rony

    2014-03-01

    Pulsar wind nebulae (PWN) provide a unique test-bed for the study of highly relativistic processes right at our astronomical doorstep. In this contribution we will show results from the first 3D RMHD simulations of PWN. Of key interest to our study is the long standing "sigma-problem" that challenges MHD models of Pulsars and their nebulae now for 3 decades. Earlier 2D MHD models were very successful in reproducing the morphology of the inner Crab nebula showing a jet, torus, concentric wisps and a variable knot. However, these models are limited to a purely toroidal field geometry which leads to an exaggerated compression of the termination shock and polar jet — in contrast to the observations. In three dimensions, the toroidal field structure is susceptible to current driven instabilities; hence kink instability and magnetic dissipation govern the dynamics of the nebula flow. This leads to a resolution of the sigma-problem once also the pulsar's obliqueness (striped wind) is taken into account. In addition, we present polarized synchrotron maps constructed from the 3D simulations, showing the wealth of morphological features reproduced in 2D is preserved in the 3D case.

  3. Some problems of pulsar physics. [magnetospheric plasma model

    NASA Technical Reports Server (NTRS)

    Arons, J.

    1979-01-01

    The theories of particle acceleration along polar field lines are reviewed, and the total energization of the charge separated plasma is summarized, when pair creation is absent. The application of these theories and plasma supply to pulsars is discussed, with attention given to the total amount of electron-positron plasma created and its momentum distribution. Various aspects of radiation emission and transport are analyzed, based on a polar current flow model with pair creation, and the phenomenon of marching subpulses is considered. The coronation beaming and the relativistically expanding current sheet models for pulsar emission are also outlined, and the paper concludes with a brief discussion of the relation between the theories of polar flow with pair plasma and the problem of the energization of the Crab Nebula.

  4. Pulsars

    NASA Astrophysics Data System (ADS)

    Stappers, Benjamin W.

    2012-04-01

    Pulsars can be considered as the ultimate time-variable source. They show variations on time-scales ranging from nanoseconds to as long as years, and they emit over almost the entire electromagnetic spectrum. The dominant modulation is associated with the rotation period, which can vary from slighty more than a millisecond to upwards of ten seconds (if we include the magnetars). Variations on time-scales shorter than the pulse period are mostly associated with emission processes and are manifested as giant pulses, microstructure and sub-pulses (to name a few). On time-scales of a rotation to a few hundred rotations are other phenomena also associated with the emission, such as nulling, moding, drifting and intermittency. By probing these and slightly longer time-scales we find that pulsars exhibit ``glitches'', which are rapid variations in spin rates. They are believed to be related to the interaction between the superfluid interior of the neutron star and the outer crust. Detailed studies of glitches can reveal much about the properties of the constituents of neutron stars-the only way to probe the physics of material at such extreme densities. Time-scales of about an hour or longer reveal that some pulsars are in binary systems, in particular the most rapidly rotating systems. Discovering and studying those binary systems provides vital clues to the evolution of massive stars, while some of the systems are also the best probes of strong-field gravity theories; the elusive pulsar-black hole binary would be the ultimate system. Pulsars are tools that allow us to probe a range of phenomena and time-scales. It is possible to measure the time of arrival of pulses from some pulsars to better than a few tens of nanoseconds over years, making them some of the most accurate clocks known. Concerning their rotation, deviations from sphericity may cause pulsars to emit gravitational waves which might then be detected by next-generation gravitational-wave detectors. Pulsars

  5. Temporal evolution of isolated pulsars; Age-Tau problem

    NASA Astrophysics Data System (ADS)

    Kutukcu, Pinar; Ankay, Askin

    2014-09-01

    In this work, we examine the evolution of a sample of isolated pulsars connected to Galactic supernova remnants (SNRs) five of which have measured braking indices. For the pulsars in our sample without measured braking index values we have calculated the estimated braking indices adopting the supernova remnant ages as the real ages of pulsar-SNR pairs assuming short initial spin periods (10-30 ms). Some of these pulsars exhibit at least one order of magnitude differences between the characteristic pulsar ages and the ages of the SNRs they are physically connected to. We adopt an exponential B-decay model, which is the decrease in the surface dipole magnetic field component perpendicular to the spin axis, in order to explain the evolutions of such pulsars on the spin period versus the spin period change diagram. The decay can be either due to a decrease in the angle between the spin axis and the magnetic axis and/or due to a decay in the surface dipole magnetic field itself. Based on a previous work by Ankay et al. on the X-ray pulsar 1E1207-5209 we show that there are some other young isolated pulsars which experience B-decay as the predominant effect throughout their observational lifetimes. As compared to ordinary radio pulsars the magneto-dipole radiation torques are not so effective for such pulsars and the characteristic decay times are significantly shorter (about three orders of magnitude). Assuming simple exponential evolutionary tracks we give possible physical interpretations for this new class of neutron stars by examining the observational data of each pulsar-SNR pair.

  6. Recent Progress in Studies of Pulsar Wind Nebulae

    NASA Astrophysics Data System (ADS)

    Slane, Patrick

    2008-01-01

    The synchrotron-emitting nebulae formed by energetic winds from young pulsars provide information on a wide range phenomena that contribute to their structure. High resolution X-ray observations reveal jets and toroidal structures in many systems, along with knot-like structures whose emission is observed to be time-variable. Large-scale filaments seen in optical and radio images mark instability regions where the expanding nebulae interact with the surrounding ejecta, and spectral studies reveal the presence of these ejecta in the form of thermal X-ray emission. Infrared studies probe the frequency region where evolutionary and magnetic field effects conspire to change the broadband synchrotron spectrum dramatically, and studies of the innermost regions of the nebulae provide constraints on the spectra of particles entering the nebula. At the highest energies, TeV gamma-ray observations provide a probe of the spectral region that, for low magnetic fields, corresponds to particles with energies just below the X-ray-emitting regime. Here I summarize the structure of pulsar wind nebulae and review several new observations that have helped drive a recent resurgence in theoretical modeling of these systems.

  7. The Pulsar Search Collaboratory: Involving High School Students in Astronomical Research -- A Progress Report

    NASA Astrophysics Data System (ADS)

    Rosen, Rachel; Heatherly, S.; McLauglin, M.; Lorimer, D.

    2010-01-01

    The National Science Foundation funded "Pulsar Search Collaboratory” project is a collaboration between the National Radio Astronomy Observatory (NRAO) in Green Bank, WV and West Virginia University aimed at provoking interest in Science-Technology-Engineering-Math (STEM) careers and increasing scientific and information technology literacy among high-school students within the state and region. Over the initial three-year phase of this program, 60 high-school teachers at schools throughout region and over 300 students will be involved in the search for new pulsars and transient objects by analyzing over 30 TB of data collected by the Green Bank Telescope in 2007. Although training is provided to teachers and student leaders via a summer workshop, additional students may join the program, learning from their peers how to conduct the data analysis. We are now in the second year of the PSC and we present a progress report from the first year of the PSC. We will summarize our approaches to implementing this challenging project, including the use of online tools to communicate with and sustain interest among the student teams, and the development of a unique graphical database through which students access and analyze pulsar plots. We will present the student results including one astronomical discovery as well as statistics on the plots that students have analyzed, including distribution among schools, number of known pulsars found, and RFI detection. Finally we will present evaluation results and lessons learned from the first year of the PSC. These include results from pre/post testing of teachers and students that show changes in student interest in STEM careers resulting from the PSC, and statistics on student participation.

  8. New Pulsar Theory

    NASA Astrophysics Data System (ADS)

    Kebede, Legesse

    2015-08-01

    Standard pulsar theory is based on fields that are conserved from progenitor stars. This has limited the scope of pulsar astronomy to a kind of study very much confined to a limited type of pulsars, so called field pulsars. The large majority of pulsars are technically eliminated from statistical studies because they are either too massive, or are of very high magnetic field with no mechanism yet known which forces them to decay to very low frequency rotators in a matter of a few thousands of years. This is one distinct property of these highly magnetized pulsars. The current presentation focuses on a new source for the generation of pulsar fields namely spinning separated surface charges and it shows that pulsar fields are strictly mass dependent. Massive neutron stars are strongly magnetized ( ≥ 1018 G) and less massive ones are weakly magnetized (1011 - 1013 G). This work therefore dismisses the current belief that there have to be two classes of pulsars (field pulsars and anomalous pulsars). It leads to a decay law that provides results that are consistent with observations from these two so called distinct classes of pulsars. This work also suggests that pulsar fields should be infinitely multi-polar which helps to successfully addresses the longtime issues of pulse shape and promises that the current problem of pulsar radiation could be solvable..

  9. Grassroots Excellence: Problems and Progress.

    ERIC Educational Resources Information Center

    Hansen, Kenneth H.

    The educational "excellence" movement is hindered by inconsistencies between goals and action and by difficulties in translating national and state goals into local policy; nonetheless, progress has occurred. Examples of "voodoo excellence," in which proposed policies will likely work against their stated objectives, are widespread. While…

  10. Radio Pulsars

    NASA Astrophysics Data System (ADS)

    Beskin, V. S.; Chernov, S. V.; Gwinn, C. R.; Tchekhovskoy, A. A.

    2015-10-01

    Almost 50 years after radio pulsars were discovered in 1967, our understanding of these objects remains incomplete. On the one hand, within a few years it became clear that neutron star rotation gives rise to the extremely stable sequence of radio pulses, that the kinetic energy of rotation provides the reservoir of energy, and that electromagnetic fields are the braking mechanism. On the other hand, no consensus regarding the mechanism of coherent radio emission or the conversion of electromagnetic energy to particle energy yet exists. In this review, we report on three aspects of pulsar structure that have seen recent progress: the self-consistent theory of the magnetosphere of an oblique magnetic rotator; the location, geometry, and optics of radio emission; and evolution of the angle between spin and magnetic axes. These allow us to take the next step in understanding the physical nature of the pulsar activity.

  11. Hurricane Prediction: Progress and Problem Areas

    ERIC Educational Resources Information Center

    Simpson, R. H.

    1973-01-01

    Describes progress made in recent decades in predicting the track and landfall of hurricanes. Examines the problems of detecting, tracking, and describing tropical cyclones, and the difficulties which continue to complicate the matter of warning and evacuating coastal residents. (JR)

  12. Hepatitis C: progress and problems.

    PubMed Central

    Cuthbert, J A

    1994-01-01

    The hepatitis C virus (HCV), a single-stranded RNA virus, is the major cause of posttransfusion hepatitis. HCV isolates differ in nucleotide and amino acid sequences. Nucleotide changes are concentrated in hypervariable regions and may be related to immune selection. In most immunocompetent persons, HCV infection is diagnosed serologically, using antigens from conserved regions. Amplification of RNA may be necessary to detect infection in immunosuppressed patients. Transmission by known parenteral routes is frequent; other means of spread are less common and may represent inapparent, percutaneous dissemination. Infection can lead to classical acute hepatitis, but most infected persons have no history of acute disease. Once infected, most individuals apparently remain carriers of the virus, with varying degrees of hepatocyte damage and fibrosis ensuing. Chronic hepatitis may lead to cirrhosis and hepatocellular carcinoma. However, disease progression varies widely, from less than 2 years to cirrhosis in some patients to more than 30 years with only chronic hepatitis in others. Determinants important in deciding outcome are unknown. Alpha interferon, which results in sustained remission in selected patients, is the only available therapy. Long-term benefits from such therapy have not been demonstrated. Prevention of HCV infection by vaccination is likely to be challenging if ongoing viral mutation results in escape from neutralization and clearance. PMID:7834603

  13. SPINN: a straightforward machine learning solution to the pulsar candidate selection problem

    NASA Astrophysics Data System (ADS)

    Morello, V.; Barr, E. D.; Bailes, M.; Flynn, C. M.; Keane, E. F.; van Straten, W.

    2014-09-01

    We describe SPINN (Straightforward Pulsar Identification using Neural Networks), a high-performance machine learning solution developed to process increasingly large data outputs from pulsar surveys. SPINN has been cross-validated on candidates from the southern High Time Resolution Universe (HTRU) survey and shown to identify every known pulsar found in the survey data while maintaining a false positive rate of 0.64 per cent. Furthermore, it ranks 99 per cent of pulsars among the top 0.11 per cent of candidates, and 95 per cent among the top 0.01 per cent. In conjunction with the PEASOUP pipeline, it has already discovered four new pulsars in a re-processing of the intermediate Galactic latitude area of HTRU, three of which have spin periods shorter than 5 ms. SPINN's ability to reduce the amount of candidates to visually inspect by up to four orders of magnitude makes it a very promising tool for future large-scale pulsar surveys. In an effort to provide a common testing ground for pulsar candidate selection tools and stimulate interest in their development, we also make publicly available the set of candidates on which SPINN was cross-validated.

  14. Post-Glitch Relaxation of Pulsar Angular Velocity in the Context of an Inverse Problem

    NASA Astrophysics Data System (ADS)

    Hayrapetyan, M. V.; Baghdasaryan, D.

    2015-06-01

    The motion of the neutron-proton vortex system in neutron stars is examined taking pinning and depinning of the vortices into account. The relaxation solution of the equations for the dynamics of pulsar rotation after glitches is compared with observational data on the Vela pulsar. It is shown that the angular rotation relaxation parameters are related both to the appearance of a "density wave" of neutron vortices during a glitch and to features of the motion of the vortices between successive glitches.

  15. Women and Education: Progress and Problems.

    ERIC Educational Resources Information Center

    Sutherland, Margaret B.

    1991-01-01

    Discusses the status of women's education throughout the world. Describes an increased access to education, progress through legislation, and women's studies. Emphasizes the concentration of women in education in the lower grades and teaching roles rather than in higher education or top administrative levels. Addresses problems such as sex role,…

  16. Teacher stress research: problems and progress.

    PubMed

    Pithers, R T

    1995-12-01

    There is a reasonably large body of published research evidence available which indicates that teaching is a 'highly' or 'extremely highly' stressful occupation for up to one-third of its professionals. Generalisations such as this one, however, are wrought with problems. These problems, for instance, range from confusion about the definition of stress through to how it is to be measured. They include methodological problems inherent in some of the research used to examine the area of teacher stress and as well include, for example, confusion about the effect of mediating variables in the production of stress and strain. This paper examines some of the more important pervasive research problems in current research on teacher stress and makes some suggestions for research progress. PMID:8580045

  17. The Amazing Pulsar Machine

    NASA Astrophysics Data System (ADS)

    Harding, Alice K.; Large Area Telescope, Fermi

    2014-01-01

    How rotation-powered pulsars accelerate particles to PeV energies and radiate pulsed emission from radio to gamma-ray wavelengths has remained a mystery for over 40 years. But in the last few years, the Fermi Large Area Telescope has revolutionized the study of pulsars and allowed us to peer deeper into the inner workings of this incredibly efficient natural accelerator. Thanks to Fermi discoveries, we now know that the high-energy emission is radiated in the outer magnetosphere, near the light cylinder, that millisecond pulsars are extremely efficient at emitting gamma-ray pulses and that the Crab nebula undergoes dramatic flaring that challenges particle acceleration theory. I will review how these discoveries, together with recent progress in global simulation of pulsar magnetospheres, are changing our models of pulsar particle acceleration, cascade pair production and high-energy emission.

  18. Dark matter-induced collapse of neutron stars: a possible link between fast radio bursts and the missing pulsar problem

    NASA Astrophysics Data System (ADS)

    Fuller, Jim; Ott, Christian D.

    2015-06-01

    Fast radio bursts (FRBs) are an emerging class of short and bright radio transients whose sources remain enigmatic. Within the Galactic Centre, the non-detection of pulsars within the inner ˜10 pc has created a missing pulsar problem that has intensified with time. With all reserve, we advance the notion that the two problems could be linked by a common solution: the collapse of neutron stars (NS) due to capture and sedimentation of dark matter (DM) within their cores. Bramante & Linden showed that certain DM properties allow for rapid NS collapse within the high DM density environments near galactic centres while permitting NS survival elsewhere. Each DM-induced collapse could generate an FRB as the NS magnetosphere is suddenly expelled. This scenario could explain several features of FRBs: their short time scales, large energies, locally produced scattering tails, and high event rates. We predict that FRBs are localized to galactic centres, and that our own galactic centre harbours a large population of NS-mass (M ˜ 1.4 M⊙) black holes. The DM-induced collapse scenario is intrinsically unlikely because it can only occur in a small region of allowable DM parameter space. However, if observed to occur, it would place tight constraints on DM properties.

  19. Pulsar Animation

    NASA Video Gallery

    Pulsars are thought to emit relatively narrow radio beams, shown as green in this animation. If these beams don't sweep toward Earth, astronomers cannot detect the radio signals. Pulsar gamma-ray e...

  20. Microstructure-determined pulsar dispersion measures and the problem of profile alignment

    SciTech Connect

    Hankins, T.H.; Izvekova, V.A.; Malofeev, V.M.; Shitov, I.P.; Rankin, J.M. National Radio Astronomy Observatory, Socorro AN SSSR, Fizicheskii Institut, Moscow Vermont, University, Burlington )

    1991-05-01

    Time-aligned profile measurements for two pulsars, combining data from the Arecibo, Puerto Rico, and Pushchino, USSR, observatories over a seven-octave frequency interval between 25 and 5000 MHZ are analyzed along with several new microstructure dispersion values. DMA(A) values of 2.9701 + or {minus} 0.0003, and 4.8470 + or {minus} 0.0003 pc/cu cm for PSR 0950+08 and 1113 + 16, respectively are obtained, with small departures from alignment that appear traceable to changes in a profile shape with frequency. These subtle changes in the profile form are noticeable only by virtue of the high time resolution and broad frequency coverage. It is noted that small low-frequency delays result when the sets of profiles are aligned optimally according to the best available microstructure dispersion values. 19 refs.

  1. Progress and problems in muscle glycogenoses.

    PubMed

    DiMauro, S; Spiegel, R

    2011-10-01

    In this selective review, we consider a number of unsolved questions regarding the glycogen storage diseases (GSD). Thus, the pathogenesis of Pompe disease (GSD II) is not simply explained by excessive intralysosomal glycogen storage and may relate to a more general dysfunction of autophagy. It is not clear why debrancher deficiency (GSD III) causes fixed myopathy rather than exercise intolerance, unless this is due to the frequent accompanying neuropathy. The infantile neuromuscular presentation of branching enzyme deficiency (GSD IV) is underdiagnosed and is finally getting the attention it deserves. On the other hand, the late-onset variant of GSD IV (adult polyglucosan body disease APBD) is one of several polyglucosan disorders (including Lafora disease) due to different etiologies. We still do not understand the clinical heterogeneity of McArdle disease (GSD V) or the molecular basis of the rare fatal infantile form. Similarly, the multisystemic infantile presentation of phosphofructokinase deficiency (GSD VII) is a conundrum. We observed an interesting association between phosphoglycerate kinase deficiency (GSD IX) and juvenile Parkinsonism, which is probably causal rather than casual. Also unexplained is the frequent and apparently specific association of phosphoglycerate mutase deficiency (GSD X) and tubular aggregates. By paying more attention to problems than to progress, we aimed to look to the future rather than to the past. PMID:22106711

  2. Constraining the solution to the last parsec problem with pulsar timing

    NASA Astrophysics Data System (ADS)

    Sampson, Laura; Cornish, Neil J.; McWilliams, Sean T.

    2015-04-01

    The detection of a stochastic gravitational-wave signal from the superposition of many inspiraling supermassive black holes with pulsar timing arrays (PTAs) is likely to occur within the next decade. With this detection will come the opportunity to learn about the processes that drive black-hole-binary systems toward merger through their effects on the gravitational-wave spectrum. We use Bayesian methods to investigate the extent to which effects other than gravitational-wave emission can be distinguished using PTA observations. We show that, even in the absence of a detection, it is possible to place interesting constraints on these dynamical effects for conservative predictions of the population of tightly bound supermassive-black-hole binaries. For instance, if we assume a relatively weak signal consistent with a low number of bound binaries and a low black-hole-mass to galaxy-mass correlation, we still find that a nondetection by a simulated array, with a sensitivity that should be reached in practice within a few years, disfavors gravitational-wave-dominated evolution with an odds ratio of ˜30 ∶1 . Such a finding would suggest either that all existing astrophysical models for the population of tightly bound binaries are overly optimistic, or else that some dynamical effect other than gravitational-wave emission is actually dominating binary evolution even at the relatively high frequencies/small orbital separations probed by PTAs.

  3. Understanding pulsar magnetospheres with the SKA

    NASA Astrophysics Data System (ADS)

    Karastergiou, A.; Johnston, S.; Karastergiou, A.; Johnston, S.; Andersson, N.; Breton, R.; Brook, P.; Gwinn, C.; Lewandowska, N.; Keane, E.; Kramer, M.; Macquart, J. P.; Serylak, M.; Shannon, R.; Stappers, B.; van Leeuwen, J.; Verbiest, J.; Weltevrede, P.; Wright, G.

    The SKA will discover tens of thousands of pulsars and provide unprecedented data quality on these, as well as the currently known population, due to its unrivalled sensitivity. Here, we outline the state of the art of our understanding of magnetospheric radio emission from pulsars and how we will use the SKA to solve the open problems in pulsar magnetospheric physics.

  4. Theoretical problems in accelerator physics. Progress report

    SciTech Connect

    Not Available

    1994-08-01

    This is the second progress report submitted under the author`s current grant and covers progress made since the submission of the first progress report in August 1993. During this period the author has continued to spend approximately one half of his time at SLAC and most of the projects reported here were carried out in collaboration with individuals and groups at SLAC. Except where otherwise noted, reference numbers in the text refer to the attached list of current contract publications. Copies of the publications, numbered in agreement with the publication list, are included with this report.

  5. PREDICTING RANGES FOR PULSARS' BRAKING INDICES

    SciTech Connect

    Magalhaes, Nadja S.; Miranda, Thaysa A.; Frajuca, Carlos

    2012-08-10

    The theoretical determination of braking indices of pulsars is still an open problem. In this paper we report results of a study concerning such determination based on a modification of the canonical model, which admits that pulsars are rotating magnetic dipoles, and on data from the seven pulsars with known braking indices. In order to test the modified model, we predict ranges for the braking indices of other pulsars.

  6. Progress with simple binary alloy solidification problems

    SciTech Connect

    Wilson, D.G.; Solomon, A.D.; Alexiades, V.

    1981-01-01

    We give a preliminary report of our studies on binary alloy solidification. In what follows we state the mathematical problem, which we assume represents the solidification of a simple binary alloy; we give a very brief introduction to two component phase diagrams, whose relations we assume hold at the solidification front; we describe our phlogiston formulation of the problem, which is derived by analogy with the enthalpy method for simpler problems; we describe the finite difference scheme, with which we computer the various constituents of our phlogiston formulation; and finally we relate our computational experience with the model so far.

  7. First-Principles Simulations of Pulsar Magnetospheres

    NASA Astrophysics Data System (ADS)

    Spitkovsky, Anatoly

    Pulsars are rotating magnetized neutron stars that produce broadband, pulsed emission. Observations with Fermi Gamma-ray Space Telescope have uncovered more than 100 gamma-ray emitting pulsars, dramatically expanding the number of such sources known, and producing unprecedented data on light curves and spectra in the gamma-ray band. The magnetospheric processes that lead to this emission are very interesting and currently not understood in detail. The main difficulty is the absence of a self-consistent model of the pulsar magnetosphere that can predict the global shape of the magnetic field and the state of the plasma throughout the magnetosphere. The standard picture envisions the magnetosphere as filled with plasma due to space-charge-limited flow of charges from the surface of the star. These charges are accelerated by strong electric fields induced by rapid stellar rotation. As charges are curved while traveling along the magnetic fields, they emit curvature radiation that can pair-produce and fill the magnetosphere with pair plasma. The currents and charges in this plasma affect magnetic field structure and particle acceleration. Until recently, no self-consistent solutions of the pulsar electrodynamics that accounted for plasma supply and production existed. Considerable progress on the global magnetospheric structure was made under assumptions about the plasma supply in the force-free and magnetohydrodynamic limits, which assume abundant plasma throughout the magnetosphere. These solutions allowed to calculate the global structure of oblique rotators and their spin-down power at the expense of losing information about particle density and acceleration, and making it difficult to compute emission spectra. Recently, the development of multidimensional kinetic simulations has brought the goal of self-consistently calculating plasma supply and magnetospheric shape of pulsars closer to reality. In this proposal, we plan to perform first three-dimensional kinetic

  8. Gamma Ray Pulsars: Observations

    NASA Technical Reports Server (NTRS)

    Thompson, David J.; White, Nicholas E. (Technical Monitor)

    2000-01-01

    High-energy gamma rays are a valuable tool for studying particle acceleration and radiation in the magnetospheres of energetic pulsars. The six or more pulsars seen by CGRO/EGRET show that: the light curves usually have double-peak structures (suggesting a broad cone of emission); gamma rays are frequently the dominant component of the radiated power; and all the spectra show evidence of a high-energy turnover. Unless a new pulsed component appears at higher energies, progress in gamma-ray pulsar studies will be greatest in the 1-20 GeV range. Ground-based telescopes whose energy ranges extend downward toward 10 GeV should make important measurements of the spectral cutoffs. The Gamma-ray Large Area Space Telescope (GLAST), now in planning for a launch in 2005, will provide a major advance in sensitivity, energy range, and sky coverage.

  9. Progressive wave expansions and open boundary problems

    NASA Technical Reports Server (NTRS)

    Hagstrom, T.; Hariharan, S. I.

    1995-01-01

    In this paper we construct progressive wave expansions and asymptotic boundary conditions for wave-like equations in exterior domains, including applications to electromagnetics, compressible flows and aero-acoustics. The development of the conditions will be discussed in two parts. The first part will include derivations of asymptotic conditions based on the well-known progressive wave expansions for the two-dimensional wave equations. A key feature in the derivations is that the resulting family of boundary conditions involves a single derivative in the direction normal to the open boundary. These conditions are easy to implement and an application in electromagnetics will be presented. The second part of the paper will discuss the theory for hyperbolic systems in two dimensions. Here, the focus will be to obtain the expansions in a general way and to use them to derive a class of boundary conditions that involve only time derivatives or time and tangential derivatives. Maxwell's equations and the compressible Euler equations are used as examples. Simulations with the linearized Euler equations are presented to validate the theory.

  10. Viking heat sterilization - Progress and problems

    NASA Technical Reports Server (NTRS)

    Daspit, L. P.; Cortright, E. M.; Stern, J. A.

    1974-01-01

    The Viking Mars landers to be launched in 1975 will carry experiments in biology, planetology, and atmospheric physics. A terminal dry-heat sterilization process using an inert gas was chosen to meet planetary quarantine requirements and preclude contamination of the biology experiment by terrestrial organisms. Deep sterilization is performed at the component level and terminal surface sterilization at the system level. Solutions to certain component problems relating to sterilization are discussed, involving the gyroscope, tape recorder, battery, electronic circuitry, and outgassing. Heat treatment placed special requirements on electronic packaging, including fastener preload monitoring and solder joints. Chemical and physical testing of nonmetallic materials was performed to establish data on their behavior in heat-treatment and vacuum environments. A Thermal Effects Test Model and a Proof Test Capsule were used. It is concluded that a space vehicle can be designed and fabricated to withstand heat sterilization requirements.

  11. Recycled pulsars

    NASA Astrophysics Data System (ADS)

    Jacoby, Bryan Anthony

    2005-11-01

    In a survey of ~4,150 square degrees, we discovered 26 previously unknown pulsars, including 7 "recycled" millisecond or binary pulsars. The most significant discovery of this survey is PSR J1909-3744, a 2.95 ms pulsar in an extremely circular 1.5 d orbit with a low-mass white dwarf companion. Though this system is a fairly typical low-mass binary pulsar (LMBP) system, it has several exceptional qualities: an extremely narrow pulse profile and stable rotation have enabled the most precise long-term timing ever reported, and a nearly edge-on orbit gives rise to a strong Shapiro delay which has allowed the most precise measurement of the mass of a millisecond pulsar: m p = (1.438 +/- 0.024) [Special characters omitted.] . Our accurate parallax distance measurement, d p = ([Special characters omitted.] ) kpc, combined with the mass of the optically-detected companion, m c = (0.2038 +/- 0.022) [Special characters omitted.] , will provide an important calibration for white dwarf models relevant to other LMBP companions. We have detected optical counterparts for two intermediate mass binary pulsar (IMBP) systems; taken together with optical detections and non-detections of several similar systems, our results indicate that the characteristic age t = c P /2 P consistently overestimates the time since the end of mass accretion in these recycled systems. We have measured orbital decay in the double neutron star system PSR B2127+11C in the globular cluster M15. This has allowed an improved measurement of the mass of the pulsar, m p = (1.3584 +/- 0.0097) [Special characters omitted.] , and companion, m c = (1.3544 +/- 0.0097) [Special characters omitted.] , as well as a test of general relativity at the 3% level. We find that the proper motions of this pulsar as well as PSR B2127+11A and PSR B2127+11B are consistent with each other and with one published measurement of the cluster proper motion. We have discovered three binary millisecond pulsars in the globular cluster M62

  12. The Parkes Pulsar Timing Array

    NASA Astrophysics Data System (ADS)

    Manchester, Richard N.

    2015-08-01

    The Parkes Pulsar Timing Array (PPTA) project uses the Parkes 64-m radio telescope to observe 22 millisecond pulsars in three bands: 40cm (band centre 732 MHz), 20cm (1369 MHz) and 10cm (3100 MHz). Coherent de-dispersion systems are used for the 40cm and 20cm bands and digital polyphase filterbanks are used for the 20cm and 10cm bands. Observations are made at intervals of two to three weeks and observations times for each pulsar in each band are typically one hour. Regular PPTA observations commenced in early 2005 but earlier timing data, primarily in the 20cm band, exist for many of the pulsars back to 1994. Pipeline processing scripts are based on PSRCHIVE routines and take into account instrumental offsets. Timing analyses include modelling of dispersion variations and red and white noise in the data. The primary scientific goal of the PPTA project is the detection of gravitational waves, either a stochastic background from supermassive black-hole binary systems in distant galaxies or from individual binary systems. The PPTA data sets have many other applications including establishment of a pulsar-based timescale, improvement of solar-system ephemerides and studies of the individual pulsars. PPTA data sets have been made available to the International Pulsar Timing Array consortium and analysis of the combined data sets is progressing. Recent developments, both instrumental and science-related, will be described.

  13. Rapid convergence of airfoil design problems using progressive optimization

    NASA Astrophysics Data System (ADS)

    Dadone, A.; Grossman, B.

    An efficient formulation for the robust design optimization of compressible fluid flow problems is presented. The methodology has three essential ingredients: a highly accurate flow solver, robust and efficient design sensitivities from a discrete adjoint formulation based on a dissipative flow solver and progressive optimization, whereby a sequence of operations, containing a partially converged flow solution, followed by an adjoint solution followed by an optimization step is performed. Furthermore, the progressive optimization involves the use of progressively finer grids. The methodology is shown to be accurate, robust and highly efficient, with a converged design optimization produced in no more than the amount of computational work to perform from one to three flow analyses.

  14. Progress on PRONGHORN Application to NGNP Related Problems

    SciTech Connect

    Dana A. Knoll

    2009-08-01

    We are developing a multiphysics simulation tool for Very High-Temperature gascooled Reactors (VHTR). The simulation tool, PRONGHORN, takes advantages of the Multiphysics Object-Oriented Simulation library, and is capable of solving multidimensional thermal-fluid and neutronics problems implicitly in parallel. Expensive Jacobian matrix formation is alleviated by the Jacobian-free Newton-Krylov method, and physics-based preconditioning is applied to improve the convergence. The initial development of PRONGHORN has been focused on the pebble bed corec concept. However, extensions required to simulate prismatic cores are underway. In this progress report we highlight progress on application of PRONGHORN to PBMR400 benchmark problems, extension and application of PRONGHORN to prismatic core reactors, and progress on simulations of 3-D transients.

  15. Pulsars Magnetospheres

    NASA Technical Reports Server (NTRS)

    Timokhin, Andrey

    2012-01-01

    Current density determines the plasma flow regime. Cascades are non-stationary. ALWAYS. All flow regimes look different: multiple components (?) Return current regions should have particle accelerating zones in the outer magnetosphere: y-ray pulsars (?) Plasma oscillations in discharges: direct radio emission (?)

  16. Higgs portals to pulsar collapse

    NASA Astrophysics Data System (ADS)

    Bramante, Joseph; Elahi, Fatemeh

    2015-06-01

    Pulsars apparently missing from the Galactic center could have been destroyed by asymmetric fermionic dark matter (mX=1 - 100 GeV ) coupled to a light scalar (mϕ=5 - 20 MeV ), which mixes with the Higgs boson. We point out that this pulsar-collapsing dark sector can resolve the core-cusp problem and will either be excluded or discovered by upcoming direct detection experiments. Another implication is a maximum pulsar age curve that increases with distance from the Galactic center, with a normalization that depends on the couplings and masses of dark sector particles. In addition, we use old pulsars outside the Galactic center to place bounds on asymmetric Higgs portal models.

  17. Pulsars for the Beginner

    ERIC Educational Resources Information Center

    DiLavore, Phillip; Wayland, James R.

    1971-01-01

    Presents the history of the discovery of pulsars, observations that have been made on pulsar radiation, and theories that have been presented for its presence and origin. Illustrations using pulsar's properties are presented in mechanics, electromagnetic radiation and thermodynamics. (DS)

  18. Geodynamic Effects of Ocean Tides: Progress and Problems

    NASA Technical Reports Server (NTRS)

    Richard, Ray

    1999-01-01

    Satellite altimetry, particularly Topex/Poseidon, has markedly improved our knowledge of global tides, thereby allowing significant progress on some longstanding problems in geodynamics. This paper reviews some of that progress. Emphasis is given to global-scale problems, particularly those falling within the mandate of the new IERS Special Bureau for Tides: angular momentum, gravitational field, geocenter motion. For this discussion I use primarily the new ocean tide solutions GOT99.2, CSR4.0, and TPXO.4 (for which G. Egbert has computed inverse-theoretic error estimates), and I concentrate on new results in angular momentum and gravity and their solid-earth implications. One example is a new estimate of the effective tidal Q at the M_2 frequency, based on combining these ocean models with tidal estimates from satellite laser ranging. Three especially intractable problems are also addressed: (1) determining long-period tides in the Arctic [large unknown effect on the inertia tensor, particularly for Mf]; (2) determining the global psi_l tide [large unknown effect on interpretations of gravimetry for the near-diurnal free wobble]; and (3) determining radiational tides [large unknown temporal variations at important frequencies]. Problems (2) and (3) are related.

  19. Three P's in Cosmology: Progress, Problems, and Perspectives

    NASA Astrophysics Data System (ADS)

    Dolgov, A. D.

    2014-04-01

    A review on the development of cosmology for a diverse audience is presented. The first historical part is devoted to the works done half a century ago with an emphasize to those performed in Russia (or more precisely, in the Soviet Union). Then the recent data on the cosmic microwave background raditation is discussed and the impact of these data on the neutrino mass and the number of neutrino species is considered. The latter is compared with the results obtained from the big bang nucleosynthesis. Next, a short description and history of the cosmological inflation is presented. The basics of the standard cosmological model and the problems of dark matter and dark energy are considered at the end of the fist section entitled "Progress". In the next short section, "Problems", one can find a list of the unsolved cosmological and astrophysical problems, which is by no means fully comprehensive. The last supershort section contains a few words about the perspectives of future development.

  20. Wideband Observations of Radio Pulsars

    NASA Astrophysics Data System (ADS)

    Pennucci, Timothy T.

    2015-08-01

    Pulsars are exotic objects which have yielded a bounty of important astrophysical results. As rapidly rotating, highly magnetized neutron stars, pulsars' stable rotation and beamed radio emission enables their use as interstellar laboratory clocks. The extraordinary timing regularity of the millisecond pulsar (MSP) population permits some of the most precise measurements in astronomy. The discovery of MSPs raised the probability of directly detecting gravitational waves for the first time. Ongoing efforts by several pulsar timing array (PTA) collaborations compliment the ground- and space-based efforts of laser interferometers. One such PTA is the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). NANOGrav has recently employed a new set of wideband instruments to increase the sensitivity of their PTA, and the future of pulsar astronomy is moving towards progressively larger bandwidths. In this dissertation, we address the benefits and issues from adopting the new instrumentation, particularly for the scientific motivations of NANOGrav. We first develop a measurement technique for simultaneously obtaining pulse times-of-arrival (TOAs) and dispersion measures (DMs) using 2D models of evolving Gaussian components. We then apply the methodology broadly to a variety of pulsars, including a bright, test MSP in a globular cluster, the Galactic Center magnetar, and the entire suite of 37 MSPs from the NANOGrav 9-year data set. For a subset of these MSPs, we make targeted observations at specific orbital phases aimed at improving the timing models and constraining the Shapiro delay. With a few exceptions, we find positive or consistent timing results from the implementation of our first generation wideband timing protocol. Some highlights include: improved measurement uncertainties, mitigation of chromatic ISM effects, a reduction in the number of timing parameters and TOAs, signs of chromatic DMs, and at least one new pulsar mass.

  1. Solving Large Problems Quickly: Progress in 2001-2003

    NASA Technical Reports Server (NTRS)

    Mowry, Todd C.; Colohan, Christopher B.; Brown, Angela Demke; Steffan, J. Gregory; Zhai, Antonia

    2004-01-01

    This document describes the progress we have made and the lessons we have learned in 2001 through 2003 under the NASA grant entitled "Solving Important Problems Faster". The long-term goal of this research is to accelerate large, irregular scientific applications which have enormous data sets and which are difficult to parallelize. To accomplish this goal, we are exploring two complementary techniques: (i) using compiler-inserted prefetching to automatically hide the I/O latency of accessing these large data sets from disk; and (ii) using thread-level data speculation to enable the optimistic parallelization of applications despite uncertainty as to whether data dependences exist between the resulting threads which would normally make them unsafe to execute in parallel. Overall, we made significant progress in 2001 through 2003, and the project has gone well.

  2. Automating the design process - Progress, problems, prospects, potential.

    NASA Technical Reports Server (NTRS)

    Heldenfels, R. R.

    1973-01-01

    The design process for large aerospace vehicles is discussed, with particular emphasis on structural design. Problems with current procedures are identified. Then, the contributions possible from automating the design process (defined as the best combination of men and computers) are considered. Progress toward automated design in the aerospace and other communities is reviewed, including NASA studies of the potential development of Integrated Programs for Aerospace-Vehicle Design (IPAD). The need for and suggested directions of future research on the design process, both technical and social, are discussed. Although much progress has been made to exploit the computer in design, it is concluded that technology is available to begin using the computer to speed communications and management as well as calculations in the design process and thus build man-computer teams that can design better, faster and cheaper.

  3. Problems and progress in aeroelasticity for interdisciplinary design

    NASA Technical Reports Server (NTRS)

    Yates, E. Carson, Jr.

    1987-01-01

    Some problems and progress in the development of aerodynamic and aeroelastic computational capabilities are reviewed with emphasis on needs for use in current interdisciplinary design procedures as well as for stand-alone analyses. The primary focus is on integral-equation methods which are well suited for general, accurate, efficient, and unified treatment of flow around vehicles having arbitrary shapes, motions, and deformations at subsonic, transonic, and supersonic speeds up to high angles of attack. Computational methods for potential flows and viscous flows are discussed, and some applications are shown. Calculation of steady and unsteady aeroelastic characteristics of aircraft with nonlinear aerodynamic behavior is also addressed briefly.

  4. TOWARD A REALISTIC PULSAR MAGNETOSPHERE

    SciTech Connect

    Kalapotharakos, Constantinos; Kazanas, Demosthenes; Harding, Alice

    2012-04-10

    We present the magnetic and electric field structures and the currents and charge densities of pulsar magnetospheres that do not obey the ideal condition, E {center_dot} B = 0. Since the acceleration of particles and the production of radiation require the presence of an electric field component parallel to the magnetic field, E{sub ||}, the structure of non-ideal pulsar magnetospheres is intimately related to the production of pulsar radiation. Therefore, knowledge of the structure of non-ideal pulsar magnetospheres is important because their comparison (including models for the production of radiation) with observations will delineate the physics and the parameters underlying the pulsar radiation problem. We implement a variety of prescriptions that support non-zero values for E{sub ||} and explore their effects on the structure of the resulting magnetospheres. We produce families of solutions that span the entire range between the vacuum and the (ideal) force-free electrodynamic solutions. We also compute the amount of dissipation as a fraction of the Poynting flux for pulsars of different angles between the rotation and magnetic axes and conclude that this is at most 20%-40% (depending on the non-ideal prescription) in the aligned rotator and 10% in the perpendicular one. We present also the limiting solutions with the property J = {rho}c and discuss their possible implication on the determination of the 'on/off' states of the intermittent pulsars. Finally, we find that solutions with values of J greater than those needed to null E{sub ||} locally produce oscillations, potentially observable in the data.

  5. Towards a Realistic Pulsar Magnetosphere

    NASA Technical Reports Server (NTRS)

    Kalapotharakos, Constantinos; Kazanas, Demosthenes; Harding, Alice; Contopoulos, Ioannis

    2012-01-01

    We present the magnetic and electric field structures as well as the currents ami charge densities of pulsar magnetospberes which do not obey the ideal condition, E(raised dot) B = O. Since the acceleration of particles and the production of radiation requires the presence of an electric field component parallel to the magnetic field, E(sub ll) the structure of non-Ideal pulsar magnetospheres is intimately related to the production of pulsar radiation. Therefore, knowledge of the structure of non-Ideal pulsar maglletospheres is important because their comparison (including models for t he production of radiation) with observations will delineate the physics and the parameters underlying the pulsar radiation problem. We implement a variety of prescriptions that support nonzero values for E(sub ll) and explore their effects on the structure of the resulting magnetospheres. We produce families of solutions that span the entire range between the vacuum and the (ideal) Force-Free Electrodynamic solutions. We also compute the amount of dissipation as a fraction of the Poynting flux for pulsars of different angles between the rotation and magnetic axes and conclude that tltis is at most 20-40% (depending on t he non-ideal prescription) in the aligned rotator and 10% in the perpendicular one. We present also the limiting solutions with the property J = pc and discuss their possible implicatioll on the determination of the "on/ off" states of the intermittent pulsars. Finally, we find that solutions with values of J greater than those needed to null E(sub ll) locally produce oscillations, potentially observable in the data.

  6. Galactic distribution of pulsars

    NASA Technical Reports Server (NTRS)

    Seiradakis, J. H.

    1977-01-01

    The density distributions of pulsars in luminosity, period, Z-distance, and galactocentric distance were derived, using a uniform sample of pulsars detected during a 408-MHz pulsar survey at Jodrell Bank. There are indications of a fine-scale structure in the spatial distributions and evidence that there is a general correlation with other galactic populations and the overall spiral structure. The electron layer in our galaxy is shown to be wider than the pulsar layer and uniform on a large scale. The number of pulsars in the galaxy has been estimated and used to derive the pulsar birthrate.

  7. Galactic distribution of pulsars

    NASA Technical Reports Server (NTRS)

    Seiradakis, J. H.

    1976-01-01

    The density distributions of pulsars in luminosity, period, Z-distance, and galactocentric distance were derived using a uniform sample of pulsars detected during a 408 MHz pulsar survey at Jodrell Bank. There are indications of a fine scale structure in the spatial distribution and evidence that there is a general correlation with other galactic populations and the overall spiral structure. The electron layer in the galaxy is shown to be wider than the pulsar layer and uniform on a large scale. The number of pulsars in the galaxy was estimated and used to derive the pulsar birthrate.

  8. Foot-and-mouth disease vaccines: progress and problems.

    PubMed

    Cao, Yimei; Lu, Zengjun; Liu, Zaixin

    2016-06-01

    Foot-and-mouth disease (FMD) has been a major threat to livestock across the world. The predominant method of controlling this disease in endemic regions is through regular vaccination with inactivated vaccine. However, there are many limitations. For instance, cultivation of virulent FMD virus (FMDV) in the manufacturing units poses a risk of escape from production sites. Vaccines may sometimes contain traces of FMD viral non-structural proteins (NSPs), therefore, interfering with the NSP-based serological differentiation infected from vaccinated animals (DIVA). Moreover, vaccines are unable to eliminate virus from carrier animals. To address the shortcomings of inactivated vaccines, many efforts are currently devoted to develop novel vaccines including attenuated and/or marker inactivated vaccines, recombinant protein vaccines, synthetic peptide vaccines, and empty capsid vaccines. Here, we review the research progress of novel vaccines, problems that remain to be solved, and also raise some suggestions that would help in the development of FMD vaccines. PMID:26760264

  9. Monitoring the progress of anytime problem-solving

    SciTech Connect

    Hansen, E.A.; Zilberstein, S.

    1996-12-31

    Anytime algorithms offer a tradeoff between solution quality and computation time that has proved useful in applying artificial intelligence techniques to time-critical problems. To exploit this tradeoff, a system must be able to determine the best time to stop deliberation and act on the currently available solution. When the rate of improvement of solution quality is uncertain, monitoring the progress of the algorithm can improve the utility of the system. This paper introduces a technique for run-time monitoring of anytime algorithms that is sensitive to the variance of the algorithm`s performance, the time-dependent utility of a solution, the ability of the run-time monitor to estimate the quality of the currently available solution, and the cost of monitoring. The paper examines the conditions under which the technique is optimal and demonstrates its applicability.

  10. Pulsar Astronomy with GLAST

    SciTech Connect

    Thorsett, Stephen

    2005-09-12

    Despite their name, the rotation powered neutron stars called "radio pulsars" are actually most luminous in the hard x-ray and gamma-ray bands. GLAST will be the first high-energy satellite with sufficient sensitivity to detect and study large numbers of these pulsars. I will review GLAST's key science goals in pulsar astrophysics and summarize the extraordinary advances in low-energy pulsar surveys since the days of CGRO.

  11. Search for Millisecond Pulsars for the Pulsar Timing Array project

    NASA Astrophysics Data System (ADS)

    Milia, S.

    2012-03-01

    pulsar and Earth locations, as well as anywhere along the line­of­sight from the Earth and each of the pulsars. This in turn produces a modulation in the rhythm of the TOAs of the pulses from all the pulsars, with the variation in the TOAs having a strength which is proportional to the amplitude of the GW and a periodicity related to the frequency of the GW. Of course if they are caused by a common physical phenomenon (like a passing­by GW), these variations of the TOAs are expected to be somehow correlated between the various pulsars, allowing us to disentangle this effect from other effects which could mimic the occurrence of such modulation, like intrinsic irregularities in the rotation of a pulsar, changing interstellar medium along the line of sight, error in the reference clocks used for determining the TOAs and so on.The consideration of the aforementioned possible sources of additional effects which could mask the signature of a genuine GW shows that a safe direct detection of a GW cannot involve the observation and timing of a single pulsar. Instead, it has been theoretically shown that high precision timing over a 5­10 years data­span of a network of suitable MSPs forming a so­ called Pulsar Timing Array (PTA) ­ in which the pulsars are used as the endpoints of arms of a huge cosmic GW detector ­ would allow us to overcome the previous problems and open the possibility of a direct detection of GWs. In particular such apparatus is able to detect GWs in the frequency range between 10 ­9 and 10­7 Hz, with the best sensitivity around the nanoHz. Given the frequency range of operation, the most favorable source of GWs for a PTA appears to be the cosmological background of GWs produced by the coalescence of supermassive binary black­holes in the early stages of the Universe evolution, at redshift around 1­2. In order to set up a suitable PTA it is necessary on one hand to search for new MSPs having the required clock stability and

  12. Nuclear DNA Amounts in Angiosperms: Progress, Problems and Prospects

    PubMed Central

    BENNETT, M. D.; LEITCH, I. J.

    2005-01-01

    CONTENTSINTRODUCTION45PROGRESS46    Improved systematic representation (species and families)46        (i) First estimates for species46        (ii) First estimates for families47PROBLEMS48    Geographical representation and distribution48    Plant life form48    Obsolescence time bomb49    Errors and inexactitudes49    Genome size, ‘complete’ genome sequencing, and, the euchromatic genome50    The completely sequenced genome50    Weeding out erroneous data52    What is the smallest reliable C-value for an angiosperm?52    What is the minimum C-value for a free-living angiosperm and other free-living organisms?53PROSPECTS FOR THE NEXT TEN YEARS54    Holistic genomics55LITERATURE CITED56APPENDIX59    Notes to the Appendix59    Original references for DNA values89 • Background The nuclear DNA amount in an unreplicated haploid chromosome complement (1C-value) is a key diversity character with many uses. Angiosperm C-values have been listed for reference purposes since 1976, and pooled in an electronic database since 1997 (http://www.kew.org/cval/homepage). Such lists are cited frequently and provide data for many comparative studies. The last compilation was published in 2000, so a further supplementary list is timely to monitor progress against targets set at the first plant genome size workshop in 1997 and to facilitate new goal setting. • Scope The present work lists DNA C-values for 804 species including first values for 628 species from 88 original sources, not included in any previous compilation, plus additional values for 176 species included in a previous compilation. • Conclusions 1998–2002 saw striking progress in our knowledge of angiosperm C-values. At least 1700 first values for species were measured (the most in any five-year period) and familial representation rose from 30 % to 50 %. The loss of many

  13. A Pulsar Eases Off the Brakes

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-10-01

    pulsar dropped suddenly by 14.5 after the outburst a change thats unprecedented both in how large and how long-lived its been.Why is this a problem? Many of the quoted properties of pulsars (like ages, magnetic fields, and luminosities) are determined based on models that envision pulsars as magnetic dipoles in a vacuum. But if this is the case, a pulsars braking index should be constant or, in more realistic scenarios, we might expect it to change slightly over the span of thousands of years. The fact that PSR 18460258 underwent such a drastic change during its outburst poses a significant challenge to these models of pulsar behavior and evolution.CitationR. F. Archibald et al 2015 ApJ 810 67. doi:10.1088/0004-637X/810/1/67

  14. High-energy pulsar models: Developments and new questions

    NASA Astrophysics Data System (ADS)

    Venter, C.; Harding, A. K.

    2014-03-01

    The past few years have seen a major advance in observational knowledge of high-energy (HE) pulsars. The Fermi Large Area Telescope (LAT) and {AGILE} have increased the number of known γ-ray pulsars by an order of magnitude, its members being divided roughly equally among millisecond pulsars (MSPs), young radio-loud pulsars, and young radio-quiet pulsars. Many new and diverse emission characteristics are being measured, while radio and X-ray follow-up observations increase the pulsar detection rate and enrich our multiwavelength picture of these extreme sources. The wealth of new data has provided impetus for further development and improvement of existing theoretical pulsar models. Geometric light curve (LC) modelling has uncovered three broad classes into which HE pulsars fall: those where the radio profile leads, is aligned with, or lags the γ-ray profile. For example, the original MSP and original black widow system are members of the second class, requiring co-located emission regions and thereby breaking with traditional notions of radio emission origin. These models imply narrow accelerator gaps in the outer magnetosphere, indicating copious pair production even in MSP magnetospheres that were previously thought to be pair-starved. The increased quality and variety of the LCs necessitate construction of ever more sophisticated models. We will review progress in global magnetosphere solutions which specify a finite conductivity on field lines above the stellar surface, filling the gap between the standard vacuum and force-free (FF; plasma-filled) models. The possibility of deriving phase-resolved spectra for the brightest pulsars, coupled with the fact that the HE pulsar population is sizable enough to allow sampling of various pulsar geometries, will enable much more stringent testing of future radiation models. Reproduction of the observed phase-resolved behavior of this disparate group will be one of the next frontiers in pulsar science, impacting on our

  15. High-Energy Pulsar Models: Developments and New Questions

    NASA Technical Reports Server (NTRS)

    Venter, C.; Harding, A. K.

    2014-01-01

    The past few years have seen a major advance in observational knowledge of high-energy (HE) pulsars. The Fermi Large Area Telescope (LAT) and AGILE have increased the number of known gamma-ray pulsars by an order of magnitude, its members being divided roughly equally among millisecond pulsars (MSPs), young radio-loud pulsars, and young radio-quiet pulsars. Many new and diverse emission characteristics are being measured, while radio and X-ray follow-up observations increase the pulsar detection rate and enrich our multiwavelength picture of these extreme sources. The wealth of new data has provided impetus for further development and improvement of existing theoretical pulsar models. Geometric light curve (LC) modelling has uncovered three broad classes into which HE pulsars fall: those where the radio profile leads, is aligned with, or lags the gamma-ray profile. For example, the original MSP and original black widow system are members of the second class, requiring co-located emission regions and thereby breaking with traditional notions of radio emission origin. These models imply narrow accelerator gaps in the outer magnetosphere, indicating copious pair production even in MSP magnetospheres that were previously thought to be pair-starved. The increased quality and variety of the LCs necessitate construction of ever more sophisticated models. We will review progress in global magnetosphere solutions which specify a finite conductivity on field lines above the stellar surface, filling the gap between the standard vacuum and force-free (FF; plasma-filled) models. The possibility of deriving phase-resolved spectra for the brightest pulsars, coupled with the fact that the HE pulsar population is sizable enough to allow sampling of various pulsar geometries, will enable much more stringent testing of future radiation models. Reproduction of the observed phase-resolved behavior of this disparate group will be one of the next frontiers in pulsar science, impacting on

  16. About pulsars dynamical evolution

    NASA Astrophysics Data System (ADS)

    López-Valdivia, R.; Álvarez, C.; de La Fuente, E.; Lorimer, D.; Kramer, M.

    2011-10-01

    Based on the assumption that pulsars are losing their rotational energy according to dot{ν}=-kν^n where ν is the frequency, dot{ν} its first derivative, and n is the braking index, four evolutionary models are created. Using them, thousands of artificial pulsar populations were generated. A comparison between these populations, and the no glitches and no milisecond pulsars reported by Hobbs et al. (2004) is performed using a Kolmogorov-Smirnov test (K-S).

  17. Revised Pulsar Spindown

    SciTech Connect

    Contopoulos, Ioannis; Spitkovsky, Anatoly; /KIPAC, Menlo Park

    2005-12-14

    We address the issue of electromagnetic pulsar spindown by combining our experience from the two limiting idealized cases which have been studied in great extent in the past: that of an aligned rotator where ideal MHD conditions apply, and that of a misaligned rotator in vacuum. We construct a spindown formula that takes into account the misalignment of the magnetic and rotation axes, and the magnetospheric particle acceleration gaps. We show that near the death line aligned rotators spin down much slower than orthogonal ones. In order to test this approach, we use a simple Monte Carlo method to simulate the evolution of pulsars and find a good fit to the observed pulsar distribution in the P-{dot P} diagram without invoking magnetic field decay. Our model may also account for individual pulsars spinning down with braking index n < 3, by allowing the corotating part of the magnetosphere to end inside the light cylinder. We discuss the role of magnetic reconnection in determining the pulsar braking index. We show, however, that n {approx} 3 remains a good approximation for the pulsar population as a whole. Moreover, we predict that pulsars near the death line have braking index values n > 3, and that the older pulsar population has preferentially smaller magnetic inclination angles. We discuss possible signatures of such alignment in the existing pulsar data.

  18. Gamma-Ray Pulsars

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.

    2011-01-01

    The Fermi Gamma-Ray Space Telescope has revolutionized the study of pulsar physics with the detection of over 80 gamma-ray pulsars. Several new populations have been discovered, including 24 radio quiet pulsars found through gamma-ray pulsations alone and about 20 millisecond gamma-ray pulsars. The gamma-ray pulsations from millisecond pulsars were discovered by both folding at periods of known radio millisecond pulsars or by detecting them as gamma-ray sources that are followed up by radio pulsar searches. The second method has resulted in a phenomenally successful synergy, with -35 new radio MSPs (to date) having been discovered at Fermi unidentified source locations and the gamma-ray pulsations having then been detected in a number of these using the radio timing solutions. The higher sensitivity and larger energy range of the Fermi Large Area Telescope has produced detailed energy-dependent light curves and phase-resolved spectroscopy on brighter pulsars, that have ruled out polar cap models as the major source of the emission in favor of outer magnetosphere accelerators. The large number of gamma-ray pulsars now allows for the first time meaningful population and sub-population studies that are revealing surprising properties of these fascinating sources.

  19. A Markov Model Analysis of Problem-Solving Progress.

    ERIC Educational Resources Information Center

    Vendlinski, Terry

    This study used a computerized simulation and problem-solving tool along with artificial neural networks (ANN) as pattern recognizers to identify the common types of strategies high school and college undergraduate chemistry students would use to solve qualitative chemistry problems. Participants were 134 high school chemistry students who used…

  20. PICsar: Particle in cell pulsar magnetosphere simulator

    NASA Astrophysics Data System (ADS)

    Belyaev, Mikhail A.

    2016-07-01

    PICsar simulates the magnetosphere of an aligned axisymmetric pulsar and can be used to simulate other arbitrary electromagnetics problems in axisymmetry. Written in Fortran, this special relativistic, electromagnetic, charge conservative particle in cell code features stretchable body-fitted coordinates that follow the surface of a sphere, simplifying the application of boundary conditions in the case of the aligned pulsar; a radiation absorbing outer boundary, which allows a steady state to be set up dynamically and maintained indefinitely from transient initial conditions; and algorithms for injection of charged particles into the simulation domain. PICsar is parallelized using MPI and has been used on research problems with ~1000 CPUs.

  1. Scientific and Technological Progress: Problems for the West.

    ERIC Educational Resources Information Center

    de Rose, Francois

    1978-01-01

    Discusses the impact of science and technology on major social problems confronting the Western world. Topics include pollution and ecology, military impact, computer science, and the benefits of science and technology. (Author/MA)

  2. The Problem of Technical Progress and Mineral Resources

    ERIC Educational Resources Information Center

    Lukashev, Konstantin I.

    1974-01-01

    Examines the estimates of known potential reserves of the major raw materials, future sources therof, the geological and technological problems associated with these, the manufacture of artifical minerals, and international cooperation in this sphere. (Author/GS)

  3. Observational properties of pulsars.

    PubMed

    Manchester, R N

    2004-04-23

    Pulsars are remarkable clocklike celestial sources that are believed to be rotating neutron stars formed in supernova explosions. They are valuable tools for investigations into topics such as neutron star interiors, globular cluster dynamics, the structure of the interstellar medium, and gravitational physics. Searches at radio and x-ray wavelengths over the past 5 years have resulted in a large increase in the number of known pulsars and the discovery of new populations of pulsars, posing challenges to theories of binary and stellar evolution. Recent images at radio, optical, and x-ray wavelengths have revealed structures resulting from the interaction of pulsar winds with the surrounding interstellar medium, giving new insights into the physics of pulsars. PMID:15105491

  4. The Fermi-Pasta-Ulam problem: fifty years of progress.

    PubMed

    Berman, G P; Izrailev, F M

    2005-03-01

    A brief review of the Fermi-Pasta-Ulam (FPU) paradox is given, together with its suggested resolutions and its relation to other physical problems. We focus on the ideas and concepts that have become the core of modern nonlinear mechanics, in their historical perspective. Starting from the first numerical results of FPU, both theoretical and numerical findings are discussed in close connection with the problems of ergodicity, integrability, chaos and stability of motion. New directions related to the Bose-Einstein condensation and quantum systems of interacting Bose-particles are also considered. PMID:15836281

  5. Detectors for high energy nuclear collisions: problems, progress and promise

    SciTech Connect

    Ludlam, T.W.

    1986-01-01

    Some perspective of the main issues in high energy nuclear collision physics is offered. How to identify and measure a quark-gluon plasma is considered to still be an open question. The types of detector configurations to be used in high-energy nucleus-nucleus experiments are discussed. Particular issues covered are measurements of lepton pair spectra, tracking systems and multitrack resolution, event-rate capabilities, backgrounds and other problems close to the beam, and calorimetry. 2 refs. (LEW)

  6. Radio efficiency of pulsars

    SciTech Connect

    Szary, Andrzej; Melikidze, George I.; Gil, Janusz; Zhang, Bing; Xu, Ren-Xin E-mail: zhang@physics.unlv.edu

    2014-03-20

    We investigate radio emission efficiency, ξ, of pulsars and report a near-linear inverse correlation between ξ and the spin-down power, E-dot , as well as a near-linear correlation between ξ and pulsar age, τ. This is a consequence of very weak, if any, dependences of radio luminosity, L, on pulsar period, P, and the period derivative, P-dot , in contrast to X-ray or γ-ray emission luminosities. The analysis of radio fluxes suggests that these correlations are not due to a selection effect, but are intrinsic to the pulsar radio emission physics. We have found that, although with a large variance, the radio luminosity of pulsars is ≈10{sup 29} erg s{sup –1}, regardless of the position in the P-- P-dot diagram. Within such a picture, a model-independent statement can be made that the death line of radio pulsars corresponds to an upper limit in the efficiency of radio emission. If we introduce the maximum value for radio efficiency into the Monte Carlo-based population syntheses we can reproduce the observed sample using the random luminosity model. Using the Kolmogorov-Smirnov test on a synthetic flux distribution reveals a high probability of reproducing the observed distribution. Our results suggest that the plasma responsible for generating radio emission is produced under similar conditions regardless of pulsar age, dipolar magnetic field strength, and spin-down rate. The magnetic fields near the pulsar surface are likely dominated by crust-anchored, magnetic anomalies, which do not significantly differ among pulsars, leading to similar conditions for generating electron-positron pairs necessary to power radio emission.

  7. Stellar evolution and pulsars.

    NASA Technical Reports Server (NTRS)

    Chiu, H.-Y.

    1972-01-01

    It has been found that pulsars are rotating magnetic neutron stars, which are created during catastrophic collapses of old stars whose nuclear fuel has long since been used up. The maximum size of pulsars, based on the fastest rotation period of 33 msec, cannot exceed 100 km. The densest star the theory predicts is the neutron star. Its diameter is only 10 km. The processes producing radiation from pulsars are discussed, giving attention to a process similar to that by which a klystron operates and to a process based on a maser mechanism.

  8. Random functions via Dyson Brownian Motion: progress and problems

    NASA Astrophysics Data System (ADS)

    Wang, Gaoyuan; Battefeld, Thorsten

    2016-09-01

    We develope a computationally efficient extension of the Dyson Brownian Motion (DBM) algorithm to generate random function in C2 locally. We further explain that random functions generated via DBM show an unstable growth as the traversed distance increases. This feature restricts the use of such functions considerably if they are to be used to model globally defined ones. The latter is the case if one uses random functions to model landscapes in string theory. We provide a concrete example, based on a simple axionic potential often used in cosmology, to highlight this problem and also offer an ad hoc modification of DBM that suppresses this growth to some degree.

  9. Electron holography for fields in solids: problems and progress.

    PubMed

    Lichte, Hannes; Börrnert, Felix; Lenk, Andreas; Lubk, Axel; Röder, Falk; Sickmann, Jan; Sturm, Sebastian; Vogel, Karin; Wolf, Daniel

    2013-11-01

    Electron holography initially was invented by Dennis Gabor for solving the problems raised by the aberrations of electron lenses in Transmission Electron Microscopy. Nowadays, after hardware correction of aberrations allows true atomic resolution of the structure, for comprehensive understanding of solids, determination of electric and magnetic nanofields is the most challenging task. Since fields are phase objects in the TEM, electron holography is the unrivaled method of choice. After more than 40 years of experimental realization and steady improvement, holography is increasingly contributing to these highly sophisticated and essential questions in materials science, as well to the understanding of electron waves and their interaction with matter. PMID:23831133

  10. Pulsar Search Results from the Arecibo Remote Command Center

    NASA Astrophysics Data System (ADS)

    Garcia, Alejandro; Stovall, K.; Banaszak, S. A.; Becker, A.; Biwer, C. M.; Boehler, K.; Caballero, K.; Christy, B.; Cohen, S.; Crawford, F.; Cuellar, A.; Danford, A.; Dartez, L. P.; Day, D.; Flanigan, J. D.; Gonzalez, A.; Gustavson, K.; Handzo, E.; Hinojosa, J.; Jenet, F.; Kaplan, D. L.; Kayal, K.; Lommen, A. N.; Longoria, C.; Lopez, J.; Lunsford, G.; Mahany, N.; Martinez, J.; Mata, A.; Miller, A.; Murray, J.; Pankow, C.; Ramirez, I.; Reser, J.; Rojas, P.; Rohr, M.; Rolph, K.; Rose, C.; Rudnik, P.; Siemens, X.; Tellez, A.; Tillman, N.; Walker, A.; Wells, B. L.; Zermeno, A.; Consortium, GBNCC; Consortium, PALFA; Consortium, GBTDrift; Consortium, AO327

    2014-01-01

    The Arecibo Remote Command Center (ARCC) at the University of Texas at Brownsville, in collaboration with various Universities, is currently engaged in searching through ongoing radio telescope surveys for radio pulsars. ARCC is an integrated research/education program that allows students at the high school and undergraduate level to be directly involved with the research at the Arecibo and Green Bank radio telescopes. We discuss the progress of our search effort with PRESTO pulsar search pipelines. Web based tools have been developed so that high school, undergraduate, and graduate students could rank the pulsar candidates created by PRESTO pipelines. We describe these tools and present our current discoveries.

  11. Molecular testing in oncology: problems, pitfalls and progress.

    PubMed

    O'Brien, Cathal P; Taylor, Sarah E; O'Leary, John J; Finn, Stephen P

    2014-03-01

    Recent advances in the understanding of the molecular basis of cancer and the development of molecular diagnostics based on this knowledge have done much to progress the fields of oncology and pathology. Technological developments such as Next Generation Sequencing (NGS) and multiplex assays have made feasible the widespread adoption of molecular diagnostics for clinical use. While these developments and advances carry much promise, there are pitfalls to implementing this testing. Choosing appropriate biomarkers is a vital first step for clinical use and being able to understand the complex relationship between predictive and prognostic biomarkers is a crucial component of this. Testing for standard of care biomarkers is not straightforward, one must choose carefully between clinical trial assays, assays that analyse the same biological phenomenon or surrogate biomarkers. Sample heterogeneity and population specific difference is assays may skew results and must be controlled for at the assay design stage. At a technical level, NGS has the potential to revolutionise laboratory practice and approaches to cancer treatment. However, use of this technology requires careful planning and implementation if one is to avoid technical and ethical quagmires. Finally, with FDA regulation of companion diagnostics one may be limited to therapy specific assays. PMID:24472389

  12. The (obscene) Challenges of Next-Generation Pulsar Surveys

    NASA Astrophysics Data System (ADS)

    Ransom, Scott M.

    2014-04-01

    In the last decade, large-scale surveys for new radio pulsars have made incredible progress, particularly in their ability to find important binary and millisecond pulsars. The reason for this progress has been Moore's Law, the same reason behind our current efforts and plans to build fantastic next-generation radio facilities. These new facilities, though, especially the radio arrays, will make pulsar searching incredibly difficult due to the (obscene) data rates that will be generated. Dealing with data rates that we cannot record will demand new ways of thinking about and processing our pulsar data. And unfortunately these challenges apply not only to the SKA in some distant future, but are with us already today in the arrays we have in operation or under construction.

  13. Pulsar glitches: the crust is not enough.

    PubMed

    Andersson, N; Glampedakis, K; Ho, W C G; Espinoza, C M

    2012-12-14

    Pulsar glitches are traditionally viewed as a manifestation of vortex dynamics associated with a neutron superfluid reservoir confined to the inner crust of the star. In this Letter we show that the nondissipative entrainment coupling between the neutron superfluid and the nuclear lattice leads to a less mobile crust superfluid, effectively reducing the moment of inertia associated with the angular momentum reservoir. Combining the latest observational data for prolific glitching pulsars with theoretical results for the crust entrainment, we find that the required superfluid reservoir exceeds that available in the crust. This challenges our understanding of the glitch phenomenon, and we discuss possible resolutions to the problem. PMID:23368300

  14. THE PECULIAR PULSAR POPULATION OF THE CENTRAL PARSEC

    SciTech Connect

    Dexter, Jason; O'Leary, Ryan M. E-mail: oleary@berkeley.edu

    2014-03-01

    Pulsars orbiting the Galactic center black hole, Sgr A*, would be potential probes of its mass, distance, and spin, and may even be used to test general relativity. Despite predictions of large populations of both ordinary and millisecond pulsars in the Galactic center, none have been detected within 25 pc by deep radio surveys. One explanation has been that hyperstrong temporal scattering prevents pulsar detections, but the recent discovery of radio pulsations from a highly magnetized neutron star (magnetar) within 0.1 pc shows that the temporal scattering is much weaker than predicted. We argue that an intrinsic deficit in the ordinary pulsar population is the most likely reason for the lack of detections to date: a ''missing pulsar problem'' in the Galactic center. In contrast, we show that the discovery of a single magnetar implies efficient magnetar formation in the region. If the massive stars in the central parsec form magnetars rather than ordinary pulsars, their short lifetimes could explain the missing pulsars. Efficient magnetar formation could be caused by strongly magnetized progenitors, or could be further evidence of a top-heavy initial mass function. Furthermore, current high-frequency surveys should already be able to detect bright millisecond pulsars, given the measured degree of temporal scattering.

  15. The Peculiar Pulsar Population of the Central Parsec

    NASA Astrophysics Data System (ADS)

    Dexter, Jason; O'Leary, Ryan M.

    2014-03-01

    Pulsars orbiting the Galactic center black hole, Sgr A*, would be potential probes of its mass, distance, and spin, and may even be used to test general relativity. Despite predictions of large populations of both ordinary and millisecond pulsars in the Galactic center, none have been detected within 25 pc by deep radio surveys. One explanation has been that hyperstrong temporal scattering prevents pulsar detections, but the recent discovery of radio pulsations from a highly magnetized neutron star (magnetar) within 0.1 pc shows that the temporal scattering is much weaker than predicted. We argue that an intrinsic deficit in the ordinary pulsar population is the most likely reason for the lack of detections to date: a "missing pulsar problem" in the Galactic center. In contrast, we show that the discovery of a single magnetar implies efficient magnetar formation in the region. If the massive stars in the central parsec form magnetars rather than ordinary pulsars, their short lifetimes could explain the missing pulsars. Efficient magnetar formation could be caused by strongly magnetized progenitors, or could be further evidence of a top-heavy initial mass function. Furthermore, current high-frequency surveys should already be able to detect bright millisecond pulsars, given the measured degree of temporal scattering.

  16. Progress with multigrid schemes for hypersonic flow problems

    NASA Technical Reports Server (NTRS)

    Radespiel, R.; Swanson, R. C.

    1991-01-01

    Several multigrid schemes are considered for the numerical computation of viscous hypersonic flows. For each scheme, the basic solution algorithm uses upwind spatial discretization with explicit multistage time stepping. Two level versions of the various multigrid algorithms are applied to the two dimensional advection equation, and Fourier analysis is used to determine their damping properties. The capabilities of the multigrid methods are assessed by solving three different hypersonic flow problems. Some new multigrid schemes based on semicoarsening strategies are shown to be quite effective in relieving the stiffness caused by the high aspect ratio cells required to resolve high Reynolds number flows. These schemes exhibit good convergence rates for Reynolds numbers up to 200 x 10(exp 6) and Mach numbers up to 25.

  17. Progress with multigrid schemes for hypersonic flow problems

    SciTech Connect

    Radespiel, R.; Swanson, R.C.

    1995-01-01

    Several multigrid schemes are considered for the numerical computation of viscous hypersonic flows. For each scheme, the basic solution algorithm employs upwind spatial discretization with explicit multistage time stepping. Two-level versions of the various multigrid algorithms are applied to the two-dimensional advection equation, and Fourier analysis is used to determine their damping properties. The capabilities of the multigrid methods are assessed by solving three different hypersonic flow problems. Some new multigrid schemes based on semicoarsening strategies are shown to be quite effective in relieving the stiffness caused by the high-aspect-ratio cells required to resolve high Reynolds number flows. These schemes exhibit good convergence rates for Reynolds numbers up to 200 X 10{sup 6} and Mach numbers up to 25. 32 refs., 31 figs., 1 tab.

  18. Geomagnetic inverse problem and data assimilation: a progress report

    NASA Astrophysics Data System (ADS)

    Aubert, Julien; Fournier, Alexandre

    2013-04-01

    In this presentation I will present two studies recently undertaken by our group in an effort to bring the benefits of data assimilation to the study of Earth's magnetic field and the dynamics of its liquid iron core, where the geodynamo operates. In a first part I will focus on the geomagnetic inverse problem, which attempts to recover the fluid flow in the core from the temporal variation of the magnetic field (known as the secular variation). Geomagnetic data can be downward continued from the surface of the Earth down to the core-mantle boundary, but not further below, since the core is an electrical conductor. Historically, solutions to the geomagnetic inverse problem in such a sparsely observed system were thus found only for flow immediately below the core mantle boundary. We have recently shown that combining a numerical model of the geodynamo together with magnetic observations, through the use of Kalman filtering, now allows to present solutions for flow throughout the core. In a second part, I will present synthetic tests of sequential geomagnetic data assimilation aiming at evaluating the range at which the future of the geodynamo can be predicted, and our corresponding prospects to refine the current geomagnetic predictions. Fournier, Aubert, Thébault: Inference on core surface flow from observations and 3-D dynamo modelling, Geophys. J. Int. 186, 118-136, 2011, doi: 10.1111/j.1365-246X.2011.05037.x Aubert, Fournier: Inferring internal properties of Earth's core dynamics and their evolution from surface observations and a numerical geodynamo model, Nonlinear Proc. Geoph. 18, 657-674, 2011, doi:10.5194/npg-18-657-2011 Aubert: Flow throughout the Earth's core inverted from geomagnetic observations and numerical dynamo models, Geophys. J. Int., 2012, doi: 10.1093/gji/ggs051

  19. Geriatric Pulsar Still Kicking

    NASA Astrophysics Data System (ADS)

    2009-02-01

    The oldest isolated pulsar ever detected in X-rays has been found with NASA's Chandra X-ray Observatory. This very old and exotic object turns out to be surprisingly active. The pulsar, PSR J0108-1431 (J0108 for short) is about 200 million years old. Among isolated pulsars -- ones that have not been spun-up in a binary system -- it is over 10 times older than the previous record holder with an X-ray detection. At a distance of 770 light years, it is one of the nearest pulsars known. Pulsars are born when stars that are much more massive than the Sun collapse in supernova explosions, leaving behind a small, incredibly weighty core, known as a neutron star. At birth, these neutron stars, which contain the densest material known in the Universe, are spinning rapidly, up to a hundred revolutions per second. As the rotating beams of their radiation are seen as pulses by distant observers, similar to a lighthouse beam, astronomers call them "pulsars". Astronomers observe a gradual slowing of the rotation of the pulsars as they radiate energy away. Radio observations of J0108 show it to be one of the oldest and faintest pulsars known, spinning only slightly faster than one revolution per second. The surprise came when a team of astronomers led by George Pavlov of Penn State University observed J0108 in X-rays with Chandra. They found that it glows much brighter in X-rays than was expected for a pulsar of such advanced years. People Who Read This Also Read... Chandra Data Reveal Rapidly Whirling Black Holes Milky Way’s Giant Black Hole Awoke from Slumber 300 Years Ago Erratic Black Hole Regulates Itself Celebrate the International Year of Astronomy Some of the energy that J0108 is losing as it spins more slowly is converted into X-ray radiation. The efficiency of this process for J0108 is found to be higher than for any other known pulsar. "This pulsar is pumping out high-energy radiation much more efficiently than its younger cousins," said Pavlov. "So, although it

  20. Fermi Pulsar Analysis

    NASA Video Gallery

    This animation illustrates how analysis of Fermi data reveals new pulsars. Fermi's LAT records the precise arrival time and approximate direction of the gamma rays it detects, but to identify a pul...

  1. Cosmic Ray Positrons from Pulsars

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.

    2010-01-01

    Pulsars are potential Galactic sources of positrons through pair cascades in their magnetospheres. There are, however, many uncertainties in establishing their contribution to the local primary positron flux. Among these are the local density of pulsars, the cascade pair multiplicities that determine the injection rate of positrons from the pulsar, the acceleration of the injected particles by the pulsar wind termination shock, their rate of escape from the pulsar wind nebula, and their propagation through the interstellar medium. I will discuss these issues in the context of what we are learning from the new Fermi pulsar detections and discoveries.

  2. Volcanic hazards and their mitigation: Progress and problems

    NASA Astrophysics Data System (ADS)

    Tilling, Robert I.

    1989-05-01

    At the beginning of the twentieth century, volcanology began to emerge as a modern science as a result of increased interest in eruptive phenomena following some of the worst volcanic disasters in recorded history: Krakatau (Indonesia) in 1883 and Mont Pelée (Martinique), Soufrière (St. Vincent), and Santa María (Guatemala) in 1902. Volcanology is again experiencing a period of heightened public awareness and scientific growth in the 1980s, the worst period since 1902 in terms of volcanic disasters and crises. A review of hazards mitigation approaches and techniques indicates that significant advances have been made in hazards assessment, volcano monitoring, and eruption forecasting. For example, the remarkable accuracy of the predictions of dome-building events at Mount St. Helens since June 1980 is unprecedented. Yet a predictive capability for more voluminous and explosive eruptions still has not been achieved. Studies of magma-induced seismicity and ground deformation continue to provide the most systematic and reliable data for early detection of precursors to eruptions and shallow intrusions. In addition, some other geophysical monitoring techniques and geochemical methods have been refined and are being more widely applied and tested. Comparison of the four major volcanic disasters of the 1980s (Mount St. Helens, U.S.A. (1980), El Chichón, Mexico (1982); Galunggung, Indonesia (1982); and Nevado del Ruíz, Colombia (1985) illustrates the importance of predisaster geoscience studies, volcanic hazards assessments, volcano monitoring, contingency planning, and effective communications between scientists and authorities. The death toll (>22,000) from the Ruíz catastrophe probably could have been greatly reduced; the reasons for the tragically ineffective implementation of evacuation measures are still unclear and puzzling in view of the fact that sufficient warnings were given. The most pressing problem in the mitigation of volcanic and associated hazards on

  3. Pulse Portraiture: Pulsar timing

    NASA Astrophysics Data System (ADS)

    Pennucci, Timothy T.; Demorest, Paul B.; Ransom, Scott M.

    2016-06-01

    Pulse Portraiture is a wideband pulsar timing code written in python. It uses an extension of the FFTFIT algorithm (Taylor 1992) to simultaneously measure a phase (TOA) and dispersion measure (DM). The code includes a Gaussian-component-based portrait modeling routine. The code uses the python interface to the pulsar data analysis package PSRCHIVE (ascl:1105.014) and also requires the non-linear least-squares minimization package lmfit (ascl:1606.014).

  4. Observations of accreting pulsars

    NASA Technical Reports Server (NTRS)

    Prince, Thomas A.; Bildsten, Lars; Chakrabarty, Deepto; Wilson, Robert B.; Finger, Mark H.

    1994-01-01

    We discuss recent observations of accreting binary pulsars with the all-sky BATSE instrument on the Compton Gamma Ray Observatory. BATSE has detected and studied nearly half of the known accreting pulsar systems. Continuous timing studies over a two-year period have yielded accurate orbital parameters for 9 of these systems, as well as new insights into long-term accretion torque histories.

  5. The Fermi LAT Pulsars

    NASA Astrophysics Data System (ADS)

    Romani, Roger W.

    2011-08-01

    The Large Area Telescope on the Fermi satellite is an impressive pulsar discovery machine, with over 75 pulse detections and counting. The populations of radio-selected, γ-selected and millisecond pulsars are now large enough to display observational patterns in the light curves and luminosities. These patterns are starting to teach us about the physics of the emission zone, which seems dominated by open field lines near the speed of light cylinder. The sample also provides initial inferences about the pulsar population. Apparently a large fraction of neutron stars have a young energetic γ-ray emitting phase, making these objects a good probe of massive star evolution. The long-lived millisecond γ-ray pulsars are even more ubiquitous and may produce a significant fraction of the γ-ray background. In any event, it is clear that the present LAT pulsar sample is dominated by nearby objects, and there is every expectation that the number, and quality, of pulsar detections will increase in years to come.

  6. Progressive Muscle Relaxation and Cognitive Restructuring: Potential Problems and Proposed Solutions.

    ERIC Educational Resources Information Center

    Kiselica, Mark S.; Baker, Stanley B.

    1992-01-01

    Reviews common problems experienced by clients during progressive muscle relaxation training (PMRT) and summarizes pertinent solutions to those problems. Discusses difficulties and solutions related to cognitive restructuring training. Notes that cognitive restructuring is often used to enhance effectiveness of PMRT. Concludes with suggestions for…

  7. Optical study of pulsars

    NASA Astrophysics Data System (ADS)

    Sanwal, Divas

    The Crab Pulsar emits radiation at all wavelengths from radio to extreme γ-rays including the optical. We have performed extremely high time resolution multicolor photometry of the Crab Pulsar at optical wavelengths to constrain the high energy emission models for pulsars. Our observations with 1 microsecond time resolution are a factor of 20 better than the previous best observations. We have completely resolved the peak of the main pulse of the Crab Pulsar in optical passbands. The peaks of the main pulse and the interpulse move smoothly from the rising branch to the falling branch with neither a flat top nor a cusp. We find that the peak of the Crab Pulsar main pulse in the B band arrives 140 microseconds before the peak of the radio pulse. The color of the emission changes across the phase. The maximum variation in the color ratio is about 25%. The bluest color occurs in the bridge region between the main pulse and the interpulse. The Crab Pulsar has faded by 2 +/- 2.8% since the previous observations in 1991 using the same instrument. The statistics of photon arrival times are consistent with atmospheric scintillation causing most of the variations in addition to the mean pulse variations in the shape. However, the autocorrelation function (ACF) of the Crab Pulsar light curve shows extra correlations at very short time scales. We identify two time scales, one at about 20 microseconds and another one at about 1000 microseconds at which we observe a break in the ACF. We conclude that these short timescale correlations are internal to the pulsar. We attribute the extra correlation observed in our data to microstructures. This is the first time evidence for microstructures has been observed outside the radio wavelengths. The upturn in the ACF at short time scales depends on the color. The U band shows about 10% more correlation at short time scales while the R band shows only about 3% change. We have also observed the young X-ray pulsar PSR 0656+14 at optical

  8. The Pulsating Pulsar Magnetosphere

    NASA Astrophysics Data System (ADS)

    Tsui, K. H.

    2015-06-01

    Following the basic principles of a charge-separated pulsar magnetosphere, we consider the magnetosphere to be stationary in space, instead of corotating, and the electric field to be uploaded from the potential distribution on the pulsar surface, set up by the unipolar induction. Consequently, the plasma of the magnetosphere undergoes guiding center drifts of the gyromotion due to the forces transverse to the magnetic field. These forces are the electric force, magnetic gradient force, and field line curvature force. Since these plasma velocities are of drift nature, there is no need to introduce an emf along the field lines, which would contradict the {{E}\\parallel }={\\boldsymbol{E}} \\cdot {\\boldsymbol{B}} =0 plasma condition. Furthermore, there is also no need to introduce the critical field line separating the electron and ion open field lines. We present a self-consistent description where the magnetosphere is described in terms of electric and magnetic fields and also in terms of plasma velocities. The fields and velocities are then connected through the space-charge densities self-consistently. We solve the pulsar equation analytically for the fields and construct the standard steady-state pulsar magnetosphere. By considering the unipolar induction inside the pulsar and the magnetosphere outside the pulsar as one coupled system, and under the condition that the unipolar pumping rate exceeds the Poynting flux in the open field lines, plasma pressure can build up in the magnetosphere, in particular, in the closed region. This could cause a periodic opening up of the closed region, leading to a pulsating magnetosphere, which could be an alternative to pulsar beacons. The closed region can also be opened periodically by the build up of toroidal magnetic field through a positive feedback cycle.

  9. Pulsar lensing geometry

    NASA Astrophysics Data System (ADS)

    Liu, Siqi; Pen, Ue-Li; Macquart, J.-P.; Brisken, Walter; Deller, Adam

    2016-05-01

    We test the inclined sheet pulsar scintillation model (Pen & Levin) against archival very long baseline interferometry (VLBI) data on PSR 0834+06 and show that its scintillation properties can be precisely reproduced by a model in which refraction occurs on two distinct lens planes. These data strongly favour a model in which grazing-incidence refraction instead of diffraction off turbulent structures is the primary source of pulsar scattering. This model can reproduce the parameters of the observed diffractive scintillation with an accuracy at the percent level. Comparison with new VLBI proper motion results in a direct measure of the ionized interstellar medium (ISM) screen transverse velocity. The results are consistent with ISM velocities local to the PSR 0834+06 sight-line (through the Galaxy). The simple 1-D structure of the lenses opens up the possibility of using interstellar lenses as precision probes for pulsar lens mapping, precision transverse motions in the ISM, and new opportunities for removing scattering to improve pulsar timing. We describe the parameters and observables of this double screen system. While relative screen distances can in principle be accurately determined, a global conformal distance degeneracy exists that allows a rescaling of the absolute distance scale. For PSR B0834+06, we present VLBI astrometry results that provide (for the first time) a direct measurement of the distance of the pulsar. For most of the recycled millisecond pulsars that are the targets of precision timing observations, the targets where independent distance measurements are not available. The degeneracy presented in the lens modelling could be broken if the pulsar resides in a binary system.

  10. Superfluidity in Millisecond Pulsars (Review)

    NASA Astrophysics Data System (ADS)

    Pines, D.; Alpar, A.

    The authors review the evidence for superfluidity in the Vela pulsar, the Crab pulsar and PSR 0525+21, and examine the prospects for observing similar consequences of superfluidity in the already-discovered millisec pulsars. They consider, inter alia, the likelihood of observing glitches, the expected post-glitch behavior, and pulsar heating by energy dissipation due to the creep of neutron vortex lines in pinned superfluid regions of the crust.

  11. Relaxation of the Angular Velocity of Pulsars after Glitches

    NASA Astrophysics Data System (ADS)

    Sedrakian, D. M.; Hayrapetyan, M. V.; Baghdasaryan, D.

    2014-03-01

    The rotational dynamics of superfluid neutron stars is examined in order to study the relaxation of the angular velocity of pulsars after glitches. The motion of the neutron-proton vortex system is investigated taking the sphericity of the superfluid core and vortex pinning and depinning into account. A relaxation solution is obtained for the angular rotation velocity of pulsars after glitches. In order to compare this solution with observational data for the Vela pulsar, the inverse problem of finding the initial distribution of vortices immediately after a glitch is solved.

  12. Joint USSR-Australia Shklovskii Memorial Symposium on Supernova Remnants and Pulsars, Pushchino, USSR, June 8-11, 1986, Proceedings

    NASA Astrophysics Data System (ADS)

    Various papers on SNRs and pulsars are presented. The topics discussed include: synthesis surveys of southern SNRs, structure and source of radio emission in old SNRs, daily observations of three period jumps of the Vela pulsar, two types of pulsar, 843 MHz observations of Cir X-1 and G321.9-0.3, radio emission model of a 'typical' pulsar, relationship between supernova type and their remnants, atlas of SNR magnetic fields, and models for the emission line spectra of oxygen-rich SNRs. Also addressed are: nonstationary phenomena in the radiation of young SNRs, SNR morphology, biannular structure in SNRs, problems of estimating distances to pulsars, spatial distribution of pulsars and SNRs, correlation properties of a short-scale microstructure of pulsar radio emission within a 100 kHz bandwidth, SNRs with jets, and decametric emission by pulsars.

  13. Geriatric Pulsar Still Kicking

    NASA Astrophysics Data System (ADS)

    2009-02-01

    The oldest isolated pulsar ever detected in X-rays has been found with NASA's Chandra X-ray Observatory. This very old and exotic object turns out to be surprisingly active. The pulsar, PSR J0108-1431 (J0108 for short) is about 200 million years old. Among isolated pulsars -- ones that have not been spun-up in a binary system -- it is over 10 times older than the previous record holder with an X-ray detection. At a distance of 770 light years, it is one of the nearest pulsars known. Pulsars are born when stars that are much more massive than the Sun collapse in supernova explosions, leaving behind a small, incredibly weighty core, known as a neutron star. At birth, these neutron stars, which contain the densest material known in the Universe, are spinning rapidly, up to a hundred revolutions per second. As the rotating beams of their radiation are seen as pulses by distant observers, similar to a lighthouse beam, astronomers call them "pulsars". Astronomers observe a gradual slowing of the rotation of the pulsars as they radiate energy away. Radio observations of J0108 show it to be one of the oldest and faintest pulsars known, spinning only slightly faster than one revolution per second. The surprise came when a team of astronomers led by George Pavlov of Penn State University observed J0108 in X-rays with Chandra. They found that it glows much brighter in X-rays than was expected for a pulsar of such advanced years. People Who Read This Also Read... Chandra Data Reveal Rapidly Whirling Black Holes Milky Way’s Giant Black Hole Awoke from Slumber 300 Years Ago Erratic Black Hole Regulates Itself Celebrate the International Year of Astronomy Some of the energy that J0108 is losing as it spins more slowly is converted into X-ray radiation. The efficiency of this process for J0108 is found to be higher than for any other known pulsar. "This pulsar is pumping out high-energy radiation much more efficiently than its younger cousins," said Pavlov. "So, although it

  14. Generative pulsar timing analysis

    NASA Astrophysics Data System (ADS)

    Lentati, L.; Alexander, P.; Hobson, M. P.

    2015-03-01

    A new Bayesian method for the analysis of folded pulsar timing data is presented that allows for the simultaneous evaluation of evolution in the pulse profile in either frequency or time, along with the timing model and additional stochastic processes such as red spin noise, or dispersion measure variations. We model the pulse profiles using `shapelets' - a complete orthonormal set of basis functions that allow us to recreate any physical profile shape. Any evolution in the profiles can then be described as either an arbitrary number of independent profiles, or using some functional form. We perform simulations to compare this approach with established methods for pulsar timing analysis, and to demonstrate model selection between different evolutionary scenarios using the Bayesian evidence. The simplicity of our method allows for many possible extensions, such as including models for correlated noise in the pulse profile, or broadening of the pulse profiles due to scattering. As such, while it is a marked departure from standard pulsar timing analysis methods, it has clear applications for both new and current data sets, such as those from the European Pulsar Timing Array and International Pulsar Timing Array.

  15. NANOGrav Millisecond Pulsar Observing Program

    NASA Astrophysics Data System (ADS)

    Nice, David J.; Nanograv

    2015-01-01

    Gravitational waves from sources such as supermassive black hole binary systems are expected to perturb times-of-flight of signals traveling from pulsars to the Earth. The NANOGrav consortium aims to measure these perturbations in high precision millisecond pulsar timing measurements and thus to directly detect gravitational waves and characterize gravitational wave sources. By observing pulsars over time spans of many years, we are most sensitive to gravitational waves at nanohertz frequencies.In this presentation we describe the NANOGrav observing program. We presently observe an array of 45 millisecond pulsars, evenly divided between the Arecibo Observatory (for pulsars with declinations between -1 and 39 degrees) and the Green Bank Telescope (for other pulsars, with two pulsars overlapping with Arecibo). Observation of a large number of pulsars allows for searches of correlated perturbations between multiple pulsar signals, which will be crucial for achieving high-significance detection of gravitational waves in the face of uncorrelated noise (from gravitational waves and rotation noise) in the individual pulsars. As new high-quality pulsars are discovered, they are added to the program.Observations of each pulsar are made with cadence of 20 to 30 days, with observations of each pulsar in two separate radio bands. Arrival times for nearly all pulsars are measured with precision better than 1 microsecond (averaged over a typical observation of 20 minutes), and in the best cases the precision is better than 100 nanoseconds.We describe the NANOGrav nine-year data release, which contains time-of-arrival measurements and high quality timing solutions from 37 pulsars observed over spans ranging between 0.7 to 9.3 years.

  16. Modelling pulsar glitches

    NASA Astrophysics Data System (ADS)

    Haskell, Brynmor

    2016-07-01

    Pulsar glitches, i.e. sudden jumps in the spin frequency of pulsars, are thought to be due to the presence of large scale superfluid components in neutron star interiors, and offer a unique insight into the physics of matter at high densities and low temperatures. Nevertheless, more than forty years after the first observation, many open questions still exist on the nature of pulsar glitches. In this talk I will review our current theoretical understanding of glitches, of their trigger mechanisms and of the hydrodynamics of superfluid neutron stars. In particular I will focus on 'superfluid vortex avalanches' and recent advances in applying this paradigm to glitch observations, and I will discuss hydrodynamical modelling of the post-glitch recovery.

  17. Tempo2: Pulsar Timing Package

    NASA Astrophysics Data System (ADS)

    Hobbs, George; Edwards, Russell

    2012-10-01

    Tempo2 is a pulsar timing package developed to be used both for general pulsar timing applications and also for pulsar timing array research in which data-sets from multiple pulsars need to be processed simultaneously. It was initially developed by George Hobbs and Russell Edwards as part of the Parkes Pulsar Timing Array project. Tempo2 is based on the original Tempo (ascl:1509.002) code and can be used (from the command-line) in a similar fashion. It is very versatile and can be extended by plugins.

  18. Accelerating pulsar timing data analysis

    NASA Astrophysics Data System (ADS)

    van Haasteren, Rutger

    2013-02-01

    The analysis of pulsar timing data, especially in pulsar timing array (PTA) projects, has encountered practical difficulties: evaluating the likelihood and/or correlation-based statistics can become prohibitively computationally expensive for large data sets. In situations where a stochastic signal of interest has a power spectral density that dominates the noise in a limited bandwidth of the total frequency domain (e.g. the isotropic background of gravitational waves), a linear transformation exists that transforms the timing residuals to a basis in which virtually all the information about the stochastic signal of interest is contained in a small fraction of basis vectors. By only considering such a small subset of these `generalized residuals', the dimensionality of the data analysis problem is greatly reduced, which can cause a large speedup in the evaluation of the likelihood: the ABC-method (Acceleration By Compression). The compression fidelity, calculable with crude estimates of the signal and noise, can be used to determine how far a data set can be compressed without significant loss of information. Both direct tests on the likelihood, and Bayesian analysis of mock data, show that the signal can be recovered as well as with an analysis of uncompressed data. In the analysis of International PTA Mock Data Challenge data sets, speedups of a factor of 3 orders of magnitude are demonstrated. For realistic PTA data sets the acceleration may become greater than six orders of magnitude due to the low signal-to-noise ratio.

  19. Academic and Social Integration and Study Progress in Problem Based Learning

    ERIC Educational Resources Information Center

    Severiens, Sabine E.; Schmidt, Henk G.

    2009-01-01

    The present study explores the effects of problem-based learning (PBL) on social and academic integration and study progress. Three hundred and five first-year students from three different psychology curricula completed a questionnaire on social and academic integration. Effects of a full-fledged PBL environment were compared to (1) effects of a…

  20. Building a Meaning Bridge: Therapeutic Progress from Problem Formulation to Understanding

    ERIC Educational Resources Information Center

    Brinegar, Meredith Glick; Salvi, Lisa M.; Stiles, William B.; Greenberg, Leslie S.

    2006-01-01

    Qualitative analyses of 2 clients' psychotherapies (client centered and process-experiential) investigated the developmental progression from formulating a problem to achieving an understanding of it. The results elaborated one segment in the 8-stage Assimilation of Problematic Experiences Sequence (APES), through which problematic parts of a…

  1. Scientific uses of pulsars.

    PubMed

    Counselman, C C; Shapiro, I I

    1968-10-18

    The recently discovered celestial sources of pulsed radio energy can be used to test general relativity, to study the solar corona, and to determine the earth's orbit and ephemeris time. The vector positions and transverse velocities of pulsars can be measured with radio interferometers; in combination with pulse-arrival-time data, the distance determination will yield the average interstellar electron density. PMID:17836655

  2. Pulsars and Acceleration Sites

    NASA Technical Reports Server (NTRS)

    Harding, Alice

    2008-01-01

    Rotation-powered pulsars are excellent laboratories for the studying particle acceleration as well as fundamental physics of strong gravity, strong magnetic fields and relativity. But even forty years after their discovery, we still do not understand their pulsed emission at any wavelength. I will review both the basic physics of pulsars as well as the latest developments in understanding their high-energy emission. Special and general relativistic effects play important roles in pulsar emission, from inertial frame-dragging near the stellar surface to aberration, time-of-flight and retardation of the magnetic field near the light cylinder. Understanding how these effects determine what we observe at different wavelengths is critical to unraveling the emission physics. Fortunately the Gamma-Ray Large Area Space Telescope (GLAST), with launch in May 2008 will detect many new gamma-ray pulsars and test the predictions of these models with unprecedented sensitivity and energy resolution for gamma-rays in the range of 30 MeV to 300 GeV.

  3. The Pulsar Search Collaboratory

    ERIC Educational Resources Information Center

    Rosen, R.; Heatherly, S.; McLaughlin, M. A.; Kondratiev, V. I.; Boyles, J. R.; Wilson, M.; Lorimer, D. R.; Lynch, R.; Ransom, S.

    2010-01-01

    The Pulsar Search Collaboratory (PSC) (NSF #0737641) is a joint project between the National Radio Astronomy Observatory and West Virginia University designed to interest high school students in science, technology, engineering, and mathematics related career paths by helping them to conduct authentic scientific research. The 3 year PSC program,…

  4. Student Discovers New Pulsar

    NASA Astrophysics Data System (ADS)

    2010-01-01

    A West Virginia high-school student has discovered a new pulsar, using data from the giant Robert C. Byrd Green Bank Telescope (GBT). Shay Bloxton, 15, a participant in a project in which students analyze data from the radio telescope, spotted evidence of the pulsar on October 15. Bloxton, along with NRAO astronomers observed the object again one month later. The new observation confirmed that the object is a pulsar, a rotating, superdense neutron star. Bloxton is a sophomore at Nicholas County High School in Summersville, West Virginia. "I was very excited when I found out I had actually made a discovery," Bloxton said. She went to Green Bank in November to participate in the follow-up observation. She termed that visit "a great experience." "It also helped me learn a lot about how observations with the GBT are actually done," she added. The project in which she participated, called the Pulsar Search Collaboratory (PSC), is a joint project of the National Radio Astronomy Observatory (NRAO) and West Virginia University, funded by a grant from the National Science Foundation. Pulsars are known for their lighthouse-like beams of radio waves that sweep through space as the neutron star rotates, creating a pulse as the beam sweeps by the Earth. First discovered in 1967, pulsars serve as valuable natural "laboratories" for physicists studying exotic states of matter, quantum mechanics and General Relativity. The GBT, dedicated in 2000, has become one of the world's leading tools for discovering and studying pulsars. The PSC, led by NRAO Education Officer Sue Ann Heatherly and Project Director Rachel Rosen, includes training for teachers and student leaders, and provides parcels of data from the GBT to student teams. The project involves teachers and students in helping astronomers analyze data from 1500 hours of observing with the GBT. The 120 terabytes of data were produced by 70,000 individual pointings of the giant, 17-million-pound telescope. Some 300 hours of the

  5. The Optimization of GBT Pulsar Data for the GBNCC Pulsar Survey

    NASA Astrophysics Data System (ADS)

    Gordon, Ashlee Nicole; Green Bank NRAO, GBNCC

    2016-01-01

    The Green Bank Telescope collects data from the Green Bank Northern Celestial Cap (GBNCC) pulsar survey in order to find new pulsars within its sensitivity and also, to confirm previously found pulsars within its sensitivity range. The collected data is then loaded into the CyberSKA website database where astronomers are tasked with rating the data sets based on its potential to be a pulsar from 0(unclassified), 1(class 1 pulsar), 2(class 2 pulsar), 3(class 3 pulsar), 4(radio frequency interference), 5(not a pulsar), 6(know pulsar), 7(harmonic of a known pulsar). This specific research done was to use previously classified pulsars to create a python script that will automatically identify the data set as a pulsar or a non-pulsar. After finding the recurring frequencies of radio frequency interference (RFI), the frequencies were then added to a pipeline to further discern pulsars from RFI.

  6. Pulsar Astrophysics at Very High Energies in the Fermi-HAWC Era

    NASA Astrophysics Data System (ADS)

    Saz Parkinson, Pablo; Belfiore, A.; HAWC Collaboration; Fermi LAT Collaboration

    2013-04-01

    Pulsar astrophysics has received a major boost in recent years with the tremendous progress achieved in the gamma-ray regime. In the 0.1-100 GeV energy range, where pulsars emit a large fraction of their energy, the Fermi Large Area Telescope (LAT) is providing an abundance of high-quality data, greatly improving our understanding of the pulsar mechanism. In addition to detecting over 120 pulsars, the improved statistics from the LAT have enabled studies of some of the brightest pulsars with exquisite detail, up to unprecedented energies (in some cases above 25 GeV), finally bridging the gap with ground-based instruments. At very high energies (VHE, > 100 GeV), recent detections by VERITAS and MAGIC of pulsations from the Crab pose a serious challenge to pulsar models. It is unclear whether the Crab is unique in this respect, or whether VHE emission is common in other pulsars. Some models predict that such emission should smoothly connect with the standard GeV emission seen by the LAT, while others point instead to a different spectral (e.g. inverse Compton) component altogether. If present in other pulsars, such a component might be found at higher energies (> 1 TeV), but its flux is highly uncertain. Further VHE observations of pulsars are crucial to distinguish between (and constrain) the competing scenarios. The High Altitude Water Cherenkov Observatory (HAWC), currently under construction in Mexico, is well-suited to perform observations of pulsars above 100 GeV. The HAWC detector has a wide field of view, high duty cycle, and excellent sensitivity 15 times better than its predecessor Milagro), and its contemporaneous operation with Fermi should enable it to carry out the first comprehensive survey of northern-hemisphere gamma-ray pulsars above 100 GeV. I will discuss the motivations, goals, timeline, and sensitivity of HAWC searches for VHE emission from pulsars.

  7. Pulsar-supernova remnant associations

    NASA Astrophysics Data System (ADS)

    Manchester, R. N.

    1994-04-01

    Pulsars and supernova remnants (SNRs) are both believed to be formed in the supernova explosions of massive stars. Therefore one might expect to see associations between the two classes of object. In fact, up until a couple of years ago, there was only a handful of believable associations and even now there are only nine or ten. It is relatively easy to explain why such a small fraction of the 600 or so known pulsars are associated with supernova remnants. The average pulsar lifetime is of the order of 106 years, whereas the average supernova remnant is detectable for about 104 years. Therefore, one would expect only about one percent of pulsars to be still associated, as is observed. It is somewhat more difficult to explain why so few of the 150 known supernova remnants have associated pulsars. The main factor is that supernova remnants are seen throughout the Galaxy whereas most pulsars are detectable only relatively close to the Sun, within a few kiloparsec. Another factor is that pulsar emission is beamed, so even if a pulsar exists in a relatively nearby supernova remnant, it may be undetectable. The most believable of the suggested associations are listed. Associations which are possible but by no means certain are indicated by question mark. For the more certain associations, the pulsar position is within the SNR boundaries (an exception is 'The Duck', where the pulsar is at the tip of the 'beak'), the distance estimates for the pulsar and SNR are compatible, and the age estimates are likewise compatible. References to most of these associations may be found in the pulsar catalog of Taylor, Manchester and Lyne (1993, Astrophys. J. Suppl., 88, 529). Recent references not included in the catalog are for PSR B1706-44 (McAdam, Osborne and Parkinson, 1993, Nature, 361, 516) and PSR B2334+61 (Kulkarni et al., 1993, Nature, 362, 135).

  8. Pulsar braking: magnetodipole vs. wind

    NASA Astrophysics Data System (ADS)

    Tong, Hao

    2016-01-01

    Pulsars are good clocks in the universe. One fundamental question is that why they are good clocks? This is related to the braking mechanism of pulsars. Nowadays pulsar timing is done with unprecedented accuracy. More pulsars have braking indices measured. The period derivative of intermittent pulsars and magnetars can vary by a factor of several. However, during pulsar studies, the magnetic dipole braking in vacuum is still often assumed. It is shown that the fundamental assumption of magnetic dipole braking (vacuum condition) does not exist and it is not consistent with the observations. The physical torque must consider the presence of the pulsar magnetosphere. Among various efforts, the wind braking model can explain many observations of pulsars and magnetars in a unified way. It is also consistent with the up-to-date observations. It is time for a paradigm shift in pulsar studies: from magnetic dipole braking to wind braking. As one alternative to the magnetospheric model, the fallback disk model is also discussed.

  9. ON THE GLOBAL STRUCTURE OF PULSAR FORCE-FREE MAGNETOSPHERE

    SciTech Connect

    Petrova, S. A.

    2013-02-20

    The dipolar magnetic field structure of a neutron star is modified by the plasma originating in the pulsar magnetosphere. In the simplest case of a stationary axisymmetric force-free magnetosphere, a self-consistent description of the fields and currents is given by the well-known pulsar equation. Here we revise the commonly used boundary conditions of the problem in order to incorporate the plasma-producing gaps and to provide a framework for a truly self-consistent treatment of the pulsar magnetosphere. A generalized multipolar solution of the pulsar equation is found, which, as compared to the customary split monopole solution, is suggested to better represent the character of the dipolar force-free field at large distances. In particular, the outer gap location entirely inside the light cylinder implies that beyond the light cylinder the null and critical lines should be aligned and become parallel to the equator at a certain altitude. Our scheme of the pulsar force-free magnetosphere, which will hopefully be followed by extensive analytic and numerical studies, may have numerous implications for different fields of pulsar research.

  10. STRONG FIELD EFFECTS ON PULSAR ARRIVAL TIMES: GENERAL ORIENTATIONS

    SciTech Connect

    Wang Yan; Creighton, Teviet; Price, Richard H.; Jenet, Frederick A.

    2009-11-10

    A pulsar beam passing close to a black hole can provide a probe of very strong gravitational fields even if the pulsar itself is not in a strong field region. In the case that the spin of the hole can be ignored, we have previously shown that all strong field effects on the beam can be understood in terms of two 'universal' functions: F(phi{sub in}) and T(phi{sub in}) of the angle of beam emission phi{sub in}; these functions are universal in that they depend only on a single parameter, the pulsar/black hole distance from which the beam is emitted. Here we apply this formalism to general pulsar-hole-observer geometries, with arbitrary alignment of the pulsar spin axis and arbitrary pulsar beam direction and angular width. We show that the analysis of the observational problem has two distinct elements: (1) the computation of the location and trajectory of an observer-dependent 'keyhole' direction of emission in which a signal can be received by the observer; and (2) the determination of an annulus that represents the set of directions containing beam energy. Examples of each are given along with an example of a specific observational scenario.

  11. The Extended Pulsar Magnetosphere

    NASA Technical Reports Server (NTRS)

    Constantinos, Kalapotharakos; Demosthenes, Kazanas; Ioannis, Contopoulos

    2012-01-01

    We present the structure of the 3D ideal MHD pulsar magnetosphere to a radius ten times that of the light cylinder, a distance about an order of magnitude larger than any previous such numerical treatment. Its overall structure exhibits a stable, smooth, well-defined undulating current sheet which approaches the kinematic split monopole solution of Bogovalov 1999 only after a careful introduction of diffusivity even in the highest resolution simulations. It also exhibits an intriguing spiral region at the crossing of two zero charge surfaces on the current sheet, which shows a destabilizing behavior more prominent in higher resolution simulations. We discuss the possibility that this region is physically (and not numerically) unstable. Finally, we present the spiral pulsar antenna radiation pattern.

  12. Pulsar Observations with Radio Telescope FAST

    NASA Astrophysics Data System (ADS)

    Nan, Ren-Dong; Wang, Qi-Ming; Zhu, Li-Chun; Zhu, Wen-Bai; Jin, Cheng-Jin; Gan, Heng-Qian

    2006-12-01

    FAST, Five hundred meter Aperture Spherical Telescope, is the Chinese effort for the international project SKA, Square Kilometer Array. An innovative engineering concept and design pave a new road to realizing huge single dish in the most effective way. Three outstanding features of the telescope are the unique karst depressions as the sites, the active main reflector which corrects spherical aberration on the ground to achieve full polarization and wide band without involving complex feed system, and the light focus cabin driven by cables and servomechanism plus a parallel robot as secondary adjustable system to carry the most precise parts of the receivers. Besides a general coverage of those critical technologies involved in FAST concept, the progresses in demonstrating model being constructed at the Miyun Radio Observatory of the NAOC is introduced. Being the most sensitive radio telescope, FAST will enable astronomers to jumpstart many of science goals, for example, the natural hydrogen line surveying in distant galaxies, looking for the first generation of shining objects, hearing the possible signal from other civilizations, etc. Among these subjects, the most striking one could be pulsar study. Large scale survey by FAST will not only improve the statistics of the pulsar population, but also may offer us a good fortune to pick up more of the most exotic, even unknown types like a sub-millisecond pulsar or a neutron star -- black hole binary as the telescope is put into operation.

  13. The pulsar spectral index distribution

    NASA Astrophysics Data System (ADS)

    Bates, S. D.; Lorimer, D. R.; Verbiest, J. P. W.

    2013-05-01

    The flux-density spectra of radio pulsars are known to be steep and, to first order, described by a power-law relationship of the form Sν ∝ να, where Sν is the flux density at some frequency ν and α is the spectral index. Although measurements of α have been made over the years for several hundred pulsars, a study of the intrinsic distribution of pulsar spectra has not been carried out. From the result of pulsar surveys carried out at three different radio frequencies, we use population synthesis techniques and a likelihood analysis to deduce what underlying spectral index distribution is required to replicate the results of these surveys. We find that in general the results of the surveys can be modelled by a Gaussian distribution of spectral indices with a mean of -1.4 and unit standard deviation. We also consider the impact of the so-called gigahertz-peaked spectrum pulsars proposed by Kijak et al. The fraction of peaked-spectrum sources in the population with any significant turnover at low frequencies appears to be at most 10 per cent. We demonstrate that high-frequency (>2 GHz) surveys preferentially select flatter spectrum pulsars and the converse is true for lower frequency (<1 GHz) surveys. This implies that any correlations between α and other pulsar parameters (for example age or magnetic field) need to carefully account for selection biases in pulsar surveys. We also expect that many known pulsars which have been detected at high frequencies will have shallow, or positive, spectral indices. The majority of pulsars do not have recorded flux density measurements over a wide frequency range, making it impossible to constrain their spectral shapes. We also suggest that such measurements would allow an improved description of any populations of pulsars with `non-standard' spectra. Further refinements to this picture will soon be possible from the results of surveys with the Green Bank Telescope and LOFAR.

  14. Computational methods for the nuclear and neutron matter problems. Progress report

    SciTech Connect

    Kalos, M.H.

    1980-01-01

    Progress on the development of Monte Carlo methods for the treatment of extensive nuclear and neutron matter and of finite nuclei is reported. Appropriate modifications in the Monte Carlo formalism were made and carried through for the V/sub 4/ potential; the previous method was satisfactory for V/sub 3/, and the latter calculations have been completed. Significant progress was made in the development of the Green's function Monte Carlo method for fermion systems. It proved useful to study a model nuclear few-body problem, in particular, a kind of three-neutron problem. This work proved successful in that a stable Monte Carlo algorithm was developed. It gave correct results for energy and wave function for a soluble (separable) test problem and reasonable results (confirmed by variational computations) for a system interacting by pairwise phenomenological potentials. A stable GFMC algorithm for many-fermion systems has not been implemented, but ancillary studies on /sup 3/He have advanced considerably. In particular, new methods for finding upper bounds have been devised in which Green's function methods are used. These have particular application to nuclear problems. Lower values of the upper bounds were found for /sup 3/He. 20 tables. (RWR)

  15. Current Results at PALFA Pulsar Survey at Arecibo Observatory

    NASA Astrophysics Data System (ADS)

    Beroiz, Martin; Stovall, K.; Jenet, F.; Cordes, J.; Lorimer, D.; Backer, D.; PALFA Consortium

    2010-01-01

    We present the current progress on the PALFALFA (Pulsar-ALFALFA) survey recently started at the Arecibo Radio Observatory. PALFALFA enhances the ALFALFA (Arecibo Legacy Fast ALFA) extragalactic HI survey by adding a commensal real-time pulsar/radio transient search pipe-line. The current analysis pipe-line runs on an 8 core (2.3 GHz) G5 Macpro at the observatory. It incorporates the PRESTO periodicity search tools together with software developed at University of Texas at Brownsville for radio transient detection. In this poster we present results, statistics, and algorithms used in the survey.

  16. Searching for Planets Around Pulsars

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-09-01

    Did you know that the very first exoplanets ever confirmed were found around a pulsar? The precise timing measurements of pulsar PSR 1257+12 were what made the discovery of its planetary companions possible. Yet surprisingly, though weve discovered thousands of exoplanets since then, only one other planet has ever been confirmed around a pulsar. Now, a team of CSIRO Astronomy and Space Science researchers are trying to figure out why.Formation ChallengesThe lack of detected pulsar planets may simply reflect the fact that getting a pulsar-planet system is challenging! There are three main pathways:The planet formed before the host star became a pulsar which means it somehow survived its star going supernova (yikes!).The planet formed elsewhere and was captured by the pulsar.The planet formed out of the debris of the supernova explosion.The first two options, if even possible, are likely to be rare occurrences but the third option shows some promise. In this scenario, after the supernova explosion, a small fraction of the material falls back toward the stellar remnant and is recaptured, forming what is known as a supernova fallback disk. According to this model, planets could potentially form out of this disk.Disk ImplicationsLed by Matthew Kerr, the CSIRO astronomers set out to systematically look for these potential planets that might have formed in situ around pulsars. They searched a sample of 151 young, energetic pulsars, scouring seven years of pulse time-of-arrival data for periodic variation that could signal the presence of planetary companions. Their methods to mitigate pulsar timing noise and model realistic orbits allowed them to have good sensitivity to low-mass planets.The results? They found no conclusive evidence that any of these pulsars have planets.This outcome carries with it some significant implications. The pulsar sample spans 2 Myr in age, in which planets should have had enough time to form in debris disks. The fact that none were detected

  17. Pulsar timing and general relativity

    NASA Technical Reports Server (NTRS)

    Backer, D. C.; Hellings, R. W.

    1986-01-01

    Techniques are described for accounting for relativistic effects in the analysis of pulsar signals. Design features of instrumentation used to achieve millisecond accuracy in the signal measurements are discussed. The accuracy of the data permits modeling the pulsar physical characteristics from the natural glitches in the emissions. Relativistic corrections are defined for adjusting for differences between the pulsar motion in its spacetime coordinate system relative to the terrestrial coordinate system, the earth's motion, and the gravitational potentials of solar system bodies. Modifications of the model to allow for a binary pulsar system are outlined, including treatment of the system as a point mass. Finally, a quadrupole model is presented for gravitational radiation and techniques are defined for using pulsars in the search for gravitational waves.

  18. Sensitivity of Pulsar Timing Arrays

    NASA Astrophysics Data System (ADS)

    Siemens, Xavier

    2015-08-01

    For the better part of the last decade, the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has been using the Green Bank and Arecibo radio telescopes to monitor millisecond pulsars. NANOGrav, along with similar international collaborations, the European Pulsar Timing Array and the Parkes Pulsar Timing Array in Australia, form a consortium of consortia: the International Pulsar Timing Array (IPTA). The goal of the IPTA is to directly detect low-frequency gravitational waves which cause small changes to the times of arrival of radio pulses from millisecond pulsars. In this talk I will discuss the work of NANOGrav and the IPTA as well as our sensitivity to gravitational waves from astrophysical sources. I will show that a detection is possible by the end of the decade.

  19. Magnetars and white dwarf pulsars

    NASA Astrophysics Data System (ADS)

    Lobato, Ronaldo V.; Malheiro, Manuel; Coelho, Jaziel G.

    2016-07-01

    The anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs) are a class of pulsars understood as neutron stars (NSs) with super strong surface magnetic fields, namely B ≳ 1014G, and for that reason are known as magnetars. However, in the last years, some SGRs/AXPs with low surface magnetic fields B ˜ (1012-1013)G have been detected, challenging the magnetar description. Moreover, some fast and very magnetic white dwarfs (WDs) have also been observed, and at least one showed X-ray energy emission as an ordinary pulsar. Following this fact, an alternative model based on WDs pulsars has been proposed to explain this special class of pulsars. In this model, AXPs and SGRs as dense and magnetized WDs can have surface magnetic field B ˜ 107-1010 G and rotate very fast with frequencies Ω ˜ 1rad/s, consistent with the observed rotation periods P ˜ (2-12)s.

  20. [Pulsar perimetry. A review and new results].

    PubMed

    Gonzalez de la Rosa, M; Gonzalez-Hernandez, M

    2013-02-01

    We present a review and update on Pulsar perimetry, which combines temporal frequency, contrast and spatial frequency stimuli. The effects of age, visual acuity, and learning on results are described. Data on threshold fluctuation, signal-to-noise ratio, and the possibility of reducing noise with filtering techniques are provided. We describe its dynamic range and the possibility of compensating for profound defects. Finally, we show the results obtained in normal patients and in those with ocular hypertension or initial glaucoma, as well as an analysis of glaucoma progression. PMID:23392836

  1. Pulsar Bursts Coming From Beachball-Sized Structures

    NASA Astrophysics Data System (ADS)

    2003-03-01

    mystery. With the help of engineers at the NRAO, Hankins and his team designed and built specialized electronic equipment that allowed them to study the pulsar's radio pulses on extremely small time scales. They took this equipment to the National Science Foundation's giant, 1,000-foot-diameter radio telescope at Arecibo. With their equipment, they analyzed the Crab pulsar's superstrong "giant" pulses, breaking them down into tiny time segments. The researchers discovered that some of the "giant" pulses contain subpulses that last no longer than two nanoseconds. That means, they say, that the regions in which these subpulses are generated can be no larger than about two feet across -- the distance that light could travel in two nanoseconds. This fact, the researchers say, is critically important to understanding how the powerful radio emission is generated. A pulsar's magnetosphere -- the region above the neutron star's magnetic poles where the radio waves are generated -- is "the most exotic environment in the Universe," said Kern. In this environment, matter exists as a plasma, in which electrically charged particles are free to respond to the very strong electric and magnetic fields in the star's atmosphere. The very short subpulses the researchers detected could only be generated, they say, by a strange process in which density waves in the plasma interact with their own electrical field, becoming progressively denser until they reach a point at which they "collapse explosively" into superstrong bursts of radio waves. "None of the other proposed mechanisms can produce such short pulses," Eilek said. "The ability to examine these pulses on such short time scales has given us a new window through which to study pulsar radio emission," she added. The Crab pulsar is one of only three pulsars known to emit superstrong "giant" pulses. "Giant" pulses occur occasionally among the steady but much weaker "normal" pulses coming from the neutron star. Some of the brief subpulses

  2. Millisecond pulsars: Timekeepers of the cosmos

    NASA Technical Reports Server (NTRS)

    Kaspi, Victoria M.

    1995-01-01

    A brief discussion on the characteristics of pulsars is given followed by a review of millisecond pulsar discoveries including the very first, PRS B1937+21, discovered in 1982. Methods of timing millisecond pulsars and the accuracy of millisecond pulsars as clocks are discussed. Possible reasons for the pulse residuals, or differences between the observed and predicted pulse arrival times for millisecond pulsars, are given.

  3. Progression to Problem Drinking Among Mexican American and White European First-Year College Students: A Multiple Group Analysis*

    PubMed Central

    Schweizer, C. Amanda; Doran, Neal; Roesch, Scott C.; Myers, Mark G.

    2011-01-01

    Objective: Problem drinking during college is a well-known phenomenon. However, predictors of progression to problematic drinking, particularly among ethnic minorities such as Mexican Americans, have received limited research attention. Method: The current study compared the rates and predictors of problem drinking progression from the first to the second year of college among four groups: Mexican American men, Mexican American women, White European men, and White European women (N = 215). At baseline, participants were all first-year college students who scored as nonproblem drinkers on the Young Adult Alcohol Problems Screening Test (YAAPST). Participants were classified as progressors or stable nondrinkers/nonproblem drinkers based on YAAPST scores 12 months later. Hypothesized predictors of progression included behavioral undercontrol, negative emotionality, alcohol use expectancies, and cultural orientation (Mexican American sample only). Differences were anticipated between gender and ethnic groups in both progression rates and predictors of progression. Results: Twenty-nine percent of the sample progressed to problematic drinking; however, no differences emerged by gender or ethnicity. For the full sample, higher behavioral undercontrol and higher negative emotionality significantly predicted progression. Differences in predictors were not found across gender and ethnic subgroups. Conclusions: The hypothesis that rates of progression to problem drinking would differ among the four gender and ethnic groups was not supported. Thus, although White European men are most often identified as at high risk for alcohol use problems, the present findings indicate that women and Mexican American students also should be targeted for prevention and/or intervention. PMID:22051211

  4. Progressive Transitions from Algorithmic to Conceptual Understanding in Student Ability To Solve Chemistry Problems: A Lakatosian Interpretation.

    ERIC Educational Resources Information Center

    Niaz, Mansoor

    The main objective of this study is to construct models based on strategies students use to solve chemistry problems and to show that these models form sequences of progressive transitions similar to what Lakatos (1970) in the history of science refers to as progressive 'problemshifts' that increase the explanatory' heuristic power of the models.…

  5. Pulsars in binary systems: probing binary stellar evolution and general relativity.

    PubMed

    Stairs, Ingrid H

    2004-04-23

    Radio pulsars in binary orbits often have short millisecond spin periods as a result of mass transfer from their companion stars. They therefore act as very precise, stable, moving clocks that allow us to investigate a large set of otherwise inaccessible astrophysical problems. The orbital parameters derived from high-precision binary pulsar timing provide constraints on binary evolution, characteristics of the binary pulsar population, and the masses of neutron stars with different mass-transfer histories. These binary systems also test gravitational theories, setting strong limits on deviations from general relativity. Surveys for new pulsars yield new binary systems that increase our understanding of all these fields and may open up whole new areas of physics, as most spectacularly evidenced by the recent discovery of an extremely relativistic double-pulsar system. PMID:15105492

  6. FSSC Science Tools: Pulsar Analysis

    NASA Technical Reports Server (NTRS)

    Thompson, Dave

    2010-01-01

    This slide presentation reviews the typical pulsar analysis, giving tips for screening of the data, the use of time series analysis, and utility tools. Specific information about analyzing Vela data is reviewed.

  7. Fermi's New Pulsar Detection Technique

    NASA Video Gallery

    To locate a pulsar in Fermi LAT data requires knowledge of the object’s sky position, its pulse period, and how the pulse rate slows over time. Computers check many different combinations of posi...

  8. Millisecond radio pulsars in globular clusters

    NASA Technical Reports Server (NTRS)

    Verbunt, Frank; Lewin, Walter H. G.; Van Paradijs, Jan

    1989-01-01

    It is shown that the number of millisecond radio pulsars, in globular clusters, should be larger than 100, applying the standard scenario that all the pulsars descend from low-mass X-ray binaries. Moreover, most of the pulsars are located in a small number of clusters. The prediction that Teran 5 and Liller 1 contain at least about a dozen millisecond radio pulsars each is made. The observations of millisecond radio pulsars in globular clusters to date, in particular the discovery of two millisecond radio pulsars in 47 Tuc, are in agreement with the standard scenario, in which the neutron star is spun up during the mass transfer phase.

  9. On the evolution of pulsars

    NASA Technical Reports Server (NTRS)

    Beskin, V. S.; Gurevich, A. V.; Istomin, Ya. N.

    1991-01-01

    Data from a previous investigation on the angle chi between the axis of rotation and the magnetic dipole axis, determined from polarization observations, provides a complete catalog which makes it possible to carry out a detailed comparison of the theoretical results of this present investigation with the observed distribution of radio pulsars over the angel chi. Before such a comparison is made, the main features of a theory for pulsar evolution is described.

  10. Pulsar distance measurements with VLBI

    NASA Astrophysics Data System (ADS)

    Deller, Adam

    A reliable estimate of the distance to a pulsar underpins the interpretation of observational results across all wavebands. While there are many model-dependent methods available, most prominently the combination of the pulsar dispersion measure and a Galactic electron density distribution model, the underlying models must be anchored by a collection of accurate, model-independent measurements. By far the largest number of reliable and model-independent pulsar distance measurements have been obtained via a determination of annual geometric parallax with Very Long Baseline Interferometry (VLBI) observations. With high sensitivity and a good control of systematic effects via careful calibration, the milli-arcsecond level native resolution means that relative positional accuracies of a few 10s of micro-arcseconds are achievable. This precision means that in principle a parallax distance is feasible for the majority of the known radio pulsar population; however, actually observing every feasible pulsar would cost a prohibitive amount of telescope time. Here, I will first describe several recent VLBI astrometry results where the provided distance has been crucial in furthering the understanding of the system. Second, I will describe the recently completed "PSRPI" program, which measured over 50 pulsar parallaxes using the Very Long Baseline Array - by far the largest pulsar parallax program to date. Third, I will describe the recently commenced "MSPSRPI" extension to the PSRPI program, which targets exclusively millisecond pulsars and aims to greatly improve the tie between the solar system barycentric frame and the International Celestial Reference Frame. Finally, I will briefly discuss the impact of developments in VLBI instrumentation, including the forthcoming Square Kilometre Array.

  11. Pulsar Observatory for Students (POS)

    NASA Astrophysics Data System (ADS)

    Joshi, Bhal Chandra; Manoharan, P. K.; Gopakumar, A.; Mitra, D.; Bagchi, Joydeep; Saikia, D. J.

    2012-07-01

    A new program, to initiate motivated undergraduate students to the methodology of pulsar astronomy in particular and radio astronomy in general, is being launched at the Ooty Radio Telescope (ORT). The ORT is a 530 m X 30 m cylindrical radio telescope operating at 325 MHz, having an equatorial mount. Its equatorial mount allows modestly trained students to make pulsar observations without any substantial help from the observatory. Due to its large collecting area, it is a sensitive instrument for pulsar astronomy, capable of detecting a large number of pulsars with short observation time. The program consists of biannual workshops that will introduce scores of students to basics of radio-astronomy and pulsars. It will also train them in the use of the ORT as well as expose them to the future prospects and excitements in the field. The second leg of the program involves live ORT observations by these trained students during various academic breaks. There is a possibility for a follow up program of highly motivated students, selected from this program, to pursue projects of their interest from the data obtained in these sensitive observations. The long term aim of the program is to enlarge the pulsar astronomy community in the country. The presentation will highlight the main features of this program and describe the experience drawn from such programs.

  12. The LOFAR Pulsar Data Pipeline

    NASA Astrophysics Data System (ADS)

    Alexov, A.; Hessels, J.; Mol, J. D.; Stappers, B.; van Leeuwen, J.

    2010-12-01

    The LOw Frequency ARray (LOFAR) for radio astronomy is being built in the Netherlands by ASTRON, with extensions throughout Europe. LOFAR operates at radio frequencies below 250 MHz. The project is an interferometric array of radio antennas grouped into stations that are distributed over an area of hundreds of kilometers. LOFAR will revolutionise low-frequency radio astronomy. Transient radio phenomena and pulsars are one of six LOFAR Key Science Projects (KSPs). As part of the Transients KSP, the Pulsar Working Group has been developing the LOFAR Pulsar Data Pipeline to both study known pulsars as well as search for new ones. The pipeline is being developed for the Blue Gene/P (BG/P) supercomputer and a large Linux cluster in order to utilize enormous amounts of computation capabilities (˜ 50 Tflops) and data streams of up to 23TB/hour. The LOFAR pipeline output will be using the Hierarchical Data Format 5 (HDF5) to efficiently store large amounts of numerical data, and to manage complex data encompassing a variety of data types, across distributed storage and processing architectures. We present the LOFAR Pulsar Data Pipeline overview, the pulsar beam-formed data format, the status of the pipeline processing as well as our future plans for developing additional transient pipelines.

  13. Radio pulsar disk electrodynamics

    NASA Technical Reports Server (NTRS)

    Michel, F. C.

    1983-01-01

    Macroscopic physics are discussed for the case of a disk close to an isolated, magnetized, rotating neutron star that acts as a Faraday disk dynamo, while the disk acts as both a load and a neutral sheet. This sheet allows the polar cap current to return to the neutron star, splitting a dipolar field into two monopolar halves. The dominant energy loss is from the stellar wind torque, and the next contribution is dissipation in the auroral zones, where the current returns to the star in a 5 cm-thick sheet. The disk itself may be a source of visible radiation comparable to that in pulsed radio frequency emission. As the pulsar ages, the disk expands and narrows into a ring which, it is suggested, may lead to a cessation of pulsed emission at periods of a few sec.

  14. Ion-proton pulsars

    NASA Astrophysics Data System (ADS)

    Jones, P. B.

    2016-07-01

    Evidence derived with minimal assumptions from existing published observations is presented to show that an ion-proton plasma is the source of radio-frequency emission in millisecond and in normal isolated pulsars. There is no primary involvement of electron-positron pairs. This conclusion has also been reached by studies of the plasma composition based on well-established particle-physics processes in neutron stars with positive polar-cap corotational charge density. This work has been published in a series of papers which are also summarized here. It is now confirmed by simple analyses of the observed radio-frequency characteristics, and its implications for the further study of neutron stars are outlined.

  15. Pulsars In The Headlines

    NASA Astrophysics Data System (ADS)

    Del Puerto, C.

    1967 was the year of the so-called “war of the six days” or “third Arab Israeli war”, the year of the Che Guevara's death in Bolivia, the year of the military coup in Greece and, in medicine, the year of the first human heart transplant. Moreover, the signing of the international agreement on the use of space with peaceful means and the crash of the Russian shuttle Soyuz-1, with Cosmonaut Vladimir Kamarov on board also happened that year. Likewise, Spanish writer and professor of journalists, José Azorín, passed away. However, here we are interested in 1967 because it was the year of the detection of pulsars, which astronomers initially confused with signals from extraterrestrials or Little Green Men. Nowadays, they are still present in the headlines.

  16. Ion-proton pulsars

    NASA Astrophysics Data System (ADS)

    Jones, P. B.

    2016-04-01

    Evidence derived with minimal assumptions from existing published observations is presented to show that an ion-proton plasma is the source of radio-frequency emission in millisecond and in normal isolated pulsars. There is no primary involvement of electron-positron pairs. This conclusion has also been reached by studies of the plasma composition based on well-established particle-physics processes in neutron stars with positive polar-cap corotational charge density. This work has been published in a series of papers which are also summarized here. It is now confirmed by simple analyses of the observed radio-frequency characteristics, and its implications for the further study of neutron stars are outlined.

  17. Progress and problems in the biology, diagnostics, and therapeutics of prion diseases.

    PubMed

    Aguzzi, Adriano; Heikenwalder, Mathias; Miele, Gino

    2004-07-01

    The term "prion" was introduced by Stanley Prusiner in 1982 to describe the atypical infectious agent that causes transmissible spongiform encephalopathies, a group of infectious neurodegenerative diseases that include scrapie in sheep, Creutzfeldt-Jakob disease in humans, chronic wasting disease in cervids, and bovine spongiform encephalopathy in cattle. Over the past twenty years, the word "prion" has been taken to signify various subtly different concepts. In this article, we refer to the prion as the transmissible principle underlying prion diseases, without necessarily implying any specific biochemical or structural identity. When Prusiner started his seminal work, the study of transmissible spongiform encephalopathies was undertaken by only a handful of scientists. Since that time, the "mad cow" crisis has put prion diseases on the agenda of both politicians and the media. Significant progress has been made in prion disease research, and many aspects of prion pathogenesis are now understood. And yet the diagnostic procedures available for prion diseases are not nearly as sensitive as they ought to be, and no therapeutic intervention has been shown to reliably affect the course of the diseases. This article reviews recent progress in the areas of pathogenesis of, diagnostics of, and therapy for prion diseases and highlights some conspicuous problems that remain to be addressed in each of these fields. PMID:15254579

  18. Progress and problems in the biology, diagnostics, and therapeutics of prion diseases

    PubMed Central

    Aguzzi, Adriano; Heikenwalder, Mathias; Miele, Gino

    2004-01-01

    The term “prion” was introduced by Stanley Prusiner in 1982 to describe the atypical infectious agent that causes transmissible spongiform encephalopathies, a group of infectious neurodegenerative diseases that include scrapie in sheep, Creutzfeldt-Jakob disease in humans, chronic wasting disease in cervids, and bovine spongiform encephalopathy in cattle. Over the past twenty years, the word “prion” has been taken to signify various subtly different concepts. In this article, we refer to the prion as the transmissible principle underlying prion diseases, without necessarily implying any specific biochemical or structural identity. When Prusiner started his seminal work, the study of transmissible spongiform encephalopathies was undertaken by only a handful of scientists. Since that time, the “mad cow” crisis has put prion diseases on the agenda of both politicians and the media. Significant progress has been made in prion disease research, and many aspects of prion pathogenesis are now understood. And yet the diagnostic procedures available for prion diseases are not nearly as sensitive as they ought to be, and no therapeutic intervention has been shown to reliably affect the course of the diseases. This article reviews recent progress in the areas of pathogenesis of, diagnostics of, and therapy for prion diseases and highlights some conspicuous problems that remain to be addressed in each of these fields. PMID:15254579

  19. Distance Indicators of Gamma-Ray Pulsars

    NASA Astrophysics Data System (ADS)

    Wang, Wei

    2013-01-01

    Distance measurements of gamma-ray pulsars are challenging questions in present pulsar studies. The Large Area Telescope (LAT) aboard the Fermi gamma-ray observatory discovered more than 100 gamma-ray pulsars including 24 new gamma-selected pulsars which nearly have no distance information. We study the relation between gamma-ray emission efficiency (η = Lγ/Ė) and pulsar parameters for young radio-selected gamma-ray pulsars with known distance information in the first gamma-ray pulsar catalog reported by Fermi/LAT. We have introduced three generation order parameters to describe gamma-ray emission properties of pulsars, and find the strong correlation of η - ζ3 a generation order parameter which reflects γ-ray photon generations in pair cascade processes induced by magnetic field absorption in pulsar magnetosphere. A good correlation of η - BLC the magnetic field at the light cylinder radius is also found. These correlations would be the distance indicators in gamma-ray pulsars to evaluate distances for gamma-selected pulsars. Distances of 25 gamma-selected pulsars are estimated, which could be tested by other distance measurement methods. Physical origin of the correlations may be also interesting for pulsar studies.

  20. Gene transfer into hematopoietic progenitor and stem cells: progress and problems.

    PubMed

    Dunbar, C E; Emmons, R V

    1994-11-01

    Gene transfer to hematopoietic cells for the purpose of "gene therapy" is a new and rapidly developing field with clinical trials in progress. A fundamental goal of research in this field is the incorporation of exogenous genes into the chromosomes of the most primitive hematopoietic progenitor cells--stem cells. Recombinantly engineered retroviral vectors are the best characterized and are currently the only vector type in clinical trials directed at the hematopoietic system. High efficiency gene transfer and expression in murine stem cells and their progeny is now routine, but in larger animal models such as dogs or primates and preliminary clinical trials, gene transfer has been less successful. Problems such as retroviral efficiency, gene expression, insertional mutagenesis and helper virus contamination are being addressed. A promising new vector, the adeno-associated virus (AAV), has shown promise and may allow production of high titer, stable, recombinant virions without helper contamination and with potentially better safety parameters. However, the technology for AAV gene transfer is currently underdeveloped, and issues related to the reproducible production of vectors must be addressed. Other non-viral vector systems are being explored, but little data are available on applications to hematopoietic cells. Better preclinical models are needed to study gene targeting and expression in human cells. An overview of recombinant retroviral and adeno-associated viral vector production, preclinical data and preliminary clinical data will be given, and problems needing to be addressed at all stages of development before broad clinical utility can be achieved will be discussed. PMID:7881358

  1. Selected problems in experimental intermediate energy. Progress report, February 1, 1994--January 31, 1997

    SciTech Connect

    Mayes, B.W.; Hungerford, E.V.; Pinsky, L.S.

    1995-09-01

    A complete description of the research program of the intermediate energy group at the University of Houston may be found in previous progress reports, renewal proposals, and proposals to the various accelerator advisory committees. Recent documents are appended to this report and summaries of current research activities are presented in the next section. The objectives of the research program are to: (1) investigate selected, forefront problems in experimental intermediate energy physics; (2) educate students in this field of research; and, (3) develop the instrumentation necessary to undertake this experimental program. Generally, the research is designed to search for physical processes which cannot be explained by conventional models of elementary interactions. As one example, we use nuclear targets where the nucleus provides a many body environment of strongly interacting particles, and where one attempts to observe the perturbation of a known interaction by this environment. These effects, however, may be masked by the complexity of the many body problem and may be difficult to observe. Therefore, experiments of this type must be carefully chosen and analyzed for deviations from the more conventional models.

  2. New Pulsars from Arecibo Drift Scan Searches

    NASA Technical Reports Server (NTRS)

    McLaughlin, M. A.; Lorimer, D. R.; Arzoumanian, Z.; Backer, D. C.; Cordes, J. M.; Fruchter, A.; Lommen, A. N.; Xilouris, K.

    2003-01-01

    We report new pulsars discovered in drift-scan data taken by two collaborations (Berkeley/Cornell and STScI/NAIC) during the latter stages of the Arecibo upgrade period. The data were taken with the Penn State Pulsar Machine and are being processed on the COBRA cluster at Jodrell Bank. Processing is roughly 70% complete and has resulted in the detection of 10 new and 31 known pulsars, in addition to a number of pulsar candidates. The 10 new pulsars include one pulsar with a spin-period of 55 ms and another with a spin period of 5.8 ms. At the completion of the processing, we expect to have discovered roughly 20 new pulsars. All new pulsars are being subjected to a program of followup observations at Arecibo to determine spin and astrometric parameters.

  3. Millisecond pulsars - Nature's most stable clocks

    NASA Astrophysics Data System (ADS)

    Taylor, Joseph H., Jr.

    1991-07-01

    The author describes the role pulsars might play in time and frequency technology. Millisecond pulsars are rapidly rotating neutron stars: spherical flywheels some 20 km in diameter, 1.4 times as massive as the Sun, and spinning as fast as several thousand radians per second. Radio noise generated in a pulsar's magnetosphere by a highly beamed process is detectable over interstellar distances, as a periodic sequence of pulses similar to the ticks of an excellent clock. High-precision comparisons between pulsar time and terrestrial atomic time show that over intervals of several years, some millisecond pulsars have fractional stabilities comparable to those of the best atomic clocks. The author briefly reviews the physics of pulsars, discusses the techniques of pulsar timing measurements, and summarizes the results of careful studies of pulsar stabilities.

  4. Fermi Finds Youthful Pulsar Among Ancient Stars

    NASA Video Gallery

    In three years, NASA's Fermi has detected more than 100 gamma-ray pulsars, but something new has appeared. Among a type of pulsar with ages typically numbering a billion years or more, Fermi has fo...

  5. Equilibrium spin pulsars unite neutron star populations

    NASA Astrophysics Data System (ADS)

    Ho, Wynn; Klus, Helen; Coe, Malcolm; Andersson, Nils

    2015-08-01

    We compare the large number of recent torque measurements of accreting pulsars with a high-mass companion to the standard model for how accretion affects the pulsar spin period. We find that many long spin period (P > 100 s) pulsars must possess either extremely weak (B < 10^10 G) or extremely strong (B > 10^14 G) magnetic fields. We argue that the strong-field solution is more compelling, in which case these pulsars are near spin equilibrium. Our results provide evidence for a fundamental link between pulsars with the slowest spin periods and strong magnetic fields around high-mass companions and pulsars with the fastest spin periods and weak fields around low-mass companions. The strong magnetic fields also connect our pulsars to magnetars and strong-field isolated radio/X-ray pulsars. The strong field and old age of our sources suggests their magnetic field penetrates into the superconducting core of the neutron star.

  6. European food and nutrition policies in action. Finland's food and nutrition policy: progress, problems and recommendations.

    PubMed

    Milio, N

    1998-01-01

    Some progress has clearly been made in several aspects of Finland's food and nutrition policy: access to nutrition information and education, improvements in mass catering, increased availability of healthier food products, and pricing and quality requirements favourable to a healthy diet. Finnish eating patterns have improved in relation to some recommended foods and macronutrients. The structural changes in farm and food production are largely the result of new political and economic realities both in Finland and internationally, resulting in the Government focusing on fiscal efficiency, decentralization and a more competitive, consumer-oriented market. This new environment is creating pressures to reduce surplus animal fat production and to expand markets in new foods for Finns and other Europeans who, for reasons of demography, health or working or living arrangements, demand new and sometimes healthier foods. Within this context, some health leaders have been able to make and work for proposals that are consistent both with political and economic imperatives and with health needs. Although the populations health status is improving and in some respects is exemplary, diet-related death and illness rates and risk factors (such as serum cholesterol and obesity) are high and their decline, along with some healthy changes in eating patterns, has slowed since the mid-1980s (ironically, since the adoption of the nutrition policy). The more slowly improvements occur, the higher will be the social and economic costs. Major problems in policy implementation exist. Although much has been done in research and demonstration and in the development of national guidelines (in public catering and labeling, for example) there is an apparent lag in translating such soft technology into action and monitoring its implementation in order to develop corrective measures at the operational level. This problem may increase with decentralized budget control and a less regulated market

  7. A New Standard Pulsar Magnetosphere

    NASA Technical Reports Server (NTRS)

    Contopoulos, Ioannis; Kalapotharakos, Constantinos; Kazanas, Demosthenes

    2014-01-01

    In view of recent efforts to probe the physical conditions in the pulsar current sheet, we revisit the standard solution that describes the main elements of the ideal force-free pulsar magnetosphere. The simple physical requirement that the electric current contained in the current layer consists of the local electric charge moving outward at close to the speed of light yields a new solution for the pulsar magnetosphere everywhere that is ideal force-free except in the current layer. The main elements of the new solution are as follows: (1) the pulsar spindown rate of the aligned rotator is 23% larger than that of the orthogonal vacuum rotator; (2) only 60% of the magnetic flux that crosses the light cylinder opens up to infinity; (3) the electric current closes along the other 40%, which gradually converges to the equator; (4) this transfers 40% of the total pulsar spindown energy flux in the equatorial current sheet, which is then dissipated in the acceleration of particles and in high-energy electromagnetic radiation; and (5) there is no separatrix current layer. Our solution is a minimum free-parameter solution in that the equatorial current layer is electrostatically supported against collapse and thus does not require a thermal particle population. In this respect, it is one more step toward the development of a new standard solution. We discuss the implications for intermittent pulsars and long-duration gamma-ray bursts. We conclude that the physical conditions in the equatorial current layer determine the global structure of the pulsar magnetosphere.

  8. A new standard pulsar magnetosphere

    SciTech Connect

    Contopoulos, Ioannis; Kalapotharakos, Constantinos; Kazanas, Demosthenes

    2014-01-20

    In view of recent efforts to probe the physical conditions in the pulsar current sheet, we revisit the standard solution that describes the main elements of the ideal force-free pulsar magnetosphere. The simple physical requirement that the electric current contained in the current layer consists of the local electric charge moving outward at close to the speed of light yields a new solution for the pulsar magnetosphere everywhere that is ideal force-free except in the current layer. The main elements of the new solution are as follows: (1) the pulsar spindown rate of the aligned rotator is 23% larger than that of the orthogonal vacuum rotator; (2) only 60% of the magnetic flux that crosses the light cylinder opens up to infinity; (3) the electric current closes along the other 40%, which gradually converges to the equator; (4) this transfers 40% of the total pulsar spindown energy flux in the equatorial current sheet, which is then dissipated in the acceleration of particles and in high-energy electromagnetic radiation; and (5) there is no separatrix current layer. Our solution is a minimum free-parameter solution in that the equatorial current layer is electrostatically supported against collapse and thus does not require a thermal particle population. In this respect, it is one more step toward the development of a new standard solution. We discuss the implications for intermittent pulsars and long-duration gamma-ray bursts. We conclude that the physical conditions in the equatorial current layer determine the global structure of the pulsar magnetosphere.

  9. What brakes the Crab pulsar?

    NASA Astrophysics Data System (ADS)

    Čadež, A.; Zampieri, L.; Barbieri, C.; Calvani, M.; Naletto, G.; Barbieri, M.; Ponikvar, D.

    2016-03-01

    Context. Optical observations provide convincing evidence that the optical phase of the Crab pulsar follows the radio one closely. Since optical data do not depend on dispersion measure variations, they provide a robust and independent confirmation of the radio timing solution. Aims: The aim of this paper is to find a global mathematical description of Crab pulsar's phase as a function of time for the complete set of published Jodrell Bank radio ephemerides (JBE) in the period 1988-2014. Methods: We apply the mathematical techniques developed for analyzing optical observations to the analysis of JBE. We break the whole period into a series of episodes and express the phase of the pulsar in each episode as the sum of two analytical functions. The first function is the best-fitting local braking index law, and the second function represents small residuals from this law with an amplitude of only a few turns, which rapidly relaxes to the local braking index law. Results: From our analysis, we demonstrate that the power law index undergoes "instantaneous" changes at the time of observed jumps in rotational frequency (glitches). We find that the phase evolution of the Crab pulsar is dominated by a series of constant braking law episodes, with the braking index changing abruptly after each episode in the range of values between 2.1 and 2.6. Deviations from such a regular phase description behave as oscillations triggered by glitches and amount to fewer than 40 turns during the above period, in which the pulsar has made more than 2 × 1010 turns. Conclusions: Our analysis does not favor the explanation that glitches are connected to phenomena occurring in the interior of the pulsar. On the contrary, timing irregularities and changes in slow down rate seem to point to electromagnetic interaction of the pulsar with the surrounding environment.

  10. Star Cluster Buzzing With Pulsars

    NASA Astrophysics Data System (ADS)

    2005-01-01

    A dense globular star cluster near the center of our Milky Way Galaxy holds a buzzing beehive of rapidly-spinning millisecond pulsars, according to astronomers who discovered 21 new pulsars in the cluster using the National Science Foundation's 100-meter Robert C. Byrd Green Bank Telescope (GBT) in West Virginia. The cluster, called Terzan 5, now holds the record for pulsars, with 24, including three known before the GBT observations. Pulsar Diagram Pulsar Diagram: Click on image for more detail. "We hit the jackpot when we looked at this cluster," said Scott Ransom, an astronomer at the National Radio Astronomy Observatory in Charlottesville, VA. "Not only does this cluster have a lot of pulsars -- and we still expect to find more in it -- but the pulsars in it are very interesting. They include at least 13 in binary systems, two of which are eclipsing, and the four fastest-rotating pulsars known in any globular cluster, with the fastest two rotating nearly 600 times per second, roughly as fast as a household blender," Ransom added. Ransom and his colleagues reported their findings to the American Astronomical Society's meeting in San Diego, CA, and in the online journal Science Express. The star cluster's numerous pulsars are expected to yield a bonanza of new information about not only the pulsars themselves, but also about the dense stellar environment in which they reside and probably even about nuclear physics, according to the scientists. For example, preliminary measurements indicate that two of the pulsars are more massive than some theoretical models would allow. "All these exotic pulsars will keep us busy for years to come," said Jason Hessels, a Ph.D student at McGill University in Montreal. Globular clusters are dense agglomerations of up to millions of stars, all of which formed at about the same time. Pulsars are spinning, superdense neutron stars that whirl "lighthouse beams" of radio waves or light around as they spin. A neutron star is what is

  11. A Wide Bandwidth Digital Recording System for Pulsar Astronomy

    NASA Astrophysics Data System (ADS)

    Jenet, F. A.; Unwin, S. C.; Prince, T. A.

    1995-12-01

    We have developed a powerful and flexible data acquisition system for pulsar astronomy, based on a 50 Mbyte/s commercial instrumentation tape recorder and a custom analog-digital VLSI digitizer chip. This system converts the problem of pulsar detection from largely hardware-oriented to mostly software-oriented. We are using the 512-node Intel Paragon XPS and Touchstone Delta supercomputers at Caltech for pulsar searching and analysis. The detection of fast pulsars requires (1) rapid time sampling, and (2) the ability to correct for dispersion (frequency-dependent time delay caused by charged particles in the interstellar medium). A conventional hardware approach involves a filterbank or correlator at the telescope, then sampling and recording the detected power. Our telescope hardware is relatively simple, performing only downconversion from RF or IF to baseband, followed by Nyquist sampling and (2-bit) digitizing the voltage signal by the custom VLSI chip, then storage on ANSI D1 videocassette. One D1-L cassette allows continuous recording of two polarizations each with 50 MHz bandwidth for 32 minutes, or 25 MHz for 64 minutes. In software we can de-disperse the pulse signals by synthesizing a filterbank with an arbitrary number of frequency channels. Coherent dedispersion can be performed on the voltage (but not power) data, allowing time resolutions down to the inverse RF bandwidth to be achieved in principle. We present first results from observations in July 1995 at the 64-m telescope at Parkes Observatory, Australia Telescope National Facility. These results on known pulsars, including faint globular cluster millisecond-period pulsars, demonstrate the capabilities of our data recording and analysis system.

  12. Torque Reversals in Disk Accreting Pulsars

    NASA Astrophysics Data System (ADS)

    Li, Jianke; Wickramasinghe, Dayal T.

    1998-07-01

    X-ray binaries in which the accreting component is a neutron star commonly exhibit significant changes in their spin. In the system Cen X-3, a disk accreting binary system, the pulsar was observed to spin up at a rate ḟ = 8 × 10-13 Hz s-1 when averaged over the past twenty years, but significant fluctuations were observed above this mean. Recent BASTE observations have disclosed that these fluctuations are much larger than previously noted, and appeared to be a system characteristic. The change in the spin state from spin-up to spin-down or vice-versa occurs on a time scale that is much shorter than the instrument can resolve (≤1 d), but appears always to be a similar amplitude, and to occur stochastically. These observations have posed a problem for the conventional torque-mass accretion relation for accreting pulsars, because in this model the spin rate is closely related to the accretion rate, and the latter needs to be finely tuned and to change abruptly to explain the observations. Here we review recent work in this direction and present a coherent picture that explains these observations. We also draw attention to some outstanding problems for future studies.

  13. Pulsar Wind Nebulae, Space Velocities and Supernova Remnant Associations

    NASA Technical Reports Server (NTRS)

    2002-01-01

    I am pleased to be able to report significant progress in my research relevant to my LTSA grant. This progress I believe is demonstrated by a long list of publications in 2002, as detailed below. I summarize the research results my collaborators and I obtained in 2002. First, my group announced the major discovery of soft-gamma-repeater-like X-ray bursts from the anomalous X-ray pulsars lE-1048.1$-$5937 and lE-2259+586, using the Rossi X-ray Timing Explorer. This result provides an elegant and long-sought-after confirmation that this class of objects and the soft gamma repeaters share a common nature, namely that they are magnetars. Magnetars are a novel manifestation of young neutron stars, quite different from conventional Crab-like radio pulsars. This discovery was made as part of our regular monitoring program, among the goals of which was to detect such outbursts.

  14. Pulsar Magnetohydrodynamic Winds

    NASA Astrophysics Data System (ADS)

    Okamoto, Isao; Sigalo, Friday B.

    2006-12-01

    The acceleration and collimation/decollimation of relativistic magnetocentrifugal winds are discussed concerning a cold plasma from a strongly magnetized, rapidly rotating neutron star in a steady axisymmetric state based on ideal magnetohydrodynamics. There exist unipolar inductors associated with the field line angular frequency, α, at the magnetospheric base surface, SB, with a huge potential difference between the poles and the equator, which drive electric current through the pulsar magnetosphere. Any ``current line'' must emanate from one terminal of the unipolar inductor and return to the other, converting the Poynting flux to the kinetic flux of the wind at finite distances. In a plausible field structure satisfying the transfield force-balance equation, the fast surface, SF, must exist somewhere between the subasymptotic and asymptotic domains, i.e., at the innermost point along each field line of the asymptotic domain of \\varpaA2/\\varpi2 ≪ 1, where \\varpiA is the Alfvénic axial distance. The criticality condition at SF yields the Lorentz factor, γF = μ\\varepsilon1/3, and the angular momentum flux, β, as the eigenvalues in terms of the field line angular velocity, α, the mass flux per unit flux tube, η, and one of the Bernoulli integrals, μδ, which are assumed to be specifiable as the boundary conditions at SB. The other Bernoulli integral, μɛ, is related to μδ as μɛ = μδ[1-(α2\\varpiA2/c2)]-1, and both μɛ and \\varpiA2 are eigenvalues to be determined by the criticality condition at SF. Ongoing MHD acceleration is possible in the superfast domain. This fact may be helpful in resolving a discrepancy between the wind theory and the Crab-nebula model. It is argued that the ``anti-collimation theorem'' holds for relativistic winds, based on the curvature of field streamlines determined by the transfield force balance. The ``theorem'' combines with the ``current-closure condition'' as a global condition in the wind zone to produce a

  15. A millisecond pulsar timing array

    NASA Astrophysics Data System (ADS)

    Hobbs, George; Manchester, Dick; Verbiest, Joris P. W.; Sarkissian, John; Bailes, Matthew; Bhat, Ramesh; Jenet, Rick; Keith, Michael; Burke-Spolaor, Sarah; van Straten, Willem; Yardley, Daniel Roger Billing; Ravi, Vikram; Oslowski, Stefan; Hotan, Aidan; Champion, David; Khoo, Jonathan; Shannon, Ryan; Chaudhary, Ankur

    2011-10-01

    The Parkes Pulsar Timing Array (PPTA) project has three primary goals: (a) detection of gravitational waves from astronomical sources, (b) establishment of a pulsar timescale, and (c) improvement of our understanding of Solar-system dynamics. There are many secondary goals, some astrophysical and some instrumental/technique oriented. Achievement of these ambitious primary goals requires frequent observations of at least 20 MSPs at two or preferably three widely spaced frequencies over several years. We wish to continue observing the PPTA sample at intervals of 2-3 weeks using both the 10/50cm and Multibeam receivers. The digital filterbanks (PDFB3, PDFB4) and the baseband systems (CPSR2; APSR) are used for data recording. With the new instruments and development of an efficient pipeline processing system, we have achieved the world's best pulsar timing precision. We are collaborating with the European and North American pulsar timing array groups (EPTA and NANOGrav, respectively) to obtain more frequent observations and a larger pulsar sample. Because of the high sensitivity and wide bandwidths required, RFI mitigation is an important part of the project. We request continuing status for this project.

  16. A millisecond pulsar timing array

    NASA Astrophysics Data System (ADS)

    Hobbs, George; Manchester, Dick; Sarkissian, John; Bailes, Matthew; Bhat, Ramesh; Keith, Michael; Burke-Spolaor, Sarah; Coles, William; van Straten, Willem; Yardley, Daniel Roger Billing; Ravi, Vikram; Oslowski, Stefan; Khoo, Jonathan; Shannon, Ryan; Wang, Jingbo; Levin, Yuri

    2013-04-01

    The Parkes Pulsar Timing Array (PPTA) project has three primary goals: (a) detection of gravitational waves from astronomical sources, (b) establishment of a pulsar timescale, and (c) improvement of our understanding of Solar-system dynamics. There are many secondary goals, some astrophysical and some instrumental/technique oriented. Achievement of these ambitious primary goals requires frequent observations of at least 20 MSPs at two or preferably three widely spaced frequencies over several years. We wish to continue observing the PPTA sample at intervals of 2-3 weeks using both the 10/50cm and Multibeam receivers. The digital filterbanks (PDFB3, PDFB4) and the baseband systems (CPSR2; APSR) are used for data recording. With the new instruments and development of an efficient pipeline processing system, we have achieved the world's best pulsar timing precision. We are collaborating with the European and North American pulsar timing array groups (EPTA and NANOGrav, respectively) to obtain more frequent observations and a larger pulsar sample. Because of the high sensitivity and wide bandwidths required, RFI mitigation is an important part of the project. We request continuing status for this project.

  17. A millisecond pulsar timing array

    NASA Astrophysics Data System (ADS)

    Hobbs, George; Manchester, Dick; Verbiest, Joris P. W.; Sarkissian, John; Bailes, Matthew; Bhat, Ramesh; Jenet, Rick; Keith, Michael; Burke-Spolaor, Sarah; van Straten, Willem; Yardley, Daniel Roger Billing; Ravi, Vikram; Oslowski, Stefan; Hotan, Aidan; Champion, David; Khoo, Jonathan; Shannon, Ryan; Chaudhary, Ankur

    2012-04-01

    The Parkes Pulsar Timing Array (PPTA) project has three primary goals: (a) detection of gravitational waves from astronomical sources, (b) establishment of a pulsar timescale, and (c) improvement of our understanding of Solar-system dynamics. There are many secondary goals, some astrophysical and some instrumental/technique oriented. Achievement of these ambitious primary goals requires frequent observations of at least 20 MSPs at two or preferably three widely spaced frequencies over several years. We wish to continue observing the PPTA sample at intervals of 2-3 weeks using both the 10/50cm and Multibeam receivers. The digital filterbanks (PDFB3, PDFB4) and the baseband systems (CPSR2; APSR) are used for data recording. With the new instruments and development of an efficient pipeline processing system, we have achieved the world's best pulsar timing precision. We are collaborating with the European and North American pulsar timing array groups (EPTA and NANOGrav, respectively) to obtain more frequent observations and a larger pulsar sample. Because of the high sensitivity and wide bandwidths required, RFI mitigation is an important part of the project. We request continuing status for this project.

  18. A millisecond pulsar timing array

    NASA Astrophysics Data System (ADS)

    Hobbs, George; Manchester, Dick; Verbiest, Joris P. W.; Sarkissian, John; Bailes, Matthew; Bhat, Ramesh; Jenet, Rick; Keith, Michael; Burke-Spolaor, Sarah; van Straten, Willem; Yardley, Daniel Roger Billing; Oslowski, Stefan; Hotan, Aidan; Champion, David; Khoo, Jonathan; Shannon, Ryan; Chaudhary, Ankur

    2011-04-01

    The Parkes Pulsar Timing Array (PPTA) project has three primary goals: (a) detection of gravitational waves from astronomical sources, (b) establishment of a pulsar timescale, and (c) improvement of our understanding of Solar-system dynamics. There are many secondary goals, some astrophysical and some instrumental/technique oriented. Achievement of these ambitious primary goals requires frequent observations of at least 20 MSPs at two or preferably three widely spaced frequencies over several years. We wish to continue observing the PPTA sample at intervals of 2-3 weeks using both the 10/50cm and Multibeam receivers. The digital filterbanks (PDFB3, PDFB4) and the baseband systems (CPSR2; APSR) are used for data recording. With the new instruments and development of an efficient pipeline processing system, we have achieved the world's best pulsar timing precision. We are collaborating with the European and North American pulsar timing array groups (EPTA and NANOGrav, respectively) to obtain more frequent observations and a larger pulsar sample. Because of the high sensitivity and wide bandwidths required, RFI mitigation is an important part of the project. We request continuing status for this project.

  19. A millisecond pulsar timing array

    NASA Astrophysics Data System (ADS)

    Hobbs, George; Manchester, Dick; Sarkissian, John; Bailes, Matthew; Bhat, Ramesh; Keith, Michael; Burke-Spolaor, Sarah; Coles, William; van Straten, Willem; Ravi, Vikram; Oslowski, Stefan; Khoo, Jonathan; Shannon, Ryan; Wang, Jingbo; Levin, Yuri

    2013-10-01

    The Parkes Pulsar Timing Array (PPTA) project has three primary goals: (a) detection of gravitational waves from astronomical sources, (b) establishment of a pulsar timescale, and (c) improvement of our understanding of Solar-system dynamics. There are many secondary goals, some astrophysical and some instrumental/technique oriented. Achievement of these ambitious primary goals requires frequent observations of at least 20 MSPs at two or preferably three widely spaced frequencies over several years. We wish to continue observing the PPTA sample at intervals of 2-3 weeks using both the 10/50cm and Multibeam receivers. The digital filterbanks (PDFB3, PDFB4) and the baseband systems (CPSR2; APSR) are used for data recording. With the new instruments and development of an efficient pipeline processing system, we have achieved the world's best pulsar timing precision. We are collaborating with the European and North American pulsar timing array groups (EPTA and NANOGrav, respectively) to obtain more frequent observations and a larger pulsar sample. Because of the high sensitivity and wide bandwidths required, RFI mitigation is an important part of the project. We request continuing status for this project.

  20. A millisecond pulsar timing array

    NASA Astrophysics Data System (ADS)

    Hobbs, George; Manchester, Dick; Verbiest, Joris P. W.; Sarkissian, John; Bailes, Matthew; Bhat, Ramesh; Jenet, Rick; Keith, Michael; Burke-Spolaor, Sarah; van Straten, Willem; Ravi, Vikram; Oslowski, Stefan; Hotan, Aidan; Champion, David; Khoo, Jonathan; Shannon, Ryan; Chaudhary, Ankur

    2012-10-01

    The Parkes Pulsar Timing Array (PPTA) project has three primary goals: (a) detection of gravitational waves from astronomical sources, (b) establishment of a pulsar timescale, and (c) improvement of our understanding of Solar-system dynamics. There are many secondary goals, some astrophysical and some instrumental/technique oriented. Achievement of these ambitious primary goals requires frequent observations of at least 20 MSPs at two or preferably three widely spaced frequencies over several years. We wish to continue observing the PPTA sample at intervals of 2-3 weeks using both the 10/50cm and Multibeam receivers. The digital filterbanks (PDFB3, PDFB4) and the baseband systems (CASPSR; APSR) are used for data recording. With the new instruments and development of an efficient pipeline processing system, we have achieved the world's best pulsar timing precision. We are collaborating with the European and North American pulsar timing array groups (EPTA and NANOGrav, respectively) to obtain more frequent observations and a larger pulsar sample. Because of the high sensitivity and wide bandwidths required, RFI mitigation is an important part of the project. We request continuing status for this project.

  1. Statistical studies of pulsar glitches

    NASA Astrophysics Data System (ADS)

    Lyne, A. G.; Shemar, S. L.; Smith, F. Graham

    2000-07-01

    Shemar & Lyne have previously presented observations and an analysis of 32 glitches and their subsequent relaxations observed in a total of 15 pulsars. These data are brought together in this paper with those published by other authors. We show quantitatively how glitch activity decreases linearly with decreasing rate of slow-down. As indicated previously from studies of the Vela pulsar, the analysis suggests that 1.7per cent of the moment of inertia of a typical neutron star is normally contained in pinned superfluid which releases its excess angular momentum at the time of a glitch. There is a broad range of glitch amplitude and there is a strong indication that pulsars with large magnetic fields suffer many small glitches while others show a smaller number of large glitches. Transient effects following glitches are very marked in young pulsars and decrease linearly with decreasing rate of slow-down, suggesting that the amount of loosely pinned superfluid decreases with age. We suggest that the low braking index of the Vela and Crab pulsars cannot be caused by a decreasing moment of inertia and should be attributed to step increases in the effective magnetic moment of the neutron star at the glitches.

  2. Monitoring The Crab Pulsar

    NASA Technical Reports Server (NTRS)

    Rots, Arnold H.; Swank, Jean (Technical Monitor)

    2001-01-01

    The monitoring of the X-ray pulses from the Crab pulsar is still ongoing at the time of this writing, and we hope to be able to continue the campaign for the life of the XTE mission. We have established beyond all doubt that: (1) the X-ray main pulse leads the radio pulse by approximately 300 microseconds, (2) this phase lag is constant and not influenced by glitches, (3) this lag does not depend on X-ray energy, (4) the relative phase of the two X-ray pulses does not vary, and (5) the spectral indices of primary, secondary, and inter-pulse are distinct and constant. At this time we are investigating whether the radio timing ephemeris can be replaced by an x-ray ephemeris and whether any long-time timing ephemeris can be established. If so, it would enable use to study variations in pulse arrival times at a longer time scales. Such a study is easier in x-rays than at radio wavelengths since the dispersion measure plays no role. These results were reported at the 2000 HEAD Meeting in Honolulu, HI. Travel was paid partly out of this grant. The remainder was applied toward the acquisition of a laptop computer that allows independent and fast analysis of all monitoring observations.

  3. Gamma-ray emission and nucleosynthesis of lithium by young pulsars

    NASA Technical Reports Server (NTRS)

    Clayton, D. D.; Dwek, E.

    1976-01-01

    It is proposed that Li-7 is produced in the Galaxy primarily by alpha-alpha collisions surrounding newly born pulsars. About 10 percent of the pulsar energy losses are converted to medium-energy alpha-particles which collide in a dominantly He nebula. The problem of the origin of lithium would be solved by the scenario, and clear-cut tests by nuclear gamma-ray astronomy are described.

  4. Integrative Convergence in Neuroscience: Trajectories, Problems, and the Need for a Progressive Neurobioethics

    NASA Astrophysics Data System (ADS)

    Giordano, J.

    The advanced integrative scientific convergence (AISC) model represents a viable approach to neuroscience. Beyond simple multi-disciplinarity, the AISC model unifies constituent scientific and technological fields to foster innovation, invention and new ways of addressing seemingly intractable questions. In this way, AISC can yield novel methods and foster new trajectories of knowledge and discovery, and yield new epistemologies. As stand-alone disciplines, each and all of the constituent fields generate practical and ethical issues, and their convergence may establish a unique set of both potential benefits and problems. To effectively attend to these contingencies requires pragmatic assessment of the actual capabilities and limits of neurofocal AISC, and an openness to what new knowledge and scientific/technological achievements may be produced, and how such outcomes can affect humanity, the human condition, society and the global environment. It is proposed that a progressive neurobioethics may be needed to establish both a meta-ethical framework upon which to structure ethical decisions, and a system and method of ethics that is inclusive, convergent and innovative, and in thus aligned with and meaningful to use of an AISC model in neuroscience.

  5. Environmental impact assessment in the Philippines: Progress, problems, and directions for the future

    SciTech Connect

    Ross, W.A. )

    1994-07-01

    The environmental impact statement (EIS) system of the Philippines is reviewed, identifying progress made in its effective implementation since 1986. Improvement in coverage is noted and real commitment to good environmental impact assessment (EIA) practice is found in those responsible for the EIS system. Project proponents show a modest acceptance of the system. Major problems remaining are: (1) the EIS system is seen as a bureaucratic requirement needed to obtain project approvals; (2) political interference determines the outcome of some environmental reviews; (3) questionable practices by public servants serve to discredit the system; and (4) the treatment of projects in environmentally critical areas is less than satisfactory. Based on the principle that it is essential to establish a credible process seen to work effectively by the public, politicians, the government bureaucracy, and proponents, suggestions for improvement are made. They deal with the treatment of EISs for projects already under construction, EIA training courses, and simple adjustments to the EIS system to focus it on the most important projects.

  6. String theories and millisecond pulsars

    NASA Astrophysics Data System (ADS)

    Sanchez, N.; Signore, M.

    1988-11-01

    We discuss the two ways of connecting string theories (cosmic, fundamental and the connection between them) to the observational reality: (i) radioastronomy observations (millisecond pulsar timing), and (ii) elementary particle phenomenology (compactification schemes). We study the limits imposed on the string parameter Gμ by recent millisecond pulsar timings. Cosmic strings derived from GUTs agree with (i). For cosmic strings derived from fundamental strings themselves there is contradiction between (i) and (ii). One of these scenarios connecting string theory to reality must be revised (or the transition from fundamental into cosmic strings rejected). Meanwhile, millisecond pulsar can select one scenario, or reject both of them. UA 336 Laboratoire Associé au CNRS, Observatoire de Meudon et Ecole Normale Supérieure, 24 rue Lhomond, F-75231 Paris Cedex 05, France.

  7. Gamma Ray Pulsars: Multiwavelength Observations

    NASA Technical Reports Server (NTRS)

    Thompson, David J.

    2004-01-01

    High-energy gamma rays are a valuable tool for studying particle acceleration and radiation in the magnetospheres of energetic pulsars. The seven or more pulsars seen by instruments on the Compton Gamma Ray Observatory (CGRO) show that: the light curves usually have double-peak structures (suggesting a broad cone of emission); gamma rays are frequently the dominant component of the radiated power; and all the spectra show evidence of a high-energy turnover. For all the known gamma-ray pulsars, multiwavelength observations and theoretical models based on such observations offer the prospect of gaining a broad understanding of these rotating neutron stars. The Gamma-ray Large Area Space Telescope (GLAST), now in planning for a launch in 2006, will provide a major advance in sensitivity, energy range, and sky coverage.

  8. Interplanetary GPS using pulsar signals

    NASA Astrophysics Data System (ADS)

    Becker, W.; Bernhardt, M. G.; Jessner, A.

    2015-11-01

    An external reference system suitable for deep space navigation can be defined by fast spinning and strongly magnetized neutron stars, called pulsars. Their beamed periodic signals have timing stabilities comparable to atomic clocks and provide characteristic temporal signatures that can be used as natural navigation beacons, quite similar to the use of GPS satellites for navigation on Earth. By comparing pulse arrival times measured on-board a spacecraft with predicted pulse arrivals at a reference location, the spacecraft position can be determined autonomously and with high accuracy everywhere in the solar system and beyond. The unique properties of pulsars make clear already today that such a navigation system will have its application in future astronautics. In this paper we describe the basic principle of spacecraft navigation using pulsars and report on the current development status of this novel technology.

  9. PINT, a New Pulsar Timing Software

    NASA Astrophysics Data System (ADS)

    Luo, Jing; Jenet, Fredrick A.; Ransom, Scott M.; Demorest, Paul; Van Haasteren, Rutger; Archibald, Anne

    2015-01-01

    We are presenting a new pulsar timing software PINT. The current pulsar timing group are heavily depending on Tempo/Tempo2, a package for analysis pulsar data. However, for a high accuracy pulsar timing related project, such as pulsar timing for gravitational waves, an alternative software is needed for the purpose of examing the results. We are developing a Tempo independent software with a different structure. Different modules is designed to be more isolated and easier to be expanded. Instead of C, we are using Python as our programming language for the advantage of flexibility and powerful docstring. Here, we are presenting the detailed design and the first result of the software.

  10. The Disturbance of a Millisecond Pulsar Magnetosphere

    NASA Astrophysics Data System (ADS)

    Shannon, R. M.; Lentati, L. T.; Kerr, M.; Bailes, M.; Bhat, N. D. R.; Coles, W. A.; Dai, S.; Dempsey, J.; Hobbs, G.; Keith, M. J.; Lasky, P. D.; Levin, Y.; Manchester, R. N.; Osłowski, S.; Ravi, V.; Reardon, D. J.; Rosado, P. A.; Spiewak, R.; van Straten, W.; Toomey, L.; Wang, J.-B.; Wen, L.; You, X.-P.; Zhu, X.-J.

    2016-09-01

    Pulsar timing has enabled some of the strongest tests of fundamental physics. Central to the technique is the assumption that the detected radio pulses can be used to accurately measure the rotation of the pulsar. Here, we report on a broadband variation in the pulse profile of the millisecond pulsar J1643‑1224. A new component of emission suddenly appears in the pulse profile, decays over four months, and results in a permanently modified pulse shape. Profile variations such as these may be the origin of timing noise observed in other millisecond pulsars. The sensitivity of pulsar-timing observations to gravitational radiation can be increased by accounting for this variability.

  11. Distribution of neutrino fluxes from pulsar shells

    NASA Astrophysics Data System (ADS)

    Shapiro, M. M.; Silberberg, R.

    According to a model considered by Berezinsky and Prilutsky (1976), a young, dense supernova shell can be a powerful source of high-energy neutrinos. In this model, ultra-high energy protons and other nuclei are accelerated at the central pulsar. The protons interact in the supernova shell and generate cascades of mesons, which in turn yield neutrinos upon decay. The pulsar luminosity function based on all the observed Galactic pulsars is considered. It is found that the high-energy neutrinos from supernovae in the Milky Way Galaxy should be readily detectable. The corresponding pulsars would be relatively low-powered pulsars.

  12. Slowly rotating pulsars and magnetic field decay

    NASA Astrophysics Data System (ADS)

    Han, J. L.

    1997-02-01

    Two dozen long period pulsars are separated from the swarm of ordinary pulsars by an obvious gap in the P versus Sd diagram (where Sd=log˙(P)+21.0), with a plausible upper boundary for ordinary pulsars. Possible pulsar evolutionary tracks are discussed to explain the diagram in terms of previously suggested scenarios of magnetic field decay. The (P-Sd) diagram is difficult to understand if there is no magnetic field decay during the active life of pulsars. However, if the magnetic fields of neutron stars decay exponentially, almost all slowly rotating pulsars must have been injected with a very long initial spin period of about 2 seconds, which seems impossible. Based on qualitative analyses, it is concluded that magnetic fields of neutron stars decay as a power-law, with a time scale related to the initial field strengths. The plausible boundary and the gap are suggested to naturally divide pulsars with distinct magnetic "genes", ie. pulsars which were born from strongly magnetized progenitors -- such as Bp stars, and pulsars born from normal massive stars. The possibility remains open that a fraction of slowly rotating pulsars were injected with long initial spin periods, while others would have a classical pulsar evolution history. It is suggested that PSR B1849+00 was born in the supernova remnant Kes-79 with an initial period of about 2 seconds.

  13. Equilibrium spin pulsars unite neutron star populations

    NASA Astrophysics Data System (ADS)

    Ho, Wynn C. G.; Klus, H.; Coe, M. J.; Andersson, Nils

    2014-02-01

    Many pulsars are formed with a binary companion from which they can accrete matter. Torque exerted by accreting matter can cause the pulsar spin to increase or decrease, and over long times, an equilibrium spin rate is achieved. Application of accretion theory to these systems provides a probe of the pulsar magnetic field. We compare the large number of recent torque measurements of accreting pulsars with a high-mass companion to the standard model for how accretion affects the pulsar spin period. We find that many long spin period (P ≳ 100 s) pulsars must possess either extremely weak (B < 1010 G) or extremely strong (B > 1014 G) magnetic fields. We argue that the strong-field solution is more compelling, in which case these pulsars are near spin equilibrium. Our results provide evidence for a fundamental link between pulsars with the slowest spin periods and strong magnetic fields around high-mass companions and pulsars with the fastest spin periods and weak fields around low-mass companions. The strong magnetic fields also connect our pulsars to magnetars and strong-field isolated radio/X-ray pulsars. The strong field and old age of our sources suggest their magnetic field penetrates into the superconducting core of the neutron star.

  14. Crustal entrainment and pulsar glitches.

    PubMed

    Chamel, N

    2013-01-01

    Large pulsar frequency glitches are generally interpreted as sudden transfers of angular momentum between the neutron superfluid permeating the inner crust and the rest of the star. Despite the absence of viscous drag, the neutron superfluid is strongly coupled to the crust due to nondissipative entrainment effects. These effects are shown to severely limit the maximum amount of angular momentum that can possibly be transferred during glitches. In particular, it is found that the glitches observed in the Vela pulsar require an additional reservoir of angular momentum. PMID:23383772

  15. Pulsar gamma rays from polar cap regions

    NASA Technical Reports Server (NTRS)

    Chiang, James; Romani, Roger W.

    1992-01-01

    The production is studied of pulsar gamma rays by energetic electrons flowing in the open field region above pulsar polar caps. The propagation was followed of curvature radiation from primary electrons, as well as hard synchrotron radiation generated by secondary pairs, through the pulsar magnetosphere for vacuum dipole open field geometries. Using data from radio and optical observations, models were constructed for the specific geometries and viewing angles appropriate to particular pulsars. These detailed models produce normalized spectra above 10 MeV, pulse profiles, beaming fractions and phase resolved spectra appropriate for direct comparison with COS-B and GRO data. Models are given for the Crab, Vela, and other potentially detectable pulsars; general agreement with existing data is good, although perturbations to the simplified models are needed for close matches. The calculations were extended to the millisecond pulsar range, which allows the production of predictions for the flux and spectra of populations of recycled pulsars and search strategies are pointed out.

  16. Low Frequency Interstellar Scattering and Pulsar Observations

    NASA Technical Reports Server (NTRS)

    Cordes, James M.

    1992-01-01

    Radio astronomy at frequencies from 2 to 30 MHz challenges time tested methods for extracting usable information from observations. One fundamental reason for this is that propagation effects due to the magnetoionic ionosphere, interplanetary medium, and interstellar matter (ISM) increase strongly with wavelength. The problems associated with interstellar scattering off of small scale irregularities in the electron density are addressed. What is known about interstellar scattering is summarized on the basis of high frequency observations, including scintillation and temporal broadening of pulsars and angular broadening of various galactic and extragalactic radio sources. Then those high frequency phenomena are addressed that are important or detectable at low frequencies. The radio sky becomes much simpler at low frequencies, most pulsars will not be seen as time varying sources, intensity variations will be quenched or will occur on time scales much longer than a human lifetime, and many sources will be angularly broadened and/or absorbed into the noise. Angular broadening measurements will help delineate the galactic distribution and power spectrum of small scale electron density irregularities.

  17. Socioeconomic Position and Health: The Differential Effects of Education versus Income on the Onset versus Progression of Health Problems

    ERIC Educational Resources Information Center

    Herd, Pamela; Goesling, Brian; House, James S.

    2007-01-01

    This article seeks to elucidate the relationship between socioeconomic position and health by showing how different facets of socioeconomic position (education and income) affect different stages (onset vs. progression) of health problems. The biomedical literature has generally treated socioeconomic position as a unitary construct. Likewise, the…

  18. Progress and problems in the prescribing/dispensing split and "divided package sales" by wholesalers.

    PubMed

    Shiragami, M; Morikubo, M; Suzuki, R; Kudo, I

    2001-01-01

    Given the rapid progress of the prescribing/dispensing split, the ability of pharmacies to obtain and stock a small quantity of pharmaceuticals is seen as essential. Toho Yakuhin's experience in "divided package sales" (wholesalers open an original package supplied by the manufacturer and sell only a part of the contents) shows that the number of orders and sales amount, and the number of pharmacies ordering in sales have remarkably increased. One or two kinds of pharmaceuticals were ordered in 73% cases, and one or two units in about 50%. This implies that "divided package sales" are utilized to obtain rarely prescribed drugs. On the other hand, five or more kinds of pharmaceuticals were ordered in 10% of cases, and ten or more units in 17%. "Divided package sales" were more used for low-price drugs. These indicated that "divided package sales" seemed to be looked upon by pharmacies as a means of obtaining a small quantity of pharmaceuticals, and seemed to be used not only in an emergency but also routinely. There are several problems for wholesalers in operating "divided package sales", such as frequent delivery, delivery cost and information supply. Pharmacies should obtain a small quantity of pharmaceuticals by the routine delivery and should share the delivery cost. Pharmaceutical manufacturers' cooperation in printing necessary information on each immediate container will be useful. Though there could be alternative ways of obtaining a small quantity of pharmaceuticals, all of them have the matter of delivery. We believe "divided package sales" will contribute to this situation. PMID:11201158

  19. The PROblem Gambling RESearch Study (PROGRESS) research protocol: a pragmatic randomised controlled trial of psychological interventions for problem gambling

    PubMed Central

    Thomas, Shane A; Merkouris, Stephanie S; Browning, Colette J; Radermacher, Harriet; Feldman, Susan; Enticott, Joanne; Jackson, Alun C

    2015-01-01

    Introduction International prevalence rates for problem gambling are estimated at 2.3%. Problem gambling is a serious global public health concern due to adverse personal and social consequences. Previous research evaluating the effectiveness of psychological interventions for the treatment of problem gambling has been compromised by methodological limitations, including small sample sizes and the use of waitlist control groups. This article describes the study protocol for a pragmatic randomised controlled trial (RCT) evaluating the effectiveness of cognitive-behavioural therapy (CBT), behaviour therapy (BT), motivational interviewing (MI) against a non-directive supportive therapy (NDST) control, in treating problem gambling. Methods and analysis This study was a mixed-methods design, with a parallel group, pragmatic RCT as the primary component, and embedded qualitative studies conducted alongside. A total of 297 participants were recruited from the community in Victoria, Australia. Individuals aged 18 years and over, could communicate in English and wished to receive treatment for a gambling problem were eligible. Participants were randomly allocated in to 1 of the 4 psychological interventions: CBT, BT, MI and NDST. Repeated measures were conducted at pretreatment and post-treatment, and 6 and 12 months post-treatment. The statistical analysis will use an intention-to-treat approach. Multilevel mixed modelling will be used to examine changes in the primary outcome measures: gambling symptom severity, using the Gambling Symptom Assessment Scale, and gambling behaviours (frequency, time and expenditure). Secondary outcomes are depression, anxiety, stress and alcohol use. Individual semistructured qualitative interviews were conducted at pretreatment and post-treatment and 12 months post-treatment for a subset of participants (n=66). Ethics and dissemination This study was approved by the Victorian Department of Justice, Monash University and the University

  20. RESISTIVE SOLUTIONS FOR PULSAR MAGNETOSPHERES

    SciTech Connect

    Li, Jason; Spitkovsky, Anatoly; Tchekhovskoy, Alexander

    2012-02-10

    The current state of the art in the modeling of pulsar magnetospheres invokes either the vacuum or force-free limits for the magnetospheric plasma. Neither of these limits can simultaneously account for both the plasma currents and the accelerating electric fields that are needed to explain the morphology and spectra of high-energy emission from pulsars. To better understand the structure of such magnetospheres, we combine accelerating fields and force-free solutions by considering models of magnetospheres filled with resistive plasma. We formulate Ohm's law in the minimal velocity fluid frame and construct a family of resistive solutions that smoothly bridges the gap between the vacuum and the force-free magnetosphere solutions. The spin-down luminosity, open field line potential drop, and the fraction of open field lines all transition between the vacuum and force-free values as the plasma conductivity varies from zero to infinity. For fixed inclination angle, we find that the spin-down luminosity depends linearly on the open field line potential drop. We consider the implications of our resistive solutions for the spin-down of intermittent pulsars and sub-pulse drift phenomena in radio pulsars.

  1. Braking Index of Isolated Pulsars

    NASA Astrophysics Data System (ADS)

    Hamil, Oliver; Stone, Jirina; Urbanec, Martin; Urbancova, Gabriela

    2015-04-01

    Isolated pulsars are rotating neutron stars with accurately measured angular velocities Ω, and their time derivatives which show unambiguously that the pulsars are slowing down. The exact mechanism of the spin-down is a question of debate in detail, but the commonly accepted view is that it arises through emission of magnetic dipole radiation (MDR). The energy loss by a rotating pulsar is proportional to a model dependent power of Ω. This relation leads to the power law Ω˙ = -K Ωn where n is called the braking index, equal to the ratio (ΩΩ̈)/ Ω˙2 . The simple MDR model predicts the value of n = 3, but observations of isolated pulsars provide rather precise values of n, individually accurate to a few percent or better, in the range 1 < n < 2.8, which is consistently less than the predictions of the MDR model. In this work, we study the dynamical limits of the MDR model as a function of angular velocity. The effects of variation in the rest mass, the moment of inertia, and the dependence on a realistic Equation of State of the rotating star are considered. Furthermore, we introduce a simulated superfluid effect by which the angular momentum of the core is eliminated from the calculation.

  2. Hunting gravitational waves using pulsars

    NASA Astrophysics Data System (ADS)

    Mayor, Louise

    2014-10-01

    With the first direct detection of gravitational waves at the top of many physicists' wish list, Louise Mayor describes how radio astronomers are hoping to reveal these ripples in space-time by pointing their telescopes at an array of distant pulsars.

  3. CHANGES IN THE CRAB PULSAR

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Scientists are learning more about how pulsars work by studying a series of Hubble Space Telescope images of the heart of the Crab Nebula. The images, taken over a period of several months, show that the Crab is a far more dynamic object than previously understood. At the center of the nebula lies the Crab Pulsar. The pulsar is a tiny object by astronomical standards -- only about six miles across -- but has a mass greater than that of the Sun and rotates at a rate of 30 times a second. As the pulsar spins its intense magnetic field whips around, acting like a sling shot, accelerating subatomic particles and sending them hurtling them into space at close to the speed of light. The tiny pulsar and its wind are the powerhouse for the entire Crab Nebula, which is 10 light-years across -- a feat comparable to an object the size of a hydrogen atom illuminating a volume of space a kilometer across. The three pictures shown here, taken from the series of Hubble images, show dramatic changes in the appearance of the central regions of the nebula. These include wisp-like structures that move outward away from the pulsar at half the speed of light, as well as a mysterious 'halo' which remains stationary, but grows brighter then fainter over time. Also seen are the effects of two polar jets that move out along the rotation axis of the pulsar. The most dynamic feature seen -- a small knot that 'dances around' so much that astronomers have been calling it a 'sprite' -- is actually a shock front (where fast-moving material runs into slower-moving material)in one of these polar jets. The telescope captured the images with the Wide Field and Planetary Camera 2 using a filter that passes light of wavelength around 550 nanometers, near the middle of the visible part of the spectrum. The Crab Nebula is located 7,000 light-years away in the constellation Taurus. Credit: Jeff Hester and Paul Scowen (Arizona State University), and NASA

  4. Rotochemical heating of millisecond and classical pulsars with anisotropic and density-dependent superfluid gap models

    NASA Astrophysics Data System (ADS)

    González-Jiménez, Nicolás; Petrovich, Cristobal; Reisenegger, Andreas

    2015-03-01

    When a rotating neutron star loses angular momentum, the progressive reduction of the centrifugal force makes it contract. This perturbs each fluid element, raising the local pressure and originating deviations from beta equilibrium, inducing reactions that release heat (`rotochemical heating'). This effect has previously been studied by Fernández & Reisenegger for non-superfluid neutron stars and by Petrovich & Reisenegger for superfluid millisecond pulsars. Both studies found that pulsars reach a quasi-steady state in which the compression driving the matter out of beta equilibrium is balanced by the reactions trying to restore the equilibrium. We extend previous studies by considering the effect of density-dependence and anisotropy of the superfluid energy gaps, for the case in which the dominant reactions are the modified Urca processes, the protons are non-superconducting, and the neutron superfluidity is parametrized by models proposed in the literature. By comparing our predictions with the surface temperature of the millisecond pulsar PSR J0437-4715 and upper limits for 21 classical pulsars, we find the millisecond pulsar can be only explained by the models with the effectively largest energy gaps (type B models), the classical pulsars require with the gap models that vanish for some angle (type C) and two different envelope compositions. Thus, no single model for neutron superfluidity can simultaneously account for the thermal emission of all available observations of non-accreting neutron stars, possibly due to our neglect of proton superconductivity.

  5. Wideband Timing of Millisecond Pulsars

    NASA Astrophysics Data System (ADS)

    Pennucci, Timothy; Demorest, Paul; Ransom, Scott M.; North American Nanohertz ObservatoryGravitational Waves (Nanograv)

    2015-01-01

    The use of backend instrumentation capable of real-time coherent dedispersion of relatively large fractional bandwidths has become commonplace in pulsar astronomy. However, along with the desired increase in sensitivity to pulsars' broadband signals, a larger instantaneous bandwidth brings a number of potentially aggravating effects that can lead to degraded timing precision. In the case of high-precision timing experiments, such as the one being carried out by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), subtle effects such as unmodeled intrinsic profile evolution with frequency, interstellar scattering, and dispersion measure variation are potentially capable of reducing the experiment's sensitivity to a gravitational wave signal. In order to account for some of these complications associated with wideband observations, we augmented the traditional algorithm by which the fundamental timing quantities are measured. Our new measurement algorithm accommodates an arbitrary two-dimensional model ``portrait'' of a pulsar's total intensity as a function of observing frequency and rotational phase, and simultaneously determines the time-of-arrival (TOA), the dispersion measure (DM), and per-frequency-channel amplitudes that account for interstellar scintillation. Our publicly available python code incorporates a Gaussian-component modeling routine that allows for independent component evolution with frequency, a ``fiducial component'', and the inclusion of scattering. Here, we will present results from the application of our wideband measurement scheme to the suite of NANOGrav millisecond pulsars, which aimed to determine the level at which the experiment is being harmed by unmodeled profile evolution. We have found thus far, and expect to continue to find, that our new measurements are at least as good as those from traditional techniques. At a minimum, by largely reducing the volume of TOAs we will decrease the computational demand

  6. The global return current in a pulsar's magnetosphere

    NASA Astrophysics Data System (ADS)

    Barzilay, Yudith

    2016-08-01

    An open issue in pulsar's models is the current adjustment between the gap current and the global current that depends on the global structure of the pulsar's magnetosphere. Here I propose a mechanism for the global return current in pulsars.

  7. Pulsar Timing Arrays - towards the SKA and beyond

    NASA Astrophysics Data System (ADS)

    Stappers, Ben

    2015-08-01

    I will discuss the development of pulsar timing arrays as we head towards the Square Kilometre Array and then beyond. This will address where progress needs to be made in terms of sensitivity to gravitational waves including improvements to existing observing approaches and new telescopes such as MeerKAT and FAST and techniques like LEAP. Developments in analytic techniques will also be discussed such as removal of interstellar medium effects, red noise and pulse profile variations. With the likelihood that the SKA will implement some form of Key Science Project approach, some ideas of how will this affect how the International Pulsar Timing Array effort and how it might evolve into a KSP will be presented.

  8. X-ray observations of Fermi LAT gamma-ray pulsars and pulsar candidates

    NASA Astrophysics Data System (ADS)

    Saz Parkinson, P.; Belfiore, A.; Caraveo, P.; De Luca, A.; Marelli, M.

    2014-07-01

    Since the launch of Fermi, in 2008, the population of known gamma-ray pulsars has exploded from just a handful, to over 150. X-ray observations have been crucial in both the discovery and the understanding of this new pulsar population. I will discuss our ongoing program of XMM, Chandra, and Swift observations of Fermi-LAT pulsars and pulsar candidates and present some of the latest results we have obtained.

  9. Gamma-Ray Pulsar Studies with GLAST

    NASA Astrophysics Data System (ADS)

    Thompson, D. J.

    2008-02-01

    Some pulsars have their maximum observable energy output in the gamma-ray band, offering the possibility of using these high-energy photons as probes of the particle acceleration and interaction processes in pulsar magnetospheres. After an extended hiatus between satellite missions, the recently-launched AGILE mission and the upcoming Gamma-ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT) will allow gamma-ray tests of the theoretical models developed based on past discoveries. With its greatly improved sensitivity, better angular resolution, and larger energy reach than older instruments, GLAST LAT should detect dozens to hundreds of new gamma-ray pulsars and measure luminosities, light curves, and phase-resolved spectra with unprecedented resolution. It will also have the potential to find radio-quiet pulsars like Geminga, using blind search techniques. Cooperation with radio and X-ray pulsar astronomers is an important aspect of the LAT team's planning for pulsar studies.

  10. Gamma-Ray Pulsar Studies With GLAST

    SciTech Connect

    Thompson, D.J.; /NASA, Goddard

    2011-11-23

    Some pulsars have their maximum observable energy output in the gamma-ray band, offering the possibility of using these high-energy photons as probes of the particle acceleration and interaction processes in pulsar magnetospheres. After an extended hiatus between satellite missions, the recently-launched AGILE mission and the upcoming Gamma-ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT) will allow gamma-ray tests of the theoretical models developed based on past discoveries. With its greatly improved sensitivity, better angular resolution, and larger energy reach than older instruments, GLAST LAT should detect dozens to hundreds of new gamma-ray pulsars and measure luminosities, light curves, and phase-resolved spectra with unprecedented resolution. It will also have the potential to find radio-quiet pulsars like Geminga, using blind search techniques. Cooperation with radio and X-ray pulsar astronomers is an important aspect of the LAT team's planning for pulsar studies.

  11. Gamma-Ray Pulsar Studies with GLAST

    SciTech Connect

    Thompson, D. J.

    2008-02-27

    Some pulsars have their maximum observable energy output in the gamma-ray band, offering the possibility of using these high-energy photons as probes of the particle acceleration and interaction processes in pulsar magnetospheres. After an extended hiatus between satellite missions, the recently-launched AGILE mission and the upcoming Gamma-ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT) will allow gamma-ray tests of the theoretical models developed based on past discoveries. With its greatly improved sensitivity, better angular resolution, and larger energy reach than older instruments, GLAST LAT should detect dozens to hundreds of new gamma-ray pulsars and measure luminosities, light curves, and phase-resolved spectra with unprecedented resolution. It will also have the potential to find radio-quiet pulsars like Geminga, using blind search techniques. Cooperation with radio and X-ray pulsar astronomers is an important aspect of the LAT team's planning for pulsar studies.

  12. Relativistic spin precession in the double pulsar.

    PubMed

    Breton, Rene P; Kaspi, Victoria M; Kramer, Michael; McLaughlin, Maura A; Lyutikov, Maxim; Ransom, Scott M; Stairs, Ingrid H; Ferdman, Robert D; Camilo, Fernando; Possenti, Andrea

    2008-07-01

    The double pulsar PSR J0737-3039A/B consists of two neutron stars in a highly relativistic orbit that displays a roughly 30-second eclipse when pulsar A passes behind pulsar B. Describing this eclipse of pulsar A as due to absorption occurring in the magnetosphere of pulsar B, we successfully used a simple geometric model to characterize the observed changing eclipse morphology and to measure the relativistic precession of pulsar B's spin axis around the total orbital angular momentum. This provides a test of general relativity and alternative theories of gravity in the strong-field regime. Our measured relativistic spin precession rate of 4.77 degrees (-0 degrees .65)(+0 degrees .66) per year (68% confidence level) is consistent with that predicted by general relativity within an uncertainty of 13%. PMID:18599782

  13. Theoretical Study of Gamma-ray Pulsars

    NASA Astrophysics Data System (ADS)

    Song, Yuzhe; Cheng, Kwong Sang; Takata, Jumpei

    2016-06-01

    We use the non-stationary three dimensional two-layer outer gap model to explain gamma-ray emissions from a pulsar magnetosphere. We found out that for some pulsars like the Geminga pulsar, it was hard to explain emissions above a level of around 1 GeV. We then developed the model into a non-stationary model. In this model we assigned a power-law distribution to one or more of the spectral parameters proposed in the previous model and calculated the weighted phaseaveraged spectrum. Though this model is suitable for some pulsars, it still cannot explain the high energy emission of the Geminga pulsar. An Inverse-Compton Scattering component between the primary particles and the radio photons in the outer magnetosphere was introduced into the model, and this component produced a sufficient number of GeV photons in the spectrum of the Geminga pulsar.

  14. A Pulsar and a Disk

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-07-01

    Recent, unusual X-ray observations from our galactic neighbor, the Small Magellanic Cloud, have led to an interesting model for SXP 214, a pulsar in a binary star system.Artists illustration of the magnetic field lines of a pulsar, a highly magnetized, rotating neutron star. [NASA]An Intriguing BinaryAn X-ray pulsar is a magnetized, rotating neutron star in a binary system with a stellar companion. Material is fed from the companion onto the neutron star, channeled by the objects magnetic fields onto a hotspot thats millions of degrees. This hotspot rotating past our line of sight is what produces the pulsations that we observe from X-ray pulsars.Located in the Small Magellanic Cloud, SXP 214 is a transient X-ray pulsar in a binary with a Be-type star. This star is spinning so quickly that material is thrown off of it to form a circumstellar disk.Recently, a team of authors led by JaeSub Hong (Harvard-Smithsonian Center for Astrophysics) have presented new Chandra X-ray observations of SXP 214, tracking it for 50 ks (~14 hours) in January 2013. These observations reveal some very unexpected behavior for this pulsar.X-ray PuzzleThe energy distribution of the X-ray emission from SXP 214 over time. Dark shades or blue colors indicate high counts, and light shades or yellow colors indicate low counts. Lower-energy X-ray emission appeared only later, after about 20 ks. [Hong et al. 2016]Three interesting pieces of information came from the Chandra observations:SXP 214s rotation period was measured to be 211.5 s an increase in the spin rate since the discovery measurement of a 214-second period. Pulsars usually spin down as they lose angular momentum over time so what caused this one to spin up?Its overall X-ray luminosity steadily increased over the 50 ks of observations.Its spectrum became gradually softer (lower energy) over time; in the first 20 ks, the spectrum only consisted of hard X-ray photons above 3 keV, but after 20 ks, softer X-ray photons below 2 ke

  15. Self-modulational formation of pulsar microstructures

    NASA Technical Reports Server (NTRS)

    Chian, A. C.-L.; Kennel, C. F.

    1983-01-01

    A nonlinear plasma theory for self-modulation of pulsar radio pulses is discussed. A nonlinear Schroedinger equation is derived for strong electromagnetic waves propagating in an electron-positron plasma. The nonlinearities arising from wave-intensity-induced particle-mass variation may excite the modulational instability of circularly and linearly polarized pulsar radiation. The resulting wave envelopes can take the form of periodic wave trains or solitons. These nonlinear stationary waveforms may account for the formation of pulsar microstructures.

  16. High-sensitivity observations of 28 pulsars

    NASA Technical Reports Server (NTRS)

    Weisberg, J. M.; Armstrong, B. K.; Backus, P. R.; Cordes, J. M.; Boriakoff, V.

    1986-01-01

    Average 430-MHz pulse profiles and, where possible, modulation indices and pulse-nulling fractions are computed for 28 pulsars. Morphological classifications are determined for most of the pulsars. It is found that core emission components tend to have lower modulation indices than conal components, and that pulsars having only a core component never exhibit pulse pulling. PSR 1612 + 07 is shown to undergo mode changes.

  17. Birth of millisecond pulsars in globular clusters

    NASA Technical Reports Server (NTRS)

    Grindlay, J. E.; Bailyn, C. D.

    1988-01-01

    It is argued here that accretion-induced collapse of white dwarfs in binaries can form millisecond pulsars directly without requiring a precursor low-mass X-ray binary stage. Ablation of the precollapse binary companion by the millisecond pulsar's radiation field, a process invoked to explain some of the characteristics of the recently discovered eclipsing millisecond pulsar, can then yield isolated neutron stars witout requiring an additional stellar encounter.

  18. Self-modulational formation of pulsar microstructures

    NASA Technical Reports Server (NTRS)

    Chian, A. C.-L.; Kennel, C. F.

    1987-01-01

    A nonlinear plasma theory for self modulation of pulsar radio pulses is discussed. A nonlinear Schroedinger equation is derived for strong electromagnetic waves propagating in an electron positron plasma. The nonlinearities arising from wave intensity induced particle mass variation may excite the modulational instability of circularly and linearly polarized pulsar radiation. The resulting wave envelopes can take the form of periodic wave trains or solitons. These nonlinear stationary waveforms may account for the formation of pulsar microstructures.

  19. Cherenkov Telescopes Results on Pulsar Wind Nebulae and Pulsars

    NASA Astrophysics Data System (ADS)

    Wilhelmi, Emma De Oña

    The last few years have seen a revolution in very high γ-ray astronomy (VHE; E>100 GeV) driven largely by a new generation of Cherenkov telescopes. These new facilities, namely H.E.S.S. (High Energy Stereoscopic System), MAGIC (Major Atmospheric Gamma Imaging Cherenkov Telescope) and its upgrade MAGIC 2, VERITAS (Very Energetic Radiation Imaging Telescope Array System) and CANGAROO (Collaboration of Australia and Nippon for a Gamma Ray Observatory in the Outback) were designed to increase the flux sensitivity in the energy regime of hundreds of GeV, expanding the observed energy range from 50 to multi-TeV, and fostered as a result a period of rapid growth in our understanding of the Non-ThermalUniverse. As a result of this fast development the number of pulsar wind nebulae (PWNe) detected has increased from a few in the early 90's to more than two dozen of firm candidates nowadays. Also, the low energy threshold achieved allows to investigate the pulsed spectra of the high energy pulsars powering PWNe. A review of the most relevant VHE results concerning pulsars and their relativistic winds is discussed here in the context of Cherenkov telescopes.

  20. Detection of new pulsars at 111 MHz

    NASA Astrophysics Data System (ADS)

    Tyul'bashev, S. A.; Tyul'bashev, V. S.; Oreshko, V. V.; Logvinenko, S. V.

    2016-02-01

    The first results of a search for pulsars using the Large Phased Array of the Lebedev Physical Institute at 111 MHz for right ascensions 0h-24h and declinations 21°-42° are reported. Data with a time resolution of 100 ms in six frequency channels within a 2.5-MHz frequency band have been processed. Thirty-four pulsars have been detected, of which seventeen were observed on this telescope earlier; ten known pulsars had not been observed earlier. Seven new pulsars have been discovered.

  1. Pulsar Electrodynamics: a Time-dependent View

    SciTech Connect

    Spitkovsky, Anatoly; /KIPAC, Menlo Park

    2006-04-10

    Pulsar spindown forms a reliable yet enigmatic prototype for the energy loss processes in many astrophysical objects including accretion disks and back holes. In this paper we review the physics of pulsar magnetospheres, concentrating on recent developments in force-free modeling of the magnetospheric structure. In particular, we discuss a new method for solving the equations of time-dependent force-free relativistic MHD in application to pulsars. This method allows to dynamically study the formation of the magnetosphere and its response to perturbations, opening a qualitatively new window on pulsar phenomena. Applications of the method to other magnetized rotators, such as magnetars and accretion disks, are also discussed.

  2. ON PULSAR DISTANCE MEASUREMENTS AND THEIR UNCERTAINTIES

    SciTech Connect

    Verbiest, J. P. W.; Lee, K. J.; Weisberg, J. M.; Chael, A. A.; Lorimer, D. R.

    2012-08-10

    Accurate distances to pulsars can be used for a variety of studies of the Galaxy and its electron content. However, most distance measures to pulsars have been derived from the absorption (or lack thereof) of pulsar emission by Galactic H I gas, which typically implies that only upper or lower limits on the pulsar distance are available. We present a critical analysis of all measured H I distance limits to pulsars and other neutron stars, and translate these limits into actual distance estimates through a likelihood analysis that simultaneously corrects for statistical biases. We also apply this analysis to parallax measurements of pulsars in order to obtain accurate distance estimates and find that the parallax and H I distance measurements are biased in different ways, because of differences in the sampled populations. Parallax measurements typically underestimate a pulsar's distance because of the limited distance to which this technique works and the consequential strong effect of the Galactic pulsar distribution (i.e., the original Lutz-Kelker bias), in H I distance limits, however, the luminosity bias dominates the Lutz-Kelker effect, leading to overestimated distances because the bright pulsars on which this technique is applicable are more likely to be nearby given their brightness.

  3. Measuring emission coordinates in a pulsar-based relativistic positioning system

    NASA Astrophysics Data System (ADS)

    Bunandar, Darius; Caveny, Scott A.; Matzner, Richard A.

    2011-11-01

    A relativistic deep space positioning system has been proposed using four or more pulsars with stable repetition rates. (Each pulsar emits pulses at a fixed repetition period in its rest frame.) The positioning system uses the fact that an event in spacetime can be fully described by emission coordinates: the proper emission time of each pulse measured at the event. The proper emission time of each pulse from four different pulsars—interpolated as necessary—provides the four spacetime coordinates of the reception event in the emission coordinate system. If more than four pulsars are available, the redundancy can improve the accuracy of the determination and/or resolve degeneracies resulting from special geometrical arrangements of the sources and the event. We introduce a robust numerical approach to measure the emission coordinates of an event in any arbitrary spacetime geometry. Our approach uses a continuous solution of the eikonal equation describing the backward null cone from the event. The pulsar proper time at the instant the null cone intersects the pulsar world line is one of the four required coordinates. The process is complete (modulo degeneracies) when four pulsar world lines have been crossed by the light cone. The numerical method is applied in two different examples: measuring emission coordinates of an event in Minkowski spacetime, using pulses from four pulsars stationary in the spacetime; and measuring emission coordinates of an event in Schwarzschild spacetime, using pulses from four pulsars freely falling toward a static black hole. These numerical simulations are merely exploratory, but with improved resolution and computational resources the method can be applied to more pertinent problems. For instance one could measure the emission coordinates, and therefore the trajectory, of the Earth.

  4. Interpretation of rapidly rotating pulsars

    SciTech Connect

    Weber, F. . Inst. fuer Theoretische Physik); Glendenning, N.K. )

    1992-08-05

    The minimum possible rotational period of pulsars, which are interpreted as rotating neutron stars, is determined by applying a representative collection of realistic nuclear equations of state. It is found that none of the selected equations of state allows for neutron star rotation at periods below 0.8--0.9 ms. Thus, this work strongly supports the suggestion that if pulsars with shorter rotational periods were found, these are likely to be strange-quark-matter stars. The conclusion that the confined hadronic phase of nucleons and nuclei is only metastable would then be almost inescapable, and the plausible ground-state in that event is the deconfined phase of (3-flavor) strange-quark-matter.

  5. The International Pulsar Timing Array

    NASA Astrophysics Data System (ADS)

    Manchester, R. N.; IPTA

    2013-11-01

    The International Pulsar Timing Array (IPTA) is an organization whose raison d’être is to facilitate collaboration between the three main existing PTAs (the EPTA in Europe, NANOGrav in North America and the PPTA in Australia) in order to realize the benefits of combined PTA data sets in reaching the goals of PTA projects. Currently, shared data sets for 50 pulsars are available for IPTA-based projects. Operation of the IPTA is administered by a Steering Committee consisting of six members, two from each PTA, plus the immediate past Chair in a non-voting capacity. A Constitution and several Agreements define the framework for the collaboration. Web pages provide information both to members of participating PTAs and to the general public. With support from an NSF PIRE grant, the IPTA facilitates the organization of annual Student Workshops and Science Meetings. These are very valuable both in training new students and in communicating current results from IPTA-based research.

  6. Pair-Starved Pulsar Magnetospheres

    NASA Technical Reports Server (NTRS)

    Muslimov, Alex G.; Harding, Alice K.

    2009-01-01

    We propose a simple analytic model for the innermost (within the light cylinder of canonical radius, approx. c/Omega) structure of open-magnetic-field lines of a rotating neutron star (NS) with relativistic outflow of charged particles (electrons/positrons) and arbitrary angle between the NS spin and magnetic axes. We present the self-consistent solution of Maxwell's equations for the magnetic field and electric current in the pair-starved regime where the density of electron-positron plasma generated above the pulsar polar cap is not sufficient to completely screen the accelerating electric field and thus establish thee E . B = 0 condition above the pair-formation front up to the very high altitudes within the light cylinder. The proposed mode1 may provide a theoretical framework for developing the refined model of the global pair-starved pulsar magnetosphere.

  7. An ultraluminous nascent millisecond pulsar

    NASA Astrophysics Data System (ADS)

    Kluźniak, Włodek; Lasota, Jean-Pierre

    2015-03-01

    If the ultraluminous source (ULX) M82 X-2 sustains its measured spin-up value of dot{ν }= 10^{-10} s^{-2}, it will become a millisecond pulsar in less than 105 yr. The observed (isotropic) luminosity of 1040 erg s-1 also supports the notion that the neutron star will spin up to a millisecond period upon accreting about 0.1 M⊙ - the reported hard X-ray luminosity of this ULX, together with the spin-up value, implies torques consistent with the accretion disc extending down to the vicinity of the stellar surface, as expected for low values of the stellar dipole magnetic field (B ≲ 109 G). This suggests a new channel of millisecond pulsar formation - in high-mass X-ray binaries - and may have implications for studies of gravitational waves, and possibly for the formation of low-mass black holes through accretion-induced collapse.

  8. Particle acceleration in pulsar magnetospheres

    NASA Technical Reports Server (NTRS)

    Baker, K. B.

    1978-01-01

    The structure of pulsar magnetospheres and the acceleration mechanism for charged particles in the magnetosphere was studied using a pulsar model which required large acceleration of the particles near the surface of the star. A theorem was developed which showed that particle acceleration cannot be expected when the angle between the magnetic field lines and the rotation axis is constant (e.g. radial field lines). If this angle is not constant, however, acceleration must occur. The more realistic model of an axisymmetric neutron star with a strong dipole magnetic field aligned with the rotation axis was investigated. In this case, acceleration occurred at large distances from the surface of the star. The magnitude of the current can be determined using the model presented. In the case of nonaxisymmetric systems, the acceleration is expected to occur nearer to the surface of the star.

  9. The magnetospheric structure of pulsars

    NASA Technical Reports Server (NTRS)

    Roberts, D. H.

    1973-01-01

    A model of pulsar magnetospheres is described which has evolved inductively from the work of Sturrock, where the radiation is produced near the surface of a neutron star. Some of the theoretical ideas of others, particularly those of Sturrock, are discussed. The braking index n and period-pulse-width distribution of pulsars are first reinvestigated by relaxing the conventional assumption that R sub Y = R sub L, where R sub Y is the radius of the neutral points marking the transition from closed to open magnetic field lines, and R sub L is the radius of the light cylinder. This is replaced by the parameterization R sub Y = R sub * (1- eta )power R sub L (eta), where R sub * is the neutron star radius. If the ratio frequency radiation is created near the surface and beamed along open field lines, it is found that a good fit to the period-pulse-width distribution can be obtained for eta in the range 0.5 = or eta = or 0.7. The relation n = 1 + 2 eta then gives n = 2.2 + or - 0.2, which is in good agreement with the values measured for the Crab pulsar.

  10. Community Ecology and Capacity: Keys to Progressing the Environmental Communication of Wicked Problems

    ERIC Educational Resources Information Center

    Caron, Rosemary M.; Serrell, Nancy

    2009-01-01

    Wicked problems are multifactorial in nature and possess no clear resolution due to numerous community stakeholder involvement. We demonstrate childhood lead poisoning as a wicked problem and illustrate how understanding a community's ecology can build community capacity to affect local environmental management by (1) forming an academic-community…

  11. Solving the Problem of Learning to Read: Children's Linguistic Awareness and Reading Progress.

    ERIC Educational Resources Information Center

    Abramson, Shareen

    A study investigated suggested interrelationships of linguistic awareness, cognitive ability, and reading achievement. The extent to which differences in reading achievement were related to differences in the other areas was also explored. The Linguistic Awareness in Reading Test (LARR), the Coloured Progressive Matrices (CPM), and the Stanford…

  12. A Search for Radio Millisecond Pulsars

    NASA Astrophysics Data System (ADS)

    Sayer, Ronald Winston

    1996-01-01

    We have built a data acquisition backend for radio pulsar search observations carried out at the NRAO 140 -foot telescope in Green Bank, West Virginia. Our system sampled 512 spectral channels over 40 MHz every 256 mus, reduced samples to one-bit precision, and wrote the resulting data stream onto magnetic tape for later, off-line processing. We have completed three surveys with this backend. In the first survey, we searched most of the Northern Hemisphere for millisecond radio pulsars. Previous surveys directed towards most of the region covered had not been as sensitive to pulsars with millisecond periods. We obtained high quality data for 15,876 deg^2 of sky. Eight new pulsars were discovered and 76 previously known pulsars were detected. Two of the eight new pulsars (PSR J1022+1001 and PSR J1518+4904) are millisecond pulsars in binary systems. PSR J1518+4904 is a 41 ms radio pulsar in an eccentric (e = 0.25) 8.6 day orbit with another stellar object, probably another neutron star. It is only the fifth double neutron star system known. The system's relativistic advance of periastron has been measured to be ˙omega = 0.0112 +/- 0.0002 ^circ yr^{-1}, implying that the total mass of the pair of stars is 2.65 +/-0.07Modot. We have searched for radio pulsar companions to 40 nearby OB runaway stars. No pulsar companions to OB runaways were discovered. One previously unknown pulsar, PSR J2044+4614, was discovered while observing towards target O star BD+45,3260. However, follow-up timing observations reveal that the pulsar is not associated with the target O star. Assuming standard models for the pulsar beaming fraction and luminosity function, we conclude that most OB runaways do not have pulsar companions. We have completed a survey for pulsed radio signals towards 27 gamma-ray sources detected by the EGRET instrument of the Compton Gamma Ray Observatory. No new pulsars were discovered.

  13. Searching for pulsars using image pattern recognition

    SciTech Connect

    Zhu, W. W.; Berndsen, A.; Madsen, E. C.; Tan, M.; Stairs, I. H.; Brazier, A.; Lazarus, P.; Lynch, R.; Scholz, P.; Stovall, K.; Cohen, S.; Dartez, L. P.; Lunsford, G.; Martinez, J. G.; Mata, A.; Ransom, S. M.; Banaszak, S.; Biwer, C. M.; Flanigan, J.; Rohr, M. E-mail: berndsen@phas.ubc.ca; and others

    2014-02-01

    In the modern era of big data, many fields of astronomy are generating huge volumes of data, the analysis of which can sometimes be the limiting factor in research. Fortunately, computer scientists have developed powerful data-mining techniques that can be applied to various fields. In this paper, we present a novel artificial intelligence (AI) program that identifies pulsars from recent surveys by using image pattern recognition with deep neural nets—the PICS (Pulsar Image-based Classification System) AI. The AI mimics human experts and distinguishes pulsars from noise and interference by looking for patterns from candidate plots. Different from other pulsar selection programs that search for expected patterns, the PICS AI is taught the salient features of different pulsars from a set of human-labeled candidates through machine learning. The training candidates are collected from the Pulsar Arecibo L-band Feed Array (PALFA) survey. The information from each pulsar candidate is synthesized in four diagnostic plots, which consist of image data with up to thousands of pixels. The AI takes these data from each candidate as its input and uses thousands of such candidates to train its ∼9000 neurons. The deep neural networks in this AI system grant it superior ability to recognize various types of pulsars as well as their harmonic signals. The trained AI's performance has been validated with a large set of candidates from a different pulsar survey, the Green Bank North Celestial Cap survey. In this completely independent test, the PICS ranked 264 out of 277 pulsar-related candidates, including all 56 previously known pulsars and 208 of their harmonics, in the top 961 (1%) of 90,008 test candidates, missing only 13 harmonics. The first non-pulsar candidate appears at rank 187, following 45 pulsars and 141 harmonics. In other words, 100% of the pulsars were ranked in the top 1% of all candidates, while 80% were ranked higher than any noise or interference. The

  14. Searching for Pulsars Using Image Pattern Recognition

    NASA Astrophysics Data System (ADS)

    Zhu, W. W.; Berndsen, A.; Madsen, E. C.; Tan, M.; Stairs, I. H.; Brazier, A.; Lazarus, P.; Lynch, R.; Scholz, P.; Stovall, K.; Ransom, S. M.; Banaszak, S.; Biwer, C. M.; Cohen, S.; Dartez, L. P.; Flanigan, J.; Lunsford, G.; Martinez, J. G.; Mata, A.; Rohr, M.; Walker, A.; Allen, B.; Bhat, N. D. R.; Bogdanov, S.; Camilo, F.; Chatterjee, S.; Cordes, J. M.; Crawford, F.; Deneva, J. S.; Desvignes, G.; Ferdman, R. D.; Freire, P. C. C.; Hessels, J. W. T.; Jenet, F. A.; Kaplan, D. L.; Kaspi, V. M.; Knispel, B.; Lee, K. J.; van Leeuwen, J.; Lyne, A. G.; McLaughlin, M. A.; Siemens, X.; Spitler, L. G.; Venkataraman, A.

    2014-02-01

    In the modern era of big data, many fields of astronomy are generating huge volumes of data, the analysis of which can sometimes be the limiting factor in research. Fortunately, computer scientists have developed powerful data-mining techniques that can be applied to various fields. In this paper, we present a novel artificial intelligence (AI) program that identifies pulsars from recent surveys by using image pattern recognition with deep neural nets—the PICS (Pulsar Image-based Classification System) AI. The AI mimics human experts and distinguishes pulsars from noise and interference by looking for patterns from candidate plots. Different from other pulsar selection programs that search for expected patterns, the PICS AI is taught the salient features of different pulsars from a set of human-labeled candidates through machine learning. The training candidates are collected from the Pulsar Arecibo L-band Feed Array (PALFA) survey. The information from each pulsar candidate is synthesized in four diagnostic plots, which consist of image data with up to thousands of pixels. The AI takes these data from each candidate as its input and uses thousands of such candidates to train its ~9000 neurons. The deep neural networks in this AI system grant it superior ability to recognize various types of pulsars as well as their harmonic signals. The trained AI's performance has been validated with a large set of candidates from a different pulsar survey, the Green Bank North Celestial Cap survey. In this completely independent test, the PICS ranked 264 out of 277 pulsar-related candidates, including all 56 previously known pulsars and 208 of their harmonics, in the top 961 (1%) of 90,008 test candidates, missing only 13 harmonics. The first non-pulsar candidate appears at rank 187, following 45 pulsars and 141 harmonics. In other words, 100% of the pulsars were ranked in the top 1% of all candidates, while 80% were ranked higher than any noise or interference. The

  15. Algebraically special space-time in relativity, black holes, and pulsar models

    NASA Technical Reports Server (NTRS)

    Adler, R. J.; Sheffield, C.

    1973-01-01

    The entire field of astronomy is in very rapid flux, and at the center of interest are problems relating to the very dense, rotating, neutron stars observed as pulsars. the hypothesized collapsed remains of stars known as black holes, and quasars. Degenerate metric form, or Kerr-Schild metric form, was used to study several problems related to intense gravitational fields.

  16. Pulsars at TeV

    NASA Astrophysics Data System (ADS)

    Edwards, P.

    1994-04-01

    The atmospheric Cerenkov technique is used to search for emission at energies above several hundred GeV from a variety of objects, including pulsars (see, e.g., reviews by Weekes, 1988, Phys. Rep., 160, 1; Weekes, 1992, Sp. Sci. Rev., 59, 315). Claims for TeV emission (from any source) should be of high significance, show gamma-ray-like properties, and be independently confirmed. By these criteria the Crab nebula is currently the only established pulsar-driven system to be observed at TeV energies (Weekes et al., 1989, Astrophys. J., 342, 379; Vacanti et al., 1991, Astrophys. J., 377, 467; Goret et al., 1993, Astron. Astrophys., 270, 401). The gamma-ray signal is not pulsed at TeV energies, leading to models of synchrotron self-Compton emission from the Crab nebula (e.g., De Jager and Harding, 1992, Astrophys. J., 396, 161), although other models have also been proposed (Kwok et al., 1991, Astrophys. J., 379, 653). While claims exist for TeV emission from, amongst others, the Vela pulsar (e.g., Bhat et al., 1987, Astron. Astrophys., 178, 242, Geminga (Vishwanath et al., 1993, Astron. Astrophys., 267, L5; Bowden et al., 1993, J. Phys. G: Nucl. Part. Phys., 19, L29), and PSR 1509-58 (Nel et al., 1992, Astrophys. pulsars have high values of E-dot/d2 (due to their proximity) and are thus potentially observable TeV sources. *The detection of TeV gamma-rays from millisecond pulsars has been considered recently by Smith (1993, Astrophys. -J., 408, 468).

  17. Case study method and problem-based learning: utilizing the pedagogical model of progressive complexity in nursing education.

    PubMed

    McMahon, Michelle A; Christopher, Kimberly A

    2011-01-01

    As the complexity of health care delivery continues to increase, educators are challenged to determine educational best practices to prepare BSN students for the ambiguous clinical practice setting. Integrative, active, and student-centered curricular methods are encouraged to foster student ability to use clinical judgment for problem solving and informed clinical decision making. The proposed pedagogical model of progressive complexity in nursing education suggests gradually introducing students to complex and multi-contextual clinical scenarios through the utilization of case studies and problem-based learning activities, with the intention to transition nursing students into autonomous learners and well-prepared practitioners at the culmination of a nursing program. Exemplar curricular activities are suggested to potentiate student development of a transferable problem solving skill set and a flexible knowledge base to better prepare students for practice in future novel clinical experiences, which is a mutual goal for both educators and students. PMID:22718667

  18. Community Ecology and Capacity: Keys to Progressing the Environmental Communication of Wicked Problems

    PubMed Central

    Caron, Rosemary M.; Serrell, Nancy

    2010-01-01

    Wicked problems are multifactorial in nature and possess no clear resolution due to numerous community stakeholder involvement. We demonstrate childhood lead poisoning as a wicked problem and illustrate how understanding a community’s ecology can build community capacity to affect local environmental management by (1) forming an academic–community partnership and (2) developing a place-specific strategy grounded in the cultural–experiential model of risk. We propose that practitioners need to consider a community’s ecology and social context of risk as it pertains to wicked problems. These factors will determine how a diverse community interprets and responds to environmental communication and capacity-building efforts. PMID:20686630

  19. Braking index of isolated pulsars

    NASA Astrophysics Data System (ADS)

    Hamil, O.; Stone, J. R.; Urbanec, M.; Urbancová, G.

    2015-03-01

    Isolated pulsars are rotating neutron stars with accurately measured angular velocities Ω , and their time derivatives that show unambiguously that the pulsars are slowing down. Although the exact mechanism of the spin-down is a question of detailed debate, the commonly accepted view is that it arises through emission of magnetic dipole radiation (MDR) from a rotating magnetized body. Other processes, including the emission of gravitational radiation, and of relativistic particles (pulsar wind), are also being considered. The calculated energy loss by a rotating pulsar with a constant moment of inertia is assumed proportional to a model dependent power of Ω . This relation leads to the power law Ω ˙ =-K Ωn where n is called the braking index. The MDR model predicts n exactly equal to 3. Selected observations of isolated pulsars provide rather precise values of n , individually accurate to a few percent or better, in the range 1

  20. Gamma-Ray Pulsar Candidates for GLAST

    NASA Technical Reports Server (NTRS)

    Thompson, D. J.

    2008-01-01

    The Gamma-ray Large Area Space Telescope (GLAST) will be launched this year, and its Large Area Telescope (LAT) is expected to discover scores to hundreds of gamma-ray pulsars. This poster discusses which of the over 1700 known pulsars, mostly visible only at radio frequencies, are likely to emit greater than 100 MeV gamma rays with intensities detectable by the LAT. The main figure of merit used to select gamma-ray pulsar candidates is sqrt(E-dot)/d2, where E-dot is the energy loss due to rotational spin-down, and d is the distance to the pulsar. The figure of merit incorporates spin-down flux at earth (proportional to E-dot/d2) times efficiency, assumed proportional to l/sqrt(E-dot). A few individual objects are cited to illustrate the issues. Since large E-dot pulsars also tend to have large timing noise and occasional glitches, their ephemerides can become inaccurate in weeks to months. To detect and study the gamma-ray emission the photons must be accurately tagged with the pulse phase. With hours to days between gamma-ray photon arrival times from a pulsar and months to years of LAT exposure needed for good detections, GLAST will rely on radio and X-ray timing measurements throughout the continuous gamma-ray observations. The poster will describe efforts to coordinate pulsar timing of the candidate gamma-ray pulsars.

  1. Gamma-Ray Pulsar Candidates for GLAST

    NASA Technical Reports Server (NTRS)

    Thompson, David J.; Smith, D. A.; Dumora, D.; Guillemot, L.; Parent, D.; Reposeur, T.; Grove, E.; Romani, R. W.; Thorsett, S. E.

    2007-01-01

    The Gamma-ray Large Area Space Telescope (GLAST) will be launched less than a year from now, and its Large Area Telescope (LAT) is expected to discover scores to hundreds of gamma-ray pulsars. This poster discusses which of the over 1700 known pulsars, mostly visible only at radio Erequencies, are likely to emit greater than l00 MeV gamma rays with intensities detectable by the LAT. The main figure of merit used to select gamma-ray pulsar candidates is sqrt(E-dot)/d^2, where E-dot is the energy loss due to rotational spindown, and d is the distance to the pulsar. The figure of merit incorporates spin-down flux at earth (proportional to E-dot/d^2) times efficiency, assumed proportional to 1/sqrt(E-dot). A few individual objects are cited to illustrate the issues. Since large E-dot pulsars also tend to have large timing noise and occasional glitches, their ephemerides can become inaccurate in weeks to months. To detect and study the gamma-ray emission the photons must be accurately tagged with the pulse phase. With hours to days between gamma-ray photon arrival times from a pulsar and months to years of LAT exposure needed for good detections, GLAST will need timing measurements throughout the continuous gamma-ray observations. The poster will describe efforts to coordinate pulsar timing of the candidate gamma-ray pulsars.

  2. Neutron Stars and the Discovery of Pulsars.

    ERIC Educational Resources Information Center

    Greenstein, George

    1985-01-01

    Part one recounted the story of the discovery of pulsars and examined the Crab Nebula, supernovae, and neutron stars. This part (experts from the book "Frozen Star") shows how an understanding of the nature of pulsars allowed astronomers to tie these together. (JN)

  3. Radio polarimetry of Galactic Centre pulsars

    NASA Astrophysics Data System (ADS)

    Schnitzeler, D. H. F. M.; Eatough, R. P.; Ferrière, K.; Kramer, M.; Lee, K. J.; Noutsos, A.; Shannon, R. M.

    2016-07-01

    To study the strength and structure of the magnetic field in the Galactic Centre (GC), we measured Faraday rotation of the radio emission of pulsars which are seen towards the GC. Three of these pulsars have the largest rotation measures (RMs) observed in any Galactic object with the exception of Sgr A⋆. Their large dispersion measures, RMs and the large RM variation between these pulsars and other known objects in the GC implies that the pulsars lie in the GC and are not merely seen in projection towards the GC. The large RMs of these pulsars indicate large line-of-sight magnetic field components between ˜ 16 and 33 μG; combined with recent model predictions for the strength of the magnetic field in the GC this implies that the large-scale magnetic field has a very small inclination angle with respect to the plane of the sky (˜12°). Foreground objects like the Radio Arc or possibly an ablated, ionized halo around the molecular cloud G0.11-0.11 could contribute to the large RMs of two of the pulsars. If these pulsars lie behind the Radio Arc or G0.11-0.11 then this proves that low-scattering corridors with lengths ≳100 pc must exist in the GC. This also suggests that future, sensitive observations will be able to detect additional pulsars in the GC. Finally, we show that the GC component in our most accurate electron density model oversimplifies structure in the GC.

  4. Radio polarimetry of Galactic centre pulsars

    NASA Astrophysics Data System (ADS)

    Schnitzeler, D. H. F. M.; Eatough, R. P.; Ferrière, K.; Kramer, M.; Lee, K. J.; Noutsos, A.; Shannon, R. M.

    2016-04-01

    To study the strength and structure of the magnetic field in the Galactic centre (GC) we measured Faraday rotation of the radio emission of pulsars which are seen towards the GC. Three of these pulsars have the largest rotation measures (RMs) observed in any Galactic object with the exception of Sgr A⋆. Their large dispersion measures, RMs and the large RM variation between these pulsars and other known objects in the GC implies that the pulsars lie in the GC and are not merely seen in projection towards the GC. The large RMs of these pulsars indicate large line-of-sight magnetic field components between ˜ 16 - 33 μG; combined with recent model predictions for the strength of the magnetic field in the GC this implies that the large-scale magnetic field has a very small inclination angle with respect to the plane of the sky (˜ 12°). Foreground objects like the Radio Arc or possibly an ablated, ionized halo around the molecular cloud G0.11-0.11 could contribute to the large RMs of two of the pulsars. If these pulsars lie behind the Radio Arc or G0.11-0.11 then this proves that low-scattering corridors with lengths ≳ 100 pc must exist in the GC. This also suggests that future, sensitive observations will be able to detect additional pulsars in the GC. Finally, we show that the GC component in our most accurate electron density model oversimplifies structure in the GC.

  5. The Binary Pulsar: Gravity Waves Exist.

    ERIC Educational Resources Information Center

    Will, Clifford

    1987-01-01

    Reviews the history of pulsars generally and the 1974 discovery of the binary pulsar by Joe Taylor and Russell Hulse specifically. Details the data collection and analysis used by Taylor and Hulse. Uses this discussion as support for Albert Einstein's theory of gravitational waves. (CW)

  6. Gamma rays from hidden millisecond pulsars

    NASA Technical Reports Server (NTRS)

    Tavani, Marco

    1992-01-01

    The properties were studied of a new class of gamma ray sources consisting of millisecond pulsars totally or partially surrounded by evaporating material from irradiated companion stars. Hidden millisecond pulsars offer a unique possibility to study gamma ray, optical and radio emission from vaporizing binaries. The relevance of this class of binaries for GRO observations and interpretation of COS-B data is emphasized.

  7. Pulsars at the Highest Energies: Questions for the GLAST and ACT's

    NASA Technical Reports Server (NTRS)

    Thompson, Dave

    2008-01-01

    The recent announcement by the MAGIC team of pulsed gamma rays from the Crab Pulsar above 25 GeV and the launch of AGILE and the Gamma-ray Large Area Space Telescope (GLAST) offer the promise of major progress in understanding the most extreme emission from pulsar magnetospheres. While waiting for detailed results, we can formulate questions to be addressed, based on past measurements and theoretical modeling. This brief review will highlight promising approaches for research into high-energy pulsed radiation.

  8. Pulsars, PTAs, and PALFA: Highlights and Opportunities

    NASA Astrophysics Data System (ADS)

    Scholz, Paul A.

    2015-08-01

    The detection of gravitational waves with nanohertz frequencies from SMBHs in merging galaxies, either a single source or a background, is greatly aided by increasing the sensitivity of pulsar timing arrays (PTAs). Increasing the number of millisecond pulsars in PTAs is one of the best ways to enhance their sensitivity. Therefore searches for new millisecond pulsars are absolutely essential to the detection of gravitational waves from merging galaxies. I will review the status of current pulsar search efforts and how they have contributed to PTAs. I will then present some of the recent highlights of the PALFA survey. Using the PALFA survey as a case study, I will outline the current challenges faced by pulsar searches, including RFI and a large number of false positives, and potential solutions to those issues.

  9. A radio pulsar spinning at 716 Hz.

    PubMed

    Hessels, Jason W T; Ransom, Scott M; Stairs, Ingrid H; Freire, Paulo C C; Kaspi, Victoria M; Camilo, Fernando

    2006-03-31

    We have discovered a 716-hertz eclipsing binary radio pulsar in the globular cluster Terzan 5 using the Green Bank Telescope. It is the fastest spinning neutron star found to date, breaking the 24-year record held by the 642-hertz pulsar B1937+21. The difficulty in detecting this pulsar, because of its very low flux density and high eclipse fraction (approximately 40% of the orbit), suggests that even faster spinning neutron stars exist. If the pulsar has a mass less than twice the mass of the Sun, then its radius must be constrained by the spin rate to be <16 kilometers. The short period of this pulsar also constrains models that suggest that gravitational radiation, through an r-mode (Rossby wave) instability, limits the maximum spin frequency of neutron stars. PMID:16410486

  10. Testing black hole superradiance with pulsar companions

    NASA Astrophysics Data System (ADS)

    Rosa, João G.

    2015-10-01

    We show that the magnetic dipole and gravitational radiation emitted by a pulsar can undergo superradiant scattering off a spinning black hole companion. We find that the relative amount of superradiant modes in the radiation depends on the pulsar's angular position relative to the black hole's equatorial plane. In particular, when the pulsar and black hole spins are aligned, superradiant modes are dominant at large angles, leading to an amplification of the pulsar's luminosity, whereas for small angles the radiation is dominantly composed of non-superradiant modes and the signal is attenuated. This results in a characteristic orbital modulation of the pulsar's luminosity, up to the percent level within our approximations, which may potentially yield a signature of superradiant scattering in astrophysical black holes and hence an important test of general relativity.

  11. [Progress and problems in pediatric surgery--the Association of Pediatric Anesthesiologists].

    PubMed

    Tamiya, K

    1984-09-01

    From the first meeting of the Japanese Society of Pediatric Surgeons in 1964 a small group discussion on anesthetic problems and patient care was held by some anesthesiologists at night. The Association of Pediatric Anesthesiologists (started in 1971) has undertaken the night meeting ever since the twelfth Annual Meeting of the Society of Pediatric Surgeons in 1975. The problems about pediatric respiratory management, neonatal emergency surgery and pediatric anesthesia were discussed frequently by doctors in different specialties. The recent decrease of mortality in neonatal surgery is thought to have come from the improvement of pediatric respiratory management. This night meeting of anesthesiologists has had a major role in the resolution of problems in pediatric respiratory impairment. The problems to be resolved in an emergency--persistent fetal circulation, barotrauma, nutritional problems in long term ventilatory support and so on--, will be discussed in the future. The purpose of this association is to elevate the quality of pediatric anesthesiologists by discussion with the other specialists of medicine and to make clear their responsibility in Children's Hospitals or Centers. PMID:6503982

  12. Einstein@Home Discovery of 24 Pulsars in the Parkes Multi-beam Pulsar Survey

    NASA Astrophysics Data System (ADS)

    Knispel, B.; Eatough, R. P.; Kim, H.; Keane, E. F.; Allen, B.; Anderson, D.; Aulbert, C.; Bock, O.; Crawford, F.; Eggenstein, H.-B.; Fehrmann, H.; Hammer, D.; Kramer, M.; Lyne, A. G.; Machenschalk, B.; Miller, R. B.; Papa, M. A.; Rastawicki, D.; Sarkissian, J.; Siemens, X.; Stappers, B. W.

    2013-09-01

    We have conducted a new search for radio pulsars in compact binary systems in the Parkes multi-beam pulsar survey (PMPS) data, employing novel methods to remove the Doppler modulation from binary motion. This has yielded unparalleled sensitivity to pulsars in compact binaries. The required computation time of ≈17, 000 CPU core years was provided by the distributed volunteer computing project Einstein@Home, which has a sustained computing power of about 1 PFlop s-1. We discovered 24 new pulsars in our search, 18 of which were isolated pulsars, and 6 were members of binary systems. Despite the wide filterbank channels and relatively slow sampling time of the PMPS data, we found pulsars with very large ratios of dispersion measure (DM) to spin period. Among those is PSR J1748-3009, the millisecond pulsar with the highest known DM (≈420 pc cm-3). We also discovered PSR J1840-0643, which is in a binary system with an orbital period of 937 days, the fourth largest known. The new pulsar J1750-2536 likely belongs to the rare class of intermediate-mass binary pulsars. Three of the isolated pulsars show long-term nulling or intermittency in their emission, further increasing this growing family. Our discoveries demonstrate the value of distributed volunteer computing for data-driven astronomy and the importance of applying new analysis methods to extensively searched data.

  13. EINSTEIN-HOME DISCOVERY OF 24 PULSARS IN THE PARKES MULTI-BEAM PULSAR SURVEY

    SciTech Connect

    Knispel, B.; Kim, H.; Allen, B.; Aulbert, C.; Bock, O.; Eggenstein, H.-B.; Fehrmann, H.; Machenschalk, B.; Eatough, R. P.; Keane, E. F.; Kramer, M.; Anderson, D.; Crawford, F.; Rastawicki, D.; Hammer, D.; Papa, M. A.; Siemens, X.; Lyne, A. G.; Miller, R. B.; Sarkissian, J.; and others

    2013-09-10

    We have conducted a new search for radio pulsars in compact binary systems in the Parkes multi-beam pulsar survey (PMPS) data, employing novel methods to remove the Doppler modulation from binary motion. This has yielded unparalleled sensitivity to pulsars in compact binaries. The required computation time of Almost-Equal-To 17, 000 CPU core years was provided by the distributed volunteer computing project Einstein-Home, which has a sustained computing power of about 1 PFlop s{sup -1}. We discovered 24 new pulsars in our search, 18 of which were isolated pulsars, and 6 were members of binary systems. Despite the wide filterbank channels and relatively slow sampling time of the PMPS data, we found pulsars with very large ratios of dispersion measure (DM) to spin period. Among those is PSR J1748-3009, the millisecond pulsar with the highest known DM ( Almost-Equal-To 420 pc cm{sup -3}). We also discovered PSR J1840-0643, which is in a binary system with an orbital period of 937 days, the fourth largest known. The new pulsar J1750-2536 likely belongs to the rare class of intermediate-mass binary pulsars. Three of the isolated pulsars show long-term nulling or intermittency in their emission, further increasing this growing family. Our discoveries demonstrate the value of distributed volunteer computing for data-driven astronomy and the importance of applying new analysis methods to extensively searched data.

  14. SCATTERING OF PULSAR RADIO EMISSION BY THE INTERSTELLAR PLASMA

    SciTech Connect

    Coles, W. A.; Rickett, B. J.; Gao, J. J.; Hobbs, G.; Verbiest, J. P. W.

    2010-07-10

    We present simulations of scattering phenomena which are important in pulsar observations, but which are analytically intractable. The simulation code, which has also been used for solar wind and atmospheric scattering problems, is available from the authors. These simulations reveal an unexpectedly important role of dispersion in combination with refraction. We demonstrate the effect of analyzing observations which are shorter than the refractive scale. We examine time-of-arrival fluctuations in detail: showing their correlation with intensity and dispersion measure, providing a heuristic model from which one can estimate their contribution to pulsar timing observations, and showing that much of the effect can be corrected making use of measured intensity and dispersion. Finally, we analyze observations of the millisecond pulsar J0437-4715, made with the Parkes radio telescope, that show timing fluctuations which are correlated with intensity. We demonstrate that these timing fluctuations can be corrected, but we find that they are much larger than would be expected from scattering in a homogeneous turbulent plasma with isotropic density fluctuations. We do not have an explanation for these timing fluctuations.

  15. Evaluation of the Brief Problem Checklist: Child and Caregiver Interviews to Measure Clinical Progress

    ERIC Educational Resources Information Center

    Chorpita, Bruce F.; Reise, Steven; Weisz, John R.; Grubbs, Kathleen; Becker, Kimberly D.; Krull, Jennifer L.

    2010-01-01

    Objective: To support ongoing monitoring of child response during treatment, we sought to develop a brief, easily administered, clinically relevant, and psychometrically sound measure. Method: We first developed child and caregiver forms of a 12-item Brief Problem Checklist (BPC) interview by applying item response theory and factor analysis to…

  16. ABE Phase III: Progress and Problems. September 1, 1969-April 1, 1970.

    ERIC Educational Resources Information Center

    Southwestern Cooperative Educational Lab., Albuquerque, NM.

    Interim information concerning the ABE III grants is provided in the three parts of this report. Part 1 (outline) describes the goals and objectives of each component; Part 2 describes accomplishments and problems to date; and Part 3 deals with coordination and supervision activities undertaken by the Lab. The components of the program are: (1)…

  17. PROGRESS IN MEETING PROBLEMS OF MIGRATORY LABOR IN MARYLAND, THIRD ANNUAL REPORT.

    ERIC Educational Resources Information Center

    NYSTROM, PAUL E.; AND OTHERS

    NUMEROUS CHANGES IN MARYLAND AGRICULTURE HAD A PRONOUNCED EFFECT UPON THE LABOR MOVEMENT. AMONG THEM WERE--CROP YIELDS, CROP PRICES AND THE RESULTANT EFFECT UPON CROP ACREAGE, MECHANIZATION OF TILLAGE, THINNINGS, AND HARVEST PROCEDURES. DESPITE INCREASED MECHANIZATION, GREATER ACREAGES MIGHT DEMAND A RATHER CONSTANT SUPPLY OF LABOR. PROBLEMS IN…

  18. Current Progress in Tissue Engineering of Heart Valves: Multiscale Problems, Multiscale Solutions

    PubMed Central

    Cheung, Daniel Y; Duan, Bin; Butcher, Jonathan T.

    2016-01-01

    Introduction Heart valve disease is an increasingly prevalent and clinically serious condition. There are no clinically effective biological diagnostics or treatment strategies. The only recourse available is replacement with a prosthetic valve, but the inability of these devices to grow or respond biologically to their environments necessitates multiple resizing surgeries and life-long coagulation treatment, especially in children. Tissue engineering has a unique opportunity to impact heart valve disease by providing a living valve conduit, capable of growth and biological integration. Areas covered This review will cover current tissue engineering strategies in fabricating heart valves and their progress towards the clinic, including molded scaffolds using naturally-derived or synthetic polymers, decellularization, electrospinning, 3D bioprinting, hybrid techniques, and in vivo engineering. Expert opinion While much progress has been made to create functional living heart valves, a clinically viable product is not yet realized. The next leap in engineered living heart valves will require a deeper understanding of how the natural multi-scale structural and biological heterogeneity of the tissue ensures its efficient function. Related, improved fabrication strategies must be developed that can replicate this de novo complexity, which is likely instructive for appropriate cell differentiation and remodeling whether seeded with autologous stem cells in vitro or endogenously recruited cells. PMID:26027436

  19. Early Pulsar Observations with LOFAR

    NASA Astrophysics Data System (ADS)

    Hessels, J. W. T.; Stappers, B.; Alexov, A.; Coenen, T.; Hassall, T.; Karastergiou, A.; Kondratiev, V. K.; Kramer, M.; van Leeuwen, J.; Mol, J. D.; Noutsos, A.; Weltevrede, P.

    This contribution to the proceedings of "A New Golden Age for Radio Astronomy" is simply intended to give some of the highlights from pulsar observations with LOFAR at the time of its official opening: June 12th, 2010. These observations illustrate that, though LOFAR is still under construction and astronomical commissioning, it is already starting to deliver on its promise to revolutionize radio astronomy in the low-frequency regime. These observations also demonstrate how LOFAR has many "next-generation" capabilities, such as wide-field multi-beaming, that will be vital to open a new Golden Age in radio astronomy through the Square Kilometer Array and its precursors.

  20. Acceleration by pulsar winds in binary systems

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.; Gaisser, T. K.

    1990-01-01

    In the absence of accretion torques, a pulsar in a binary system will spin down due to electromagnetic dipole radiation and the spin-down power will drive a wind of relativistic electron-positron pairs. Winds from pulsars with short periods will prevent any subsequent accretion but may be confined by the companion star atmosphere, wind, or magnetosphere to form a standing shock. The authors investigate the possibility of particle acceleration at such a pulsar wind shock and the production of very high energy (VHE) and ultra high energy (UHE) gamma rays from interactions of accelerated protons in the companion star's wind or atmosphere. They find that in close binaries containing active pulsars, protons will be shock accelerated to a maximum energy dependent on the pulsar spin-down luminosity. If a significant fraction of the spin-down power goes into particle acceleration, these systems should be sources of VHE and possibly UHE gamma rays. The authors discuss the application of the pulsar wind model to binary sources such as Cygnus X-3, as well as the possibility of observing VHE gamma-rays from known binary radio pulsar systems.

  1. Acceleration by pulsar winds in binary systems

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.; Gaisser, T. K.

    1990-01-01

    In the absence of accretion torques, a pulsar in a binary system will spin down due to electromagnetic dipole radiation, and the spin-down power will drive a wind of relativistic electron-position pairs. Winds from pulsars with short periods will prevent any subsequent accretion but may be confined by the companion star atmosphere, wind, or magnetosphere to form a standing shock. This paper investigates the possibility of particle acceleration at such a pulsar wind shock and the production of VHE and UHE gamma-rays from interactions of accelerated protons in the companion star's wind or atmosphere. It is found that, in close binaries containing active pulsars, protons will be shock accelerated to a maximum energy dependent on the pulsar spin-down luminosity. If a significant fraction of the spin-down power goes into particle acceleration, these systems should be sources of VHE and possibly UHE gamma-rays. The application of the pulsar wind model to binary sources such as Cygnus X-3 is discussed, as well as the possibility of observing VHE gamma-rays from known binary radio pulsar systems.

  2. Particles generation and cooling of pulsar magnetosphere

    NASA Astrophysics Data System (ADS)

    Kryvdyk, Volodymyr

    2016-07-01

    The generation of secondary particles (neutrinos, neutrons, electrons, protons, mesons) and gamma-ray photons because of nuclear interactions in magnetospheres of pulsars and magnetars are considered. By means of the nuclear interactions, the primarily accelerated electrons and protons in the pulsar magnetosphere will be generated secondary particles and photons, which will also generate particles and gamma-ray photons by cascading interactions. Namely from these particles and photons, which arise because of multiple interactions, and will consist of the pulsar magnetosphere. It is important that in pulsar magnetosphere will generate the powerful flux of neutral particles (neutrons) and a neutrino that do not interact with the magnetic field and are free to go out with her, bringing out energy and cooling magnetosphere. So, we obtain a powerful new channel cooling pulsar magnetosphere. This is a new result, which shows that cooling of pulsar and magnetars is not only a result of the processes generating neutrinos in the inner core, but also due to the generation of neutrino and neutrons in the pulsar magnetosphere and subsequently their exit in the interstellar environment.

  3. A Chandra Search for a Pulsar Wind Nebula around PSR B1055-52

    NASA Astrophysics Data System (ADS)

    Posselt, B.; Spence, G.; Pavlov, G. G.

    2015-10-01

    The nearby, middle-aged PSR B1055-52 has many properties in common with the Geminga pulsar. Motivated by the Geminga's enigmatic and prominent pulsar wind nebula (PWN), we searched for extended emission around PSR B1055-52 with Chandra ACIS. For an energy range 0.3-1 keV, we found a 4σ flux enhancement in a 4\\buildrel{\\prime\\prime}\\over{.} 9-20\\prime\\prime annulus around the pulsar. There is a slight asymmetry in the emission close, 1\\buildrel{\\prime\\prime}\\over{.} 5-4\\prime\\prime , to the pulsar. The excess emission has a luminosity of about 1029 erg s-1 in an energy range 0.3-8 keV for a distance of 350 pc. Overall, the faint extended emission around \\text{PSR B1055-52} is consistent with a PWN of an aligned rotator moving away from us along the line of sight with supersonic velocity, but a contribution from a dust scattering halo cannot be excluded. Comparing the properties of other nearby, middle-aged pulsars, we suggest that the geometry—the orientations of rotation axis, magnetic field axis, and the sight-line—is the deciding factor for a pulsar to show a prominent PWN. We also report on an ≳ 30% flux decrease of PSR B1055-52 between the 2000 XMM-Newton and our 2012 Chandra observation. We tentatively attribute this flux decrease to a cross-calibration problem, but further investigations of the pulsar are required to exclude actual intrinsic flux changes.

  4. A Study of Dynamical and Emission Variabilities in Pulsars

    NASA Astrophysics Data System (ADS)

    Seymour, Andrew D.

    Pulsars are rapidly rotating highly magnetized neutron stars thought to have been formed in the core-collapse supernova of massive stars. Ever since their discovery, pulsars have shown complex behaviors. This is certainly true for their emission mechanism, which is still not fully understood. This is primarily because of the abrupt changes that appear in the pulse profile. Recent discoveries have shown that these emission changes effect the spin dynamics, particularly the spin-down rate. This indicates that pulsar emissions are even more complex than previously thought. The goal of this thesis is to apply new analysis techniques to help shed light on the pulsar emission problem. Over the past decade, it has become apparent that a class of `bursting pulsars' exist with the discovery of PSR J1752+2359 and PSR J1938+2213. In these pulsars, a sharp increase in the emission intensity is observed that then tends to systematically drop-off from pulse-to-pulse. We describe the discovery of such a relationship in high-sensitivity observations of the young (characteristic age of 90; 000 yrs) 0.33 s pulsar B0611+22 at both 327 MHz and 1400 MHz with the Arecibo observatory. While it was previously shown that B0611+22 has mode-switching properties, the data presented here show that this pulsar emits bursts with characteristic time-scales of several hundred seconds. At 327 MHz, the pulsar shows steady behavior in one emission mode which is enhanced by bursting emission slightly offset in pulse phase from this steady emission. Contrastingly at 1400 MHz, the two modes appear to behave in a competing operation while still offset in phase. Using a uctuation spectrum analysis, we also investigate each mode independently for sub-pulse drifting. Neither emission mode (i.e. during bursts or persistent emission) shows the presence of the drifting sub-pulse phenomenon. While further examples of this behavior and studies at different wavelengths are required, it appears that this

  5. A Study of Dynamical and Emission Variabilities in Pulsars

    NASA Astrophysics Data System (ADS)

    Seymour, Andrew D.

    Pulsars are rapidly rotating highly magnetized neutron stars thought to have been formed in the core-collapse supernova of massive stars. Ever since their discovery, pulsars have shown complex behaviors. This is certainly true for their emission mechanism, which is still not fully understood. This is primarily because of the abrupt changes that appear in the pulse profile. Recent discoveries have shown that these emission changes effect the spin dynamics, particularly the spin-down rate. This indicates that pulsar emissions are even more complex than previously thought. The goal of this thesis is to apply new analysis techniques to help shed light on the pulsar emission problem. Over the past decade, it has become apparent that a class of `bursting pulsars' exist with the discovery of PSR J1752+2359 and PSR J1938+2213. In these pulsars, a sharp increase in the emission intensity is observed that then tends to systematically drop-off from pulse-to-pulse. We describe the discovery of such a relationship in high-sensitivity observations of the young (characteristic age of 90; 000 yrs) 0.33 s pulsar B0611+22 at both 327 MHz and 1400 MHz with the Arecibo observatory. While it was previously shown that B0611+22 has mode-switching properties, the data presented here show that this pulsar emits bursts with characteristic time-scales of several hundred seconds. At 327 MHz, the pulsar shows steady behavior in one emission mode which is enhanced by bursting emission slightly offset in pulse phase from this steady emission. Contrastingly at 1400 MHz, the two modes appear to behave in a competing operation while still offset in phase. Using a uctuation spectrum analysis, we also investigate each mode independently for sub-pulse drifting. Neither emission mode (i.e. during bursts or persistent emission) shows the presence of the drifting sub-pulse phenomenon. While further examples of this behavior and studies at different wavelengths are required, it appears that this

  6. Fluctuating neutron star magnetosphere: braking indices of eight pulsars, frequency second derivatives of 222 pulsars and 15 magnetars

    NASA Astrophysics Data System (ADS)

    Ou, Z. W.; Tong, H.; Kou, F. F.; Ding, G. Q.

    2016-04-01

    Eight pulsars have low braking indices, which challenge the magnetic dipole braking of pulsars. 222 pulsars and 15 magnetars have abnormal distribution of frequency second derivatives, which also make contradiction with classical understanding. How neutron star magnetospheric activities affect these two phenomena are investigated by using the wind braking model of pulsars. It is based on the observational evidence that pulsar timing is correlated with emission and both aspects reflect the magnetospheric activities. Fluctuations are unavoidable for a physical neutron star magnetosphere. Young pulsars have meaningful braking indices, while old pulsars' and magnetars' fluctuation item dominates their frequency second derivatives. It can explain both the braking index and frequency second derivative of pulsars uniformly. The braking indices of eight pulsars are the combined effect of magnetic dipole radiation and particle wind. During the lifetime of a pulsar, its braking index will evolve from three to one. Pulsars with low braking index may put strong constraint on the particle acceleration process in the neutron star magnetosphere. The effect of pulsar death should be considered during the long term rotational evolution of pulsars. An equation like the Langevin equation for Brownian motion was derived for pulsar spin-down. The fluctuation in the neutron star magnetosphere can be either periodic or random, which result in anomalous frequency second derivative and they have similar results. The magnetospheric activities of magnetars are always stronger than those of normal pulsars.

  7. Studies in nonlinear problems of energy. Progress report, January 1, 1992--December 31, 1992

    SciTech Connect

    Matkowsky, B.J.

    1992-07-01

    Emphasis has been on combustion and flame propagation. The research program was on modeling, analysis and computation of combustion phenomena, with emphasis on transition from laminar to turbulent combustion. Nonlinear dynamics and pattern formation were investigated in the transition. Stability of combustion waves, and transitions to complex waves are described. Combustion waves possess large activation energies, so that chemical reactions are significant only in thin layers, or reaction zones. In limit of infinite activation energy, the zones shrink to moving surfaces, (fronts) which must be found during the analysis, so that (moving free boundary problems). The studies are carried out for limiting case with fronts, while the numerical studies are carried out for finite, though large, activation energy. Accurate resolution of the solution in the reaction zones is essential, otherwise false predictions of dynamics are possible. Since the the reaction zones move, adaptive pseudo-spectral methods were developed. The approach is based on a synergism of analytical and computational methods. The numerical computations build on and extend the analytical information. Furthermore, analytical solutions serve as benchmarks for testing the accuracy of the computation. Finally, ideas from analysis (singular perturbation theory) have induced new approaches to computations. The computational results suggest new analysis to be considered. Among the recent interesting results, was spatio-temporal chaos in combustion. One goal is extension of the adaptive pseudo-spectral methods to adaptive domain decomposition methods. Efforts have begun to develop such methods for problems with multiple reaction zones, corresponding to problems with more complex, and more realistic chemistry. Other topics included stochastics, oscillators, Rysteretic Josephson junctions, DC SQUID, Markov jumps, laser with saturable absorber, chemical physics, Brownian movement, combustion synthesis, etc.

  8. Classical Accreting Pulsars with NICER

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, Colleen A.

    2014-01-01

    Soft excesses are very common center dot Lx > 1038 erg/s - reprocessing by optically thick material at the inner edge of the accretion disk center dot Lx < 1036 erg/s - photoionized or collisionally heated diffuse gas or thermal emission from the NS surface center dot Lx 1037 erg/s - either or both types of emission center dot NICER observations of soft excesses in bright X-ray pulsars combined with reflection modeling will constrain the ionization state, metalicity and dynamics of the inner edge of the magnetically truncated accretion disk Reflection models of an accretion disk for a hard power law - Strong soft excess below 3 keV from hot X-ray heated disk - For weakly ionized case: strong recombination lines - Are we seeing changes in the disk ionization in 4U1626-26? 13 years of weekly monitoring with RXTE PCA center dot Revealed an unexpectedly large population of Be/X-ray binaries compared to the Milky Way center dot Plotted luminosities are typical of "normal" outbursts (once per orbit) center dot The SMC provides an excellent opportunity to study a homogenous population of HMXBs with low interstellar absorption for accretion disk studies. Monitoring with NICER will enable studies of accretion disk physics in X-ray pulsars center dot The SMC provides a potential homogeneous low-absorption population for this study center dot NICER monitoring and TOO observations will also provide measurements of spinfrequencies, QPOs, pulsed fluxes, and energy spectra.

  9. Gamma ray pulsars: Models and observations

    NASA Technical Reports Server (NTRS)

    Thompson, David J.

    1990-01-01

    The two known gamma ray pulsars, the Crab and Vela, were used as guides for the development of models of high-energy radiation from spinning neutron stars. Two general classes of models were developed: those with the gamma radiation originating in the pulsar magnetosphere far from the neutron star surface (outer gap models) and those with the gamma radiation coming from above the polar cap (polar cap models). The goal is to indicate how EGRET can contribute to understanding gamma-ray pulsars, and especially how it can help distinguish between models for emission.

  10. Limits to the Stability of Pulsar Time

    NASA Technical Reports Server (NTRS)

    Petit, Gerard

    1996-01-01

    The regularity of the rotation rate of millisecond pulsars is the underlying hypothesis for using these neutron stars as 'celestial clocks'. Given their remote location in our galaxy and to our lack of precise knowledge on the galactic environment, a number of phenomena effect the apparent rotation rate observed on Earth. This paper reviews these phenomena and estimates the order of magnitude of their effect. It concludes that an ensemble pulsar time based on a number of selected millisecond pulsars should have a fractional frequency stability close to 2 x 10(sup -15) for an averaging time of a few years.

  11. Pulsar wind model for the spin-down behavior of intermittent pulsars

    SciTech Connect

    Li, L.; Tong, H.; Yan, W. M.; Yuan, J. P.; Wang, N.; Xu, R. X.

    2014-06-10

    Intermittent pulsars are part-time radio pulsars. They have higher slow down rates in the on state (radio-loud) than in the off state (radio-quiet). This gives evidence that particle wind may play an important role in pulsar spindown. The effect of particle acceleration is included in modeling the rotational energy loss rate of the neutron star. Applying the pulsar wind model to the three intermittent pulsars (PSR B1931+24, PSR J1841–0500, and PSR J1832+0029) allows their magnetic fields and inclination angles to be calculated simultaneously. The theoretical braking indices of intermittent pulsars are also given. In the pulsar wind model, the density of the particle wind can always be the Goldreich-Julian density. This may ensure that different on states of intermittent pulsars are stable. The duty cycle of particle wind can be determined from timing observations. It is consistent with the duty cycle of the on state. Inclination angle and braking index observations of intermittent pulsars may help to test different models of particle acceleration. At present, the inverse Compton scattering induced space charge limited flow with field saturation model can be ruled out.

  12. Progress and problems with the use of suicide genes for targeted cancer therapy.

    PubMed

    Karjoo, Zahra; Chen, Xuguang; Hatefi, Arash

    2016-04-01

    Among various gene therapy methods for cancer, suicide gene therapy attracts a special attention because it allows selective conversion of non-toxic compounds into cytotoxic drugs inside cancer cells. As a result, therapeutic index can be increased significantly by introducing high concentrations of cytotoxic molecules to the tumor environment while minimizing impact on normal tissues. Despite significant success at the preclinical level, no cancer suicide gene therapy protocol has delivered the desirable clinical significance yet. This review gives a critical look at the six main enzyme/prodrug systems that are used in suicide gene therapy of cancer and familiarizes readers with the state-of-the-art research and practices in this field. For each enzyme/prodrug system, the mechanisms of action, protein engineering strategies to enhance enzyme stability/affinity and chemical modification techniques to increase prodrug kinetics and potency are discussed. In each category, major clinical trials that have been performed in the past decade with each enzyme/prodrug system are discussed to highlight the progress to date. Finally, shortcomings are underlined and areas that need improvement in order to produce clinical significance are delineated. PMID:26004498

  13. Providing solutions to energy and environmental problems. Quarterly technical progress report, January--March 1995

    SciTech Connect

    Not Available

    1995-05-01

    Brief progress reprots are presented for the following tasks: development and demonstration of a practical electric downhole steam generator for thermal recovery of heavy oil and tar; wetting behavior of selected crude oil/brine/rock systems; coal gasification, power generation and product market study; the impact of leachate from clean coal technology waste on the stability of clay liners; injection into coal seams for simultaneous co[sub 2] mitigation and enhanced recovery of coalbed methane; optimization of carbonizer operations in the FMC coke process; chemical sensor and field screening technology development; demonstration of the Koppleman Series C'' process using a batch; test unit with powder river basin coal as feed; remote chemical sensor development; market assessment and technical feasibility study of PFBC ash use; solid state NMR analysis of naturally and artificially matured kerogens; contained recovery of oily wastes field demonstration with bell lumber and pole; insitu treatment of manufactured gas plant contaminated soils; development and demonstration of a wood-fired. Gas turbine system; solid state NMR analysis of mowry formation shale from different sedimentary basins; and acid-mine drainage prevention, control, and treatment development for the stockett/sand coulee area

  14. Providing solutions to energy and environmental problems. Quarterly technical progress report, October--December 1994

    SciTech Connect

    Not Available

    1995-02-01

    Progress reports are briefly described for the following tasks: Development and demonstration of a practical electric downhole steam generator for thermal recovery of heavy oil and tar; wetting behavior of selected crude oil/brine/rock systems; coal gasification, power generation and product market study; the impact of leachate from clean coal technology waste on the stability of clay liners; injecton into coal seams for simultaneous CO[sub 2] mitigation and enhanced recovery of coalbed methane; optimization of carbonizer operations in the FMC coke process; chemical sensor and field screening technology development; demonstration of the Koppleman Series C'' process using a batch; test unit with powder river basin coal as feed; remote chemical sensor development; market assessment and technical feasibility study of PFBC ash use; solid state NMR analysis of naturally and artificially matured kerogens; contained recovery of oily wastes field demonstration with bell lumber and pole; insitu treatment of manufactured gas plant contaminated soils; development and demonstration of a wood-fired gas turbine system; solid state NMR analysis of Mowry Formation Shale from different sedimentary basins; and acid-mine drainage prevention, control, and treatment development for the stockett/sand coulee area

  15. Astronomers Discover Fastest-Spinning Pulsar

    NASA Astrophysics Data System (ADS)

    2006-01-01

    Astronomers using the National Science Foundation's Robert C. Byrd Green Bank Telescope have discovered the fastest-spinning neutron star ever found, a 20-mile-diameter superdense pulsar whirling faster than the blades of a kitchen blender. Their work yields important new information about the nature of one of the most exotic forms of matter known in the Universe. Pulsar Graphic Pulsars Are Spinning Neutron Stars CREDIT: Bill Saxton, NRAO/AUI/NSF (Click on image for larger version) "We believe that the matter in neutron stars is denser than an atomic nucleus, but it is unclear by how much. Our observations of such a rapidly rotating star set a hard upper limit on its size, and hence on how dense the star can be.," said Jason Hessels, a graduate student at McGill University in Montreal. Hessels and his colleagues presented their findings to the American Astronomical Society's meeting in Washington, DC. Pulsars are spinning neutron stars that sling "lighthouse beams" of radio waves or light around as they spin. A neutron star is what is left after a massive star explodes at the end of its "normal" life. With no nuclear fuel left to produce energy to offset the stellar remnant's weight, its material is compressed to extreme densities. The pressure squeezes together most of its protons and electrons to form neutrons; hence, the name "neutron star." "Neutron stars are incredible laboratories for learning about the physics of the fundamental particles of nature, and this pulsar has given us an important new limit," explained Scott Ransom, an astronomer at the National Radio Astronomy Observatory and one of Hessels' collaborators on this work. The scientists discovered the pulsar, named PSR J1748-2446ad, in a globular cluster of stars called Terzan 5, located some 28,000 light-years from Earth in the constellation Sagittarius. The newly-discovered pulsar is spinning 716 times per second, or at 716 Hertz (Hz), readily beating the previous record of 642 Hz from a pulsar

  16. Neutron stars and millisecond pulsars from accretion-induced collapse in globular clusters

    NASA Technical Reports Server (NTRS)

    Bailyn, Charles D.; Grindlay, Jonathan E.

    1990-01-01

    This paper examines the limits on the number of millisecond pulsars which could be formed in globular clusters by the generally accepted scenario (in which a neutron star is created by the supernova of an initially massive star and subsequently captures a companion to form a low-mass X-ray binary which eventually becomes a millisecond pulsar). It is found that, while the number of observed low-mass X-ray binaries can be adequately explained in this way, the reasonable assumption that the pulsar luminosity function in clusters extends below the current observational limits down to the luminosity of the faintest millisecond pulsars in the field suggests a cluster population of millisecond pulsars which is substantially larger than the standard model can produce. Alleviating this problem by postulating much shorter lifetimes for the X-ray binaries requires massive star populations sufficiently large that the mass loss resulting from their evolution would be likely to unbind the cluster. It is argued that neutron star formation in globular clusters by accretion-induced collapse of white dwarfs may resolve the discrepancy in birthrates.

  17. Observing the dynamics of supermassive black hole binaries with pulsar timing arrays.

    PubMed

    Mingarelli, C M F; Grover, K; Sidery, T; Smith, R J E; Vecchio, A

    2012-08-24

    Pulsar timing arrays are a prime tool to study unexplored astrophysical regimes with gravitational waves. Here, we show that the detection of gravitational radiation from individually resolvable supermassive black hole binary systems can yield direct information about the masses and spins of the black holes, provided that the gravitational-wave-induced timing fluctuations both at the pulsar and at Earth are detected. This in turn provides a map of the nonlinear dynamics of the gravitational field and a new avenue to tackle open problems in astrophysics connected to the formation and evolution of supermassive black holes. We discuss the potential, the challenges, and the limitations of these observations. PMID:23002736

  18. Properties of young pulsar wind nebulae: TeV detectability and pulsar properties

    NASA Astrophysics Data System (ADS)

    Tanaka, Shuta J.; Takahara, Fumio

    2013-03-01

    Among dozens of young pulsar wind nebulae (PWNe), some have been detected in TeV γ-rays (TeV PWNe), while others have not (non-TeV PWNe). The TeV emission detectability is not correlated with either the spin-down power or the characteristic age of the central pulsars and it is an open question as to what determines the detectability. To study this problem, we investigate the spectral evolution of five young non-TeV PWNe: 3C 58, G310.6-1.6, G292.0+1.8, G11.2-0.3 and SNR B0540-69.3. We use a spectral evolution model that was developed in our previous works to be applied to young TeV PWNe. The TeV γ-ray flux upper limits of non-TeV PWNe give upper or lower limits on parameters such as the age of the PWN and the fraction of spin-down power going into magnetic energy injection (the fraction parameter). Combined with other independent observational and theoretical studies, we can guess a plausible value of the parameters for each object. For 3C 58, we prefer parameters with an age of 2.5 kyr and fraction parameter of 3.0 × 10-3, although the spectral modelling alone does not rule out a lower age and a higher fraction parameter. The fraction parameter of 3.0 × 10-3 is also consistent for other non-TeV PWNe and thus the value is regarded as common to young PWNe, including TeV PWNe. Moreover, we find that the intrinsic properties of the central pulsars are similar: 1048-50 erg for the initial rotational energy and 1042-44 erg for the magnetic energy (2 × 1012-3 × 1013 G for the dipole magnetic field strength at the surface). The TeV detectability is correlated with the total injected energy and the energy density of the interstellar radiation field around PWNe. Except for the case of G292.0+1.8, broken power-law injection of the particles reproduces the broad-band emission from non-TeV PWNe well.

  19. ENHANCED DISSIPATION RATE OF MAGNETIC FIELD IN STRIPED PULSAR WINDS BY THE EFFECT OF TURBULENCE

    SciTech Connect

    Takamoto, Makoto; Inoue, Tsuyoshi; Inutsuka, Shu-ichiro E-mail: inouety@phys.aoyama.ac.jp

    2012-08-10

    In this paper, we report on turbulent acceleration of the dissipation of the magnetic field in the post-shock region of a Poynting flux-dominated flow, such as the Crab pulsar wind nebula. We have performed two-dimensional resistive relativistic magnetohydrodynamics simulations of subsonic turbulence driven by the Richtmyer-Meshkov instability at the shock fronts of the Poynting flux-dominated flows in pulsar winds. We find that turbulence stretches current sheets which substantially enhances the dissipation of the magnetic field, and that most of the initial magnetic field energy is dissipated within a few eddy-turnover times. We also develop a simple analytical model for turbulent dissipation of the magnetic field that agrees well with our simulations. The analytical model indicates that the dissipation rate does not depend on resistivity even in the small resistivity limit. Our findings can possibly alleviate the {sigma}-problem in the Crab pulsar wind nebulae.

  20. Chandra Observations of the Crab Pulsar as a Function of Pulse Phase

    NASA Technical Reports Server (NTRS)

    Weisskopf, Martin C.; Tennant, Allyn F.; Becker, Werner; Juda, Michael; Elsner, Ronald F.; Kolodziejczak, Jeffery J.; Murray, Stephen S.; Paerels, Frits; Swartz, Douglas A.; Shibazaki, Noriaki; Whitaker, Martin C. (Technical Monitor)

    2001-01-01

    The Chandra X-Ray Observatory was used to observe the Crab Nebula and its pulsar using the LETGS, i.e. the Low-Energy Transmission Grating (LETG) with the High Resolution Camera Spectroscopy detector (HRC-S). Data from the zeroth-order image was utilized to isolate the pulsar from the surrounding nebula and to measure the pulsar emission as a function of pulse phase. HRC timing problems were overcome by developing special techniques to process the data. For the first time, pulsed x-ray emission has been detected at all pulse phases, allowing us to set a new upper limit to the thermal emission from the surface of the neutron star.

  1. Quasars, pulsars, black holes and HEAO's

    NASA Technical Reports Server (NTRS)

    Doolitte, R. F.; Moritz, K.; Whilden, R. D. C.

    1974-01-01

    Astronomical surveys are discussed by large X-ray, gamma ray, and cosmic ray instruments carried onboard high-energy astronomy observatories. Quasars, pulsars, black holes, and the ultimate benefits of the new astronomy are briefly discussed.

  2. Timing of millisecond pulsars in globular clusters

    NASA Astrophysics Data System (ADS)

    D'Amico, Nichi; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Kramer, Michael; Sarkissian, John; Lyne, Andrew; Burgay, Marta; Corongiu, Alessandro; Camilo, Fernando; Bailes, Matthew; van Straten, Willem

    2014-10-01

    Timing of the dozen pulsars discovered by us in P303 is ensuring high quality results: (a) the peculiarities (in position or projected acceleration) of all the 5 millisecond pulsars in NGC6752 suggested the presence of non thermal dynamics in the core, perhaps due to black-holes of intermediate mass; (b) the eclipsing pulsar in NGC6397 is a stereotype for studying the late evolution of exotic binaries. We propose to continue our timing project focusing mostly on NGC6397 at 10cm, for studying the orbital secular evolution, the eclipse region, and the role played by the high energy photons released from the pulsar in the ejection of matter from the binary system.

  3. Timing of millisecond pulsars in globular clusters

    NASA Astrophysics Data System (ADS)

    D'Amico, Nichi; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Kramer, Michael; Sarkissian, John; Lyne, Andrew; Burgay, Marta; Corongiu, Alessandro; Camilo, Fernando; Bailes, Matthew; van Straten, Willem

    2013-10-01

    Timing of the dozen pulsars discovered by us in P303 is ensuring high quality results: (a) the peculiarities (in position or projected acceleration) of all the 5 millisecond pulsars in NGC6752 suggested the presence of non thermal dynamics in the core, perhaps due to black-holes of intermediate mass; (b) the eclipsing pulsar in NGC6397 is a stereotype for studying the late evolution of exotic binaries. We propose to continue our timing project focusing mostly on NGC6752 at 20cm (in order to measure additional parameters useful to constrain the existence of a black-hole) and NGC6397 at 10cm (for studying the orbital secular evolution, the eclipse region, and the role played by the high energy photons released from the pulsar in the ejection of matter from the binary system).

  4. Timing of millisecond pulsars in globular clusters

    NASA Astrophysics Data System (ADS)

    D'Amico, Nichi; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Kramer, Michael; Sarkissian, John; Lyne, Andrew; Burgay, Marta; Corongiu, Alessandro; Camilo, Fernando; Bailes, Matthew; van Straten, Willem

    2014-04-01

    Timing of the dozen pulsars discovered by us in P303 is ensuring high quality results: (a) the peculiarities (in position or projected acceleration) of all the 5 millisecond pulsars in NGC6752 suggested the presence of non thermal dynamics in the core, perhaps due to black-holes of intermediate mass; (b) the eclipsing pulsar in NGC6397 is a stereotype for studying the late evolution of exotic binaries. We propose to continue our timing project focusing mostly on NGC6752 at 20cm (in order to measure additional parameters useful to constrain the existence of a black-hole) and NGC6397 at 10cm (for studying the orbital secular evolution, the eclipse region, and the role played by the high energy photons released from the pulsar in the ejection of matter from the binary system).

  5. Outlook for Detecting Gravitational Waves with Pulsars

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-04-01

    Though the recent discovery of GW150914 is a thrilling success in the field of gravitational-wave astronomy, LIGO is only one tool the scientific community is using to hunt for these elusive signals. After 10 years of unsuccessful searching, how likely is it that pulsar-timing-array projects will make their own first detection soon?Frequency ranges for gravitational waves produced by different astrophysical sources. Pulsar timing arrays such as the EPTA and IPTA are used to detect low-frequency gravitational waves generated by the stochastic background and supermassive black hole binaries. [Christopher Moore, Robert Cole and Christopher Berry]Supermassive BackgroundGround-based laser interferometers like LIGO are ideal for probing ripples in space-time caused by the merger of stellar-mass black holes; these mergers cause chirps in the frequency range of tens to thousands of hertz. But how do we pick up the extremely low-frequency, nanohertz background signal caused by the orbits of pairs of supermassive black holes? For that, we need pulsar timing arrays.Pulsar timing arrays are sets of pulsars whose signals are analyzed to look for correlations in the pulse arrival time. As the space-time between us and a pulsar is stretched and then compressed by a passing gravitational wave, the pulsars pulses should arrive a little late and then a little early. Comparing these timing residuals in an array of pulsars could theoretically allow for the detection of the gravitational waves causing them.Globally, there are currently four pulsar timing array projects actively searching for this signal, with a fifth planned for the future. Now a team of scientists led by Stephen Taylor (NASA-JPL/Caltech) has estimated the likelihood that these projects will successfully detect gravitational waves in the future.Probability for SuccessExpected detection probability of the gravitational-wave background as a function of observing time, for five different pulsar timing arrays. Optimistic

  6. Wavelet based recognition for pulsar signals

    NASA Astrophysics Data System (ADS)

    Shan, H.; Wang, X.; Chen, X.; Yuan, J.; Nie, J.; Zhang, H.; Liu, N.; Wang, N.

    2015-06-01

    A signal from a pulsar can be decomposed into a set of features. This set is a unique signature for a given pulsar. It can be used to decide whether a pulsar is newly discovered or not. Features can be constructed from coefficients of a wavelet decomposition. Two types of wavelet based pulsar features are proposed. The energy based features reflect the multiscale distribution of the energy of coefficients. The singularity based features first classify the signals into a class with one peak and a class with two peaks by exploring the number of the straight wavelet modulus maxima lines perpendicular to the abscissa, and then implement further classification according to the features of skewness and kurtosis. Experimental results show that the wavelet based features can gain comparatively better performance over the shape parameter based features not only in the clustering and classification, but also in the error rates of the recognition tasks.

  7. The origin of planets orbiting millisecond pulsars

    NASA Technical Reports Server (NTRS)

    Tavani, Marco; Brookshaw, Leigh

    1992-01-01

    A model for the formation of planets around millisecond pulsar which no longer have stellar companions is suggested. Detailed hydrodynamical models are presented which suggest that planet formation can occur either in a low-mass X-ray binary progenitor to a progenitor of a star-vaporizing millisecond pulsar when the neutron star is accreting material driven off its companion by X-ray irradiation or after a pulsar has formed and is vaporizing its companion. In both cases a circumbinary disk is created in which planets can form on a timescale of 10 exp 5 to 10 exp 6 yrs and the planets can survive a second phase in which the companion star moves toward the pulsar and is completely vaporized.

  8. Black widow pulsars: the price of promiscuity

    NASA Astrophysics Data System (ADS)

    King, A. R.; Davies, M. B.; Beer, M. E.

    2003-10-01

    The incidence of evaporating `black widow' pulsars (BWPs) among all millisecond pulsars is far higher in globular clusters than in the field. This implies a special formation mechanism for them in clusters. Cluster millisecond pulsars in wide binaries with white dwarf companions exchange them for turnoff-mass stars. These new companions eventually overflow their Roche lobes because of encounters and tides. The millisecond pulsars eject the overflowing gas from the binary, giving mass loss on the binary evolution time-scale. The systems are only observable as BWPs at epochs where this evolution is slow, making the mass loss transparent and the lifetime long. This explains why observed BWPs have low-mass companions. We suggest that at least some field BWPs were ejected from globular clusters or entered the field population when the cluster itself was disrupted.

  9. The origin of the Guitar pulsar

    NASA Astrophysics Data System (ADS)

    Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M.

    2009-11-01

    Among a sample of 140 OB associations and clusters, we want to identify probable parent associations for the Guitar pulsar (PSR B2224+65), which would then also constrain its age. For this purpose, we are using an Euler-Cauchy technique, treating the vertical component of the Galactic potential to calculate the trajectories of the pulsar and each association into the past. To include errors, we use Monte Carlo simulations varying the initial parameters within their error intervals. The whole range of possible pulsar radial velocities is taken into account during the simulations. We find that the Guitar pulsar most probably originated from the Cygnus OB3 association ~0.8Myr ago, inferring a current radial velocity of vr ~ -30kms-1, consistent with the inclination of its bow shock.

  10. Gamma rays from pulsar wind shock acceleration

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.

    1990-01-01

    A shock forming in the wind of relativistic electron-positron pairs from a pulsar, as a result of confinement by surrounding material, could convert part of the pulsar spin-down luminosity to high energy particles through first order Fermi acceleration. High energy protons could be produced by this mechanism both in supernova remnants and in binary systems containing pulsars. The pion-decay gamma-rays resulting from interaction of accelerated protons with surrounding target material in such sources might be observable above 70 MeV with EGRET (Energetic Gamma-Ray Experimental Telescope) and above 100 GeV with ground-based detectors. Acceleration of protons and expected gamma-ray fluxes from SN1987A, Cyg X-3 type sources and binary pulsars are discussed.

  11. Testing Gravity Using Pulsar Scintillation Measurements

    NASA Astrophysics Data System (ADS)

    Yang, Huan; Nishizawa, Atsushi; Pen, Ue-Li

    2016-03-01

    We propose to use pulsar scintillation measurements to test predictions of alternative theories of gravity. Comparing to single-path pulsar timing measurements, the scintillation measurements can achieve a factor of 104 ~105 improvement in timing accuracy, due to the effect of multi-path interference. The self-noise from pulsar also does not affect the interference pattern, where the data acquisition timescale is 103 seconds instead of years. Therefore it has unique advantages in measuring gravitational effect or other mechanisms (at mHz and above frequencies) on light propagation. We illustrate its application in constraining scalar gravitational-wave background and measuring gravitational-wave speed, in which cases the sensitivities are greatly improved with respect to previous limits. We expect much broader applications in testing gravity with existing and future pulsar scintillation observations.

  12. Exploring the Universe with Pulsar Timing Arrays

    NASA Astrophysics Data System (ADS)

    Burke-Spolaor, Sarah

    2016-03-01

    It is an exciting time for pulsar timing arrays, as their upper limits on gravitational radiation are carving into the expected strength of gravitational waves from several source populations in the Universe. Cosmic strings, inflationary gravitational waves, and binary supermassive black holes are all expected contributors to the nanohertz to microhertz band probed by pulsar timing arrays: they might be discovered as bursting sources, as continuously oscillating signals, or as an ensemble population in a stochastic background. This presentation will discuss the predicted intensity and form of these sources, and how the upper limits set by pulsar timing arrays are being used to set unique constraints on source properties, and to measure galaxy evolution in the nearby Universe. Looking to the future, we will explore how pulsar timing arrays can characterize their target source populations, and we will present the prospects for multi-messenger detection.

  13. Timing of New Magellanic Cloud Pulsars

    NASA Astrophysics Data System (ADS)

    Crawford, Fronefield; Lorimer, Duncan Ross; Ridley, Joshua

    2013-10-01

    Recently, we announced the discovery of eight new radio pulsars in the Large Magellanic Cloud (LMC) from a search of an archival search Parkes multibeam survey (Manchester et al. 2006) and a new high-resolution Parkes survey (Parkes proposal P743). Although these new discoveries represent a 50 % increase in the number of known pulsars in the LMC, none of these eight pulsars have yet been timed to determine accurate positions, physical characteristics, or to establish the presence of any binary companions. We request a total of 70 hours in the 2013OCTS term to time these pulsars. An additional 45 hours will be requested in the 2014APRS term to provide a full year of timing observations which will complete this project.

  14. Timing of New Magellanic Cloud Pulsars

    NASA Astrophysics Data System (ADS)

    Crawford, Fronefield; Lorimer, Duncan Ross; Ridley, Joshua; StJohn, Demi

    2014-04-01

    Recently, we announced the discovery of eight new radio pulsars in the Large Magellanic Cloud (LMC) from a search of an archival Parkes multibeam survey (Manchester et al. 2006) and a new high-resolution Parkes survey (Parkes proposals P682 and P743). Although these new discoveries represent a 50% increase in the number of known pulsars in the LMC, none of these eight pulsars have yet been timed to determine accurate positions, physical characteristics, or to establish the presence of any binary companions. We request a total of 60 hours in the 2014APRS term to time these pulsars. This will be combined with the 32 hours that were allocated in the 2013OCTS term to provide a full year of timing observations which will complete this project.

  15. Outer magnetospheric fluctuations and pulsar timing noise

    NASA Technical Reports Server (NTRS)

    Cheng, K. S.

    1987-01-01

    The Cheng, Ho, and Ruderman (1986) outer-magnetosphere gap model was used to investigate the stability of Crab-type outer magnetosphere gaps for pulsars having the parameter (Omega-square B) similar to that of the Crab pulsar. The Lamb, Pines, and Shaham (1978) fluctuating magnetosphere noise model was applied to the Crab pulsar to examine the type of the equation of state that best describes the structure of the neutron star. The noise model was also applied to other pulsars, and the theoretical results were compared with observational data. The results of the comparison are consistent with the stiff equation of state, as suggested by the vortex creep model of the neutron star interior. The timing-noise observations also contribute to the evidence for the existence of superfluid in the core of the neutron star.

  16. Progress through Predicament: How Collaborating on Tough Problems Cultivates a Successful, Supportive Community

    NASA Astrophysics Data System (ADS)

    Aceves, Ana; Albanna, Badr; Corbo, Joel; Quan, Gina

    2012-03-01

    How can a physics department best support its students and encourage success during their academic careers, particularly for those traditionally underrepresented in physics? A well-designed, well-taught curriculum is a necessary component, but there are important steps a department can take in addition to improving what happens in the classroom. The Compass Project at UC Berkeley is a program that focuses on supporting students in the physical sciences inside and outside the classroom. Compass's philosophy is that students can learn better if they feel like they are a part of a supportive community brought together by working on meaningful and difficult problems. For Compass, this community starts in the classroom, where students tackle real-world physics projects together. It continues to develop during their engagement with organizational decision-making, through which students take ownership over many of Compass's programs and shape them to better meet their needs. Compass is not a program done to or for students, it is a program of and by students to meet the challenges they face. Through conversations with students, survey results, and video data, our talk will demonstrate the importance of these types of experiences for supporting student success.

  17. Vela Pulsar and Its Synchrotron Nebula

    NASA Astrophysics Data System (ADS)

    Helfand, D. J.; Gotthelf, E. V.; Halpern, J. P.

    2001-07-01

    We present high-resolution Chandra X-ray observations of PSR B0833-45, the 89 ms pulsar associated with the Vela supernova remnant. We have acquired two observations separated by 1 month to search for changes in the pulsar and its environment following an extreme glitch in its rotation frequency. We find a well-resolved nebula with a toroidal morphology remarkably similar to that observed in the Crab Nebula, along with an axial Crab-like jet. Between the two observations, taken ~3×105 s and ~3×106 s after the glitch, the flux from the pulsar is found to be steady to within 0.75% the 3 σ limit on the fractional increase in the pulsar's X-ray flux is <~10-5 of the inferred glitch energy. We use this limit to constrain parameters of glitch models and neutron star structure. We do find a significant increase in the flux of the nebula's outer arc; if associated with the glitch, the inferred propagation velocity is >~0.7c, similar to that seen in the brightening of the Crab Nebula wisps. We propose an explanation for the X-ray structure of the Vela synchrotron nebula based on a model originally developed for the Crab Nebula. In this model, the bright X-ray arcs are the shocked termination of a relativistic equatorial pulsar wind that is contained within the surrounding kidney-bean shaped synchrotron nebula comprising the postshock, but still relativistic, flow. In a departure from the Crab model, the magnetization parameter σ of the Vela pulsar wind is allowed to be of order unity; this is consistent with the simplest MHD transport of magnetic field from the pulsar to the nebula, where B<=4×10-4 G. The inclination angle of the axis of the equatorial torus with respect to the line of sight is identical to that of the rotation axis of the pulsar as previously measured from the polarization of the radio pulse. The projection of the rotation axis on the sky may also be close to the direction of proper motion of the pulsar if previous radio measurements were confused by

  18. Phase Coherent Observations and Millisecond Pulsar Searches

    NASA Astrophysics Data System (ADS)

    Shrauner, Jay Arthur

    1997-07-01

    We have built a new radio astronomical receiving system designed specifically for very high precision timing and polarimetry of fast pulsars. Unlike most detectors currently used to study pulsars, this instrument does not square the received signal at the time of observation. Instead, voltages proportional to the instantaneous electric vectors of incoming signals are digitized, time-tagged, and recorded on high speed magnetic media. During processing, the data streams are convolved with an inverse 'chirp' function that completely removes the phase retardation introduced by interstellar dispersion. The intrinsic time resolution of this system is the inverse of the system bandwidth, typically well under 1 μs. We have tested this and another phase-coherent observing-system in observations using the Arecibo 305 m and Green Bank 140 foot telescopes. With these two sets of observations we have studied giant pulses, performed high precision timing, and obtained high-resolution polarization profiles and accurate dispersion We have verified the existence of pulses with intensities hundreds of measures. times the mean for both the main pulse and interpulse of PSR B1937+21, and have established that the amplitudes of both types of giant pulses have similar power-law distributions. The giant pulses are narrower than the average pulses, systematically delayed by 40-50 μs, and many are nearly 100% circularly polarized. We have also conducted two searches of the Northern hemisphere for pulsars. The first used the original pulsar discovery telescope in Cambridge, England to search the entire Northern hemisphere at 81.5 MHz, with an average sensitivity to slow pulsars of 230 mJy. Although we obtained flux densities and pulse profiles of 20 known pulsars, no new pulsars were discovered. The second search effort covered a total of 384 deg2 of previously unsearched sky at 430 MHz using the Arecibo telescope, with an average sensitivity to slow pulsars of 0.83 mJy. We discovered 7

  19. Pulsar-aided SETI experimental observations

    NASA Technical Reports Server (NTRS)

    Heidmann, J.; Biraud, F.; Tarter, J.

    1989-01-01

    The rotational frequencies of pulsars are used to select preferred radio frequencies for SETI. Pulsar rotational frequencies are converted into SETI frequencies in the 1-10 GHz Galactic radio window. Experimental observations using the frequencies are conducted for target stars closer than 25 parsecs, unknown targets in a globular cluster, and unknown targets in the Galaxy closer than 2.5 kpc. The status of these observations is discussed.

  20. On the magnetosphere of an accelerated pulsar

    NASA Astrophysics Data System (ADS)

    Brennan, T. Daniel; Gralla, Samuel E.

    2014-05-01

    We report on a remarkable class of exact solutions to force-free electrodynamics that has four-current along the light cones of an arbitrary timelike worldline in flat spacetime. No symmetry is assumed, and the solutions are given in terms of a free function of three variables. The field configuration should describe the outer magnetosphere of a pulsar moving on the worldline. The power radiated is the sum of an acceleration (Larmor-type) term and a pulsar-type term.

  1. The Vela Pulsar and Its Synchrotron Nebula

    NASA Astrophysics Data System (ADS)

    Helfand, D.; Gotthelf, E.; Halpern, J.

    2000-10-01

    We present high-resolution Chandra X-ray observations of PSR0833-45, the 89 ms pulsar associated with the Vela supernova remnant. We have acquired two observations of the pulsar separated by one month to search for morphological changes in the pulsar and its environment following an extreme glitch in its rotation frequency. We find a well-resolved nebula with a morphology remarkably similar to the torus-like structure observed in the Crab Nebula, along with an axial Crab-like jet. The flux from the pulsar is found to be steady to within 0.75 %; the 3 sigma limit on the fractional increase in the pulsar's X-ray flux is <10-5 of the inferred glitch energy. We use this limit to constrain parameters of glitch models and neutron star structure. We do find a significant increase in the flux of the nebula's outer torus; if associated with the glitch, the inferred propogation velocity is ~0.5c, similar to that seen in the brightening of the Crab Nebula wisps. We propose an explanation for the X-ray structure of the Vela synchrotron nebula based on a model originally developed for the Crab Nebula. In this model, the bright, arc-shaped X-ray wisps are the shocked termination of a relativistic equatorial pulsar wind which is contained within the surrounding kidney-bean shaped synchrotron nebula which comprises the post-shock, but still relativistic, flow. In a departure from the Crab model, the magnetization parameter of the Vela pulsar wind is required to be of order unity; this is consistent with the simplest MHD transport of magnetic field from the pulsar to the nebula, where B ~ 4 x 10-4G.

  2. Maturation grade of coals as revealed by Raman spectroscopy: Progress and problems

    NASA Astrophysics Data System (ADS)

    Quirico, Eric; Rouzaud, Jean-Noël; Bonal, Lydie; Montagnac, Gilles

    2005-08-01

    The present study questions the sensitivity and the accuracy of Raman spectroscopy as a tool for determining the maturity of natural organic matter (NOM). It focuses on the definition of optimized experimental parameters in order to maximize the quality of the Raman signal and control the accuracy and reproducibility of measurements. A series of 11 coals has been investigated, sampling a wide maturity range (2-7% vitrinite reflectance VR). The role of experimental parameters is first investigated. An excitation wavelength of 514.5 nm gives better results than 457.9 and 632.8 nm, minimizing the fluorescence background observed in the spectra of low-rank coals. Both Raman and fluorescence spectra were investigated with time-resolved experiments in air and argon. These data show that fluorescence and Raman spectra are sensitive to acquisition time and laser power parameters, and reveal a physicochemical instability of the samples under laser irradiation, mostly due to photo-oxidation processes. These data clearly show that the experiments, especially in air, should be performed with strictly constant acquisition parameters. In addition, the results of a whole series of coal measurements performed in air under constant experimental conditions show that Raman spectroscopy is definitely sensitive to the maturity of coal samples with VR > ˜1%. The most sensitive spectral maturity tracers are the width of the D-band (FWHM-D), the ratio of the peak intensities of the D- and G-bands ( ID/ IG), the normalized ratio of the band integrated intensities AD/[ AD + AG] for the maturity range VR = 3-7% and the width of the G-band (FWHM-G) for VR = 1-5%. However, the accuracy and reproducibility are definitely weaker in such measurements compared to the standard VR. Future work must solve the problem of sample stability under laser irradiation, and greatly increase the number of samples to improve the statistical significance of the results.

  3. Meeting the Need for Child Care: Problems and Progress. Hearing before a Subcommittee of the Committee on Government Operations. House of Representatives, One Hundredth Congress, First Session.

    ERIC Educational Resources Information Center

    Congress of the U. S., Washington, DC. House Committee on Government Operations.

    A hearing was held to identify problems and assess progress in the provision of affordable, high quality child care. Testimony concerned: (1) problems working parents have had in providing care for their young children; (2) day care initiatives and needs in California; (3) ways in which San Mateo County used its housing and community development…

  4. DETECTING GRAVITATIONAL WAVE MEMORY WITH PULSAR TIMING

    SciTech Connect

    Cordes, J. M.; Jenet, F. A. E-mail: merlyn@phys.utb.edu

    2012-06-10

    We compare the detectability of gravitational bursts passing through the solar system with those passing near each millisecond pulsar in an N-pulsar timing array. The sensitivity to Earth-passing bursts can exploit the correlation expected in pulse arrival times while pulsar-passing bursts, though uncorrelated between objects, provide an N-fold increase in overall time baseline that can compensate for the lower sensitivity. Bursts with memory from mergers of supermassive black holes produce step functions in apparent spin frequency that are the easiest to detect in pulsar timing. We show that the burst rate and amplitude distribution, while strongly dependent on inadequately known cosmological evolution, may favor detection in the pulsar terms rather than the Earth timing perturbations. Any contamination of timing data by red spin noise makes burst detection more difficult because both signals grow with the length of the time data span T. Furthermore, the different bursts that could appear in one or more data sets of length T Almost-Equal-To 10 yr also affect the detectability of the gravitational wave stochastic background that, like spin noise, has a red power spectrum. A burst with memory is a worthwhile target in the timing of multiple pulsars in a globular cluster because it should produce a correlated signal with a time delay of less than about 10 years in some cases.

  5. Precision Pulsar Timing at the DSN

    NASA Astrophysics Data System (ADS)

    Majid, Walid A.

    2015-01-01

    Millisecond pulsars are a class of radio pulsars with extremely stable rotations. The excellent timing stability of millisecond pulsars can be used to study a wide variety of astrophysical phenomena. In particular, observations of a large sample of these pulsars can be used to detect the presence of low-frequency gravitational waves. We have developed a precision pulsar timing backend for the Deep Space Network (DSN), which will allow the use of short gaps in tracking schedules to observe and time pulses from an ensemble of millisecond pulsars. The NASA Deep Space Network (DSN) operates clusters of large dish antennas (up to 70-m in diameter), located roughly equi-distant around the Earth, for communication and tracking of deep-space spacecraft. The backend system will be capable of removing entirely the dispersive effects of propagation of radio waves through the interstellar medium in real-time. We will describe our development work, initial results, and prospects for future observations scheduled later this year.This research was performed at the Jet Propulsion Laboratory,California Institute of Technology, under the Research and TechnologyDevelopment Program, under a contract with the National Aeronautics andSpace Administration.

  6. Precision Pulsar Timing at the DSN

    NASA Astrophysics Data System (ADS)

    Majid, Walid A.

    2016-01-01

    Millisecond pulsars are a class of radio pulsars with extremely stable rotations. The excellent timing stability of millisecond pulsars can be used to study a wide variety of astrophysical phenomena. In particular, observations of a large sample of these pulsars can be used to detect the presence of low-frequency gravitational waves. We have developed and are now commissioning a precision pulsar timing backend for the Deep Space Network (DSN), which will allow the use of short gaps in tracking schedules to observe and time pulses from an ensemble of millisecond pulsars. The NASA Deep Space Network (DSN) operates clusters of large dish antennas (up to 70-m in diameter), located roughly equi-distant around the Earth, for communication and tracking of deep-space spacecraft. The backend system is capable of removing entirely the dispersive effects of propagation of radio waves through the interstellar medium in real-time. We will describe our development work, initial results, and prospects for future observations scheduled over the next few years.

  7. A novel mechanism for creating double pulsars

    NASA Technical Reports Server (NTRS)

    Sigurdsson, Steinn; Hernquist, Lars

    1992-01-01

    Simulations of encounters between pairs of hard binaries, each containing a neutron star and a main-sequence star, reveal a new formation mechanism for double pulsars in dense cores of globular clusters. In many cases, the two normal stars are disrupted to form a common envelope around the pair of neutron stars, both of which will be spun up to become millisecond pulsars. We predict that a new class of pulsars, double millisecond pulsars, will be discovered in the cores of dense globular clusters. The genesis proceeds through a short-lived double-core common envelope phase, with the envelope ejected in a fast wind. It is possible that the progenitor may also undergo a double X-ray binary phase. Any circular, short-period double pulsar found in the galaxy would necessarily come from disrupted disk clusters, unlike Hulse-Taylor class pulsars or low-mass X-ray binaries which may be ejected from clusters or formed in the galaxy.

  8. Pulsar observations with the MAGIC telescopes

    NASA Astrophysics Data System (ADS)

    Fidalgo, David

    2016-07-01

    The vast majority of spectra of gamma-ray pulsars exhibit an exponential cut-off at a few GeV, as seen by the Large Area Telescope (LAT) on board of the Fermi satellite. Due to this cut-off, current Imaging Atmospheric Cherenkov Telescopes (IACTs) with an energy threshold as low as 30 GeV, struggle to detect pulsars. So far, emission above 50 GeV has been confirmed only for the Crab and Vela pulsars. In the case of the former, the spectrum even extends up to about 1 TeV firmly revealing a second emission component. To further understand the emission mechanism of gamma-ray pulsars, the MAGIC collaboration continues the search of pulsars above 50 GeV. In this talk we report on recent results on the Crab and Geminga Pulsar obtained with the MAGIC telescopes, including the analysis of data taken with a new trigger system lowering the energy threshold of the MAGIC telescopes.

  9. Observing pulsars and fast transients with LOFAR

    NASA Astrophysics Data System (ADS)

    Stappers, B. W.; Hessels, J. W. T.; Alexov, A.; Anderson, K.; Coenen, T.; Hassall, T.; Karastergiou, A.; Kondratiev, V. I.; Kramer, M.; van Leeuwen, J.; Mol, J. D.; Noutsos, A.; Romein, J. W.; Weltevrede, P.; Fender, R.; Wijers, R. A. M. J.; Bähren, L.; Bell, M. E.; Broderick, J.; Daw, E. J.; Dhillon, V. S.; Eislöffel, J.; Falcke, H.; Griessmeier, J.; Law, C.; Markoff, S.; Miller-Jones, J. C. A.; Scheers, B.; Spreeuw, H.; Swinbank, J.; Ter Veen, S.; Wise, M. W.; Wucknitz, O.; Zarka, P.; Anderson, J.; Asgekar, A.; Avruch, I. M.; Beck, R.; Bennema, P.; Bentum, M. J.; Best, P.; Bregman, J.; Brentjens, M.; van de Brink, R. H.; Broekema, P. C.; Brouw, W. N.; Brüggen, M.; de Bruyn, A. G.; Butcher, H. R.; Ciardi, B.; Conway, J.; Dettmar, R.-J.; van Duin, A.; van Enst, J.; Garrett, M.; Gerbers, M.; Grit, T.; Gunst, A.; van Haarlem, M. P.; Hamaker, J. P.; Heald, G.; Hoeft, M.; Holties, H.; Horneffer, A.; Koopmans, L. V. E.; Kuper, G.; Loose, M.; Maat, P.; McKay-Bukowski, D.; McKean, J. P.; Miley, G.; Morganti, R.; Nijboer, R.; Noordam, J. E.; Norden, M.; Olofsson, H.; Pandey-Pommier, M.; Polatidis, A.; Reich, W.; Röttgering, H.; Schoenmakers, A.; Sluman, J.; Smirnov, O.; Steinmetz, M.; Sterks, C. G. M.; Tagger, M.; Tang, Y.; Vermeulen, R.; Vermaas, N.; Vogt, C.; de Vos, M.; Wijnholds, S. J.; Yatawatta, S.; Zensus, A.

    2011-06-01

    Low frequency radio waves, while challenging to observe, are a rich source of information about pulsars. The LOw Frequency ARray (LOFAR) is a new radio interferometer operating in the lowest 4 octaves of the ionospheric "radio window": 10-240 MHz, that will greatly facilitate observing pulsars at low radio frequencies. Through the huge collecting area, long baselines, and flexible digital hardware, it is expected that LOFAR will revolutionize radio astronomy at the lowest frequencies visible from Earth. LOFAR is a next-generation radio telescope and a pathfinder to the Square Kilometre Array (SKA), in that it incorporates advanced multi-beaming techniques between thousands of individual elements. We discuss the motivation for low-frequency pulsar observations in general and the potential of LOFAR in addressing these science goals. We present LOFAR as it is designed to perform high-time-resolution observations of pulsars and other fast transients, and outline the various relevant observing modes and data reduction pipelines that are already or will soon be implemented to facilitate these observations. A number of results obtained from commissioning observations are presented to demonstrate the exciting potential of the telescope. This paper outlines the case for low frequency pulsar observations and is also intended to serve as a reference for upcoming pulsar/fast transient science papers with LOFAR.

  10. On gigahertz spectral turnovers in pulsars

    NASA Astrophysics Data System (ADS)

    Rajwade, K.; Lorimer, D. R.; Anderson, L. D.

    2016-01-01

    Pulsars are known to emit non-thermal radio emission that is generally a power-law function of frequency. In some cases, a turnover is seen at frequencies around 100 MHz. Kijak et al. have reported the presence of a new class of `Gigahertz Peaked Spectrum' (GPS) pulsars that show spectral turnovers at frequencies around 1 GHz. We apply a model based on free-free thermal absorption to explain these turnovers in terms of surrounding material such as the dense environments found in H II regions, pulsar wind nebulae, or in cold, partially ionized molecular clouds. We show that the turnover frequency depends on the electron temperature of the environment close to the pulsar, as well as the emission measure along the line of sight. We fitted this model to the radio fluxes of known GPS pulsars and show that it can replicate the GHz turnover. From the thermal absorption model, we demonstrate that normal pulsars would exhibit a GPS-like behaviour if they were in a dense environment. We discuss the application of this model in the context of determining the population of neutron stars within the central parsec of the Galaxy. We show that a non-negligible fraction of this population might exhibit high-frequency spectral turnovers, which has implications on the detectability of these sources in the Galactic Centre.

  11. Ground-penetrating radar and its use in sedimentology: principles, problems and progress

    NASA Astrophysics Data System (ADS)

    Neal, Adrian

    2004-08-01

    Ground-penetrating radar (GPR, also referred to as ground-probing radar, surface-penetrating radar, subsurface radar, georadar or impulse radar) is a noninvasive geophysical technique that detects electrical discontinuities in the shallow subsurface (<50 m). It does this by generation, transmission, propagation, reflection and reception of discrete pulses of high-frequency (MHz) electromagnetic energy. During the 1980s radar systems became commercially available, but it was not until the mid-1990s that sedimentary geologists and others began to widely exploit the technique. During the last decade numerous sedimentological studies have used GPR to reconstruct past depositional environments and the nature of sedimentary processes in a variety of environmental settings; to aid hydrogeological investigations, including groundwater reservoir characterisation, and to assist in hydrocarbon reservoir analogue studies. This is because in correctly processed radar profiles, and at the resolution of a survey, primary reflections usually parallel primary depositional structure. Despite the wide use of GPR, a number of fundamental problems remain in its application to sedimentary research. In particular, there are a wide range of approaches to the processing of radar data and interpretation techniques used on the final subsurface images vary widely, with little consensus over a common methodology. This review attempts to illustrate that methods for the collection, processing and interpretation of radar data are intimately linked and that thorough understanding of the nature, limitations and implications of each step is required if realistic sedimentological data are to be generated. In order to extract the maximum amount of meaningful information, the user must understand the scientific principles that underlie the technique, the effects of the data collection regime employed, the implications of the technique's finite resolution and depth of penetration, the nature and causes

  12. The Velocity Distribution of Isolated Radio Pulsars

    NASA Technical Reports Server (NTRS)

    Arzoumanian, Z.; Chernoff, D. F.; Cordes, J. M.; White, Nicholas E. (Technical Monitor)

    2002-01-01

    We infer the velocity distribution of radio pulsars based on large-scale 0.4 GHz pulsar surveys. We do so by modelling evolution of the locations, velocities, spins, and radio luminosities of pulsars; calculating pulsed flux according to a beaming model and random orientation angles of spin and beam; applying selection effects of pulsar surveys; and comparing model distributions of measurable pulsar properties with survey data using a likelihood function. The surveys analyzed have well-defined characteristics and cover approx. 95% of the sky. We maximize the likelihood in a 6-dimensional space of observables P, dot-P, DM, absolute value of b, mu, F (period, period derivative, dispersion measure, Galactic latitude, proper motion, and flux density). The models we test are described by 12 parameters that characterize a population's birth rate, luminosity, shutoff of radio emission, birth locations, and birth velocities. We infer that the radio beam luminosity (i) is comparable to the energy flux of relativistic particles in models for spin-driven magnetospheres, signifying that radio emission losses reach nearly 100% for the oldest pulsars; and (ii) scales approximately as E(exp 1/2) which, in magnetosphere models, is proportional to the voltage drop available for acceleration of particles. We find that a two-component velocity distribution with characteristic velocities of 90 km/ s and 500 km/ s is greatly preferred to any one-component distribution; this preference is largely immune to variations in other population parameters, such as the luminosity or distance scale, or the assumed spin-down law. We explore some consequences of the preferred birth velocity distribution: (1) roughly 50% of pulsars in the solar neighborhood will escape the Galaxy, while approx. 15% have velocities greater than 1000 km/ s (2) observational bias against high velocity pulsars is relatively unimportant for surveys that reach high Galactic absolute value of z distances, but is severe for

  13. Pulsar-irradiated stars in dense globular clusters

    NASA Technical Reports Server (NTRS)

    Tavani, Marco

    1992-01-01

    We discuss the properties of stars irradiated by millisecond pulsars in 'hard' binaries of dense globular clusters. Irradiation by a relativistic pulsar wind as in the case of the eclipsing millisecond pulsar PSR 1957+20 alter both the magnitude and color of the companion star. Some of the blue stragglers (BSs) recently discovered in dense globular clusters can be irradiated stars in binaries containing powerful millisecond pulsars. The discovery of pulsar-driven orbital modulations of BS brightness and color with periods of a few hours together with evidence for radio and/or gamma-ray emission from BS binaries would valuably contribute to the understanding of the evolution of collapsed stars in globular clusters. Pulsar-driven optical modulation of cluster stars might be the only observable effect of a new class of binary pulsars, i.e., hidden millisecond pulsars enshrouded in the evaporated material lifted off from the irradiated companion star.

  14. Spectral Analysis of Timing Noise in NANOGrav Pulsars

    NASA Astrophysics Data System (ADS)

    Perrodin, Delphine; Jenet, F. A.; Lommen, A. N.; Finn, L. S.; Demorest, P. B.

    2012-01-01

    The NANOGrav collaboration seeks to detect gravitational waves from distant supermassive black hole sources using a pulsar timing array. In order to search for gravitational waves, it is necessary to have a good characterization of the timing noise for each pulsar of the pulsar timing array. Red noise is common in millisecond pulsars, and we need to quantify how much red noise is present for each pulsar. This can be done by looking at the power spectra of the pulsar timing residuals. However because the pulsar data are non-uniformly sampled, one cannot simply do a Fourier analysis. Also, commonly used least-square fitting methods such as the Lomb-Scargle analysis are not adequate for steep red spectra. Instead, we compute the power spectra of NANOGrav pulsar timing residuals using the Cholesky transformation, which eliminates spectral leakage. This is done with the help of the TEMPO2 ``SpectralModel" plugin developed by William Coles and George Hobbs.

  15. Spectral Analysis of Timing Noise in NANOGrav Pulsars

    NASA Astrophysics Data System (ADS)

    Perrodin, Delphine

    2011-07-01

    The NANOGrav collaboration seeks to detect gravitational waves from distant supermassive black hole sources using a pulsar timing array. In order to search for gravitational waves, it is necessary to have a good characterization of the timing noise for each pulsar of the pulsar timing array. Red noise is common in millisecond pulsars, and we need to quantify how much red noise is present for each pulsar. This can be done by looking at the power spectra of the pulsar timing residuals. However because the pulsar data are non-uniformly sampled, one cannot simply do a Fourier analysis. Also, commonly used least-square fitting methods such as the Lomb-Scargle analysis are not adequate for steep red spectra. Instead, we compute the power spectra of NANOGrav pulsar timing residuals using the Cholesky transformation, which eliminates spectral leakage. This is done with the help of the TEMPO2 "SpectralModel" plugin developed by William Coles and George Hobbs.

  16. Basic physics and cosmology from pulsar timing data

    NASA Technical Reports Server (NTRS)

    Taylor, J. H.

    1991-01-01

    Radio pulsars provide unparalleled opportunities for making measurements of astrophysically interesting phenomena. The author concentrates on two particular applications of high precision timing observations of pulsars: tests of relativistic gravitation theory using the binary pulsar 1913+16, and tests of cosmological models using timing data from millisecond pulsars. New upper limits are presented for the energy density of a cosmic background of low frequency gravitational radiation.

  17. A novel approach toward gravitational wave analyses with pulsar timing arrays

    NASA Astrophysics Data System (ADS)

    Mingarelli, Chiara M. F.; University of Birmingham Gravitational Wave Group (A. Vecchio, K. Grover, R. Smith, T. Sidery, I. Mandel)

    2015-01-01

    My doctoral studies provide a novel approach toward gravitational wave (GW) analyses, including the generalization of nanoHertz stochastic GW background searches, strict limits on when assumptions made in GW background analyses break down, and how to extract information about the masses and spins of supermassive black hole binaries using pulsar timing arrays. A pulsar timing array is galactic-scale nanoHertz GW detector that looks for small deviations in the ultra-stable arrival time of radio pulses from millisecond pulsars to infer the presence of GWs. I show that the standard analysis for isotropic stochastic GW backgrounds can be generalized in a conceptually straightforward way to the case of generic anisotropic background radiation. If evidence for a signal is found in the data, testing the assumption of isotropy could be one of the methods to confirm its cosmological origin. However, if one expects some deviations from isotropy, which may be the case for a background created by a finite population of supermassive black hole binaries, my method can be used to extract constraints on the underlying physical population. Moreover, I assess the assumptions made when computing the correlation functions used in the stochastic GW background searches, and found that when pulsars are separated by less than 3o, correlated phase changes can occur between the pulsars which are important to model. Lastly I show that the detection of GWs from individual supermassive black hole binary systems can yield direct information about the masses and spins of the black holes, provided that the GW-induced timing fluctuations both at the pulsar and at Earth are detected. This in turn provides a map of the nonlinear dynamics of the gravitational field and a new avenue to tackle open problems in astrophysics connected to the formation and evolution of supermassive black holes.

  18. BOOK REVIEW: Rotation and Accretion Powered Pulsars

    NASA Astrophysics Data System (ADS)

    Kaspi, V. M.

    2008-03-01

    Pulsar astrophysics has come a long way in the 40 years since the discovery of the first pulsar by Bell and Hewish. From humble beginnings as bits of 'scruff' on the Cambridge University group's chart recorder paper, the field of pulsars has blossomed into a major area of mainstream astrophysics, with an unparalleled diversity of astrophysical applications. These range from Nobel-celebrated testing of general relativity in the strong-field regime to constraining the equation-of-state of ultradense matter; from probing the winds of massive stars to globular cluster evolution. Previous notable books on the subject of pulsars have tended to focus on some particular topic in the field. The classic text Pulsars by Manchester and Taylor (1977 San Francisco, CA: Freeman) targeted almost exclusively rotation-powered radio pulsars, while the Mészáros book High-Energy Radiation from Magnetized Neutron Stars (1992 Chicago, IL: University of Chicago Press) considered both rotation- and accretion-powered neutron stars, but focused on their radiation at x-ray energies and above. The recent book Neutron Stars 1 by Haensel et al (2007 Berlin: Springer) considers only the equation of state and neutron-star structure. Into this context appears Rotation and Accretion Powered Pulsars, by Pranab Ghosh. In contrast to other books, here the author takes an encyclopedic approach and attempts to synthesize practically all of the major aspects of the two main types of neutron star. This is ambitious. The only comparable undertaking is the useful but more elementary Lyne and Graham-Smith text Pulsar Astronomy (1998 Cambridge: Cambridge University Press), or Compact Stellar X-ray Sources (eds Lewin and van der Klis, 2006 Cambridge: Cambridge University Press), an anthology of technical review articles that also includes black hole topics. Rotation and Accretion Powered Pulsars thus fills a clear void in the field, providing a readable, graduate-level book that covers nearly everything you

  19. Chandra Associates Pulsar and Historic Supernova

    NASA Astrophysics Data System (ADS)

    2001-01-01

    SAN DIEGO -- Scientists using NASA’s Chandra X-ray Observatory have found new evidence that a pulsar in the constellation of Sagittarius was created when a massive star exploded, witnessed by Chinese astronomers in the year 386 AD. If confirmed, this will be only the second pulsar to be clearly associated with a historic event. These results were presented today by Victoria Kaspi and Mallory Roberts of McGill University at the American Astronomical Society meeting. Also participating in the research were Gautum Vasisht from the Jet Propulsion Laboratory, Eric Gotthelf from Columbia University, Michael Pivovaroff from Therma-Wave, Inc., and Nobuyuki Kawai from the Institute of Physical and Chemical Research, Japan. The scientists used Chandra to locate the pulsar exactly at the geometric center of the supernova remnant known as G11.2-0.3. This location provides very strong evidence that the pulsar, a neutron star that is rotating 14 times a second, was formed in the supernova of 386 AD, and therefore has an age of 1615 years. "Determining the true ages of astronomical objects is notoriously difficult, and for this reason, historical records of supernovas are of great importance,"said Kaspi."In roughly the past 2,000 years, fewer than 10 reports of probable supernovae have been archived mostly by Asian astronomers. Of those handful, the remnant of 1054 AD, the Crab Nebula, was until now the only pulsar whose birth could be associated with a historic event - and, hence, the only neutron star that has a firm age." Between mid-April and mid-May in the year 386 AD, a young "guest star", presumably a supernova, was recorded by Chinese observers in the direction of the sky now known as the constellation of Sagittarius. In the 1970s, radio astronomers discovered an expanding nebula of gas and high-energy particles, called G11.2-0.3, that is believed to be the remnant of that explosion. In 1997, a team of X-ray astronomers used Japan’s ASCA satellite to discover a pulsar

  20. Physics of Rotation Powered Pulsars and Their Nebulae

    NASA Technical Reports Server (NTRS)

    Arons, Jonathan

    1997-01-01

    This letter is my progress report for the Astrophysics Theory grant. The first goal of the research supported by this grant is to produce a time dependent theory of the unsteady relativistic collisionless shock wave terminating the relativistic wind from a pulsar, and compare the predicted surface brightness fluctuations to Hubble Space Telescope observations of the wisps in the Crab Nebula. The second goal is to model the production of electron-positron pairs over the polar caps of rotation powered pulsars, and use the results to predict the heating of the surface due to particle trapping and bombardment of the atmosphere at the base of the polar field lines. We have succeeded in creating a one dimensional hybrid code, in which the electron-positron pairs incident on the shock structure are modeled as a relativistic, adiabatic, ideal MHD fluid, while the heavy ions are treated as particles using a particle-in-cell algorithm. The electromagnetic fields are evaluated from the currents and charge densities in the pairs and the ions, while the particles and the fluid accelerate in response to the computed self-consistent electromagnetic fields. The results are promising, in that the underlying ion cyclotron instability generates finite amplitude, propagating magnetosonic waves in the pairs, whose wavelengths and frequencies, when translated into physical units, are comparable to the observed running waves of brightness observed by HST near the Crab pulsar. The code is undergoing a number of tests, to assure us that this preliminary correspondence is not an artifact. In the coming year, the observational appearance of the models will be computed and compared to the HST observations of the Crab now in hand, and used to predict the HST results which will be obtained the year after next. WE also developed a one dimensional cascade theory for pair creation over pulsars' polar caps. A linear integral equation describing the synchrotron cascade has been derived and solved by

  1. Unusual flux-distance relationship for pulsars suggested by analysis of the Australia national telescopy facility pulsar catalogue

    SciTech Connect

    Singleton, John; Perez, M R; Singleton, J; Ardavan, H; Ardavan, A

    2009-01-01

    We analyze pulsar fluxes at 1400 MHz (S(1400)) and distances d taken from the Australia National Telescope Facility (ATNF) Pulsar Catalogue. Under the assumption that pulsar populations in different parts of the Galaxy are similar, we find that either (a) pulsar fluxes diminish with distance according to a non-standard power law (we suggest S(1400){proportional_to} 1/d rather than {proportional_to} 1/d{sup 2}) or (b) that there are very significant (i.e. order of magnitude) errors in the distance estimates quoted in the ATNF Catalogue. The former conclusion (a) supports a recent model for pulsar emission that has also successfully explained the frequency spectrum of the Crab pulsar over 16 orders of magnitude of frequency, whilst alternative (b) would necessitate a radical re-evaluation of both the dispersion method for estimating pulsar distances and current ideas about the distribution of pulsars within our Galaxy.

  2. The distance indicators in gamma-ray pulsars

    NASA Astrophysics Data System (ADS)

    Wang, Wei

    2013-03-01

    Distance measurements of gamma-ray pulsars are challenging questions in present pulsar studies. The Large Area Telescope (LAT) aboard the Fermi gamma-ray observatory discovered more than 100 gamma-ray pulsars, including 34 new gamma-selected pulsars which nearly have no distance information. We study the relation between gamma-ray emission efficiency (η=L γ/Ė) and pulsar parameters, for young radio-selected gamma-ray pulsars with known distance information. We have introduced three generation order parameters to describe gamma-ray emission properties of pulsars, and find a strong correlation between η and ζ3, the generation order parameter which reflects γ-ray photon generations in pair cascade processes induced by magnetic field absorption in pulsar magnetosphere. A good correlation between η and B LC, the magnetic field at the light cylinder radius, is also found. These correlations can serve as distance indicators in gamma-ray pulsars, to evaluate distances for gamma-selected pulsars. Distances of 35 gamma-selected pulsars are estimated, which could be tested by other distance measurement methods. The physical origin of the correlations may be also interesting for pulsar studies.

  3. Radio wave propagation in pulsar magnetospheres

    NASA Astrophysics Data System (ADS)

    Petrova, S. A.; Lyubarskii, Yu. E.

    Pulsar magnetospheres are known to contain an ultrarelativistic highly magnetized plasma which streams along the open magnetic lines. The radio emission observed from pulsars is believed to originate sufficiently deep in the open field line tube, so that the characteristics of outgoing waves can be influenced by propagation in the magnetospheric plasma. Refraction of radio waves in pulsar magnetospheres appears to be efficient. The effect not only influences the observed pulse width and its frequency dependency. It can alter the apparent spatial structure of pulsar emission region which can be derived from the observations of pulsar interstellar scintillations. Transverse ray separation versus pulse longitude calculated allowing for magnetospheric refraction appears to be in qualitative agreement with that observed. In particular, the nonmonotonic character of the curve can be attributed to nonmonotonic distribution of the plasma number density across the open field line tube which makes the rays emitted at different spatial locations deviate in the opposite directions. Proceeding from the frequency dependence of refraction some predictions are made about the frequency evolution of the apparent spatial structure of pulsar emission region. Magnetospheric refraction can also determine the profile shape giving rise to ray grouping into separate components. It will be demonstrated that the salient features of profile morphology can be explained within the frame of a primordial hollow-cone emission model taking into account refraction of rays in pulsar plasma. Then the frequency evolution of profile structure is naturally interpreted as a consequence of frequency dependence of refraction. As the waves propagate in the magnetospheric plasma their polarization also evolves essentially. In the vicinity of the emission region normal waves are linearly polarized and propagate independently, with the polarization plane following the orientation of the local magnetic field. As

  4. Turn-over in pulsar spectra: From young pulsars to millisecond ones

    NASA Astrophysics Data System (ADS)

    Kijak, J.; Lewandowski, W.; Serylak, M.

    2008-02-01

    The evidence for turn-over in young pulsar radio spectra at high frequencies is presented. The frequency at which a spectrum shows the maximum flux density is called the peak frequency. This peak frequency appears to depend on pulsar age and dispersion measure. A possible relation with pulsar age is interesting. Millisecond pulsars, which are very old objects, may show no evidence for spectral turn-over down to 100 MHz. Some studied pulsars with turn-over at high frequencies have been shown to have very interesting interstellar environments. This could suggest that the turn-over phenomenon is associated with the enviromental conditions around the neutron stars, rahter than being related intrinsically with the radio emission mechanism. Although there are no earlier reports of such a connection, a more detailed study on larger sample of pulsars is needed to address this idea more quantitatively. In this context, future observations below 200 MHz using LOFAR will allow us to investigate turn-over in radio pulsar spectra.

  5. THE PULSAR SEARCH COLLABORATORY: DISCOVERY AND TIMING OF FIVE NEW PULSARS

    SciTech Connect

    Rosen, R.; Swiggum, J.; McLaughlin, M. A.; Lorimer, D. R.; Yun, M.; Boyles, J.; Heatherly, S. A.; Scoles, S.; Lynch, R.; Kondratiev, V. I.; Ransom, S. M.; Moniot, M. L.; Thompson, C.; Cottrill, A.; Raycraft, M.; Weaver, M.; Snider, A.; Dudenhoefer, J.; Allphin, L.; Thorley, J.; and others

    2013-05-01

    We present the discovery and timing solutions of five new pulsars by students involved in the Pulsar Search Collaboratory, a NSF-funded joint program between the National Radio Astronomy Observatory and West Virginia University designed to excite and engage high-school students in Science, Technology, Engineering, and Mathematics (STEM) and related fields. We encourage students to pursue STEM fields by apprenticing them within a professional scientific community doing cutting edge research, specifically by teaching them to search for pulsars. The students are analyzing 300 hr of drift-scan survey data taken with the Green Bank Telescope at 350 MHz. These data cover 2876 deg{sup 2} of the sky. Over the course of five years, more than 700 students have inspected diagnostic plots through a web-based graphical interface designed for this project. The five pulsars discovered in the data have spin periods ranging from 3.1 ms to 4.8 s. Among the new discoveries are PSR J1926-1314, a long period, nulling pulsar; PSR J1821+0155, an isolated, partially recycled 33 ms pulsar; and PSR J1400-1438, a millisecond pulsar in a 9.5 day orbit whose companion is likely a white dwarf star.

  6. Detection and localization of continuous gravitational waves with pulsar timing arrays: the role of pulsar terms

    NASA Astrophysics Data System (ADS)

    Zhu, X.-J.; Wen, L.; Xiong, J.; Xu, Y.; Wang, Y.; Mohanty, S. D.; Hobbs, G.; Manchester, R. N.

    2016-09-01

    A pulsar timing array is a Galactic-scale detector of nanohertz gravitational waves (GWs). Its target signals contain two components: the `Earth term' and the `pulsar term' corresponding to GWs incident on the Earth and pulsar, respectively. In this work we present a Frequentist method for the detection and localization of continuous waves that takes into account the pulsar term and is significantly faster than existing methods. We investigate the role of pulsar terms by comparing a full-signal search with an Earth-term-only search for non-evolving black hole binaries. By applying the method to synthetic data sets, we find that (i) a full-signal search can slightly improve the detection probability (by about five per cent); (ii) sky localization is biased if only Earth terms are searched for and the inclusion of pulsar terms is critical to remove such a bias; (iii) in the case of strong detections (with signal-to-noise ratio ≳30), it may be possible to improve pulsar distance estimation through GW measurements.

  7. Isolated pulsar spin evolution on the diagram

    NASA Astrophysics Data System (ADS)

    Ridley, J. P.; Lorimer, D. R.

    2010-05-01

    We look at two contrasting spin-down models for isolated radio pulsars and, accounting for selection effects, synthesize observable populations. While our goal is to reproduce all of the observable characteristics, in this paper we pay particular attention to the form of the spin period versus period derivative () diagram and its dependence on various pulsar properties. We analyse the initial spin period, the braking index, the magnetic field, various beaming models as well as the pulsar's luminosity. In addition to considering the standard magnetic dipole model for pulsar spin-down, we also consider the recent hybrid model proposed by Contopoulos and Spitkovsky. The magnetic dipole model, however, does a better job of reproducing the observed pulsar population. We conclude that random alignment angles and period-dependent luminosity distributions are essential to reproduce the observed diagram. We also consider the time decay of alignment angles and attempt to reconcile various models currently being studied. We conclude that in order to account for recent evidence for the alignment found by Weltevrede and Johnston, the braking torque on a neutron star should not depend strongly on the inclination. Our simulation code is publicly available and includes a web-based interface to examine the results and make predictions for yields of current and future surveys.

  8. PULSAR WIND NEBULAE WITH THICK TOROIDAL STRUCTURE

    SciTech Connect

    Chevalier, Roger A.; Reynolds, Stephen P. E-mail: reynolds@ncsu.edu

    2011-10-10

    We investigate a class of pulsar wind nebulae that show synchrotron emission from a thick toroidal structure. The best studied such object is the small radio and X-ray nebula around the Vela pulsar, which can be interpreted as the result of interaction of a mildly supersonic inward flow with the recent pulsar wind. Such a flow near the center of a supernova remnant can be produced in a transient phase when the reverse shock reaches the center of the remnant. Other nebulae with a thick toroidal structure are G106.6+2.9 and G76.9+1.0. Their structure contrasts with young pulsar nebulae like the Crab Nebula and 3C 38, which show a more chaotic, filamentary structure in the synchrotron emission. In both situations, a torus-jet structure is present where the pulsar wind passes through a termination shock, indicating the flow is initially toroidal. We suggest that the difference is due to the Rayleigh-Taylor instability that operates when the outer boundary of the nebula is accelerating into freely expanding supernova ejecta. The instability gives rise to mixing in the Crab and related objects, but is not present in the nebulae with thick toroidal regions.

  9. Gamma-ray pulsar studies with COMPTEL

    NASA Astrophysics Data System (ADS)

    Hermsen, W.; Kuiper, L.; Diehl, R.; Lichti, G.; Schoenfelder, V.; Strong, A. W.; Connors, A.; Ryan, J.; Bennett, K.; Busetta, M.; Carraminana, A.; Buccheri, R.; Grenier, I. A.

    1994-06-01

    Since the launch of the Compton Gamma-Ray Observatory (CGRO) the number of detected gamma-ray pulsars increased from two to six. COMPTEL, on-board CGRO and sensitive to gamma-rays with energies between approximately 0.7 and 30 MeV, detected three of these unambiguously. The classical Crab and Vela pulsars have been observed on several occasions and detailed pulse patterns and spectral parameters have been derived. The new CGRO gamma-ray pulsar PSR B1509-58 has been detected by COMPTEL at a significance level above 4 sigma, consistently in a timing and spatial analysis. A likely detection of Geminga has been obtained at an approximately 3 sigma level. This indication is found in a phase interval in which COS B data showed the presence of a new variable component, Interpeak 2, exhibiting a very soft spectrum above 50 MeV. The diversities in light-curve sphapes and spectral distributions, the apparent time variabilities, and the significant differences in the fractions of the spin-down power radiated at gamma-ray energies in this small sample of gamma-ray pulsars pose important constraints to pulsar modeling.

  10. LUMINOSITY EVOLUTION OF GAMMA-RAY PULSARS

    SciTech Connect

    Hirotani, Kouichi

    2013-04-01

    We investigate the electrodynamic structure of a pulsar outer-magnetospheric particle accelerator and the resulting gamma-ray emission. By considering the condition for the accelerator to be self-sustained, we derive how the trans-magnetic-field thickness of the accelerator evolves with the pulsar age. It is found that the thickness is small but increases steadily if the neutron-star envelope is contaminated by sufficient light elements. For such a light element envelope, the gamma-ray luminosity of the accelerator is kept approximately constant as a function of age in the initial 10,000 yr, forming the lower bound of the observed distribution of the gamma-ray luminosity of rotation-powered pulsars. If the envelope consists of only heavy elements, on the other hand, the thickness is greater, but it increases less rapidly than a light element envelope. For such a heavy element envelope, the gamma-ray luminosity decreases relatively rapidly, forming the upper bound of the observed distribution. The gamma-ray luminosity of a general pulsar resides between these two extreme cases, reflecting the envelope composition and the magnetic inclination angle with respect to the rotation axis. The cutoff energy of the primary curvature emission is regulated below several GeV even for young pulsars because the gap thickness, and hence the acceleration electric field, is suppressed by the polarization of the produced pairs.

  11. IS CALVERA A GAMMA-RAY PULSAR?

    SciTech Connect

    Halpern, J. P.

    2011-07-20

    Originally selected as a neutron star (NS) candidate in the ROSAT All-Sky Survey, 1RXS J141256.0+792204 ('Calvera') was discovered to be a 59 ms X-ray pulsar in a pair of XMM-Newton observations by Zane et al. Surprisingly, their claimed detection of this pulsar in Fermi {gamma}-ray data requires no period derivative, severely restricting its dipole magnetic field strength, spin-down luminosity, and distance to small values. This implies that the cooling age of Calvera is much younger than its characteristic spin-down age. If so, it could be a mildly recycled pulsar, or the first 'orphaned' central compact object (CCO). Here we show that the published Fermi ephemeris fails to align the pulse phases of the two X-ray observations with each other, which indicates that the Fermi detection is almost certainly spurious. Analysis of additional Fermi data also does not confirm the {gamma}-ray detection. This leaves the spin-down rate of Calvera less constrained, and its place among the families of NSs uncertain. It could still be either an ordinary pulsar, a mildly recycled pulsar, or an orphaned CCO.

  12. Polarization Properties of Rotation Powered Pulsars

    NASA Technical Reports Server (NTRS)

    Harding Alice K.

    2009-01-01

    Polarization measurements of rotation-powered pulsars and their nebulae have unique diagnostic potential. The polarization position angle of the pulsar wind nebula, as is know for the Crab pulsar, can tell us the orientation of the spin axis. Phase-resolved polarimetry of pulsars has had enormous diagnostic capability at radio and optical wavelengths and could also be a powerful diagnostic in the X-ray range. Measurement of the polarization properties as a function of pulse phase can therefore provide a multidimensional mapping of the pulsar emission. In the 'rotating vector' model, radiation originating near a magnetic pole is expected to show a characteristic S-shaped swing of the position angle vs. pulse phase. In this case it is possible to determine the magnetic inclination and viewing angles. Radiation originating further from the poles or further above the neutron star surface will have a more complex polarization signature, as a result of relativistic effects of aberration and time-of-flight delays and may also cause depolarization of the signal. I will discuss predicted polarization properties of pulsed emission in polar cap models, where radiation originates near the neutron star surface at the magnetic poles, and in slot gap and outer gap models, where radiation originates over a range of altitudes out to the speed-of-light cylinder.

  13. Gamma-ray Pulsars: Models and Predictions

    NASA Technical Reports Server (NTRS)

    Harding Alice K.; White, Nicholas E. (Technical Monitor)

    2000-01-01

    Pulsed emission from gamma-ray pulsars originates inside the magnetosphere, from radiation by charged particles accelerated near the magnetic poles or in the outer gaps. In polar cap models, the high energy spectrum is cut off by magnetic pair production above an energy that is, dependent on the local magnetic field strength. While most young pulsars with surface fields in the range B = 10(exp 12) - 10(exp 13) G are expected to have high energy cutoffs around several GeV, the gamma-ray spectra of old pulsars having lower surface fields may extend to 50 GeV. Although the gamma-ray emission of older pulsars is weaker, detecting pulsed emission at high energies from nearby sources would be an important confirmation of polar cap models. Outer gap models predict more gradual high-energy turnovers of the primary curvature emission around 10 GeV, but also predict an inverse Compton component extending to TeV energies. Detection of pulsed TeV emission, which would not survive attenuation at the polar caps, is thus an important test of outer gap models. Next-generation gamma-ray telescopes sensitive to GeV-TeV emission will provide critical tests of pulsar acceleration and emission mechanisms.

  14. Pulsar Observations Using the First Station of the Long Wavelength Array and the LWA Pulsar Data Archive

    NASA Astrophysics Data System (ADS)

    Stovall, K.; Ray, P. S.; Blythe, J.; Dowell, J.; Eftekhari, T.; Garcia, A.; Lazio, T. J. W.; McCrackan, M.; Schinzel, F. K.; Taylor, G. B.

    2015-08-01

    We present initial pulsar results from the first station of the Long Wavelength Array (LWA1) obtained during the commissioning period of LWA1 and in early science results. We present detections of periodic emission from 44 previously known pulsars, including 3 millisecond pulsars. The effects of the interstellar medium (ISM) on pulsar emission are significantly enhanced at the low frequencies of the LWA1 band (10–88 MHz), making LWA1 a very sensitive instrument for characterizing changes in the dispersion measure (DM) and other effects from the ISM. Pulsars also often have significant evolution in their pulse profile at low frequency and a break in their spectral index. We report DM measurements for 44 pulsars, mean flux density measurements for 36 pulsars, and multi-frequency component spacing and widths for 15 pulsars with more than one profile component. For 27 pulsars, we report spectral index measurements within our frequency range. We also introduce the LWA1 Pulsar Data Archive, which stores reduced data products from LWA1 pulsar observations. Reduced data products for the observations presented here can be found in the archive. Reduced data products from future LWA1 pulsar observations will also be made available through the archive.

  15. Progress on The GEMS (Gravity Electro-Magnetism-Strong) Theory of Field Unification and Its Application to Space Problems

    SciTech Connect

    Brandenburg, J. E.

    2008-01-21

    Progress on the GEMS (Gravity Electro-Magnetism-Strong), theory is presented as well as its application to space problems. The GEMS theory is now validated through the Standard Model of physics. Derivation of the value of the Gravitation constant based on the observed variation of {alpha} with energy: results in the formula G congruent with ({Dirac_h}/2{pi})c/M{sub {eta}}{sub c}{sup 2} exp(-1/(1.61{alpha})), where {alpha} is the fine structure constant,({Dirac_h}/2{pi}), is Planck's constant, c, is the speed of light, and M{sub {eta}}{sub c} is the mass of the {eta}{sub cc} Charmonium meson that is shown to be identical to that derived from the GEM postulates. Covariant formulation of the GEM theory is now possible through definition of the spacetime metric tensor as a portion of the EM stress tensor normalized by its own trace: g{sub ab} = 4(F{sup c}{sub a}F{sub cb})/(F{sup ab}F{sub ab}), it is found that this results in a massless ground state vacuum and a Newtonian gravitation potential {phi} = 1/2 E{sup 2}/B{sup 2}. It is also found that a Lorentz or flat-space metric is recovered in the limit of a full spectrum ZPF.

  16. Homozygous SLC6A17 Mutations Cause Autosomal-Recessive Intellectual Disability with Progressive Tremor, Speech Impairment, and Behavioral Problems

    PubMed Central

    Iqbal, Zafar; Willemsen, Marjolein H.; Papon, Marie-Amélie; Musante, Luciana; Benevento, Marco; Hu, Hao; Venselaar, Hanka; Wissink-Lindhout, Willemijn M.; Vulto-van Silfhout, Anneke T.; Vissers, Lisenka E.L.M.; de Brouwer, Arjan P.M.; Marouillat, Sylviane; Wienker, Thomas F.; Ropers, Hans Hilger; Kahrizi, Kimia; Nadif Kasri, Nael; Najmabadi, Hossein; Laumonnier, Frédéric; Kleefstra, Tjitske; van Bokhoven, Hans

    2015-01-01

    We report on Dutch and Iranian families with affected individuals who present with moderate to severe intellectual disability and additional phenotypes including progressive tremor, speech impairment, and behavioral problems in certain individuals. A combination of exome sequencing and homozygosity mapping revealed homozygous mutations c.484G>A (p.Gly162Arg) and c.1898C>G (p.Pro633Arg) in SLC6A17. SLC6A17 is predominantly expressed in the brain, encodes a synaptic vesicular transporter of neutral amino acids and glutamate, and plays an important role in the regulation of glutamatergic synapses. Prediction programs and 3D modeling suggest that the identified mutations are deleterious to protein function. To directly test the functional consequences, we investigated the neuronal subcellular localization of overexpressed wild-type and mutant variants in mouse primary hippocampal neuronal cells. Wild-type protein was present in soma, axons, dendrites, and dendritic spines. p.Pro633Arg altered SLC6A17 was found in soma and proximal dendrites but did not reach spines. p.Gly162Arg altered SLC6A17 showed a normal subcellular distribution but was associated with an abnormal neuronal morphology mainly characterized by the loss of dendritic spines. In summary, our genetic findings implicate homozygous SLC6A17 mutations in autosomal-recessive intellectual disability, and their pathogenic role is strengthened by genetic evidence and in silico and in vitro functional analyses. PMID:25704603

  17. Dating of sediments from four Swiss prealpine lakes with (210)Pb determined by gamma-spectrometry: progress and problems.

    PubMed

    Putyrskaya, V; Klemt, E; Röllin, S; Astner, M; Sahli, H

    2015-07-01

    In this paper the most important problems in dating lake sediments with unsupported (210)Pb are summarized and the progress in gamma-spectrometry of the unsupported (210)Pb is discussed. The main topics of these studies concern sediment samples preparation for gamma-spectrometry, measurement techniques and data analysis, as well as understanding of accumulation and sedimentation processes in lakes. The vertical distributions of artificial ((137)Cs, (241)Am, (239)Pu) and natural radionuclides ((40)K, (210,214)Pb, (214)Bi) as well as stable trace elements (Fe, Mn, Pb) in sediment cores from four Swiss lakes were used as examples for the interpretation, inter-comparison and validation of depth-age relations established by three (210)Pb-based models (CF-CSR, CRS and SIT). The identification of turbidite layers and the influence of the turbidity flows on the accuracy of sediment dating is demonstrated. Time-dependent mass sedimentation rates in lakes Brienz, Thun, Biel and Lucerne are discussed and compared with published data. PMID:25875007

  18. Timing of millisecond pulsars in globular clusters

    NASA Astrophysics Data System (ADS)

    D'Amico, Nichi; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Kramer, Michael; Sarkissian, John; Lyne, Andrew; Burgay, Marta; Corongiu, Alessandro; Camilo, Fernando; Bailes, Matthew; van Straten, Willem

    2011-10-01

    Timing of the dozen pulsars discovered by us in P303 is ensuring high quality results: (a) the peculiarities (in position or projected acceleration) of all the 5 millisecond pulsars in NGC6752 suggested the presence of non thermal dynamics in the core, perhaps due to black-holes of intermediate mass; (b) the eclipsing pulsar in NGC6397 is a stereotype for studying the late evolution of exotic binaries. We propose to continue our timing project focusing mostly on NGC6752 at 20cm (in order to measure additional parameters useful to constrain the existence of a black-hole) and NGC6397 at 10cm (for studying the orbital secular evolution, the eclipse region, and the mechanisms leading to the ejection of matter from the binary system).

  19. Timing of millisecond pulsars in globular clusters

    NASA Astrophysics Data System (ADS)

    D'Amico, Nichi; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Kramer, Michael; Sarkissian, John; Lyne, Andrew; Burgay, Marta; Corongiu, Alessandro; Camilo, Fernando; Bailes, Matthew; van Straten, Willem

    2011-04-01

    Timing of the dozen pulsars discovered by us in P303 is ensuring high quality results: (a) the peculiarities (in position or projected acceleration) of all the 5 millisecond pulsars in NGC6752 suggested the presence of non thermal dynamics in the core, perhaps due to black-holes of intermediate mass; (b) the eclipsing pulsar in NGC6397 is a stereotype for studying the late evolution of exotic binaries. We propose to continue our timing project focusing mostly on NGC6752 at 20cm (in order to measure additional parameters useful to constrain the existence of a black-hole) and NGC6397 at 10cm (for studying the orbital secular evolution, the eclipse region, and the mechanisms leading to the ejection of matter from the binary system).

  20. Timing of millisecond pulsars in globular clusters

    NASA Astrophysics Data System (ADS)

    D'Amico, Nichi; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Kramer, Michael; Sarkissian, John; Lyne, Andrew; Burgay, Marta; Corongiu, Alessandro; Camilo, Fernando; Bailes, Matthew; van Straten, Willem

    2013-04-01

    Timing of the dozen pulsars discovered by us in P303 is ensuring high quality results: (a) the peculiarities (in position or projected acceleration) of all the 5 millisecond pulsars in NGC6752 suggested the presence of non thermal dynamics in the core, perhaps due to black-holes of intermediate mass; (b) the eclipsing pulsar in NGC6397 is a stereotype for studying the late evolution of exotic binaries. We propose to continue our timing project focusing mostly on NGC6752 at 20cm (in order to measure additional parameters useful to constrain the existence of a black-hole) and NGC6397 at 10cm (for studying the orbital secular evolution, the eclipse region, and the mechanisms leading to the ejection of matter from the binary system).

  1. Timing of millisecond pulsars in globular clusters

    NASA Astrophysics Data System (ADS)

    D'Amico, Nichi; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Kramer, Michael; Sarkissian, John; Lyne, Andrew; Burgay, Marta; Corongiu, Alessandro; Camilo, Fernando; Bailes, Matthew; van Straten, Willem

    2010-10-01

    Timing of the dozen pulsars discovered by us in P303 is ensuring high quality results: (a) the peculiarities (in position or projected acceleration) of all the 5 millisecond pulsars in NGC6752 suggested the presence of non thermal dynamics in the core, perhaps due to black-holes of intermediate mass; (b) the eclipsing pulsar in NGC6397 is a stereotype for studying the late evolution of exotic binaries. We propose to continue our timing project focusing mostly on NGC6752 at 20cm (in order to measure additional parameters useful to constrain the existence of a black-hole) and NGC6397 at 10cm (for studying the eclipse region and the orbital secular evolution).

  2. Timing of millisecond pulsars in globular clusters

    NASA Astrophysics Data System (ADS)

    D'Amico, Nichi; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Kramer, Michael; Sarkissian, John; Lyne, Andrew; Burgay, Marta; Corongiu, Alessandro; Camilo, Fernando; Bailes, Matthew; van Straten, Willem

    2012-10-01

    Timing of the dozen pulsars discovered by us in P303 is ensuring high quality results: (a) the peculiarities (in position or projected acceleration) of all the 5 millisecond pulsars in NGC6752 suggested the presence of non thermal dynamics in the core, perhaps due to black-holes of intermediate mass; (b) the eclipsing pulsar in NGC6397 is a stereotype for studying the late evolution of exotic binaries. We propose to continue our timing project focusing mostly on NGC6752 at 20cm (in order to measure additional parameters useful to constrain the existence of a black-hole) and NGC6397 at 10cm (for studying the orbital secular evolution, the eclipse region, and the mechanisms leading to the ejection of matter from the binary system).

  3. Timing of millisecond pulsars in globular clusters

    NASA Astrophysics Data System (ADS)

    D'Amico, Nichi; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Kramer, Michael; Sarkissian, John; Lyne, Andrew; Burgay, Marta; Corongiu, Alessandro; Camilo, Fernando; Bailes, Matthew; van Straten, Willem

    2012-04-01

    Timing of the dozen pulsars discovered by us in P303 is ensuring high quality results: (a) the peculiarities (in position or projected acceleration) of all the 5 millisecond pulsars in NGC6752 suggested the presence of non thermal dynamics in the core, perhaps due to black-holes of intermediate mass; (b) the eclipsing pulsar in NGC6397 is a stereotype for studying the late evolution of exotic binaries. We propose to continue our timing project focusing mostly on NGC6752 at 20cm (in order to measure additional parameters useful to constrain the existence of a black-hole) and NGC6397 at 10cm (for studying the orbital secular evolution, the eclipse region, and the mechanisms leading to the ejection of matter from the binary system).

  4. Polarisation properties of pulsars at optical wavelengths

    NASA Astrophysics Data System (ADS)

    Mignani, Roberto; Marelli, Martino; Shearer, Andrew; Slowikowska, Agnieszka

    2016-07-01

    Polarisation measurements of pulsars offer unique insights into their highly-magnetised relativistic environments and represent a primary test for neutron star magnetosphere models and radiation emission mechanisms. Besides the radio band, optical observations have been, so far, best suited to these goals, with polarisation measurements in the X-rays becoming possible in the near future thanks to missions, such as XIPE and IXPE. In this talk, we review the status of the optical polarisation measurements of pulsars and we foresee possible synergies between X-ray polarimetry observations of selected pulsars with, e.g XIPE and IXPE, and optical observations with the next generation of extremely large telescope, such as the E-ELT.

  5. An approximate model for pulsar navigation simulation

    NASA Astrophysics Data System (ADS)

    Jovanovic, Ilija; Enright, John

    2016-02-01

    This paper presents an approximate model for the simulation of pulsar aided navigation systems. High fidelity simulations of these systems are computationally intensive and impractical for simulating periods of a day or more. Simulation of yearlong missions is done by abstracting navigation errors as periodic Gaussian noise injections. This paper presents an intermediary approximate model to simulate position errors for periods of several weeks, useful for building more accurate Gaussian error models. This is done by abstracting photon detection and binning, replacing it with a simple deterministic process. The approximate model enables faster computation of error injection models, allowing the error model to be inexpensively updated throughout a simulation. Testing of the approximate model revealed an optimistic performance prediction for non-millisecond pulsars with more accurate predictions for pulsars in the millisecond spectrum. This performance gap was attributed to noise which is not present in the approximate model but can be predicted and added to improve accuracy.

  6. Pulsar timing and the Fermi mission

    NASA Astrophysics Data System (ADS)

    Kerr, Matthew; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Hobbs, George; Romani, Roger W.; Thompson, David J.; Weltevrede, Patrick; Shannon, Ryan; Petroff, Emily; Brook, Paul

    2014-04-01

    We request time to observe 180 pulsars on a regular basis in order to provide the accurate ephemerides necessary for the detection and characterisation of gamma-ray pulsars with the Fermi satellite. The main science goals are to increase the number of known gamma-ray pulsars (both radio loud and radio quiet), to determine accurate pulse profiles, and to characterise their high energy (phase-resolved) spectra. In the radio, the observations will also allow us to find glitches, characterise timing noise, investigate dispersion and rotation measure variability, and enhance our knowledge of single pulse phenomenology. To date, we are (co-)authors on 45 papers arising from the collaboration and P574 data. The data have contributed to the PhD theses of Lucas Guillemot and Damien Parent from the Bordeaux Fermi group and Kyle Watters from Stanford. Currently four students have active projects using the radio datasets.

  7. Young Pulsar Timing and the Fermi Mission

    NASA Astrophysics Data System (ADS)

    Kerr, Matthew; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Hobbs, George; Romani, Roger W.; Thompson, David J.; Weltevrede, Patrick; Shannon, Ryan; Petroff, Emily; Brook, Paul

    2014-10-01

    We request time to observe 230 pulsars on a regular basis in order to provide the accurate ephemerides necessary for the detection and characterisation of gamma-ray pulsars with the Fermi satellite. The main science goals are to increase the number of known gamma-ray pulsars (both radio loud and radio quiet), to determine accurate pulse profiles, and to characterise their high energy (phase-resolved) spectra. In the radio, the observations will also allow us to find glitches, characterise timing noise, investigate dispersion and rotation measure variability, and enhance our knowledge of single pulse phenomenology. To date, we are (co-)authors on 45 papers arising from the collaboration and P574 data. The data have contributed to the PhD theses of Lucas Guillemot and Damien Parent from the Bordeaux Fermi group and Kyle Watters from Stanford. Currently four students have active projects using the radio datasets.

  8. Gravitational Radiation from Compact Binary Pulsars

    NASA Astrophysics Data System (ADS)

    Antoniadis, John

    An outstanding question in modern Physics is whether general relativity (GR) is a complete description of gravity among bodies at macroscopic scales. Currently, the best experiments supporting this hypothesis are based on high-precision timing of radio pulsars. This chapter reviews recent advances in the field with a focus on compact binary millisecond pulsars with white-dwarf (WD) companions. These systems—if modeled properly—provide an unparalleled test ground for physically motivated alternatives to GR that deviate significantly in the strong-field regime. Recent improvements in observational techniques and advances in our understanding of WD interiors have allowed for a series of precise mass measurements is such systems. These masses, combined with high-precision radio timing of the pulsars, result to stringent constraints on the radiative properties of gravity, qualitatively very different from what was available in the past.

  9. Pulsars and Fast Transients with LOFAR

    NASA Astrophysics Data System (ADS)

    Stappers, Ben; Hessels, Jason; Alexov, Anastasia; Anderson, Kenneth; Coenen, Thijs; Hassall, Tom; Karastergiou, Aris; Kondratiev, Vlad; Kramer, Michael; van Leeuwen, Joeri; Mol, Jan David; Noutsos, A.; Romein, John; Weltevrede, Patrick; Fender, Robert; Wijers, Ralph

    2011-08-01

    The LOw Frequency ARray is the first of the next generation of radio telescopes to be completed. It uses large numbers of small receptors and vast computing and data transport capabilities to achieve a high degree of sensitivity over large fields of view. It uses two different types of receptor to enable it to observe over the frequency range 10-260 MHz. Here we report on some of the capabilities of this telescope for pulsar and fast transient research. We also present some results of the commissioning work that we have been carrying out which highlight the exciting potential of this telescope. These include simultaneous imaging and pulsar observations, simultaneous observations spanning 30-8000 MHz, a large number of known pulsars detected in the high band and the detection of PSR B0809+74 down to a frequency of 16 MHz.

  10. Electromagnetic processes in the atmosphere of pulsars

    NASA Technical Reports Server (NTRS)

    Yukhimuk, A. K.

    1974-01-01

    The work consists of two parts. The first deals with the fine structure of radio pulses. Based on kinetic theory, processes occurring in the plasma shell of a pulsar when external electromagnetic radiation is present are investigated. It is shown that electromagnetic waves cause electrons to drift relative to ions, and initiate longitudinal oscillations. A dispersion equation describing the longitudinal oscillations in magnetized plasma is derived. Conditions for excitation of oscillations are found. Correlation functions of electron density are calculated, along with the coefficients of electromagnetic wave scattering. It is shown that variations in the amplitude of pulsar pulses are associated with scintillations caused by fluctuations in the plasma electron density. The second part of the study presents a mechanism for the radio emission of pulsars. The model of a rotating and a pulsating star, a neutron star with dipolar or more complex magnetic field, is examined.

  11. Gamma-ray pulsars: A gold mine

    NASA Astrophysics Data System (ADS)

    Grenier, Isabelle A.; Harding, Alice K.

    2015-08-01

    The most energetic neutron stars, powered by their rotation, are capable of producing pulsed radiation from the radio up to γ rays with nearly TeV energies. These pulsars are part of the universe of energetic and powerful particle accelerators, using their uniquely fast rotation and formidable magnetic fields to accelerate particles to ultra-relativistic speed. The extreme properties of these stars provide an excellent testing ground, beyond Earth experience, for nuclear, gravitational, and quantum-electrodynamical physics. A wealth of γ-ray pulsars has recently been discovered with the Fermi Gamma-Ray Space Telescope. The energetic γ rays enable us to probe the magnetospheres of neutron stars and particle acceleration in this exotic environment. We review the latest developments in this field, beginning with a brief overview of the properties and mysteries of rotation-powered pulsars, and then discussing γ-ray observations and magnetospheric models in more detail. xml:lang="fr"

  12. ACCELERATING HIGH-ENERGY PULSAR RADIATION CODES

    SciTech Connect

    Venter, C.; De Jager, O. C.

    2010-12-20

    Curvature radiation (CR) is believed to be a dominant mechanism for creating gamma-ray emission from pulsars and is emitted by relativistic particles that are constrained to move along curved magnetic field lines. Additionally, synchrotron radiation (SR) is expected to be radiated by both relativistic primaries (involving cyclotron resonant absorption of radio photons and re-emission of SR photons), or secondary electron-positron pairs (created by magnetic or photon-photon pair production processes involving CR gamma rays in the pulsar magnetosphere). When calculating these high-energy spectra, especially in the context of pulsar population studies where several millions of CR and SR spectra have to be generated, it is profitable to consider approximations that would save computational time without sacrificing too much accuracy. This paper focuses on one such approximation technique, and we show that one may gain significantly in computational speed while preserving the accuracy of the spectral results.

  13. EVIDENCE OF AN ASTEROID ENCOUNTERING A PULSAR

    SciTech Connect

    Brook, P. R.; Karastergiou, A.; Buchner, S.; Roberts, S. J.; Keith, M. J.; Johnston, S.; Shannon, R. M.

    2014-01-10

    Debris disks and asteroid belts are expected to form around young pulsars due to fallback material from their original supernova explosions. Disk material may migrate inward and interact with a pulsar's magnetosphere, causing changes in torque and emission. Long-term monitoring of PSR J0738–4042 reveals both effects. The pulse shape changes multiple times between 1988 and 2012. The torque, inferred via the derivative of the rotational period, changes abruptly from 2005 September. This change is accompanied by an emergent radio component that drifts with respect to the rest of the pulse. No known intrinsic pulsar processes can explain these timing and radio emission signatures. The data lead us to postulate that we are witnessing an encounter with an asteroid or in-falling debris from a disk.

  14. X-rays from the eclipsing pulsar 1957+20

    NASA Technical Reports Server (NTRS)

    Fruchter, A. S.; Bookbinder, J.; Garcia, M. R.; Bailyn, C. D.

    1992-01-01

    The detection of soft X-rays of about 1 keV energy from the eclipsing pulsar PSR1957+20 is reported. This high-energy radiation should be a valuable diagnostic of the wind in this recycled pulsar system. Possible sources of the X-ray emission are the interstellar nebula driven by the pulsar wind, the interaction between the pulsar and its evaporating companion, and the pulsar itself. The small apparent size of the X-ray object argues against the first of these possibilities and suggests that the X-rays are produced within the binary.

  15. The space velocities of radio pulsars

    NASA Astrophysics Data System (ADS)

    Loginov, A. A.; Nikitina, E. B.; Malov, I. F.

    2016-02-01

    Known models proposed to explain the high space velocities of pulsars based on asymmetry of the transport coefficients of different sorts of neutrinos or electromagnetic radiation can be efficient only in the presence of high magnetic fields (to 1016 G) or short rotation periods for the neutron stars (of the order of 1 ms). This current study shows that the observed velocities are not correlated with either the pulsar periods or their surface magnetic fields. The initial rotation periods are estimated in a model for the magnetedipolar deceleration of their spin, aßsuming that the pulsar ages are equal to their kinematic ages. The initial period distribution is bimodal, with peaks at 5 ms and 0.5 s, and similar to the current distribution of periods. It is shown that asymmetry of the pulsar electromagnetic radiation is insufficient to give rise to additional acceleration of pulsars during their evolution after the supernova explosion that gave birth to them. The observations testify to deceleration of the motion, most likely due to the influence of the interstellar medium and interactions with nearby objects. The time scale for the exponential decrease in the magnetic field τ D and in the angle between the rotation axis and magnetic moment τ ß are estimated, yielding τ β = 1.4 million years. The derived dependence of the transverse velocity of a pulsar on the angle between the line of sight and the rotation axis of the neutron star corresponds to the expected dependence for acceleration mechanisms associated with asymmetry of the radiation emitted by the two poles of the star.

  16. A survey for Hα pulsar bow shocks

    SciTech Connect

    Brownsberger, Sasha; Romani, Roger W. E-mail: sashab@stanford.edu

    2014-04-01

    We report on a survey for Hα bow shock emission around nearby γ-detected energetic pulsars. This survey adds three Balmer-dominated neutron star bow shocks to the six previously confirmed examples. In addition to the shock around Fermi pulsar PSR J1741–2054, we now report Hα structures around two additional γ-ray pulsars, PSR J2030+4415 and PSR J1509–5850. These are the first known examples of Hα nebulae with pre-ionization halos. With new measurements, we show that a simple analytic model can account for the angular size and flux of the bow shocks' apices. The latter, in particular, provides a new pulsar probe and indicates large moments of inertia and smaller distances than previously assumed in several cases. In particular, we show that the re-measured PSR J0437–4715 shock flux implies I = (1.7 ± 0.2) × 10{sup 45}/(f {sub HI}sin i) g cm{sup 2}. We also derive a distance d ≈ 0.72 kpc for the γ-ray only pulsar PSR J2030+4415 and revised distances for PSRs J1959+2048 (1.4 kpc) and J2555+6535 (∼1 kpc), smaller than the conventional DM-estimated values. Finally, we report upper limits for 94 additional LAT pulsars. An estimate of the survey sensitivity indicates that for a warm neutral medium filling factor φ{sub WNM} ∼ 0.3 there should be a total of approximately nine Hα bow shocks in our LAT-targeted survey; given that seven such objects are now known, a much larger φ{sub WNM} seems problematic.

  17. A Search for Pulsar Companions to OB Runaway Stars

    NASA Astrophysics Data System (ADS)

    Sayer, R. W.; Nice, D. J.; Kaspi, V. M.

    1996-04-01

    We have searched for radio pulsar companions to 40 nearby OB runaway stars. Observations were made at 575 and 770 MHz with the NRAO 140 foot (43 m) telescope. The survey was sensitive to long- period pulsars with flux densities of 1 mJy or more. No pulsar companions to OB runaways were discovered. One previously unknown pulsar was discovered, PSR J2044 +4614, while observing toward target 0 star BD +45°3260. Follow-up timing observations of the pulsar measured its position to high precision, revealing a 9' separation between the pulsar and the target star, unequivocally indicating they are not associated. The pulsar is ordinary, except that its dispersion measure, 315 pc cm-3, is unusually high given its Galactic longitude, l = 85°. The nondetection of pulsars bound to target stars places an upper limit of 8% (95% confidence) for the fraction of runaway OB stars with pulsar companions detectable via pulsed radio emission by surveys such as ours. Assuming standard models for the pulsar beaming fraction and luminosity function, we conclude most OB runaways do not have pulsar companions.

  18. Is the sub-millisecond pulsar strange?

    NASA Technical Reports Server (NTRS)

    Frieman, Joshua A.; Olinto, Angela V.

    1989-01-01

    The possibility that the submillisecond pulsar from supernova 1987A is composed of strange matter is theoretically discussed. It is shown that for a range of hadron parameters, the maximum rotation rate of secularly stable strange stars may exceed that of the half-millisecond pulsar and the nonrotating maximum mass is greater than 1.52 solar mass. The low-mass companion(s) to SN1987A, inferred from the periodic modulations of the optical signal, can be accounted for by stable strange-matter lump(s) ejected from the young strange star.

  19. Recycling Pulsars: spins, masses and ages

    NASA Astrophysics Data System (ADS)

    Tauris, T. M.; Kramer, M.; Langer, N.

    2013-03-01

    Although the first millisecond pulsars (MSPs) were discovered 30 years ago we still do not understand all details of their formation process. Here, we present new results from Tauris, Langer & Kramer (2012) on the recycling scenario leading to radio MSPs with helium or carbon-oxygen white dwarf companions via evolution of low- and intermediate mass X-ray binaries (LMXBs, IMXBs). We discuss the location of the spin-up line in the PṖ-diagram and estimate the amount of accreted mass needed to obtain a given spin period and compare with observations. Finally, we constrain the true ages of observed recycled pulsars via calculated isochrones in the PṖ-diagram.

  20. Pulsar Wind Nebulae as Cosmic Pevatrons: A Current Sheet's Tale

    NASA Astrophysics Data System (ADS)

    Arons, Jonathan

    2012-11-01

    I outline, from a theoretical and somewhat personal perspective, significant features of Pulsar Wind Nebulae (PWNe) as Cosmic Accelerators. I pay special attention to the recently discovered gamma ray "flares" in the Crab Nebula's emission, focusing on the possibility, raised by the observations, that the accelerating electric field exceeds the magnetic field, suggesting that reconnection in the persistent current layer (a "current sheet") plays a significant role in the behavior of this well studied Pevatron. I address the present status of the termination shock model for the particle accelerator that converts the wind flow energy to the observed non-thermal particle spectra, concluding that it has a number of major difficulties related to the transverse magnetic geometry of the shock wave. I discuss recent work on the inferred pair outflow rates, which are in excess of those predicted by existing theories of pair creation, and use those results to point out that the consequent mass loading of the wind reduces the wind's bulk flow 4-velocity to the point that dissipation of the magnetic field in a pulsar's wind upstream of the termination shock is restored to life as a viable model for the solution of the " σ" problem. I discuss some suggestions that current starvation in the current flow supporting the structured ("striped") upstream magnetic field perhaps induces a transition to superluminal wave propagation. I show that current starvation probably does not occur, because those currents are carried in the current sheet separating the stripes rather than in the stripes themselves.

  1. Equilibrium in the oblique rotating outer pulsar magnetosphere

    NASA Astrophysics Data System (ADS)

    Endean, Geoffrey

    1995-06-01

    A simple solution to the problem of plasma equilibrium outside the velocity-of-light cylinder of the oblique rotating pulsar magnetosphere is presented. The magnetic field has a swept-back, open spiral structure with zero axial component. The corotational motion of the plasma just inside the velocity-of-light cylinder transits to radial motion at large radius while maintaining highly relativistic speed throughout. There are no streaming currents along the magnetic field lines, but, in addition to a net charge density and associated convection current density, there is a non-force-free axial current density which is arbitraily large at the velocity-of-light cylinder but gives a finite current when integrated over radius. This axial current density is directly responsible for pulses of coherent radiation. The solution presented applies independently of the inclination angle and nondipolar content of the source magnetic field of the pulsar and includes both the axisymmetric field and the fully oblique or orthogonal field as special cases. It is a plasma equilibrium solution, with any similarities to vacuum fields, particularly outside the velocity-of-light cylinder, being purely coincidental.

  2. Pulsars "Lying About Their Ages," Astronomers Say, Throwing Theories Into Doubt

    NASA Astrophysics Data System (ADS)

    2000-07-01

    stars and how they work. For example, Helfand pointed out that there are cases in which astronomers concluded that a pulsar and supernova remnant, while nearby, are not related because the pulsar's "characteristic age" was much younger than the age calculated for the supernova remnant. "We now ought to re-examine those cases," Helfand said. While the older age for B1757-24 poses problems for some astrophysical theories, the pulsar's slower speed actually helps current theory in one area, according to Helfand. Neutron stars are thought to get a "kick" because the supernova explosion that creates them is not symmetrical. "The high velocity for this object was difficult to explain through that theory," Helfand said. "The lower speed is easier to explain." If the "characteristic ages" are not, in fact, the true ages of the neutron stars, the implications extend beyond astronomy to particle physics. "Neutron stars, as the densest objects in the Universe, provide a unique laboratory for physics. Physicists look at neutron stars as a way of showing how matter acts under these extreme conditions. Part of what they need to know in order to draw proper conclusions is the age of the neutron star. If that changes, so do many of their theories," said Gaensler, whose work is supported by a Hubble Fellowship awarded by the Space Telescope Science Institute. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

  3. Constraining Gamma-Ray Pulsar Gap Models with a Simulated Pulsar Population

    NASA Technical Reports Server (NTRS)

    Pierbattista, Marco; Grenier, I. A.; Harding, A. K.; Gonthier, P. L.

    2012-01-01

    With the large sample of young gamma-ray pulsars discovered by the Fermi Large Area Telescope (LAT), population synthesis has become a powerful tool for comparing their collective properties with model predictions. We synthesised a pulsar population based on a radio emission model and four gamma-ray gap models (Polar Cap, Slot Gap, Outer Gap, and One Pole Caustic). Applying gamma-ray and radio visibility criteria, we normalise the simulation to the number of detected radio pulsars by a select group of ten radio surveys. The luminosity and the wide beams from the outer gaps can easily account for the number of Fermi detections in 2 years of observations. The wide slot-gap beam requires an increase by a factor of 10 of the predicted luminosity to produce a reasonable number of gamma-ray pulsars. Such large increases in the luminosity may be accommodated by implementing offset polar caps. The narrow polar-cap beams contribute at most only a handful of LAT pulsars. Using standard distributions in birth location and pulsar spin-down power (E), we skew the initial magnetic field and period distributions in a an attempt to account for the high E Fermi pulsars. While we compromise the agreement between simulated and detected distributions of radio pulsars, the simulations fail to reproduce the LAT findings: all models under-predict the number of LAT pulsars with high E , and they cannot explain the high probability of detecting both the radio and gamma-ray beams at high E. The beaming factor remains close to 1.0 over 4 decades in E evolution for the slot gap whereas it significantly decreases with increasing age for the outer gaps. The evolution of the enhanced slot-gap luminosity with E is compatible with the large dispersion of gamma-ray luminosity seen in the LAT data. The stronger evolution predicted for the outer gap, which is linked to the polar cap heating by the return current, is apparently not supported by the LAT data. The LAT sample of gamma-ray pulsars

  4. PULSAR BINARY BIRTHRATES WITH SPIN-OPENING ANGLE CORRELATIONS

    SciTech Connect

    O'Shaughnessy, Richard; Kim, Chunglee E-mail: ckim@astro.lu.s

    2010-05-20

    One ingredient in an empirical birthrate estimate for pulsar binaries is the fraction of sky subtended by the pulsar beam: the pulsar beaming fraction. This fraction depends on both the pulsar's opening angle and the misalignment angle between its spin and magnetic axes. The current estimates for pulsar binary birthrates are based on an average value of beaming fractions for only two pulsars, i.e., PSRs B1913+16 and B1534+12. In this paper, we revisit the observed pulsar binaries to examine the sensitivity of birthrate predictions to different assumptions regarding opening angle and alignment. Based on empirical estimates for the relative likelihood of different beam half-opening angles and misalignment angles between the pulsar rotation and magnetic axes, we calculate an effective beaming correction factor, f{sub b,eff}, whose reciprocal is equivalent to the average fraction of all randomly selected pulsars that point toward us. For those pulsars without any direct beam geometry constraints, we find that f{sub b,eff} is likely to be smaller than 6, a canonically adopted value when calculating birthrates of Galactic pulsar binaries. We calculate f{sub b,eff} for PSRs J0737-3039A and J1141-6545, applying the currently available constraints for their beam geometry. As in previous estimates of the posterior probability density function P(R) for pulsar binary birthrates R, PSRs J0737-3039A and J1141-6545 still significantly contribute to, if not dominate, the Galactic birthrate of tight pulsar-neutron star (NS) and pulsar-white dwarf (WD) binaries, respectively. Our median posterior present-day birthrate predictions for tight PSR-NS binaries, wide PSR-NS binaries, and tight PSR-WD binaries given a preferred pulsar population model and beaming geometry are 89 Myr{sup -1}, 0.5 Myr{sup -1}, and 34 Myr{sup -1}, respectively. For long-lived PSR-NS binaries, these estimates include a weak (x1.6) correction for slowly decaying star formation in the galactic disk. For pulsars

  5. Chandra Examines a Quadrillion-Volt Pulsar

    NASA Astrophysics Data System (ADS)

    2001-09-01

    The high-voltage environment of one of the most energetic and strongly magnetized pulsars known has been surveyed by NASA's Chandra X-ray Observatory. A team of astronomers found a powerful jet of high-energy particles extending over a distance of 20 light years and bright arcs believed to be due to particles of matter and anti-matter generated by the pulsar. The team of US, Canadian, and Japanese scientists pointed Chandra at the rapidly spinning neutron star B1509-58, located 19,000 light years away in the constellation of Circinus, for over five hours. These results were announced at the "Two Years of Science with Chandra" symposium in Washington, DC. "Jets and arcs on this vast scale have never been seen in any other pulsar," said Bryan Gaensler of the Smithsonian Astrophysical Observatory. "The spectacular images we have obtained of this source are letting us test theories as to how pulsars unleash so much energy." The features seen with Chandra give the scientists insight into the process by which voltages of more than 7000 trillion volts are created around rotating neutron stars (the dense remnants of supernova explosions) and how these extreme voltages affect their environment. B1509-58 is of particular interest because it has a much stronger magnetic field than the Crab Nebula pulsar, which exhibits similar features on a much smaller scale. The general picture emerging from these results is that high-energy particles of matter and antimatter are streaming away from the neutron star along its poles and near its equator. The particles leaving the poles produce the jets; astronomers speculate that only one side of the jet is apparent in B1509-58, indicating that this one side is beamed in our direction, while the other is rushing away. "Until this observation, no one knew for sure whether such tremendous voltages and energy outputs were a trademark of all pulsars, or if the Crab was an oddball," said Vicky Kaspi of McGill University in Montreal. "Now thanks

  6. Do asteroids evaporate near pulsars? Induction heating by pulsar waves revisited

    NASA Astrophysics Data System (ADS)

    Kotera, Kumiko; Mottez, Fabrice; Voisin, Guillaume; Heyvaerts, Jean

    2016-07-01

    Aims: We investigate the evaporation of close-by pulsar companions, such as planets, asteroids, and white dwarfs, by induction heating. Methods: Assuming that the outflow energy is dominated by a Poynting flux (or pulsar wave) at the location of the companions, we calculate their evaporation timescales, by applying the Mie theory. Results: Depending on the size of the companion compared to the incident electromagnetic wavelength, the heating regime varies and can lead to a total evaporation of the companion. In particular, we find that inductive heating is mostly inefficient for small pulsar companions, although it is generally considered the dominant process. Conclusions: Small objects like asteroids can survive induction heating for 104 yr at distances as small as 1 R⊙ from the neutron star. For degenerate companions, induction heating cannot lead to evaporation and another source of heating (likely by kinetic energy of the pulsar wind) has to be considered. It was recently proposed that bodies orbiting pulsars are the cause of fast radio bursts; the present results explain how those bodies can survive in the pulsar's highly energetic environment.

  7. Flux Density Variations in the Parkes Pulsar Timing Array Millisecond Pulsars

    NASA Astrophysics Data System (ADS)

    Spiewak, Renée; Shannon, Ryan; Hobbs, George; Kerr, Matthew

    2015-01-01

    Precise timing of an ensemble of pulsars spread across the sky (a pulsar timing array, PTA) can be used to search for gravitational waves. The Parkes Pulsar Timing Array project (PPTA) currently observes 23 pulsars with the Parkes Radio Telescope, largely in the southern sky, with the primary goal of searching for gravitational waves. The pulsars in the sample show large variations in flux density due to refractive scintillation in the interstellar medium (ISM). These flux variations cause timing uncertainty to vary by more than an order of magnitude. A better understanding of flux-density variations associated with the interstellar medium (ISM) is crucial for optimizing observing strategy and increase the sensitivity of the PPTA to gravitational waves. Flux-density variations can also potentially be caused by magnetospheric state changes. We use flux density time series and structure functions to examine both the properties of the ISM and search for intrinsic flux variation in these pulsars. We present intriguing features of the datasets and general implications of the results.

  8. Pulsar J1823-3021A

    NASA Video Gallery

    This video shows the on and off state of gamma rays from pulsar J1823-3021A as seen by Fermi's Large Area Telescope (LAT). The object pulses 183.8 times a second and has a spin period of 5.44 milli...

  9. Shedding Light on the Pulsar Wind

    NASA Astrophysics Data System (ADS)

    Khangulyan, Dmitry; Aharonian, Felix; Bogovalov, Sergey V.

    2012-07-01

    Pulsars are believed to eject ultrarelativistic electron-positron winds that propagate to the large distances leading to the formation of the extended non-thermal sources known as plerions. The wind has been proposed to originate close to the light cylinder, and carry the rotational energy losses of the pulsar. At the beginning the wind is dominated by electromagnetic energy (Poynting flux), but at some later stage the wind is accelerated with most of the Poynting flux being converted to the kinetic energy of bulk motion. Such winds have not been yet observed, therefore the proposed scenario has been deemed inconclusive. The `cold' winds (in the sense of the low energy of the electrons in the frame of moving plasma) represent a form of "dark substance" since, despite the very high energy of the wind particles, the wind emission is extremely weak. In fact, the pulsar winds are visible only in inverse Compton gamma-rays. Recent observations in high energy (HE) and very high energy (VHE) domains with Fermi Large Area Telescope (Fermi/LAT) and ground based Cherenkov detectors Magic and Veritas allow the key properties of the pulsar winds to be measured in a few important systems.

  10. Observations of the Eclipsing Millisecond Pulsar

    NASA Astrophysics Data System (ADS)

    Bookbinder, Jay

    1990-12-01

    FRUCHTER et al. (1988a) HAVE RECENTLY DISCOVERED a 1.6 MSEC PULSAR (PSR 1957+20) IN A 9.2 HOUR ECLIPSING BINARY SYSTEM. THE UNUSUAL BEHAVIOR OF THE DISPERSION MEASURE AS A FUNCTION OF ORBITAL PHASE, AND THE DISAPPEARANCE OF THE PULSAR SIGNAL FOR 50 MINUTES DURING EACH ORBIT, IMPLIES THAT THE ECLIPSES ARE DUE TO A PULSAR-INDUCED WIND FLOWING OFF OF THE COMPANION. THE OPTICAL COUNTERPART IS A 21ST MAGNITUDE OBJECT WHICH VARIES IN INTENSITY OVER THE BINARY PERIOD; ACCURATE GROUND-BASED OBSERVATIONS ARE PREVENTED BY THE PROXIMITY (0.7") OF A 20TH MAGNITUDE K DWARF. WE PROPOSE TO OBSERVE THE OPTICAL COUNTERPART IN A TWO-PART STUDY. FIRST, THE WF/PC WILL PROVIDE ACCURATE MULTICOLOR PHOTOMETRY, ENABLING US TO DETERMINE UNCONTAMINATED MAGNITUDES AND COLORS BOTH AT MAXIMUM (ANTI-ECLIPSE) AS WELL AS AT MINIMUM (ECLIPSE). SECOND, WE PROPOSE TO OBSERVE THE EXPECTED UV LINE EMISSION WITH FOS, ALLOWING FOR AN INTIAL DETERMINATION OF THE TEMPERATURE AND DENSITY STRUCTURE AND ABUNDANCES OF THE WIND THAT IS BEING ABLATED FROM THE COMPANION. STUDY OF THIS UNIQUE SYSTEM HOLDS ENORMOUS POTENTIAL FOR THE UNDERSTANDING OF THE RADIATION FIELD OF A MILLISECOND PULSAR AND THE EVOLUTION OF LMXRBs AND MSPs IN GENERAL. WE EXPECT THESE OBSERVATIONS TO PLACE VERY SIGNIFICANT CONTRAINTS ON MODELS OF THIS UNIQUE OBJECT.

  11. Pulsar Radiation Models - Radio to High Energies

    NASA Astrophysics Data System (ADS)

    Venter, Christo; Harding, Alice

    Rotation-powered pulsars emit over nearly 19 decades of energy. Although an all-encompassing answer as to the origin of this broad-band emission remains elusive nearly 50 years after their discovery, the theorist does have a few tools in his / her toolkit to aid investigation. Phase-averaged spectra give clues as to the emitting particles, their acceleration, environment, and the radiation mechanism. Moreover, the phase-evolution of spectra constrains the radiation energetics and environment as different parts of the magnetosphere are exposed to the observer during the pulsar's rotation. A detailed model furthermore critically depends on the specification of the emission geometry. Modeling the light curves probes this fundamental geometric assumption, which is closely tied to the posited magnetospheric structure. Studying many versions of the same system helps to constrain critical population-averaged quantities, discover population trends, and probe model performance for different regions of phase space. When coupled with population synthesis, such modeling can provide powerful discrimination between competing emission models. Polarization properties may provide complementary constraints on the magnetic field orientation and pulsar geometry. Lastly, comparison of parameters inferred from independent models for the different wavebands yields necessary crosschecks. It is indeed fortunate that the past few years have witnessed an incredible increase in number and improved characterization of rotation-powered pulsars. We will review how the enhanced quality and quantity of data are providing impetus for further model refinement.

  12. Modeling Pulsar Trajectories to Determine Birth Locations

    NASA Astrophysics Data System (ADS)

    Shapiro-Albert, Brent; Chatterjee, Shami; Cordes, James M.; Hallenbeck, Gregory L.; Vlemmings, Wouter

    2016-01-01

    Neutron stars are the remnants of massive stars after their deaths in supernova explosions. They typically have higher velocities than their progenitor stellar population due to either kicks from supernova asymmetries or from remnant velocities of compact binaries after they are disrupted by explosions. Velocities are large enough that pulsars will typically move large distances from their birth sites. By determining the present day location and velocity, we project back to twice the pulsars characteristic age to constrain the location of the progenitor star (within the uncertainty of the unknown line-of-sight velocity component). We use precision measurements of the proper motion and parallax determined with the Very Long Baseline Array as input to trajectory modeling that includes deceleration in the Galactic potential. Using a python implementation utilizing astropy and galpy, we verify the results of Vlemmings et al. (2004, ApJ, 610, 402) on two pulsars, B2020+28 and B2012+51, which found that the two objects very likely originated in the same star cluster and whose progenitor stars could have been in the same binary system. We have applied the trace back algorithm to other pulsars using the most recent astrometric measurements to identify their birth locations. Results on these objects will be reported.

  13. Pulsars at the Center of the Galaxy

    NASA Astrophysics Data System (ADS)

    Majid, Walid A.; Prince, Thomas A.

    2016-06-01

    Over the past few years, a number of groups using data from NASA’s space-borne Fermi LAT instrument have identified excess gamma-ray flux toward the inner degree of the Galactic Center (GC), with an even larger significant excess within 0.2 degrees. At present there are two leading candidates for this excess: dark matter annihilation and a population of unresolved millisecond pulsars (MSPs). We are currently developing dedicated instrumentation to carry out a sensitive search for the pulsars in this region of the galaxy using a newly developed front end and receiver on a Deep Space Network large diameter antenna in Australia. In this presentation, we will provide an overview of the challenges encountered with pulsar searches at the GC region and a summary of previous and ongoing efforts to survey this region with radio telescopes. We will also provide preliminary results from our recent observations of the GC region at 2 and 8 GHz and will conclude with prospects for detection of perhaps hundreds of pulsars in this region with new generations of radio telescopes now under construction.

  14. Pulsars at the Center of the Galaxy

    NASA Astrophysics Data System (ADS)

    Majid, Walid A.

    2016-04-01

    Over the past few years, a number of groups using data from NASA’s space-borne Fermi LAT instrument have identified excess gamma-ray flux toward the inner few degrees of the Galactic Center (GC), with an even larger significant excess within 1 degree of this region. At present there are two leading candidates for this excess: dark matter annihilation and a population of unresolved millisecond pulsars (MSPs). We are currently developing dedicated instrumentation to carry out a sensitive search for the pulsars in this region of the galaxy using a newly developed front end and receiver on a Deep Space Network large diameter antenna in Australia. In this presentation, we will provide an overview of the challenges encountered with pulsar searches at the GC region and a summary of previous and ongoing efforts to survey this region with radio telescopes. We will also provide preliminary results from our recent observations of the GC region at 2 and 8 GHz and will conclude with prospects for detection of perhaps hundreds of pulsars in this region with new generations of radio telescopes now under construction.

  15. Pulsars at the Center of the Galaxy

    NASA Astrophysics Data System (ADS)

    Majid, Walid

    2016-07-01

    Over the past few years, a number of groups using data from NASA's space-borne Fermi LAT instrument have identified excess gamma-ray flux toward the inner 1º of the Galactic Center (GC), with an even larger significant excess within 0.2º degrees. At present there are two leading candidates for this excess: dark matter annihilation and a population of unresolved millisecond pulsars (MSPs). We are currently developing dedicated instrumentation to carry out a sensitive search for the pulsars in this region of the galaxy using a newly developed front end and receiver on a Deep Space Network large diameter antenna in Australia. In this presentation, we will provide an overview of the challenges encountered with pulsar searches at the GC region and a summary of previous and ongoing efforts to survey this region with radio telescopes. We will also provide preliminary results from our recent observations of the GC region at 2 and 8 GHz and will conclude with prospects for detection of perhaps hundreds of pulsars in this region with new generations of radio telescopes now under construction.

  16. DETECTING MASSIVE GRAVITONS USING PULSAR TIMING ARRAYS

    SciTech Connect

    Lee, Kejia; Kramer, Michael; Jenet, Fredrick A.; Price, Richard H.; Wex, Norbert

    2010-10-20

    At the limit of weak static fields, general relativity becomes Newtonian gravity with a potential field that falls off as inverse distance rather than a theory of Yukawa-type fields with a finite range. General relativity also predicts that the speed of disturbances of its waves is c, the vacuum light speed, and is non-dispersive. For these reasons, the graviton, the boson for general relativity, can be considered to be massless. Massive gravitons, however, are features of some alternatives to general relativity. This has motivated experiments and observations that, so far, have been consistent with the zero-mass graviton of general relativity, but further tests will be valuable. A basis for new tests may be the high sensitivity gravitational wave (GW) experiments that are now being performed and the higher sensitivity experiments that are being planned. In these experiments, it should be feasible to detect low levels of dispersion due to non-zero graviton mass. One of the most promising techniques for such a detection may be the pulsar timing program that is sensitive to nano-Hertz GWs. Here, we present some details of such a detection scheme. The pulsar timing response to a GW background with the massive graviton is calculated, and the algorithm to detect the massive graviton is presented. We conclude that, with 90% probability, massless gravitons can be distinguished from gravitons heavier than 3 x 10{sup -22} eV (Compton wavelength {lambda}{sub g} = 4.1 x 10{sup 12} km), if bi-weekly observation of 60 pulsars is performed for 5 years with a pulsar rms timing accuracy of 100 ns. If 60 pulsars are observed for 10 years with the same accuracy, the detectable graviton mass is reduced to 5 x 10{sup -23} eV ({lambda}{sub g} = 2.5 x 10{sup 13} km); for 5 year observations of 100 or 300 pulsars, the sensitivity is respectively 2.5 x 10{sup -22} ({lambda}{sub g} = 5.0 x 10{sup 12} km) and 10{sup -22} eV ({lambda}{sub g} = 1.2 x 10{sup 13} km). Finally, a 10 year

  17. High-Energy Emission From Millisecond Pulsars

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.; Usov, Vladimir V.; Muslimov, Alex G.

    2004-01-01

    The X-ray and gamma-ray spectrum of rotation-powered millisecond pulsars is investigated in a model for acceleration and pair cascades on open field lines above the polar caps. Although these pulsars have low surface magnetic fields, their short periods allow them to have large magnetospheric potential drops, but the majority do not produce sufficient pairs to completely screen the accelerating electric field. In these sources, the primary and secondary electrons continue to accelerate to high altitude and their Lorentz factors are limited by curvature and synchrotron radiation reaction. The accelerating particles maintain high Lorentz factors and undergo cyclotron resonant absorption of radio emission, that produces and maintains a large pitch angle, resulting in a strong synchrotron component. The resulting spectra consist of several distinct components: curvature radiation from primary electrons dominating from 1 - 100 GeV, synchrotron radiation from primary and secondary electrons dominating up to about 100 MeV, and much weaker inverse-Compton radiation from primary electrons a t 0.1 - 1 TeV. We find that the relative size of these components depends on pulsar period, period derivative, and neutron star mass and radius with the level of the synchrotron component also depending sensitively on the radio emission properties. This model is successful in describing the observed X-ray and gamma-ray spectrum of PSR J0218+4232 as synchrotron radiation, peaking around 100 MeV and extending up to a turnover around several GeV. The predicted curvature radiation components from a number of millisecond pulsars, as well as the collective emission from the millisecond pulsars in globular clusters, should be detectable with AGILE and GLAST. We also discuss a hidden population of X-ray-quiet and radio-quiet millisecond pulsars which have evolved below the pair death line, some of which may be detectable by telescopes sensitive above 1 GeV. Subject headings: pulsars: general

  18. Multi-wavelength analysis of young pulsars: an overview.

    NASA Astrophysics Data System (ADS)

    Maritz, J. M.; Meintjes, P. J.; Buchner, S. J.

    Young pulsars emit a broad spectrum of radiation that range from radio to gamma ray energies. These pulsars are considered as rotation powered pulsars that spin rapidly and are strongly magnetized. Following the discovery of pulsars nearly four decades ago, the population of known pulsars already reached a number of roughly two thousand. This known population of pulsars includes both millisecond and normal pulsars that were discovered by several telescopes. We analyze both HartRAO radio data and Fermi gamma ray data of the Vela pulsar. We also explore a proposed method of probing the electron column density of the instellar gas through analyzing the gamma ray diffuse data associated with the Fermi two-year observation. This paper serves as an overview of gamma ray and radio timing analysis of bright young pulsars with respect to the use of open source timing analysis tools (Tempo2, Psrchive, Enrico and the Fermi tools). We reason that the multi-wavelength picture of pulsars can help clarify questions regarding the origin of pulsed radiation emission mechanisms in several energy bands, but that radio observations will prove adequate for timing noise analysis, given the accurate and long radio data sets. The process of identifying gravitational waves in timing data, rests on gaining a deeper insight into the timing noise phenomena.

  19. A glitch in the millisecond pulsar J0613-0200

    NASA Astrophysics Data System (ADS)

    McKee, J. W.; Janssen, G. H.; Stappers, B. W.; Lyne, A. G.; Caballero, R. N.; Lentati, L.; Desvignes, G.; Jessner, A.; Jordan, C. A.; Karuppusamy, R.; Kramer, M.; Cognard, I.; Champion, D. J.; Graikou, E.; Lazarus, P.; Osłowski, S.; Perrodin, D.; Shaifullah, G.; Tiburzi, C.; Verbiest, J. P. W.

    2016-09-01

    We present evidence for a small glitch in the spin evolution of the millisecond pulsar J0613-0200, using the EPTA Data Release 1.0, combined with Jodrell Bank analogue filterbank times of arrival (TOAs) recorded with the Lovell telescope and Effelsberg Pulsar Observing System TOAs. A spin frequency step of 0.82(3) nHz and frequency derivative step of -1.6(39) × 10-19 Hz s-1 are measured at the epoch of MJD 50888(30). After PSR B1821-24A, this is only the second glitch ever observed in a millisecond pulsar, with a fractional size in frequency of Δν/ν = 2.5(1) × 10-12, which is several times smaller than the previous smallest glitch. PSR J0613-0200 is used in gravitational wave searches with pulsar timing arrays, and is to date only the second such pulsar to have experienced a glitch in a combined 886 pulsar-years of observations. We find that accurately modelling the glitch does not impact the timing precision for pulsar timing array applications. We estimate that for the current set of millisecond pulsars included in the International Pulsar Timing Array, there is a probability of ˜50 per cent that another glitch will be observed in a timing array pulsar within 10 years.

  20. Developing gamma-ray pulsar simulation tools for GLAST

    SciTech Connect

    Razzano, Massimiliano

    2007-07-12

    Pulsars are among the most intriguing sources in the gamma-ray Universe and their high-energy emission remains today quite mysterious. The Gamma-ray Large Area Space Telescope (GLAST) will study the pulsar gamma-ray emission in great detail and will discover a great number of new gamma-ray pulsars. Here are presented the latest developments of the tools that have been created for producing accurate simulations of gamma-ray pulsars emission. The main simulator is called PulsarSpectrum and can reproduce gamma-ray emission with great detail, taking also into account advanced timing effects, e.g. period increase with time, barycentric corrections and higher-order timing noise currently under development. Detailed spectral features can also be simulated with PulsarSpectrum, such as phase-dependent spectra. A suite of ancillary tools have also been built to provide a realistic pulsar population with related timing solutions. Anyway PulsarSpectrum can also simulate pulsar populations coming from external synthesis codes. All these tools are presently used within the GLAST collaboration for testing the LAT Science Analysis Environment tools and for better study of LAT capabilities for pulsar science.

  1. The Twisting Jet from the Vela Pulsar

    NASA Astrophysics Data System (ADS)

    Teter, M. A.; Pavlov, G. G.; Sanwal, D.; Kargaltsev, O.

    2002-05-01

    Observations of the Vela pulsar-wind nebula (PWN) with Chandra have revealed a long, thin filament -- an extension of the pulsar's jet beyond the bright outer arc confining the PWN in the direction of the pulsar's proper motion. This curved external jet terminates in a region of enhanced emission (a blob) at a distance of about 100'' (0.15 pc) from the pulsar, larger than the size of the PWN. The shape of the jet and its brightness are seen to vary on a timescale as short as a few days, its remote parts move in the sky plane with apparent velocities of up to 0.2 c. The X-ray spectrum of the external jet, including the termination blob, shows no spectral features. It is well described by a power-law model with a photon-index of γ ~= 1.2 (slightly harder than the average spectrum of the PWN, γ ~= 1.5). This indicates that the jet's radiation is due to synchrotron emission of relativistic particles in a magnetic field. The fact that the jet remains confined, although it twists at large distances from the pulsar, suggests a self-confining structure of its magnetic field. The varying shape and intensity of this stream of relativistic particles can be associated with varying local conditions in the Vela SNR and/or large-scale MHD instabilities and internal variations of the magnetic field within the jet. We will present a movie with a sequence of 12 Chandra images over past two years, demonstrating the structure of the twisting jet, and discuss various interpretations of these observations. The work was partially supported by SAO grant GO2-3091X and NASA grant NAG5-10865.

  2. OSCILLATION-DRIVEN MAGNETOSPHERIC ACTIVITY IN PULSARS

    SciTech Connect

    Lin, Meng-Xiang; Xu, Ren-Xin; Zhang, Bing E-mail: r.x.xu@pku.edu.cn

    2015-02-01

    We study the magnetospheric activity in the polar cap region of pulsars under stellar oscillations. The toroidal oscillation of the star propagates into the magnetosphere, which provides additional voltage due to unipolar induction, changes Goldreich-Julian charge density from the traditional value due to rotation, and hence influences particle acceleration. We present a general solution of the effect of oscillations within the framework of the inner vacuum gap model and consider three different inner gap modes controlled by curvature radiation, inverse Compton scattering, and two-photon annihilation, respectively. With different pulsar parameters and oscillation amplitudes, one of three modes would play a dominant role in defining the gap properties. When the amplitude of oscillation exceeds a critical value, mode changing occurs. Oscillations also lead to a change of the size of the polar cap. As applications, we show the inner gap properties under oscillations in both normal pulsars and anomalous X-ray pulsars/soft gamma-ray repeaters (AXPs/SGRs). We interpret the onset of radio emission after glitches/flares in AXPs/SGRs as due to oscillation-driven magnetic activities in these objects, within the framework of both the magnetar model and the solid quark star model. Within the magnetar model, radio activation may be caused by the enlargement of the effective polar cap angle and the radio emission beam due to oscillation, whereas within the solid quark star angle, it may be caused by activation of the pulsar inner gap from below the radio emission death line due to an oscillation-induced voltage enhancement. The model can also explain the glitch-induced radio profile change observed in PSR J1119–6127.

  3. COHERENTLY DEDISPERSED GATED IMAGING OF MILLISECOND PULSARS

    SciTech Connect

    Roy, Jayanta; Bhattacharyya, Bhaswati

    2013-03-10

    Motivated by the need for rapid localization of newly discovered faint millisecond pulsars (MSPs), we have developed a coherently dedispersed gating correlator. This gating correlator accounts for the orbital motions of MSPs in binaries while folding the visibilities with a best-fit topocentric rotational model derived from a periodicity search in a simultaneously generated beamformer output. Unique applications of the gating correlator for sensitive interferometric studies of MSPs are illustrated using the Giant Metrewave Radio Telescope (GMRT) interferometric array. We could unambiguously localize five newly discovered Fermi MSPs in the on-off gated image plane with an accuracy of {+-}1''. Immediate knowledge of such a precise position enables the use of sensitive coherent beams of array telescopes for follow-up timing observations which substantially reduces the use of telescope time ({approx}20 Multiplication-Sign for the GMRT). In addition, a precise a priori astrometric position reduces the effect of large covariances in the timing fit (with discovery position, pulsar period derivative, and an unknown binary model), which in-turn accelerates the convergence to the initial timing model. For example, while fitting with the precise a priori position ({+-}1''), the timing model converges in about 100 days, accounting for the effect of covariance between the position and pulsar period derivative. Moreover, such accurate positions allow for rapid identification of pulsar counterparts at other wave bands. We also report a new methodology of in-beam phase calibration using the on-off gated image of the target pulsar, which provides optimal sensitivity of the coherent array removing possible temporal and spacial decoherences.

  4. TINY HICCUPS TO TITANIC EXPLOSIONS: Tackling Transients in Anomalous X-ray Pulsars

    NASA Astrophysics Data System (ADS)

    Kaspi, Victoria

    2011-09-01

    The past decade has seen major progress in neutron star astrophysics, with the discovery of magnetars in general, and the recognition that the Anomalous X-ray Pulsars (AXPs) fall in this class. AXPs have recently revealed surprising and dramatic variability behavior, which theorists have begun to show are highly constraining of physical models of magnetars, including their crusts, atmospheres, coronae and magnetospheres. In this proposal, we request Chandra/ACIS-S Target-of-Opportunity observations of one major Anomalous X-ray Pulsar (AXP) outburst in AO13, in order to study in detail the evolution of the spectrum, pulsed fraction and pulse profile, for quantitative confrontation with recently developed models for the structure and electrodynamics of magnetars.

  5. TINY HICCUPS TO TITANIC EXPLOSIONS: Tackling Transients in Anomalous X-ray Pulsars

    NASA Astrophysics Data System (ADS)

    Kaspi, Victoria

    2010-09-01

    The past decade has seen major progress in neutron star astrophysics, with the discovery of magnetars in general, and the recognition that the Anomalous X-ray Pulsars (AXPs) fall in this class. AXPs have recently revealed surprising and dramatic variability behavior, which theorists have begun to show are highly constraining of physical models of magnetars, including their crusts, atmospheres, coronae and magnetospheres. In this proposal, we request Chandra/ACIS-S Target-of-Opportunity observations of one major Anomalous X-ray Pulsar (AXP) outburst in AO12, in order to study in detail the evolution of the spectrum, pulsed fraction and pulse profile, for quantitative confrontation with recently developed models for the structure and electrodynamics of magnetars.

  6. Experimental Constraints on γ-Ray Pulsar Gap Models and the Pulsar GeV to Pulsar Wind Nebula TeV Connection

    NASA Astrophysics Data System (ADS)

    Abeysekara, A. U.; Linnemann, J. T.

    2015-05-01

    The pulsar emission mechanism in the gamma ray energy band is poorly understood. Currently, there are several models under discussion in the pulsar community. These models can be constrained by studying the collective properties of a sample of pulsars, which became possible with the large sample of gamma ray pulsars discovered by the Fermi Large Area Telescope. In this paper we develop a new experimental multi-wavelength technique to determine the beaming factor ≤ft( {{f}{Ω }} \\right) dependance on spin-down luminosity of a set of GeV pulsars. This technique requires three input parameters: pulsar spin-down luminosity, pulsar phase-averaged GeV flux, and TeV or X-ray flux from the associated pulsar wind nebula (PWN). The analysis presented in this paper uses the PWN TeV flux measurements to study the correlation between {{f}{Ω }} and \\dot{E}. The measured correlation has some features that favor the Outer Gap model over the Polar Cap, Slot Gap, and One Pole Caustic models for pulsar emission in the energy range of 0.1-100 GeV, but one must keep in mind that these simulated models failed to explain many of the most important pulsar population characteristics. A tight correlation between the pulsar GeV emission and PWN TeV emission was also observed, which suggests the possibility of a linear relationship between the two emission mechanisms. In this paper we also discuss a possible mechanism to explain this correlation.

  7. PEACE: pulsar evaluation algorithm for candidate extraction - a software package for post-analysis processing of pulsar survey candidates

    NASA Astrophysics Data System (ADS)

    Lee, K. J.; Stovall, K.; Jenet, F. A.; Martinez, J.; Dartez, L. P.; Mata, A.; Lunsford, G.; Cohen, S.; Biwer, C. M.; Rohr, M.; Flanigan, J.; Walker, A.; Banaszak, S.; Allen, B.; Barr, E. D.; Bhat, N. D. R.; Bogdanov, S.; Brazier, A.; Camilo, F.; Champion, D. J.; Chatterjee, S.; Cordes, J.; Crawford, F.; Deneva, J.; Desvignes, G.; Ferdman, R. D.; Freire, P.; Hessels, J. W. T.; Karuppusamy, R.; Kaspi, V. M.; Knispel, B.; Kramer, M.; Lazarus, P.; Lynch, R.; Lyne, A.; McLaughlin, M.; Ransom, S.; Scholz, P.; Siemens, X.; Spitler, L.; Stairs, I.; Tan, M.; van Leeuwen, J.; Zhu, W. W.

    2013-07-01

    Modern radio pulsar surveys produce a large volume of prospective candidates, the majority of which are polluted by human-created radio frequency interference or other forms of noise. Typically, large numbers of candidates need to be visually inspected in order to determine if they are real pulsars. This process can be labour intensive. In this paper, we introduce an algorithm called Pulsar Evaluation Algorithm for Candidate Extraction (PEACE) which improves the efficiency of identifying pulsar signals. The algorithm ranks the candidates based on a score function. Unlike popular machine-learning-based algorithms, no prior training data sets are required. This algorithm has been applied to data from several large-scale radio pulsar surveys. Using the human-based ranking results generated by students in the Arecibo Remote Command Center programme, the statistical performance of PEACE was evaluated. It was found that PEACE ranked 68 per cent of the student-identified pulsars within the top 0.17 per cent of sorted candidates, 95 per cent within the top 0.34 per cent and 100 per cent within the top 3.7 per cent. This clearly demonstrates that PEACE significantly increases the pulsar identification rate by a factor of about 50 to 1000. To date, PEACE has been directly responsible for the discovery of 47 new pulsars, 5 of which are millisecond pulsars that may be useful for pulsar timing based gravitational-wave detection projects.

  8. Einstein@Home Finds an Elusive Pulsar

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-08-01

    Since the release of the second Fermi-LAT catalog in 2012, astronomers have been hunting for 3FGL J1906.6+0720, a gamma-ray source whose association couldn't be identified. Now, personal-computer time volunteered through the Einstein@Home project has resulted in the discovery of a pulsar that has been hiding from observers for years. A Blind Search: Identifying sources detected by Fermi-LAT can be tricky: the instrument's sky resolution is limited, so the position of the source can be hard to pinpoint. The gamma-ray source 3FGL J1906.6+0720 appeared in both the second and third Fermi-LAT source catalogs, but even after years of searching, no associated radio or X-ray source had been found. A team of researchers, led by Colin Clark of the Max Planck Institute for Gravitational Physics, suspected that the source might be a gamma-ray pulsar. To confirm this, however, they needed to detect pulsed emission — something inherently difficult given the low photon count and the uncertain position of the source. The team conducted a blind search for pulsations coming from the general direction of the gamma-ray source. Two things were needed for this search: clever data analysis and a lot of computing power. The data analysis algorithm was designed to be adaptive: it searched a 4-dimensional parameter space that included a safety margin, allowing the algorithm to wander if the source was at the edge of the parameter space. The computing power was contributed by tens of thousands of personal computers volunteered by participants in the Einstein@Home project, making much shorter work out of a search that would have required dozens of years on a single laptop. The sky region around the newly discovered pulsar. The dotted ellipse shows the 3FGL catalog 95% confidence region for the source. The data analysis algorithm was designed to search an area 50% larger (given by the dashed ellipse), but it was allowed to “walk away” within the gray shaded region if the source seemed to

  9. A NON-RADIAL OSCILLATION MODEL FOR PULSAR STATE SWITCHING

    SciTech Connect

    Rosen, R.; McLaughlin, M. A.; Thompson, S. E.

    2011-02-10

    Pulsars are unique astrophysical laboratories because of their clock-like timing precision, providing new ways to test general relativity and detect gravitational waves. One impediment to high-precision pulsar timing experiments is timing noise. Recently, Lyne et al. showed that the timing noise in a number of pulsars is due to quasi-periodic fluctuations in the pulsars' spin-down rates and that some of the pulsars have associated changes in pulse profile shapes. Here we show that a non-radial oscillation model based on asteroseismological theory can explain these quasi-periodic fluctuations. Application of this model to neutron stars will increase our knowledge of neutron star emission and neutron star interiors and may improve pulsar timing precision.

  10. Vela-like Pulsars: A Bridge Between Young and Old

    NASA Technical Reports Server (NTRS)

    Finley, John P.

    1997-01-01

    This grant was in support of a guest observation using the ASCA satellite of the young, spin-powered pulsar PSR B1706-44. The pulsar is interesting for several reasons: 1) it is young and shares many similar characteristics with the Vela pulsar, 2) it is one of a few pulsars which has been detected by the EGRET detector aboard the CGRO satellite, and 3) it is one of the confirmed sources of TeV gamma-rays discovered with ground based telescopes. The goals of the observation were to search for pulsations in the X-ray domain and to study the near stellar environment to determine if the pulsar is embedded within a compact nebula as in the case of the Vela pulsar.

  11. Free at Last: AN Energetic Pulsar Escapes its Supernova Remnant

    NASA Astrophysics Data System (ADS)

    Camilo, Fernando

    2002-09-01

    PSR J1016-5857 is a young and energetic pulsar located just outside the supernova remnant (SNR) G284.3-1.8. The morphology of the system argues that the pulsar has a high space velocity, and has caught up with and now overtaken its associated SNR. We have identified an EINSTEIN source, which in the above hypothesis is likely to be a cometary nebula powered by the pulsar. We here propose a short CHANDRA observation of this X-ray source to determine whether it is indeed associated with the pulsar. With the resulting morphological data, we can confirm or refute the pulsar/SNR association, and can probe the pulsar's spin history and interaction with its environment.

  12. The Multipupil Fiber Spectroscopy of the Crab-pulsar Neighbourhood

    NASA Astrophysics Data System (ADS)

    Zharikov, S.; Shibanov, Y.; Koptsevich, A.; Afanas'ev, V.; Dodonov, S.

    2001-03-01

    We present the spatially resolved optical spectroscopy of the 12 arcsec × 24 arcsec Crab pulsar neighbourhood in the range λ λ 4600 - 5700 Å made with the Multipupil Fiber Spectrograph at the 6 m telescope of the SAO RAS. The spectra exhibit blue- and red-shifted strong [O III] and weaker Hβ and He II emission lines with the shifts and intensities varying with the position in the field. They hint the presence of a cone-like rotating structure centered at the pulsar position and oriented along the symmetry axis of the compact, torus-like pulsar nebula seen in optical continuum and soft X-rays. The kinematic structure is most likely associated with the pulsar nebula. If so, the compact nebular rotates counter-clockwise with respect to its symmetry axis, or the pulsar spin axis, and the estimated rotational velocity within cylindrical radii of several thousand AU from the pulsar is ~ 2000-3000 km/s.

  13. Switched magnetospheric regulation of pulsar spin-down.

    PubMed

    Lyne, Andrew; Hobbs, George; Kramer, Michael; Stairs, Ingrid; Stappers, Ben

    2010-07-23

    Pulsars are famed for their rotational clocklike stability and their highly repeatable pulse shapes. However, it has long been known that there are unexplained deviations (often termed timing noise) from the rate at which we predict these clocks should run. We show that timing behavior often results from two different spin-down rates. Pulsars switch abruptly between these states, often quasi-periodically, leading to the observed spin-down patterns. We show that for six pulsars the timing noise is correlated with changes in the pulse shape. Many pulsar phenomena, including mode changing, nulling, intermittency, pulse-shape variability, and timing noise, are therefore linked and are caused by changes in the pulsar's magnetosphere. We consider the possibility that high-precision monitoring of pulse profiles could lead to the formation of highly stable pulsar clocks. PMID:20576852

  14. CONSTRAINING PULSAR MAGNETOSPHERE GEOMETRY WITH {gamma}-RAY LIGHT CURVES

    SciTech Connect

    Romani, Roger W.; Watters, Kyle P. E-mail: kwatters@stanford.ed

    2010-05-01

    We demonstrate a method for quantitatively comparing {gamma}-ray pulsar light curves with magnetosphere beaming models. With the Fermi LAT providing many pulsar discoveries and high-quality pulsar light curves for the brighter objects, such a comparison allows greatly improved constraints on the emission zone geometry and the magnetospheric physics. Here we apply the method to Fermi LAT light curves of a set of bright pulsars known since EGRET or before. We test three approximate models for the magnetosphere structure and two popular schemes for the location of the emission zone, the two pole caustic model and the outer gap (OG) model. We find that OG models and relatively physical B fields approximating force-free dipole magnetospheres are preferred at high statistical significance. An application to the full LAT pulsar sample will allow us to follow the emission zone's evolution with pulsar spindown.

  15. Timing Young Pulsars: Challenges to Standard Pulsar Spin-Down Models

    NASA Astrophysics Data System (ADS)

    Livingstone, Margaret Anne

    Pulsars are rapidly rotating neutron stars which are often noted for their very regular rotation rates. Young pulsars, however, frequently exhibit two types of deviations from steady spin down, "glitches" - sudden jumps in spin frequency, which provide insight into pulsar interiors, and "timing noise," a smooth stochastic wander of the pulse phase over long time periods. The youngest pulsars also offer a window into the physics that govern pulsar spin down via the measurement of the "braking index" - a parameter that relates the observable spin frequency of the pulsar with the slowing down torque acting on the neutron star. This thesis discusses long-term timing observations of two young pulsars. First, we present observations of PSR J0205+6449, acquired with the Green Bank Telescope, the Jodrell Bank Observatory and the Rossi X-ray Timing Explorer . We present phase-coherent timing analyses showing timing noise and two spin-up glitches. We also present an X-ray pulse profile analysis showing that the pulsar is detected up to ∼40 keV and does not vary appreciably over four years. We report the phase offset between the radio and X-ray pulse, showing that the radio pulse leads by φ = 0.10 ± 0.01 in phase. We compile measurements of phase offsets for this and other X-ray and γ-ray pulsars and show that there is no relationship between pulse period and phase offset. Next, we present 10 years of monitoring of PSR J1846-0258 with the Rossi X-ray Timing Explorer . We report the first measurement of the braking index for this pulsar, n = 2.65 ± 0.01, only the sixth such measurement ever made, and show that the pulsar experienced a small glitch in 2001. In May 2006, PSR J1846-0258 was briefly transformed: it exhibited a series of X-ray bursts, a dramatic increase in the source flux, and significant softening of its X-ray spectrum - behaviours best explained in the context of the magnetar model. PSR J1846-0258 was thus identified as the first rotation-powered pulsar

  16. Limits on neutron Lorentz violation from pulsar timing

    SciTech Connect

    Altschul, Brett

    2007-01-15

    Pulsars are the most accurate naturally occurring clocks, and data about them can be used to set bounds on neutron-sector Lorentz violations. If SO(3) rotation symmetry is completely broken for neutrons, then pulsars' rotation speeds will vary periodically. Pulsar timing data limits the relevant Lorentz-violating coefficients to be smaller than 1.7x10{sup -8} at at least 90% confidence.

  17. On magnetic pair production above fast pulsar polar caps

    NASA Technical Reports Server (NTRS)

    An, S.

    1985-01-01

    Magnetic pair production is one of high-energy electromagnetic conversion processes important to the development of pair-photon cascades in pulsars. On the basis of current polar cap models, the properties of magnetic pair production in fast pulsars are discussed. Suppose there is a roughly dipole magnetic field at the stellar surface, the author estimate the effects on non-zero curvature of magnetic field lines upon curvature radiation from primary particles and pair production rate near the surface of pulsars.

  18. A Crash Course in using Pulsars to Detect Gravitational Waves

    NASA Astrophysics Data System (ADS)

    Lommen, Andrea N.; NANOGrav

    2014-01-01

    A collection of well-timed millisecond pulsars makes a “pulsar timing array”, an “observatory” capable of detecting and characterizing small perturbations in spacetime called gravitational waves. In this 12-minute crash course you will learn how pulsars are timed, how you can use them to detect gravitational waves, who and what telescopes are engaged in this international enterprise, and how you can get involved.

  19. Pulsar Polar Cap and Slot Gap Models: Confronting Fermi Data

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.

    2012-01-01

    Rotation-powered pulsars are excellent laboratories for studying particle acceleration as well as fundamental physics of strong gravity, strong magnetic fields and relativity. I will review acceleration and gamma-ray emission from the pulsar polar cap and slot gap. Predictions of these models can be tested with the data set on pulsars collected by the Large Area Telescope on the Fermi Gamma-Ray Telescope over the last four years, using both detailed light curve fitting and population synthesis.

  20. Timing analysis for 20 millisecond pulsars in the Parkes Pulsar Timing Array

    NASA Astrophysics Data System (ADS)

    Reardon, D. J.; Hobbs, G.; Coles, W.; Levin, Y.; Keith, M. J.; Bailes, M.; Bhat, N. D. R.; Burke-Spolaor, S.; Dai, S.; Kerr, M.; Lasky, P. D.; Manchester, R. N.; Osłowski, S.; Ravi, V.; Shannon, R. M.; van Straten, W.; Toomey, L.; Wang, J.; Wen, L.; You, X. P.; Zhu, X.-J.

    2016-01-01

    We present timing models for 20 millisecond pulsars in the Parkes Pulsar Timing Array. The precision of the parameter measurements in these models has been improved over earlier results by using longer data sets and modelling the non-stationary noise. We describe a new noise modelling procedure and demonstrate its effectiveness using simulated data. Our methodology includes the addition of annual dispersion measure (DM) variations to the timing models of some pulsars. We present the first significant parallax measurements for PSRs J1024-0719, J1045-4509, J1600-3053, J1603-7202, and J1730-2304, as well as the first significant measurements of some post-Keplerian orbital parameters in six binary pulsars, caused by kinematic effects. Improved Shapiro delay measurements have resulted in much improved pulsar mass measurements, particularly for PSRs J0437-4715 and J1909-3744 with Mp = 1.44 ± 0.07 and 1.47 ± 0.03 M⊙, respectively. The improved orbital period-derivative measurement for PSR J0437-4715 results in a derived distance measurement at the 0.16 per cent level of precision, D = 156.79 ± 0.25 pc, one of the most fractionally precise distance measurements of any star to date.

  1. Pulsar gamma-rays: Spectra luminosities and efficiencies

    NASA Technical Reports Server (NTRS)

    Harding, A. K.

    1980-01-01

    The general characteristics of pulsar gamma ray spectra are presented for a model where the gamma rays are produced by curvature radiation from energetic particles above the polar cap and attenuated by pair production. The shape of the spectrum is found to depend on pulsar period, magnetic field strength, and primary particle energy. By a comparison of numerically calculated spectra with the observed spectra of the Crab and Vela pulsars, it is determined that primary particles must be accelerated to energies of about 3 x 10 to the 7th power mc sq. A genaral formula for pulsar gamma ray luminosity is determined and is found to depend on period and field strength.

  2. Multiwavelength Constraints on Pulsar Populations in the Galactic Center

    NASA Astrophysics Data System (ADS)

    Wharton, R. S.; Chatterjee, S.; Cordes, J. M.; Deneva, J. S.; Lazio, T. J. W.

    2012-07-01

    The detection of radio pulsars within the central few parsecs of the Galaxy would provide a unique probe of the gravitational and magneto-ionic environments in the Galactic center (GC) and, if close enough to Sgr A*, precise tests of general relativity in the strong-field regime. While it is difficult to find pulsars at radio wavelengths because of interstellar scattering, the payoff from detailed timing of pulsars in the GC warrants a concerted effort. To motivate pulsar surveys and help define search parameters for them, we constrain the pulsar number and spatial distribution using a wide range of multiwavelength measurements. These include the five known radio pulsars within 15' of Sgr A*, non-detections in high-frequency pulsar surveys of the central parsec, radio and gamma-ray measurements of diffuse emission, a catalog of radio point sources from an imaging survey, infrared observations of massive star populations in the central few parsecs, candidate pulsar wind nebulae in the inner 20 pc, and estimates of the core-collapse supernova rate based on X-ray measurements. We find that under current observational constraints, the inner parsec of the Galaxy could harbor as many as ~103 active radio pulsars that are beamed toward Earth. Such a large population would distort the low-frequency measurements of both the intrinsic spectrum of Sgr A* and the free-free absorption along the line of sight of Sgr A*.

  3. Future Facilities for Gamma-Ray Pulsar Studies

    NASA Technical Reports Server (NTRS)

    Thompson, D. J.

    2003-01-01

    Pulsars seen at gamma-ray energies offer insight into particle acceleration to very high energies, along with information about the geometry and interaction processes in the magnetospheres of these rotating neutron stars. During the next decade, a number of new gamma-ray facilities will become available for pulsar studies. This brief review describes the motivation for gamma-ray pulsar studies, the opportunities for such studies, and some specific discussion of the capabilities of the Gamma-ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT) for pulsar measurements.

  4. Pulsar searches: From radio to gamma-rays

    NASA Astrophysics Data System (ADS)

    Chandler, Adam M.

    2003-08-01

    We report the results of four different pulsar searches, covering radio, X-ray, and gamma-ray wavelengths. These searches targeted pulsars in virtually all of their guises: young and old, long-period and short-period, accretion-powered and rotation-powered. Ten new pulsars were discovered. There are very few known gamma-ray pulsars, all of which were found by folding gamma-ray data with a pulse period known from other wavelengths. Some emission models indicate that there may be a large number of gamma-ray pulsars that are undetectable at lower energies. We searched several of the brightest unidentified gamma-ray sources for pulsations. This was the first attempt to identify gamma-ray pulsars by directly searching gamma- ray data. No new identifications resulted; we report upper limits. Even more rare than gamma-ray pulsars are accreting millisecond pulsars. We searched for coherent pulsations from Aql X-1, a low-mass X-ray binary suspected of harboring such an object. No pulsations were detected, and we argue that the quiescent emission of this system has a thermal origin. The two radio searches included here were both designed to detect millisecond pulsars. First, we report the results of a large area survey from Arecibo. Five new slow pulsars were discovered, including an apparent orthogonal rotator and an extremely unusual bursting radio pulsar. No short-period pulsars were discovered and we place some of the first useful observational constraints on the limiting spin period of a neutron star. We also performed pointed searches of several globular clusters using the new Green Bank Telescope. Three new binary millisecond pulsars were found in M62. These were the first new objects found with the GBT, and they bring the total pulsar population in M62 to six. We also discovered two isolated pulsars, one each in NGC 6544 and NGC 6624. Many of the methods we developed will be relevant to future searches. Perhaps the most significant contribution is a dynamic power

  5. The LWA1 Northern Celestial Cap Pulsar Survey

    NASA Astrophysics Data System (ADS)

    Garcia, Alejandro; Stovall, K.; Jenet, F.; Cutchin, S.; Kassim, N. E.; Majid, W. A.; Ray, P. S.; Taylor, G. B.

    2013-01-01

    The LWA1 Northern Celestial Cap (LNCC) pulsar survey, which is targeting the frequency range from 30 to 62 MHz, will be the first part of an all sky pulsar/radio transient survey using the first station (LWA1) of the Long Wavelength Array (LWA) telescope. This poster will focus on the search parameters for the pipelines that will process the LNCC survey data. The current status of the survey will also be discussed as well as preliminary results. Based on simulations it is estimated that about 75 pulsars will be detected with perhaps as many as 10 of them being new pulsars.

  6. MULTIWAVELENGTH CONSTRAINTS ON PULSAR POPULATIONS IN THE GALACTIC CENTER

    SciTech Connect

    Wharton, R. S.; Chatterjee, S.; Cordes, J. M.; Deneva, J. S.; Lazio, T. J. W.

    2012-07-10

    The detection of radio pulsars within the central few parsecs of the Galaxy would provide a unique probe of the gravitational and magneto-ionic environments in the Galactic center (GC) and, if close enough to Sgr A*, precise tests of general relativity in the strong-field regime. While it is difficult to find pulsars at radio wavelengths because of interstellar scattering, the payoff from detailed timing of pulsars in the GC warrants a concerted effort. To motivate pulsar surveys and help define search parameters for them, we constrain the pulsar number and spatial distribution using a wide range of multiwavelength measurements. These include the five known radio pulsars within 15' of Sgr A*, non-detections in high-frequency pulsar surveys of the central parsec, radio and gamma-ray measurements of diffuse emission, a catalog of radio point sources from an imaging survey, infrared observations of massive star populations in the central few parsecs, candidate pulsar wind nebulae in the inner 20 pc, and estimates of the core-collapse supernova rate based on X-ray measurements. We find that under current observational constraints, the inner parsec of the Galaxy could harbor as many as {approx}10{sup 3} active radio pulsars that are beamed toward Earth. Such a large population would distort the low-frequency measurements of both the intrinsic spectrum of Sgr A* and the free-free absorption along the line of sight of Sgr A*.

  7. Observing peculiar γ-ray pulsars with AGILE

    NASA Astrophysics Data System (ADS)

    Pilia, M.; Pellizzoni, A.

    2011-08-01

    The AGILE γ-ray satellite provides large sky exposure levels (>=109 cm2 s per year on the Galactic Plane) with sensitivity peaking at E ~100 MeV where the bulk of pulsar energy output is typically released. Its ~1 μs absolute time tagging capability makes it perfectly suited for the study of γ-ray pulsars. AGILE collected a large number of γ-ray photons from EGRET pulsars (>=40,000 pulsed counts for Vela) in two years of observations unveiling new interesting features at sub-millisecond level in the pulsars' high-energy light-curves, γ-ray emission from pulsar glitches and Pulsar Wind Nebulae. AGILE detected about 20 nearby and energetic pulsars with good confidence through timing and/or spatial analysis. Among the newcomers we find pulsars with very high rotational energy losses, such as the remarkable PSR B1509-58 with a magnetic field in excess of 1013 Gauss, and PSR J2229+6114 providing a reliable identification for the previously unidentified EGRET source 3EG2227+6122. Moreover, the powerful millisecond pulsar B1821-24, in the globular cluster M28, is detected during a fraction of the observations.

  8. Mildly Recycled Pulsars at High-Energies

    NASA Astrophysics Data System (ADS)

    Pellizzoni, A.

    2011-08-01

    Mildly recyled pulsars (MRP), conventionally defined as neutron star having spin period in the 20-100 ms range and surface magnetic field <1011 Gauss, probably rise from binary systems (disrupted or not) with an intermediate or an high mass companion. Despite their relatively low spin-down energies compared to the ``fully'' recycled millisecond pulsars (arising from common low mass X-ray binaries), nearby MRPs can be detected by deep X-ray observations and by timing analysis of the very long data span provided by gamma-ray space detectors. The discovery of peculiar timing and spectral properties, possibly transitional, of the MRPs can be of the utmost importance to link different classes of neutron stars and study their evolution.

  9. Extreme-Ultraviolet Observations of Nine Pulsars

    NASA Astrophysics Data System (ADS)

    Seon, Kwang-Il; Edelstein, Jerry

    1998-05-01

    We report the observation of nine pulsars using the Lexan (100 Å) band of the Extreme Ultraviolet Explorer scanning telescopes. The observations, none of which resulted in positive detections, are used to derive limits to the temperature of surface thermal radiation from the objects. We compare the temperature limits with predictions from neutron star cooling models. The N_H I toward our targets limits our ability to establish rigorous limits needed to discriminate among the models. We also derive a limit to heating by magnetic monopole flux-catalyzed nucleon decay for the very old pulsar PSR J1455-3330, which is similar to the limit derived for PSR B1929+10 and 3 orders of magnitude larger than the limit for PSR J0437-4715.

  10. Gravitational wave emission from oscillating millisecond pulsars

    NASA Astrophysics Data System (ADS)

    Alford, Mark G.; Schwenzer, Kai

    2015-02-01

    Neutron stars undergoing r-mode oscillation emit gravitational radiation that might be detected on the Earth. For known millisecond pulsars the observed spin-down rate imposes an upper limit on the possible gravitational wave signal of these sources. Taking into account the physics of r-mode evolution, we show that only sources spinning at frequencies above a few hundred Hertz can be unstable to r-modes, and we derive a more stringent universal r-mode spin-down limit on their gravitational wave signal. We find that this refined bound limits the gravitational wave strain from millisecond pulsars to values below the detection sensitivity of next generation detectors. Young sources are therefore a more promising option for the detection of gravitational waves emitted by r-modes and to probe the interior composition of compact stars in the near future.

  11. Minority Student Scientists Searching for Pulsars

    NASA Astrophysics Data System (ADS)

    Rodriguez-Zermeno, Adrienne; Miller, A.; Stovall, K.; Jenet, F.

    2007-12-01

    Modern astronomy offers the means to excite students about science. At the Arecibo Remote Command Center (ARCC) part of University of Texas at Brownsville's Center for Gravitational Wave Astronomy (CGWA), high school and undergraduate students experience what it is like to be a scientist by assisting in the international effort to identify pulsars as part of the P-ALFA survey. By participating in the ARCC, students start their contribution to the P-ALFA project by remotely controlling the Arecibo telescope for data collection. Then, using a web-based software instrument developed by researchers at the CGWA, students analyze the data to identify potential pulsar candidates. These early career students have become a vital part of this data analysis pipeline. Here we discuss this implementation as a case study of authentic research experiences for minority students.

  12. Gamma-Ray Pulsar Studies with GLAST

    NASA Technical Reports Server (NTRS)

    Thompson, David J.

    2007-01-01

    This viewgraph presentation reviews the prospects of extending the understanding of gamma ray pulsars, and answering the open questions left from the limited observations that are available from current observatories. There are 2 new gamma ray observatories that are either on orbit or will be shortly launched: (1) Astro-rivelatore Gamma a Immagini LEggero (AGILE), and Gamma-ray Large Area Space Telescope (GLAST). On board GLAST there will be two instruments Large Area Telescope (LAT), and GLAST Burst Monitor (GBM).

  13. PARTICLE TRANSPORT IN YOUNG PULSAR WIND NEBULAE

    SciTech Connect

    Tang Xiaping; Chevalier, Roger A. E-mail: rac5x@virginia.edu

    2012-06-20

    The model for pulsar wind nebulae (PWNe) as a result of the magnetohydrodynamic (MHD) downstream flow from a shocked, relativistic pulsar wind has been successful in reproducing many features of the nebulae observed close to central pulsars. However, observations of well-studied young nebulae like the Crab Nebula, 3C 58, and G21.5-0.9 do not show the toroidal magnetic field on a larger scale that might be expected in the MHD flow model; in addition, the radial variation of spectral index due to synchrotron losses is smoother than expected in the MHD flow model. We find that pure diffusion models can reproduce the basic data on nebular size and spectral index variation for the Crab, 3C 58, and G21.5-0.9. Most of our models use an energy-independent diffusion coefficient; power-law variations of the coefficient with energy are degenerate with variation in the input particle energy distribution index in the steady state, transmitting boundary case. Energy-dependent diffusion is a possible reason for the smaller diffusion coefficient inferred for the Crab. Monte Carlo simulations of the particle transport allowing for advection and diffusion of particles suggest that diffusion dominates over much of the total nebular volume of the Crab. Advection dominates close to the pulsar and is likely to play a role in the X-ray half-light radius. The source of diffusion and mixing of particles is uncertain, but may be related to the Rayleigh-Taylor instability at the outer boundary of a young PWN or to instabilities in the toroidal magnetic field structure.

  14. Pulsar PRS 0656 + 14 - Period and spindown

    NASA Technical Reports Server (NTRS)

    Domingue, D.; Rankin, J. M.; Weisberg, J. M.; Backus, P. R.

    1986-01-01

    Observations from various sources are used to explain the larger-than-expected period noted for pulsar 0656 + 14 on July 7, 1984 (Ashworth and Lyne, 1981). No indication of orbital motion was found, and most of the observations are consistent with a simple secular spindown. The derived period derivative of (54.3 + or - 1.3) x 10 to the -15th at epoch 2444300 is far greater than the previously reported value.

  15. Tests of general relativity using pulsars

    NASA Technical Reports Server (NTRS)

    Reichley, P. E.

    1971-01-01

    The arrival times of the pulses from each pulsar are measured by a cesium clock. The observations are all made at a frequency of 2388 MHz (12.5 cm wavelength) on a 26 m dish antenna. The effect of interstellar charged particles is a random one that increases the noise level on the arrival time measurements. The variation in clock rate is shown consisting of two effects: the time dilation effect of special relativity and the red shift effect of general relativity.

  16. FERMI-LAT SEARCH FOR PULSAR WIND NEBULAE AROUND GAMMA-RAY PULSARS

    SciTech Connect

    Ackermann, M.; Ajello, M.; Bechtol, K.; Berenji, B.; Bloom, E. D.; Borgland, A. W.; Bouvier, A.; Buehler, R.; Baldini, L.; Bellazzini, R.; Bregeon, J.; Brez, A.; Ballet, J.; Bastieri, D.; Buson, S.; Bonamente, E.; Brigida, M.; Bruel, P.

    2011-01-01

    The high sensitivity of the Fermi-LAT (Large Area Telescope) offers the first opportunity to study faint and extended GeV sources such as pulsar wind nebulae (PWNe). After one year of observation the LAT detected and identified three PWNe: the Crab Nebula, Vela-X, and the PWN inside MSH 15-52. In the meantime, the list of LAT detected pulsars increased steadily. These pulsars are characterized by high energy loss rates ( E-dot ) from {approx}3 x 10{sup 33} erg s{sup -1} to 5 x 10{sup 38} erg s{sup -1} and are therefore likely to power a PWN. This paper summarizes the search for PWNe in the off-pulse windows of 54 LAT-detected pulsars using 16 months of survey observations. Ten sources show significant emission, seven of these likely being of magnetospheric origin. The detection of significant emission in the off-pulse interval offers new constraints on the {gamma}-ray emitting regions in pulsar magnetospheres. The three other sources with significant emission are the Crab Nebula, Vela-X, and a new PWN candidate associated with the LAT pulsar PSR J1023-5746, coincident with the TeV source HESS J1023-575. We further explore the association between the HESS and the Fermi source by modeling its spectral energy distribution. Flux upper limits derived for the 44 remaining sources are used to provide new constraints on famous PWNe that have been detected at keV and/or TeV energies.

  17. LEAP: the Large European Array for Pulsars

    NASA Astrophysics Data System (ADS)

    Bassa, C. G.; Janssen, G. H.; Karuppusamy, R.; Kramer, M.; Lee, K. J.; Liu, K.; McKee, J.; Perrodin, D.; Purver, M.; Sanidas, S.; Smits, R.; Stappers, B. W.

    2016-02-01

    The Large European Array for Pulsars (LEAP) is an experiment that harvests the collective power of Europe's largest radio telescopes in order to increase the sensitivity of high-precision pulsar timing. As part of the ongoing effort of the European Pulsar Timing Array, LEAP aims to go beyond the sensitivity threshold needed to deliver the first direct detection of gravitational waves. The five telescopes presently included in LEAP are the Effelsberg Telescope, the Lovell Telescope at Jodrell Bank, the Nançay Radio Telescope, the Sardinia Radio Telescope and the Westerbork Synthesis Radio Telescope. Dual polarization, Nyquist-sampled time series of the incoming radio waves are recorded and processed offline to form the coherent sum, resulting in a tied-array telescope with an effective aperture equivalent to a 195-m diameter circular dish. All observations are performed using a bandwidth of 128 MHz centred at a frequency of 1396 MHz. In this paper, we present the design of the LEAP experiment, the instrumentation, the storage and transfer of data and the processing hardware and software. In particular, we present the software pipeline that was designed to process the Nyquist-sampled time series, measure the phase and time delays between each individual telescope and a reference telescope and apply these delays to form the tied-array coherent addition. The pipeline includes polarization calibration and interference mitigation. We also present the first results from LEAP and demonstrate the resulting increase in sensitivity, which leads to an improvement in the pulse arrival times.

  18. Constraining Binary Stellar Evolution With Pulsar Timing

    NASA Astrophysics Data System (ADS)

    Ferdman, Robert D.; Stairs, I. H.; Backer, D. C.; Burgay, M.; Camilo, F.; D'Amico, N.; Demorest, P.; Faulkner, A.; Hobbs, G.; Kramer, M.; Lorimer, D. R.; Lyne, A. G.; Manchester, R.; McLaughlin, M.; Nice, D. J.; Possenti, A.

    2006-06-01

    The Parkes Multibeam Pulsar Survey has yielded a significant number of very interesting binary and millisecond pulsars. Two of these objects are part of an ongoing timing study at the Green Bank Telescope (GBT). PSR J1756-2251 is a double-neutron star (DNS) binary system. It is similar to the original Hulse-Taylor binary pulsar system PSR B1913+16 in its orbital properties, thus providing another important opportunity to test the validity of General Relativity, as well as the evolutionary history of DNS systems through mass measurements. PSR J1802-2124 is part of the relatively new and unstudied "intermediate-mass" class of binary system, which typically have spin periods in the tens of milliseconds, and/or relatively massive (> 0.7 solar masses) white dwarf companions. With our GBT observations, we have detected the Shapiro delay in this system, allowing us to constrain the individual masses of the neutron star and white dwarf companion, and thus the mass-transfer history, in this unusual system.

  19. Magnetized stimulated scattering in pulsar winds

    NASA Technical Reports Server (NTRS)

    Sincell, Mark W.; Krolik, Julian H.

    1992-01-01

    The effects of stimulated scattering on a collimated high brightness temperature beam of photons traversing a relativistically streaming magnetized plasma are studied. Under the assumption that the center of the photon beam is parallel to the bulk motion, we calculate the scattering rate as a function of the angular spread of the beam and the Lorentz factor gamma. Magnetization changes the photon recoil, without which stimulated scattering has no effect. It also introduces a strong dependence on frequency and polarization: if the photon frequency matches the electron cyclotron frequency, the scattering rate of photons polarized perpendicular to the magnetic field can be substantially enhanced relative to Thomson, and if the photon frequency is much less than the cyclotron frequency, the scattering is suppressed. Applying these calculations to pulsars, we find that stimulated scattering of the radio beam in the magnetized wind believed to exist outside the light cylinder can substantially alter the spectrum and polarization state of the radio signal. We suggest that the scattering rate is so high in some pulsars that the ability of the radio signal to penetrate the pulsar magnetosphere requires modification of either the conventional model of the magnetosphere or assumptions about the effects of stimulated scattering upon a beam.

  20. Genesis stories for the millisecond pulsar

    NASA Technical Reports Server (NTRS)

    Ruderman, M. A.; Shaham, J.

    1983-01-01

    Theoretical models proposed to explain the origin of the millisecond pulsar (MP) PSR 1937+214 are reviewed, examining their ability to explain its low surface dipole magnetic field (B), its low birth temperature (less than 10 to the 8th K), the absence of a companion or remnant, and its low velocity perpendicular to the Galactic plane. The models discussed are a single isolated explosion forming a rapidly spinning neutron star, spin-up of a dead pulsar by accretion from a companion, collapse of an accreting spinning white dwarf, and fusion of a tight binary composed of two old neutron stars. Although all of the models have difficulties in explaining one or more of the MP characteristics, the second model is found to be most probable in the light of present knowledge. The lack of a companion is explained by its tidal disruption after it had fed the accreting pre-pulsar for 1 Gyr or more and its mass had decreased to about 0.01 solar mass. Neutron stars accreting in this way have been observed in Galactic-bulge X-ray sources.

  1. Multiwavelength Emission From Pulsar Slot Gaps

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.; Stern, Julie; Dyks, Jarek

    2008-01-01

    We present results of a 3D model of optical to gamma-ray emission from the slot gap accelerator of a rotation-powered pulsar. Primary electrons accelerating to high altitude in the pulsar magnetosphere at the outer edge of the open field volume, as well as electron-positron pairs on field line interior to the slot gap, radiate curvature, inverse Compton and synchrotron radiation. Both primaries and pairs undergo cyclotron resonant absorption of radio photons, allowing them to maintain significant pitch angles and to produce a broad spectrum of emission from infra-red to GeV energies. Synchrotron radiation from pairs with a power-law energy spectrum dominate the spectrum up to 10 MeV. Synchrotron and curvature radiation of primaries dominates from 10 MeV up to a few GeV. The high-energy pulse profiles are dominated by caustics on trailing field lines. In the case of the Crab pulsar, the radio conal emission may also form caustics in phase with the high-energy peaks. If resonant absorption of radio emission produces high-energy synchroti-on radiation, emission below 200 Mev is expected to exhibit correlations in time and phase with the radio emission.

  2. OBSERVABILITY OF PULSAR BEAM BENDING BY THE Sgr A* BLACK HOLE

    SciTech Connect

    Stovall, Kevin; Creighton, Teviet; Price, Richard H.; Jenet, Fredrick A.

    2012-01-10

    According to some models, there may be a significant population of radio pulsars in the Galactic center. In principle, a beam from one of these pulsars could pass close to the supermassive black hole (SMBH) at the center, be deflected, and be detected by Earth telescopes. Such a configuration would be an unprecedented probe of the properties of spacetime in the moderate- to strong-field regime of the SMBH. We present here background on the problem, and approximations for the probability of detection of such beams. We conclude that detection is marginally possible with current telescopes, but that telescopes that will be operating in the near future, with an appropriate multiyear observational program, will have a reasonable chance of detecting a beam deflected by the SMBH.

  3. SEXTANT X-Ray Pulsar Navigation Demonstration: Flight System and Test Results

    NASA Technical Reports Server (NTRS)

    Winternitz, Luke M. B.; Mitchell, Jason W.; Hassouneh, Munther A.; Valdez, Jennifer E.; Price, Samuel R.; Semper, Sean R.; Yu, Wayne H.; Ray, Paul S.; Wood, Kent S.; Arzoumanian, Zaven; Gendreau, Keith C.

    2016-01-01

    The Station Explorer for X-ray Timing and Navigation Technology (SEXTANT) is a technology demonstration enhancement to the Neutron-star Interior Composition Explorer (NICER) mission. NICER is a NASA Explorer Mission of Opportunity that will be hosted on the International Space Station (ISS). SEXTANT will, for the first time, demonstrate real-time, on-board X-ray Pulsar Navigation (XNAV), a significant milestone in the quest to establish a GPS-like navigation capability available throughout our Solar System and beyond. This paper gives an overview of the SEXTANT system architecture and describes progress prior to environmental testing of the NICER flight instrument. It provides descriptions and development status of the SEXTANT flight software and ground system, as well as detailed description and results from the flight software functional and performance testing within the highfidelity Goddard Space Flight Center (GSFC) X-ray Navigation Laboratory Testbed (GXLT) software and hardware simulation environment. Hardware-in-the-loop simulation results are presented, using the engineering model of the NICER timing electronics and the GXLT pulsar simulator-the GXLT precisely controls NASA GSFC's unique Modulated X-ray Source to produce X-rays that make the NICER detector electronics appear as if they were aboard the ISS viewing a sequence of millisecond pulsars.

  4. SEXTANT X-Ray Pulsar Navigation Demonstration: Flight System and Test Results

    NASA Technical Reports Server (NTRS)

    Winternitz, Luke; Mitchell, Jason W.; Hassouneh, Munther A.; Valdez, Jennifer E.; Price, Samuel R.; Semper, Sean R.; Yu, Wayne H.; Ray, Paul S.; Wood, Kent S.; Arzoumanian, Zaven; Gendreau, Keith C.

    2016-01-01

    The Station Explorer for X-ray Timing and Navigation Technology (SEXTANT) is a technology demonstration enhancement to the Neutron-star Interior Composition Explorer (NICER) mission. NICER is a NASA Explorer Mission of Opportunity that will be hosted on the International Space Station (ISS). SEXTANT will, for the first time, demonstrate real-time, on-board X-ray Pulsar Navigation (XNAV), a significant milestone in the quest to establish a GPS-like navigation capability available throughout our Solar System and beyond. This paper gives an overview of the SEXTANT system architecture and describes progress prior to environmental testing of the NICER flight instrument. It provides descriptions and development status of the SEXTANT flight software and ground system, as well as detailed description and results from the flight software functional and performance testing within the high-fidelity Goddard Space Flight Center (GSFC) X-ray Navigation Laboratory Testbed (GXLT) software and hardware simulation environment. Hardware-in-the-loop simulation results are presented, using the engineering model of the NICER timing electronics and the GXLT pulsar simulator-the GXLT precisely controls NASA GSFC's unique Modulated X-ray Source to produce X-rays that make the NICER detector electronics appear as if they were aboard the ISS viewing a sequence of millisecond pulsars

  5. Radio pulsar death lines to SGRs/AXPs and white dwarfs pulsars

    NASA Astrophysics Data System (ADS)

    Lobato, Ronaldo V.; Coelho, J. G.; Malheiro, M.

    2015-12-01

    Recently, an alternative model based on white dwarfs pulsars has been proposed to explain a class of pulsars known as Soft Gamma Repeaters (SGR) and Anomalus X-Ray Pulsars (AXP) [1], usually named as magnetars. In this model, the magnetized white dwarfs can have surface magnetic field B ˜ 107 - 1010 G and rotate very fast with angular frequencies Ω ˜ 1 rad/s, allowing them to produce large electromagnetic (EM) potentials and generate electron-positron pairs. These EM potentials are comparable with the ones of neutron star pulsars with strong magnetic fields and even larger. In this study we consider two possible processes associated with the particle acceleration, both of them are common used to explain radio emission in neutron star pulsars: in the first process the pair production happens near to the star polar caps, i.e. inside of the light cylinder where magnetic field lines are closed; in the second one the creation of pair happens in the outer magnetosphere, i.e. far away of the star surface where magnetic field lines are open [2]. The analysis of the possibility of radio emission were done for 23 SGRs/AXPs of the McGill Online Magnetar Catalog [3] that contains the current information available on these sources. The results of this work show that the model where the particles production occur in the outer magnetosphere emission "o2" is the process compatible with the astronomical observations of absence of radio emission for almost all SGRs/AXPs when these sources are understood as white dwarf pulsars. Our work is a first attempted to find an explanation for the puzzle why for almost all the SGRs/AXPs was expected radio emission, but it was observed in only four of them. These four sources, as it was suggested recently [4], seem to belong to an high magnetic field neutron star pulsar category, different from all the others SGRs/AXPs that our work indicate to belong to a new class of white dwarf pulsars, very fast and magnetized.

  6. Radio pulsar death lines to SGRs/AXPs and white dwarfs pulsars

    SciTech Connect

    Lobato, Ronaldo V.; Malheiro, M.; Coelho, J. G.

    2015-12-17

    Recently, an alternative model based on white dwarfs pulsars has been proposed to explain a class of pulsars known as Soft Gamma Repeaters (SGR) and Anomalus X-Ray Pulsars (AXP) [1], usually named as magnetars. In this model, the magnetized white dwarfs can have surface magnetic field B ∼ 10{sup 7} − 10{sup 10} G and rotate very fast with angular frequencies Ω ∼ 1 rad/s, allowing them to produce large electromagnetic (EM) potentials and generate electron-positron pairs. These EM potentials are comparable with the ones of neutron star pulsars with strong magnetic fields and even larger. In this study we consider two possible processes associated with the particle acceleration, both of them are common used to explain radio emission in neutron star pulsars: in the first process the pair production happens near to the star polar caps, i.e. inside of the light cylinder where magnetic field lines are closed; in the second one the creation of pair happens in the outer magnetosphere, i.e. far away of the star surface where magnetic field lines are open [2]. The analysis of the possibility of radio emission were done for 23 SGRs/AXPs of the McGill Online Magnetar Catalog [3] that contains the current information available on these sources. The results of this work show that the model where the particles production occur in the outer magnetosphere emission “o2” is the process compatible with the astronomical observations of absence of radio emission for almost all SGRs/AXPs when these sources are understood as white dwarf pulsars. Our work is a first attempted to find an explanation for the puzzle why for almost all the SGRs/AXPs was expected radio emission, but it was observed in only four of them. These four sources, as it was suggested recently [4], seem to belong to an high magnetic field neutron star pulsar category, different from all the others SGRs/AXPs that our work indicate to belong to a new class of white dwarf pulsars, very fast and magnetized.

  7. AB INITIO PULSAR MAGNETOSPHERE: THREE-DIMENSIONAL PARTICLE-IN-CELL SIMULATIONS OF AXISYMMETRIC PULSARS

    SciTech Connect

    Philippov, Alexander A.; Spitkovsky, Anatoly

    2014-04-20

    We perform ''first-principles'' relativistic particle-in-cell simulations of aligned pulsar magnetosphere. We allow free escape of particles from the surface of a neutron star and continuously populate the magnetosphere with neutral pair plasma to imitate pair production. As pair plasma supply increases, we observe the transition from a charge-separated ''electrosphere'' solution with trapped plasma and no spin-down to a solution close to the ideal force-free magnetosphere with electromagnetically dominated pulsar wind. We calculate the magnetospheric structure, current distribution, and spin-down power of the neutron star. We also discuss particle acceleration in the equatorial current sheet.

  8. High-School Teams Joining Massive Pulsar Search

    NASA Astrophysics Data System (ADS)

    2008-09-01

    High school students and teachers will join astronomers on the cutting edge of science under a program to be operated by the National Radio Astronomy Observatory (NRAO) and West Virginia University (WVU), and funded by the National Science Foundation (NSF). The program, called the Pulsar Search Collaboratory, will engage West Virginia students and teachers in a massive search for new pulsars using data from the Robert C. Byrd Green Bank Telescope (GBT). Sue Ann Heatherly Sue Ann Heatherly, NRAO Education Officer CREDIT: Bill Saxton, NRAO/AUI/NSF (Click on image for larger version) The NSF announced a $892,838 grant to NRAO and WVU to conduct the three-year program. The project will involve 60 teachers and some 600 students in helping astronomers analyze data from 1500 hours of observing time on the GBT. The 120 terabytes of data produced by some 70,000 individual pointings of the giant, 17-million-pound telescope is expected to reveal dozens of previously-unknown pulsars. "The students in this program will be partners in frontier research, discovering new pulsars and measuring changes in pulsars already known," said Sue Ann Heatherly, the NRAO Education Officer in Green Bank and Principal Investigator in the project. Pulsars are superdense neutron stars, the corpses of massive stars that have exploded as supernovae. As the neutron star spins, lighthouse-like beams of radio waves, streaming from the poles of its powerful magnetic field, sweep through space. When one of these beams sweeps across the Earth, radio telescopes can capture the pulse of radio waves. Pulsars serve as exotic laboratories for studying the physics of extreme conditions. Scientists can learn valuable new information about the physics of subatomic particles, electromagnetics, and General Relativity by observing pulsars and the changes they undergo over time. The Pulsar Search Collaboratory (PSC) combines the capabilities of NRAO and WVU to provide a unique opportunity for teachers and students

  9. Fifty Years of Pulsar Candidate Selection: From simple filters to a new principled real-time classification approach

    NASA Astrophysics Data System (ADS)

    Lyon, R. J.; Stappers, B. W.; Cooper, S.; Brooke, J. M.; Knowles, J. D.

    2016-04-01

    Improving survey specifications are causing an exponential rise in pulsar candidate numbers and data volumes. We study the candidate filters used to mitigate these problems during the past fifty years. We find that some existing methods such as applying constraints on the total number of candidates collected per observation, may have detrimental effects on the success of pulsar searches. Those methods immune to such effects are found to be ill-equipped to deal with the problems associated with increasing data volumes and candidate numbers, motivating the development of new approaches. We therefore present a new method designed for on-line operation. It selects promising candidates using a purpose-built tree-based machine learning classifier, the Gaussian Hellinger Very Fast Decision Tree (GH-VFDT), and a new set of features for describing candidates. The features have been chosen so as to i) maximise the separation between candidates arising from noise and those of probable astrophysical origin, and ii) be as survey-independent as possible. Using these features our new approach can process millions of candidates in seconds (˜1 million every 15 seconds), with high levels of pulsar recall (90%+). This technique is therefore applicable to the large volumes of data expected to be produced by the Square Kilometre Array (SKA). Use of this approach has assisted in the discovery of 20 new pulsars in data obtained during the LOFAR Tied-Array All-Sky Survey (LOTAAS).

  10. Electromagnetic tornado in the vacuum gap of a pulsar

    SciTech Connect

    Kontorovich, V. M.

    2010-06-15

    The solution for an electromagnetic tornado that describes the motion in the discharge filament of breakdown in the vacuum gap of a pulsar has been obtained. This solution can serve as an explanation of the observed circular polarization of giant radiation pulses from pulsars.

  11. Detecting Dark Matter with Imploding Pulsars in the Galactic Center

    NASA Astrophysics Data System (ADS)

    Bramante, Joseph; Linden, Tim

    2014-11-01

    The paucity of old millisecond pulsars observed at the galactic center of the Milky Way could be the result of dark matter accumulating in and destroying neutron stars. In regions of high dark matter density, dark matter clumped in a pulsar can exceed the Schwarzschild limit and collapse into a natal black hole which destroys the pulsar. We examine what dark matter models are consistent with this hypothesis and find regions of parameter space where dark matter accumulation can significantly degrade the neutron star population within the galactic center while remaining consistent with observations of old millisecond pulsars in globular clusters and near the solar position. We identify what dark matter couplings and masses might cause a young pulsar at the galactic center to unexpectedly extinguish. Finally, we find that pulsar collapse age scales inversely with the dark matter density and linearly with the dark matter velocity dispersion. This implies that maximum pulsar age is spatially dependent on position within the dark matter halo of the Milky Way. In turn, this pulsar age spatial dependence will be dark matter model dependent.

  12. Pulsar populations and unidentified γ-ray sources

    NASA Astrophysics Data System (ADS)

    Harding, A. K.; Gonthier, P. L.; Grenier, I. A.; Perrot, C. A.

    The EGRET telescope on the Compton Gamma-ray Observatory detected over 200 sources and the majority of these are still unidentified. At least three subpopulations of EGRET sources have been associated with the Galaxy: bright sources lying along the Galactic plane, weaker sources spatially correlated with the Gould Belt and a high-latitude, halo population. Many of these sources may be pulsars and there are more than two-dozen radio pulsars in or near EGRET source error boxes, most of them recently discovered in the Parkes Multibeam Survey. We present results from several population synthesis studies of pulsars in the Galaxy, which predict the number of pulsars detected by γ-ray and radio surveys assuming models for the high-energy emission beam and its relation to the radio beam. Future γ-ray pulsar detections by AGILE and GLAST together with the recent large rise in the radio pulsar population will give greatly improved statistics. The relative numbers of radio and γ-ray pulsars detected in the plane and in the Gould Belt populations will provide an important discriminator between models of high-energy emission and will profoundly affect the numbers and birth rate of pulsars in the Galaxy.

  13. Detecting dark matter with imploding pulsars in the galactic center.

    PubMed

    Bramante, Joseph; Linden, Tim

    2014-11-01

    The paucity of old millisecond pulsars observed at the galactic center of the Milky Way could be the result of dark matter accumulating in and destroying neutron stars. In regions of high dark matter density, dark matter clumped in a pulsar can exceed the Schwarzschild limit and collapse into a natal black hole which destroys the pulsar. We examine what dark matter models are consistent with this hypothesis and find regions of parameter space where dark matter accumulation can significantly degrade the neutron star population within the galactic center while remaining consistent with observations of old millisecond pulsars in globular clusters and near the solar position. We identify what dark matter couplings and masses might cause a young pulsar at the galactic center to unexpectedly extinguish. Finally, we find that pulsar collapse age scales inversely with the dark matter density and linearly with the dark matter velocity dispersion. This implies that maximum pulsar age is spatially dependent on position within the dark matter halo of the Milky Way. In turn, this pulsar age spatial dependence will be dark matter model dependent. PMID:25415895

  14. Discovery of two new pulsars in 47 Tucanae (NGC 104)

    NASA Astrophysics Data System (ADS)

    Pan, Z.; Hobbs, G.; Li, D.; Ridolfi, A.; Wang, P.; Freire, P.

    2016-06-01

    We report the discovery of two new millisecond pulsars (PSRs J0024-7204aa and J0024-7204ab) in the globular cluster 47 Tucanae (NGC 104). Our results bring the total number of pulsars in 47 Tucanae to 25. These pulsars were discovered by reprocessing archival observations from the Parkes radio telescope. We reprocessed the data using a standard search procedure based on the PRESTO software package as well as using a new method in which we incoherently added the power spectra corresponding to ˜1100 h of observations. The newly discovered PSR J0024-7204aa, has a pulse frequency of ˜541 Hz (corresponding to a ˜1.84 ms period), which is higher than any other pulsars currently known in the cluster and ranks 12th amongst all the currently known pulsars. The dispersion measure of this pulsar, 24.941(7) cm-3 pc, is the highest in the cluster. The second discovered pulsar, PSR J0024-7204ab, is an isolated pulsar with a pulse frequency of ˜270 Hz (corresponding to a period of ˜3.70 ms).

  15. HST Imaging of the Pulsar Wind Nebula CTB 80

    NASA Astrophysics Data System (ADS)

    Hester, J.

    2000-12-01

    CTB80 is a remarkable pulsar wind nebula seen as the pulsar is passing through the shell of its own supernova remnant. HST images taken in the light of [O III], [S II], and Hα show the structure of a complex bow shock with a radiative central component and two Balmer-dominated lobes. Continuum images show the presence of a small diffuse knot of emission offset approximately 0.5'' from the location of the radio pulsar along a line bisecting the lobes. We interpret the knot as synchrotron emission, and note that its luminosity and offset from the pulsar make it remarkably like the knot seen 0.5'' to the south east of the Crab pulsar. We propose that the structure of the bow shock in CTB 80 is the result of an axisymmetric bipolar pulsar wind, much like that seen in the Crab Nebula, in which polar jets from the pulsar are responsible for forming the lobes. Shear flow from the relativistic jets may be responsible for stripping the cooling and recombination layer off of the back side of the shocks in the lobes. We predict that X-ray images of CTB 80 will show the presence of both a strong equatorial wind and synchrotron jets along the axis defined by the pulsar, the knot, and the lobes.

  16. Pulsar Simulations for the Fermi Large Area Telescope

    NASA Technical Reports Server (NTRS)

    Razzano, M.; Harding, A. K.; Baldini, L.; Bellazzini, R.; Bregeon, J.; Burnett, T.; Chiang, J.; Digel, S. W.; Dubois, R.; Kuss, M. W.; Latronico, L.; McEnery, J. E.; Omodei, N.; Pesce-Rollins, M.; Sgro, C.; Spandre, G.; Thompson, D. J.

    2009-01-01

    Pulsars are among the prime targets for the Large Area Telescope (LAT) aboard the recently launched Fermi observatory. The LAT will study the gamma-ray Universe between 20 MeV and 300 GeV with unprecedented detail. Increasing numbers of gamma-ray pulsars are being firmly identified, yet their emission mechanisms are far from being understood. To better investigate and exploit the tAT capabilities for pulsar science. a set of new detailed pulsar simulation tools have been developed within the LAT collaboration. The structure of the pulsar simulator package (PulsarSpeccrum) is presented here. Starting from photon distributions in energy and phase obtained from theoretical calculations or phenomenological considerations, gamma-rays are generated and their arrival times at the spacecraft are determined by taking Into account effects such as barycentric effects and timing noise. Pulsars in binary systems also can be simulated given orbital parameters. We present how simulations can be used for generating a realistic set of gamma rays as observed by the LAT, focusing on some case studies that show the performance of the LAT for pulsar observations.

  17. Prospects for Pulsar Studies with the GLAST Large Area Telescope

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.

    2007-01-01

    The Large Area Telescope (LAT) on the Gamma-ray Large Area Space Telescope (GLAST), due to launch in November 2007, will have unprecedented sensitivity and energy resolution for gamma-rays in the range of 30 MeV to 200 GeV. GLAST is therefore expected to provide major advances in the understanding of high-energy emission from rotation-powered pulsars. As the only presently known galactic GeV source class; pulsars will be one of the most important sources for study with GLAST. The main science goals of the LAT for pulsar studies include an increase in the number of detected radio-loud and radio-quiet gamma-ray pulsars, including millisecond pulsars, giving much better statistics for elucidating population characteristics, measurement of the high-energy spectrum and the shape of spectral cutoffs and determining pulse profiles for a variety of pulsars of different age. Further, measurement of phase-resolved spectra and energy dependent pulse profiles of the brighter pulsars should allow detailed tests of magnetospheric particle acceleration and radiation mechanisms, by comparing data with theoretical models that have been developed. Additionally, the LAT will have the sensitivity to allow blind pulsation searches of nearly all unidentified EGRET sources, to possibly uncover more radio-quiet Geminga-like pulsars.

  18. Prospects for Pulsar Studies with the GLAST Large Area Telescope

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.

    2006-01-01

    The Large Area Telescope (LAT) on the Gamma-ray Large Area Space Telescope (GLAST) will have unprecedented sensitivity and energy resolution for gamma-rays in the range of 30 MeV to 200 GeV. GLAST is therefore expected to provide major advances in the understanding of high-energy emission from rotation-powered pulsars. As the only presently known galactic GeV source class, pulsars will be one of the most important sources for study with GLAST. The main science goals of the LAT for pulsar studies include an increase in the number of detected radio-loud and radio-quiet gamma ray pulsars, including millisecond pulsars, giving much better statistics for elucidating population characteristics, measurement of the high-energy spectrum and the shape of spectral cutoffs and determining pulse profiles for a variety of pulsars of different age. Further, measurement of phase-resolved spectra and energy dependent pulse profiles of the brighter pulsars should allow detailed tests of magnetospheric particle acceleration and radiation mechanisms, by comparing data with theoretical models that have been developed. Additionally, the LAT will have the sensitivity to allow blind pulsation searches of nearly all unidentified EGRET sources, to possibly uncover more radio-quiet Geminga-like pulsars.

  19. An alternative numerical method for the stationary pulsar magnetosphere

    NASA Astrophysics Data System (ADS)

    Takamori, Yohsuke; Okawa, Hirotada; Takamoto, Makoto; Suwa, Yudai

    2014-02-01

    Stationary pulsar magnetospheres in the force-free system are governed by the pulsar equation. In 1999, Contopoulos, Kazanas, and Fendt (hereafter CKF) numerically solved the pulsar equation and obtained a pulsar magnetosphere model called the CKF solution that has both closed and open magnetic field lines. The CKF solution is a successful solution, but it contains a poloidal current sheet that flows along the last open field line. This current sheet is artificially added to make the current system closed. In this paper, we suggest an alternative method to solve the pulsar equation and construct pulsar magnetosphere models without a current sheet. In our method, the pulsar equation is decomposed into Ampère's law and the force-free condition. We numerically solve these equations simultaneously with a fixed poloidal current. As a result, we obtain a pulsar magnetosphere model without a current sheet, which is similar to the CKF solution near the neutron star and has a jet-like structure at a distance along the pole. In addition, we discuss physical properties of the model and find that the force-free condition breaks down in a vicinity of the light cylinder due to dissipation that is included implicitly in the numerical method.

  20. Detecting stochastic backgrounds of gravitational waves with pulsar timing arrays

    NASA Astrophysics Data System (ADS)

    Siemens, Xavier

    2016-03-01

    For the past decade the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has been using the Green Bank Telescope and the Arecibo Observatory to monitor millisecond pulsars. NANOGrav, along with two other international collaborations, the European Pulsar Timing Array and the Parkes Pulsar Timing Array in Australia, form a consortium of consortia: the International Pulsar Timing Array (IPTA). The goal of the IPTA is to directly detect low-frequency gravitational waves which cause small changes to the times of arrival of radio pulses from millisecond pulsars. In this talk I will discuss the work of NANOGrav and the IPTA, as well as our sensitivity to stochastic backgrounds of gravitational waves. I will show that a detection of the background produced by supermassive black hole binaries is possible by the end of the decade. Supported by the NANOGrav Physics Frontiers Center.

  1. PROPAGATION AND STABILITY OF SUPERLUMINAL WAVES IN PULSAR WINDS

    SciTech Connect

    Mochol, Iwona; Kirk, John G. E-mail: john.kirk@mpi-hd.mpg.de

    2013-07-01

    Nonlinear electromagnetic waves with superluminal phase velocity can propagate in the winds around isolated pulsars, and around some pulsars in binary systems. Using a short-wavelength approximation, we find and analyze an integrable system of equations that govern their evolution in spherical geometry. A confined mode is identified that stagnates to finite pressure at large radius and can form a precursor to the termination shock. Using a simplified criterion, we find this mode is stable for most isolated pulsars, but may be unstable if the external pressure is high, such as in the pulsar wind nebulae in starburst galaxies and in W44. Pulsar winds in eccentric binary systems, such as PSR 1259-63, may go through phases with stable and unstable electromagnetic precursors, as well as phases in which the density is too high for these modes to propagate.

  2. Do the enigmatic ``Infrared-Faint Radio Sources'' include pulsars?

    NASA Astrophysics Data System (ADS)

    Hobbs, George; Middelberg, Enno; Norris, Ray; Keith, Michael; Mao, Minnie; Champion, David

    2009-04-01

    The Australia Telescope Large Area Survey (ATLAS) team have surveyed seven square degrees of sky at 1.4GHz. During processing some unexpected infrared-faint radio sources (IFRS sources) were discovered. The nature of these sources is not understood, but it is possible that some of these sources may be pulsars within our own galaxy. We propose to observe the IFRS sources with steep spectral indices using standard search techniques to determine whether or not they are pulsars. A pulsar detection would 1) remove a subset of the IFRS sources from the ATLAS sample so they would not need to be observed with large optical/IR telescopes to find their hosts and 2) be intrinsically interesting as the pulsar would be a millisecond pulsar and/or have an extreme spatial velocity.

  3. Pulsar Search Results from the Arecibo Remote Command Center

    NASA Astrophysics Data System (ADS)

    Rodriguez, Miguel; Stovall, Kevin; Banaszak, Shawn A.; Becker, Alison; Biwer, Christopher M.; Boehler, Keith; Caballero, Keeisi; Christy, Brian; Cohen, Stephanie; Crawford, Fronefield; Cuellar, Andres; Danford, Andrew; Percy Dartez, Louis; Day, David; Flanigan, Joseph D.; Fonrouge, Aldo; Gonzalez, Adolfo; Gustavson, Kathy; Handzo, Emma; Hinojosa, Jesus; Jenet, Fredrick A.; Kaplan, David L. A.; Lommen, Andrea N.; Longoria, Chasity; Lopez, Janine; Lunsford, Grady; Mahany, Nicolas; Martinez, Jose; Mata, Alberto; Miller, Andy; Murray, James; Pankow, Chris; Ramirez, Ivan; Reser, Jackie; Rojas, Pablo; Rohr, Matthew; Rolph, Kristina; Rose, Caitlin; Rudnik, Philip; Siemens, Xavier; Tellez, Andrea; Tillman, Nicholas; Walker, Arielle; Wells, Bradley L.; Zaldivar, Jonathan; Zermeno, Adrienne; Gbncc Consortium, Palfa Consortium, Gbtdrift Consortium, Ao327 Consortium

    2015-01-01

    This poster presents the pulsar discoveries made by students in the Arecibo Remote Command Center (ARCC) program. The ARCC program was started at the University of Texas - Brownsville (UTB) within the Center for Advanced Radio Astronomy (CARA) as a group of scientists, faculty, graduate, undergraduate, and high school students interested in astrophysics. It has since expanded to form other ARCC programs at the University of Wisconsin-Milwaukee (UWM) and Franklin and Marshall College (F&M). The students in the ARCC group control the world's largest radio telescopes to search and discover pulsars. Pulsars are exotic neutron stars that emit beams of electromagnetic radiation. ARCC students use a web application to view and rate the images of radio pulsar candidates based on their signal characteristics. To date, ARCC students have searched through thousands of candidates and have discovered 61 pulsars to date.

  4. Pulsar rotation and dispersion measures and the galactic magnetic field.

    NASA Technical Reports Server (NTRS)

    Manchester, R. N.

    1972-01-01

    Use of observations of pulsar polarization and pulse time of arrival at frequencies between 250 and 500 MHz to determine rotation and dispersion measures for 19 and 21 pulsars, respectively. These measurements have been used to calculate mean line-of-sight components of the magnetic field in the path to the pulsars. These and other observations show that there is probably no contribution to the observed rotation measure from the pulsar itself. Low-latitude, low-dispersion pulsars are observed to have strong field components, and a strong dependence of rotation-measure sign on galactic longitude has been found. The observations are consistent with a relatively uniform field of about 3.5 microgauss directed toward about l = 90 deg in the local region, but appear to be inconsistent with the helical model for the local field.

  5. Binary millisecond pulsar discovery via gamma-ray pulsations.

    PubMed

    Pletsch, H J; Guillemot, L; Fehrmann, H; Allen, B; Kramer, M; Aulbert, C; Ackermann, M; Ajello, M; de Angelis, A; Atwood, W B; Baldini, L; Ballet, J; Barbiellini, G; Bastieri, D; Bechtol, K; Bellazzini, R; Borgland, A W; Bottacini, E; Brandt, T J; Bregeon, J; Brigida, M; Bruel, P; Buehler, R; Buson, S; Caliandro, G A; Cameron, R A; Caraveo, P A; Casandjian, J M; Cecchi, C; Çelik, Ö; Charles, E; Chaves, R C G; Cheung, C C; Chiang, J; Ciprini, S; Claus, R; Cohen-Tanugi, J; Conrad, J; Cutini, S; D'Ammando, F; Dermer, C D; Digel, S W; Drell, P S; Drlica-Wagner, A; Dubois, R; Dumora, D; Favuzzi, C; Ferrara, E C; Franckowiak, A; Fukazawa, Y; Fusco, P; Gargano, F; Gehrels, N; Germani, S; Giglietto, N; Giordano, F; Giroletti, M; Godfrey, G; Grenier, I A; Grondin, M-H; Grove, J E; Guiriec, S; Hadasch, D; Hanabata, Y; Harding, A K; den Hartog, P R; Hayashida, M; Hays, E; Hill, A B; Hou, X; Hughes, R E; Jóhannesson, G; Jackson, M S; Jogler, T; Johnson, A S; Johnson, W N; Kataoka, J; Kerr, M; Knödlseder, J; Kuss, M; Lande, J; Larsson, S; Latronico, L; Lemoine-Goumard, M; Longo, F; Loparco, F; Lovellette, M N; Lubrano, P; Massaro, F; Mayer, M; Mazziotta, M N; McEnery, J E; Mehault, J; Michelson, P F; Mitthumsiri, W; Mizuno, T; Monzani, M E; Morselli, A; Moskalenko, I V; Murgia, S; Nakamori, T; Nemmen, R; Nuss, E; Ohno, M; Ohsugi, T; Omodei, N; Orienti, M; Orlando, E; de Palma, F; Paneque, D; Perkins, J S; Piron, F; Pivato, G; Porter, T A; Rainò, S; Rando, R; Ray, P S; Razzano, M; Reimer, A; Reimer, O; Reposeur, T; Ritz, S; Romani, R W; Romoli, C; Sanchez, D A; Saz Parkinson, P M; Schulz, A; Sgrò, C; do Couto e Silva, E; Siskind, E J; Smith, D A; Spandre, G; Spinelli, P; Suson, D J; Takahashi, H; Tanaka, T; Thayer, J B; Thayer, J G; Thompson, D J; Tibaldo, L; Tinivella, M; Troja, E; Usher, T L; Vandenbroucke, J; Vasileiou, V; Vianello, G; Vitale, V; Waite, A P; Winer, B L; Wood, K S; Wood, M; Yang, Z; Zimmer, S

    2012-12-01

    Millisecond pulsars, old neutron stars spun up by accreting matter from a companion star, can reach high rotation rates of hundreds of revolutions per second. Until now, all such "recycled" rotation-powered pulsars have been detected by their spin-modulated radio emission. In a computing-intensive blind search of gamma-ray data from the Fermi Large Area Telescope (with partial constraints from optical data), we detected a 2.5-millisecond pulsar, PSR J1311-3430. This unambiguously explains a formerly unidentified gamma-ray source that had been a decade-long enigma, confirming previous conjectures. The pulsar is in a circular orbit with an orbital period of only 93 minutes, the shortest of any spin-powered pulsar binary ever found. PMID:23112297

  6. High Energy Emission from Pulsar Magnetospheres and Winds

    NASA Astrophysics Data System (ADS)

    Spitkovsky, Anatoly

    Recent gamma-ray observations of pulsars and their nebulae suggest an important role played by magnetic reconnection in determining the structure of the magnetosphere and the wind and in the acceleration of particles that lead to the high energy emission. Strong current sheets that are susceptible to magnetic dissipation are found near the light cylinder of the pulsar and persist throughout the wind. This proposal investigates the processes that occur in these current sheets, and determines their structure and particle acceleration properties. A suite of relativistic MHD and particle-in-cell kinetic simulations will be used to obtain the global 3D geometry of the magnetosphere, flow geometry in the current sheet, and calculate the dissipation of the current both near the pulsar and in the termination shock of the pulsar wind. The results will be applied to modeling the beaming in pulsar gamma-ray light curves, and to understanding particle acceleration in broadband and flaring nebular emission.

  7. The Annular Gap: Gamma-Ray & Radio Emission of Pulsars

    NASA Astrophysics Data System (ADS)

    Qiao, G. J.; Du, Y. J.; Han, J. L.; Xu, R. X.

    2013-01-01

    Pulsars have been found more than 40 years. Observations from radio to gamma-rays present abundant information. However, the radiation mechanism is still an open question. It is found that the annular gap could be formed in the magnetosphere of pulsars (neutron stars or quark stars), which combines the advantages of the polar cap, slot gap and outer gap models. It is emphasized that observations of some radio pulsars, normal and millisecond gamma-ray pulsars (MSGPs) show that the annular gap would play a very important role. Here we show some observational and theoretical evidences about the annular gap. For example, bi-drifting sub-pulses; radio and gamma-ray millisecond pulsars and so on.

  8. Microarcsecond VLBI Pulsar Astrometry with PSRπ. I. Two Binary Millisecond Pulsars with White Dwarf Companions

    NASA Astrophysics Data System (ADS)

    Deller, A. T.; Vigeland, S. J.; Kaplan, D. L.; Goss, W. M.; Brisken, W. F.; Chatterjee, S.; Cordes, J. M.; Janssen, G. H.; Lazio, T. J. W.; Petrov, L.; Stappers, B. W.; Lyne, A.

    2016-09-01

    Model-independent distance constraints to binary millisecond pulsars (MSPs) are of great value to both the timing observations of the radio pulsars and multiwavelength observations of their companion stars. Astrometry using very long baseline interferometry (VLBI) can be employed to provide these model-independent distances with very high precision via the detection of annual geometric parallax. Using the Very Long Baseline Array, we have observed two binary MSPs, PSR J1022+1001 and J2145–0750, over a two-year period and measured their distances to be {700}-10+14 pc and {613}-14+16 pc respectively. We use the well-calibrated distance in conjunction with revised analysis of optical photometry to tightly constrain the nature of their massive (M∼ 0.85 {M}ȯ ) white dwarf companions. Finally, we show that several measurements of the parallax and proper motion of PSR J1022+1001 and PSR J2145–0750 obtained by pulsar timing array projects are incorrect, differing from the more precise VLBI values by up to 5σ. We investigate possible causes for the discrepancy, and find that imperfect modeling of the solar wind is a likely candidate for the errors in the timing model given the low ecliptic latitude of these two pulsars.

  9. Microarcsecond VLBI Pulsar Astrometry with PSRπ. I. Two Binary Millisecond Pulsars with White Dwarf Companions

    NASA Astrophysics Data System (ADS)

    Deller, A. T.; Vigeland, S. J.; Kaplan, D. L.; Goss, W. M.; Brisken, W. F.; Chatterjee, S.; Cordes, J. M.; Janssen, G. H.; Lazio, T. J. W.; Petrov, L.; Stappers, B. W.; Lyne, A.

    2016-09-01

    Model-independent distance constraints to binary millisecond pulsars (MSPs) are of great value to both the timing observations of the radio pulsars and multiwavelength observations of their companion stars. Astrometry using very long baseline interferometry (VLBI) can be employed to provide these model-independent distances with very high precision via the detection of annual geometric parallax. Using the Very Long Baseline Array, we have observed two binary MSPs, PSR J1022+1001 and J2145–0750, over a two-year period and measured their distances to be {700}-10+14 pc and {613}-14+16 pc respectively. We use the well-calibrated distance in conjunction with revised analysis of optical photometry to tightly constrain the nature of their massive (M˜ 0.85 {M}ȯ ) white dwarf companions. Finally, we show that several measurements of the parallax and proper motion of PSR J1022+1001 and PSR J2145–0750 obtained by pulsar timing array projects are incorrect, differing from the more precise VLBI values by up to 5σ. We investigate possible causes for the discrepancy, and find that imperfect modeling of the solar wind is a likely candidate for the errors in the timing model given the low ecliptic latitude of these two pulsars.

  10. FREQUENCY DEPENDENCE OF PULSE WIDTH FOR 150 RADIO NORMAL PULSARS

    SciTech Connect

    Chen, J. L.; Wang, H. G.

    2014-11-01

    The frequency dependence of the pulse width is studied for 150 normal pulsars, mostly selected from the European Pulsar Network, for which the 10% multifrequency pulse widths can be well fit with the Thorsett relationship W {sub 10} = Aν{sup μ} + W {sub 10,} {sub min}. The relative fraction of pulse width change between 0.4 GHz and 4.85 GHz, η = (W {sub 4.85} – W {sub 0.4})/W {sub 0.4}, is calculated in terms of the best-fit relationship for each pulsar. It is found that 81 pulsars (54%) have η < –10% (group A), showing considerable profile narrowing at high frequencies, 40 pulsars (27%) have –10% ≤η ≤ 10% (group B), meaning a marginal change in pulse width, and 29 pulsars (19%) have η > 10% (group C), showing a remarkable profile broadening at high frequencies. The fractions of the group-A and group-C pulsars suggest that the profile narrowing phenomenon at high frequencies is more common than the profile broadening phenomenon, but a large fraction of the group-B and group-C pulsars (a total of 46%) is also revealed. The group-C pulsars, together with a portion of group-B pulsars with slight pulse broadening, can hardly be explained using the conventional radius-to-frequency mapping, which only applies to the profile narrowing phenomenon. Based on a recent version of the fan beam model, a type of broadband emission model, we propose that the diverse frequency dependence of pulse width is a consequence of different types of distribution of emission spectra across the emission region. The geometrical effect predicting a link between the emission beam shrinkage and spectrum steepening is tested but disfavored.

  11. Spin-down of Pulsars, and Their Electromagnetic and Gravitational Wave Radiations

    NASA Astrophysics Data System (ADS)

    Yue-zhu, Zhang; Yan-yan, Fu; Yi-huan, Wei; Cheng-min, Zhang; Shao-hua, Yu; Yuan-yue, Pan; Yuan-qi, Guo; De-hua, Wang

    2016-04-01

    Pulsars posses extremely strong magnetic fields, and their magnetic axis does not coincide with their rotation axis, this causes the pulsars to emit electromagnetic radiations. Pulsars rely on their rotational energy to compensate for the energy loss caused by the electromagnetic radiation, which leads to the gradually decelerated spin of pulsars. According to the theoretical deduction, we have calculated the initial period of the Crab Nebula pulsar, and derived the period evolution of the pulsar at any time in the future under the effect of the electromagnetic radiation. Considered the possible existence of quadrupole moment in the mass distribution of a pulsar, the gravitational wave radiation will also make the pulsar spin down, hence the variation of spin period of the Crab pulsar under the effect of gravitational wave radiation is further analyzed. Finally, combining the two kinds of radiation mechanisms, the evolution of spin period of the Crab pulsar under the joint action of these two kinds of radiation mechanisms is analyzed.

  12. Advanced computational methods for nodal diffusion, Monte Carlo, and S{sub N} problems. Progress report, January 1, 1992--March 31, 1993

    SciTech Connect

    Martin, W.R.

    1993-01-01

    This document describes progress on five efforts for improving effectiveness of computational methods for particle diffusion and transport problems in nuclear engineering: (1) Multigrid methods for obtaining rapidly converging solutions of nodal diffusion problems. A alternative line relaxation scheme is being implemented into a nodal diffusion code. Simplified P2 has been implemented into this code. (2) Local Exponential Transform method for variance reduction in Monte Carlo neutron transport calculations. This work yielded predictions for both 1-D and 2-D x-y geometry better than conventional Monte Carlo with splitting and Russian Roulette. (3) Asymptotic Diffusion Synthetic Acceleration methods for obtaining accurate, rapidly converging solutions of multidimensional SN problems. New transport differencing schemes have been obtained that allow solution by the conjugate gradient method, and the convergence of this approach is rapid. (4) Quasidiffusion (QD) methods for obtaining accurate, rapidly converging solutions of multidimensional SN Problems on irregular spatial grids. A symmetrized QD method has been developed in a form that results in a system of two self-adjoint equations that are readily discretized and efficiently solved. (5) Response history method for speeding up the Monte Carlo calculation of electron transport problems. This method was implemented into the MCNP Monte Carlo code. In addition, we have developed and implemented a parallel time-dependent Monte Carlo code on two massively parallel processors.

  13. On Being "in the Field": Practice, Progress and Problems in Research with Young People in Rural Areas.

    ERIC Educational Resources Information Center

    Leyshon, Michael

    2002-01-01

    Describes research methods used and problems encountered in fieldwork with rural English youth. Discusses the researcher's positionality and self, making local connections and finding "gatekeepers," building trust with young people, issues of youth safety versus confidentiality, types of communication and parental consent, the imaginative…

  14. Anxiety as a Predictor of Age at First Use of Substances and Progression to Substance Use Problems among Boys

    ERIC Educational Resources Information Center

    Marmorstein, Naomi R.; White, Helene Raskin; Loeber, Rolf; Stouthamer-Loeber, Magda

    2010-01-01

    This study examined associations of generalized and social anxiety with (1) age at first use of tobacco, alcohol, and marijuana and (2) interval from first use to first problem use of each substance. Participants were 503 males who comprised the youngest cohort (first assessed in the first grade) of the Pittsburgh Youth Study, a longitudinal…

  15. Arecibo Pulsar Survey Using ALFA. IV. Mock Spectrometer Data Analysis, Survey Sensitivity, and the Discovery of 40 Pulsars

    NASA Astrophysics Data System (ADS)

    Lazarus, P.; Brazier, A.; Hessels, J. W. T.; Karako-Argaman, C.; Kaspi, V. M.; Lynch, R.; Madsen, E.; Patel, C.; Ransom, S. M.; Scholz, P.; Swiggum, J.; Zhu, W. W.; Allen, B.; Bogdanov, S.; Camilo, F.; Cardoso, F.; Chatterjee, S.; Cordes, J. M.; Crawford, F.; Deneva, J. S.; Ferdman, R.; Freire, P. C. C.; Jenet, F. A.; Knispel, B.; Lee, K. J.; van Leeuwen, J.; Lorimer, D. R.; Lyne, A. G.; McLaughlin, M. A.; Siemens, X.; Spitler, L. G.; Stairs, I. H.; Stovall, K.; Venkataraman, A.

    2015-10-01

    The on-going Arecibo Pulsar-ALFA (PALFA) survey began in 2004 and is searching for radio pulsars in the Galactic plane at 1.4 GHz. Here we present a comprehensive description of one of its main data reduction pipelines that is based on the PRESTO software and includes new interference-excision algorithms and candidate selection heuristics. This pipeline has been used to discover 40 pulsars, bringing the survey’s discovery total to 144 pulsars. Of the new discoveries, eight are millisecond pulsars (MSPs; P\\lt 10 ms) and one is a Fast Radio Burst (FRB). This pipeline has also re-detected 188 previously known pulsars, 60 of them previously discovered by the other PALFA pipelines. We present a novel method for determining the survey sensitivity that accurately takes into account the effects of interference and red noise: we inject synthetic pulsar signals with various parameters into real survey observations and then attempt to recover them with our pipeline. We find that the PALFA survey achieves the sensitivity to MSPs predicted by theoretical models but suffers a degradation for P≳ 100 ms that gradually becomes up to ˜10 times worse for P\\gt 4 {{s}} at {DM}\\lt 150 pc cm-3. We estimate 33 ± 3% of the slower pulsars are missed, largely due to red noise. A population synthesis analysis using the sensitivity limits we measured suggests the PALFA survey should have found 224 ± 16 un-recycled pulsars in the data set analyzed, in agreement with the 241 actually detected. The reduced sensitivity could have implications on estimates of the number of long-period pulsars in the Galaxy.

  16. Particle Acceleration in Dissipative Pulsar Magnetospheres

    NASA Technical Reports Server (NTRS)

    Kazanas, Z.; Kalapotharakos, C.; Harding, A.; Contopoulos, I.

    2012-01-01

    Pulsar magnetospheres represent unipolar inductor-type electrical circuits at which an EM potential across the polar cap (due to the rotation of their magnetic field) drives currents that run in and out of the polar cap and close at infinity. An estimate ofthe magnitude of this current can be obtained by dividing the potential induced across the polar cap V approx = B(sub O) R(sub O)(Omega R(sub O)/c)(exp 2) by the impedance of free space Z approx eq 4 pi/c; the resulting polar cap current density is close to $n {GJ} c$ where $n_{GJ}$ is the Goldreich-Julian (GJ) charge density. This argument suggests that even at current densities close to the GJ one, pulsar magnetospheres have a significant component of electric field $E_{parallel}$, parallel to the magnetic field, a condition necessary for particle acceleration and the production of radiation. We present the magnetic and electric field structures as well as the currents, charge densities, spin down rates and potential drops along the magnetic field lines of pulsar magnetospheres which do not obey the ideal MHD condition $E cdot B = 0$. By relating the current density along the poloidal field lines to the parallel electric field via a kind of Ohm's law $J = sigma E_{parallel}$ we study the structure of these magnetospheres as a function of the conductivity $sigma$. We find that for $sigma gg OmegaS the solution tends to the (ideal) Force-Free one and to the Vacuum one for $sigma 11 OmegaS. Finally, we present dissipative magnetospheric solutions with spatially variable $sigma$ that supports various microphysical properties and are compatible with the observations.

  17. Elementary Wideband Timing of Radio Pulsars

    NASA Astrophysics Data System (ADS)

    Pennucci, Timothy T.; Demorest, Paul B.; Ransom, Scott M.

    2014-08-01

    We present an algorithm for the simultaneous measurement of a pulse time-of-arrival (TOA) and dispersion measure (DM) from folded wideband pulsar data. We extend the prescription from Taylor's 1992 work to accommodate a general two-dimensional template "portrait," the alignment of which can be used to measure a pulse phase and DM. We show that there is a dedispersion reference frequency that removes the covariance between these two quantities and note that the recovered pulse profile scaling amplitudes can provide useful information. We experiment with pulse modeling by using a Gaussian-component scheme that allows for independent component evolution with frequency, a "fiducial component," and the inclusion of scattering. We showcase the algorithm using our publicly available code on three years of wideband data from the bright millisecond pulsar J1824-2452A (M28A) from the Green Bank Telescope, and a suite of Monte Carlo analyses validates the algorithm. By using a simple model portrait of M28A, we obtain DM trends comparable to those measured by more standard methods, with improved TOA and DM precisions by factors of a few. Measurements from our algorithm will yield precisions at least as good as those from traditional techniques, but is prone to fewer systematic effects and is without ad hoc parameters. A broad application of this new method for dispersion measure tracking with modern large-bandwidth observing systems should improve the timing residuals for pulsar timing array experiments, such as the North American Nanohertz Observatory for Gravitational Waves.

  18. Cosmic-ray Positrons from Millisecond Pulsars

    NASA Astrophysics Data System (ADS)

    Venter, C.; Kopp, A.; Harding, A. K.; Gonthier, P. L.; Büsching, I.

    2015-07-01

    Observations by the Fermi Large Area Telescope of γ-ray millisecond pulsar (MSP) light curves imply copious pair production in their magnetospheres, and not exclusively in those of younger pulsars. Such pair cascades may be a primary source of Galactic electrons and positrons, contributing to the observed enhancement in positron flux above ∼10 GeV. Fermi has also uncovered many new MSPs, impacting Galactic stellar population models. We investigate the contribution of Galactic MSPs to the flux of terrestrial cosmic-ray electrons and positrons. Our population synthesis code predicts the source properties of present-day MSPs. We simulate their pair spectra invoking an offset-dipole magnetic field. We also consider positrons and electrons that have been further accelerated to energies of several TeV by strong intrabinary shocks in black widow (BW) and redback (RB) systems. Since MSPs are not surrounded by pulsar wind nebulae or supernova shells, we assume that the pairs freely escape and undergo losses only in the intergalactic medium. We compute the transported pair spectra at Earth, following their diffusion and energy loss through the Galaxy. The predicted particle flux increases for non-zero offsets of the magnetic polar caps. Pair cascades from the magnetospheres of MSPs are only modest contributors around a few tens of GeV to the lepton fluxes measured by the Alpha Magnetic Spectrometer, PAMELA, and Fermi, after which this component cuts off. The contribution by BWs and RBs may, however, reach levels of a few tens of percent at tens of TeV, depending on model parameters.

  19. Elementary wideband timing of radio pulsars

    SciTech Connect

    Pennucci, Timothy T.; Demorest, Paul B.; Ransom, Scott M. E-mail: pdemores@nrao.edu

    2014-08-01

    We present an algorithm for the simultaneous measurement of a pulse time-of-arrival (TOA) and dispersion measure (DM) from folded wideband pulsar data. We extend the prescription from Taylor's 1992 work to accommodate a general two-dimensional template 'portrait', the alignment of which can be used to measure a pulse phase and DM. We show that there is a dedispersion reference frequency that removes the covariance between these two quantities and note that the recovered pulse profile scaling amplitudes can provide useful information. We experiment with pulse modeling by using a Gaussian-component scheme that allows for independent component evolution with frequency, a 'fiducial component', and the inclusion of scattering. We showcase the algorithm using our publicly available code on three years of wideband data from the bright millisecond pulsar J1824–2452A (M28A) from the Green Bank Telescope, and a suite of Monte Carlo analyses validates the algorithm. By using a simple model portrait of M28A, we obtain DM trends comparable to those measured by more standard methods, with improved TOA and DM precisions by factors of a few. Measurements from our algorithm will yield precisions at least as good as those from traditional techniques, but is prone to fewer systematic effects and is without ad hoc parameters. A broad application of this new method for dispersion measure tracking with modern large-bandwidth observing systems should improve the timing residuals for pulsar timing array experiments, such as the North American Nanohertz Observatory for Gravitational Waves.

  20. OPTIMAL STRATEGIES FOR CONTINUOUS GRAVITATIONAL WAVE DETECTION IN PULSAR TIMING ARRAYS

    SciTech Connect

    Ellis, J. A.; Siemens, X.; Creighton, J. D. E.

    2012-09-10

    Supermassive black hole binaries (SMBHBs) are expected to emit a continuous gravitational wave signal in the pulsar timing array (PTA) frequency band (10{sup -9} to 10{sup -7} Hz). The development of data analysis techniques aimed at efficient detection and characterization of these signals is critical to the gravitational wave detection effort. In this paper, we leverage methods developed for LIGO continuous wave gravitational searches and explore the use of the F-statistic for such searches in pulsar timing data. Babak and Sesana have used this approach in the context of PTAs to show that one can resolve multiple SMBHB sources in the sky. Our work improves on several aspects of prior continuous wave search methods developed for PTA data analysis. The algorithm is implemented fully in the time domain, which naturally deals with the irregular sampling typical of PTA data and avoids spectral leakage problems associated with frequency domain methods. We take into account the fitting of the timing model and have generalized our approach to deal with both correlated and uncorrelated colored noise sources. We also develop an incoherent detection statistic that maximizes over all pulsar-dependent contributions to the likelihood. To test the effectiveness and sensitivity of our detection statistics, we perform a number of Monte Carlo simulations. We produce sensitivity curves for PTAs of various configurations and outline an implementation of a fully functional data analysis pipeline. Finally, we present a derivation of the likelihood maximized over the gravitational wave phases at the pulsar locations, which results in a vast reduction of the search parameter space.

  1. Detecting gravitational wave bursts with Pulsar Timing

    NASA Astrophysics Data System (ADS)

    Cornish, Neil; Ellis, Justin

    2016-03-01

    The history of astronomy has shown that the Universe is full of suprises. One of the great hopes for gravitational wave astronomy is the discovery of unanticipated phenomena. To accomplish this we need to develop flexible analysis techniques that are able to detect signals with arbitrary waveform morphology. Here I will describe a multi-wavelet approach for the analysis of timing residuals from a pulsar timing array. Please schedule my talk immediately after the related talk by my co-author Justin Ellis.

  2. Magnetospheric structure of rotation powered pulsars

    SciTech Connect

    Arons, J. California Univ., Livermore, CA . Inst. of Geophysics and Planetary Physics)

    1991-01-07

    I survey recent theoretical work on the structure of the magnetospheres of rotation powered pulsars, within the observational constraints set by their observed spindown, their ability to power synchrotron nebulae and their ability to produce beamed collective radio emission, while putting only a small fraction of their energy into incoherent X- and gamma radiation. I find no single theory has yet given a consistent description of the magnetosphere, but I conclude that models based on a dense outflow of pairs from the polar caps, permeated by a lower density flow of heavy ions, are the most promising avenue for future research. 106 refs., 4 figs., 2 tabs.

  3. Accretion powered X-ray pulsars

    NASA Technical Reports Server (NTRS)

    White, N. E.; Swank, J. H.; Holt, S. S.

    1982-01-01

    A unified description of the properties of 14 X-ray pulsars is presented and compared with the current theoretical understanding of these systems. The sample extends over six orders of magnitude in luminosity, with the only trend in the phase averaged spectra being that the lower luminosity systems appear to have less abrupt high energy cutoffs. There is no correlation of luminosity with power law index, high energy cutoff energy or iron line EW. Detailed pulse phase spectroscopy is given for five systems.

  4. On the detectability of eccentric binary pulsars

    NASA Astrophysics Data System (ADS)

    Bagchi, Manjari; Lorimer, Duncan R.; Wolfe, Spencer

    2013-06-01

    By generalizing earlier work of Johnston and Kulkarni, we present a detailed description of the reduction in the signal-to-noise ratio for observations of binary pulsars. We present analytical expressions, and provide software, to calculate the sensitivity reduction for orbits of arbitrary eccentricity. We find that this reduction can be quite significant, especially in the case of a massive companion like another neutron star or a black hole. On the other hand, the reduction is less for highly eccentric orbits. We also demonstrate that this loss of sensitivity can be recovered by employing `acceleration search' or `acceleration-jerk search' algorithms.

  5. Neutron star binaries, pulsars and burst sources

    NASA Technical Reports Server (NTRS)

    Lamb, F. K.

    1981-01-01

    Unresolved issues involving neutron star binaries, pulsars, and burst sources are described. Attention is drawn to the types of observations most likely to resolve them. Many of these observations are likely to be carried out during the next decade by one or more missions that have been approved or proposed. Flux measurements with an imaging detector and broad-band spectroscopic studies in the energy range 30-150 keV are discussed. The need for soft X-ray and X-ray observations with an instrument which has arcminute angular resolution and an effective area substantially greater than of ROSAT or EXOSAT is also discussed.

  6. Pulsar population synthesis using palfa detections and pulsar search collaboratory discoveries including a wide DNS system and a nearby MSP

    NASA Astrophysics Data System (ADS)

    Swiggum, Joseph Karl

    Using the ensemble of detections from pulsar surveys, we can learn about the sizes and characteristics of underlying populations. In this thesis, I analyze results from the Pulsar Arecibo L-band Feed Array (PALFA) precursor and Green Bank Telescope 350 MHz Drift Scan surveys; I examine survey sensitivity to see how detections can inform pulsar population models, I look at new ways of including young scientists -- high school students -- in the discovery process and I present timing solutions for students' discoveries (including a nearby millisecond pulsar and a pulsar in a wide-orbit double neutron star system). The PALFA survey is on-going and uses the ALFA 7-beam receiver at 1400 MHz to search both inner and outer Galactic sectors visible from Arecibo (32° ?£? 77° and 168° ?£? 214°) close to the Galactic plane (|b| ? 5°) for pulsars. The PALFA precursor survey observed a subset of this region, (|b| ? 1°) and detected 45 pulsars, including one known millisecond pulsar (MSP) and 11 previously unknown, long-period (normal) pulsars. I assess the sensitivity of the PALFA precursor survey and use the number of normal pulsar and MSP detections to infer the size of each underlying Galactic population. Based on 44 normal pulsar detections and one MSP, we constrain each population size to 107,000+36,000-25,000 and 15,000 +85,000-6,000 respectively with 95% confidence. Based on these constraints, we predict yields for the full PALFA survey and find a deficiency in normal pulsar detections, possibly due to radio frequency interference and/or scintillation, neither of which are currently accounted for in population simulations. The GBT 350 MHz Drift Scan survey collected data in the summer of 2007 while the GBT was stationary, undergoing track replacement. Results discussed here come from ~20% of the survey data, which were processed and donated to the Pulsar Search Collaboratory (PSC). The PSC is a joint outreach program between WVU and NRAO, involving high school

  7. Imprints of relic gravitational waves on pulsar timing

    NASA Astrophysics Data System (ADS)

    Tong, Ming-Lei; Ding, Yong-Heng; Zhao, Cheng-Shi; Gao, Feng; Yan, Bao-Rong; Yang, Ting-Gao; Gao, Yu-Ping

    2016-03-01

    Relic gravitational waves (RGWs), a background originating during inflation, would leave imprints on pulsar timing residuals. This makes RGWs an important source for detection of RGWs using the method of pulsar timing. In this paper, we discuss the effects of RGWs on single pulsar timing, and quantitatively analyze the timing residuals caused by RGWs with different model parameters. In principle, if the RGWs are strong enough today, they can be detected by timing a single millisecond pulsar with high precision after the intrinsic red noises in pulsar timing residuals are understood, even though simultaneously observing multiple millisecond pulsars is a more powerful technique for extracting gravitational wave signals. We correct the normalization of RGWs using observations of the cosmic microwave background (CMB), which leads to the amplitudes of RGWs being reduced by two orders of magnitude or so compared to our previous works. We obtained new constraints on RGWs using recent observations from the Parkes Pulsar Timing Array, employing the tensor-to-scalar ratio r = 0.2 due to the tensor-type polarization observations of CMB by BICEP2 as a reference value, even though its reliability has been brought into question. Moreover, the constraints on RGWs from CMB and Big Bang nucleosynthesis will also be discussed for comparison.

  8. The Pulsar Quartet: Listening to a Galactic Symphony

    NASA Astrophysics Data System (ADS)

    Kiziltan, Bülent

    2014-06-01

    Pulsars are exotic dead stars that emit very regular radio pulses. These pulses are attributed to their regular rotation. Some pulsars are spinning fast enough that the audio equivalent waveform of their pulses fall within our hearing range. If human ears were tuned to radio waves it would have been possible to ‘hear’ these very compact stars. We produced the audio waveform of these pulsar signals and mapped them onto a frequency chart to find the corresponding musical notes. We use these ‘audible' pulsars like musical instruments in a symphony orchestra to play a full quartet. At the same time, an accompanying visual interface shows the realistic distribution of all pulsars in our own Galaxy. Pulsars shine as they play each note in the quartet with realistic brightening and subsequent dimming proportional to their rotational energies. This can serve as an educational tool at all levels to demonstrate many interesting aspects of stellar evolution and articulate an aesthetic connection of us with the cosmos. Interested in watching the light show while the Milky Way Pulsar Orchestra plays a quartet?

  9. High Energy Cosmic Rays and Neutrinos from Newborn Pulsars

    NASA Astrophysics Data System (ADS)

    Fang, Ke; Kotera, Kumiko; Olinto, Angela

    2013-04-01

    Newborn pulsars offer favorable sites for cosmic ray acceleration and interaction. Particles could be striped off the star surface and accelerated in the pulsar wind up to PeV-100 EeV energies, depending on the pulsar's birth period and magnetic field strength. Once accelerated, the cosmic rays interact with the surrounding supernova ejecta until they escape the source. By assuming a normal distribution of pulsar birth periods centered at 300,ms, we find the combined contribution of extragalactic pulsars produce ultrahigh energy cosmic rays that agree with both the observed energy spectrum and composition trend reported by the Auger Observatory. Meanwhile, we point out their Galactic counterparts naturally give rise to a cosmic ray flux peaked at very high energies (VHE, between 10^16 and 10^18 ,eV), which can bridge the gap between predictions of cosmic rays produced by supernova remnants and the observed spectrum and composition just below the ankle. Young pulsars in the universe would also contribute to a diffuse neutrino background due to the photomeson interactions, whose detectability and typical neutrino energy are discussed. Lastly, we predict a neutrino emission level for the future birth of a nearby pulsar.

  10. Detecting Pulsars with Interstellar Scintillation in Variance Images

    NASA Astrophysics Data System (ADS)

    Dai, S.; Johnston, S.; Bell, M. E.; Coles, W. A.; Hobbs, G.; Ekers, R. D.; Lenc, E.

    2016-08-01

    Pulsars are the only cosmic radio sources known to be sufficiently compact to show diffractive interstellar scintillations. Images of the variance of radio signals in both time and frequency can be used to detect pulsars in large-scale continuum surveys using the next generation of synthesis radio telescopes. This technique allows a search over the full field of view while avoiding the need for expensive pixel-by-pixel high time resolution searches. We investigate the sensitivity of detecting pulsars in variance images. We show that variance images are most sensitive to pulsars whose scintillation time-scales and bandwidths are close to the subintegration time and channel bandwidth. Therefore, in order to maximise the detection of pulsars for a given radio continuum survey, it is essential to retain a high time and frequency resolution, allowing us to make variance images sensitive to pulsars with different scintillation properties. We demonstrate the technique with Murchision Widefield Array data and show that variance images can indeed lead to the detection of pulsars by distinguishing them from other radio sources.

  11. Detecting the errors in solar system ephemeris by pulsar timing

    NASA Astrophysics Data System (ADS)

    Li, Liang; Guo, Li; Wang, Guang-Li

    2016-04-01

    Pulsar timing uses planetary ephemerides to convert the measured pulse arrival time at an observatory to the arrival time at the Solar System barycenter (SSB). Since these planetary ephemerides cannot be perfect, a method of detecting the associated errors based on a pulsar timing array is developed. By using observations made by an array of 18 millisecond pulsars from the Parkes Pulsar Timing Array, we estimated the vector uncertainty from the Earth to the SSB of JPL DE421, which reflects the offset of the ephemeris origin with respect to the ideal SSB, in different piecewise intervals of pulsar timing data, and found consistent results. To investigate the stability and reliability of our method, we divided all the pulsars into two groups. Both groups yield largely consistent results, and the uncertainty of the Earth-SSB vector is several hundred meters, which is consistent with the accuracy of JPL DE421. As an improvement in the observational accuracy, pulsar timing will be helpful to improve the solar system ephemeris in the future.

  12. Pulsar Wind Nebulae, Space Velocities and Supernova Remnant

    NASA Technical Reports Server (NTRS)

    2005-01-01

    The original proposal for this LTSA grant was for X-ray studies of pulsars, and especially pulsar wind nebulae and what they could tell us about pulsar properties, especially their space velocities. By any metric, this program has been very successful. No fewer than 14 papers on directly related topics (and several dozen more on related topics) have been published in refereed journals with the PI as lead or co-author, all observational results that have had significant impact on the field. These include the first X-ray detection of the "Duck" pulsar, a clear demonstration that estimated pulsar ages can be off by over an order of magnitude (via observations of the young supernova remnant G11.2-0.3) and the detection of the first pulsar wind nebula around a millisecond pulsar. These publications have also resulted in 4 press releases. Moreover, they also represent the thesis work of two PhD students at MIT (Froney Crawford and Mike Pivovaroff) and one postdoctoral fellow, Bryan Gaensler, now Assistant Professor at Harvard.

  13. PRESTO: PulsaR Exploration and Search TOolkit

    NASA Astrophysics Data System (ADS)

    Ransom, Scott

    2011-07-01

    PRESTO is a large suite of pulsar search and analysis software. It was primarily designed to efficiently search for binary millisecond pulsars from long observations of globular clusters (although it has since been used in several surveys with short integrations and to process a lot of X-ray data as well). To date, PRESTO has discovered well over a hundred and fifty pulsars, including approximately 100 recycled pulsars, about 80 of which are in binaries. It is written primarily in ANSI C, with many of the recent routines in Python. Written with portability, ease-of-use, and memory efficiency in mind, it can currently handle raw data from the following pulsar machines or formats: PSRFITS search-format data (as from GUPPI at the GBT and the Mock Spectrometers at Arecibo)SPIGOT at the GBTMost Wideband Arecibo Pulsar Processor (WAPP) at AreciboThe Parkes and Jodrell Bank 1-bit filterbank formatsBerkeley-Caltech Pulsar Machine (BCPM) at the GBT (may it RIP...)8-bit filterbank format from SIGPROC (other formats will be added if required)A time series composed of single precision (i.e. 4-byte) floating point dataPhoton arrival times (or events) in ASCII or double-precision binary formats

  14. On Detecting Millisecond Pulsars at the Galactic Center

    NASA Astrophysics Data System (ADS)

    Macquart, Jean-Pierre; Kanekar, Nissim

    2015-06-01

    The lack of detected pulsars at the Galactic Center (GC) region is a long-standing mystery. We argue that the high stellar density in the central parsec around the GC is likely to result in a pulsar population dominated by millisecond pulsars (MSPs), similar to the situation in globular cluster environments. Earlier GC pulsar searches have been largely insensitive to such an MSP population, accounting for the lack of pulsar detections. We estimate the best search frequency for such an MSP population with present and upcoming broad-band radio telescopes for two possible scattering scenarios, the “weak-scattering” case suggested by the recent detection of a magnetar close to the GC, and the “strong-scattering” case, with the scattering screen located close to the GC. The optimal search frequencies are ≈8 GHz (weak-scattering) and ≈25 GHz (strong-scattering), for pulsars with periods 1-20 ms, assuming that GC pulsars have a luminosity distribution similar to that those in the rest of the Milky Way. We find that 10-30 hr integrations with the Very Large Array and the Green Bank Telescope would be sufficient to detect MSPs at the GC distance in the weak-scattering case. However, if the strong-scattering case is indeed applicable to the GC, observations with the full Square Kilometre Array would be needed to detect the putative MSP population.

  15. Prospects for Pulsar Studies with the GLAST Large Area Telescope

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.

    2007-01-01

    The Large Area Telescope (LAT) on the Gamma-ray Large Area Space Telescope (GLAST), due to launch in November 2007, will have unprecedented sensitivity and energy resolution for gamma-rays in the range of 30 MeV to 200 GeV. GLAST is therefore expected to provide major advances in the understanding of high-energy emission from rotation-powered p ulsars. As the only presently known galactic GeV source class, pulsar s will be one of the most important sources for study with GLAST. The main science goals of the LAT for pulsar studies include an increase in the number of detected radio-loud and radio-quiet gamma-ray pulsar s, including millisecond pulsars, giving much better statistics for e lucidating population characteristics, measurement of the high-energy spectrum and the shape of spectral cutoffs and determining pulse profiles for a variety of pulsars of different age. Further, measurement of phase-resolved spectra and energy dependent pulse profiles of the brighter pulsars should allow detailed tests of magnetospheric partic le acceleration and radiation mechanisms, by comparing data with theo retical models that have been developed. Additionally, the LAT will have the sensitivity to allow blind pulsation searches of nearly all un identified EGRET sources, to possibly uncover more radio-quiet Geming a-like pulsars.

  16. X-ray emission from two nearby millisecond pulsars

    NASA Technical Reports Server (NTRS)

    Thorsett, S. E.

    1994-01-01

    This grant, titled 'X-Ray Emission from Two Nearby Millisecond Pulsars,' included ROSAT observations of the nearby pulsars PSR J2322+20 and PSR J2019+24. Neither was detected, although the observations were among the most sensitive ever made towards millisecond pulsars, reaching 1.5 x 10(exp 29) and 2.7 x 10(exp 29) erg s(exp -1) (0.1-2.4 keV), respectively. This is about, or slightly below, the predicted level of emission from the Seward and Wang empirical prediction, based on an extrapolation from slower pulsars. To understand the significance of this result, we have compared these limits with observations of four other millisecond pulsars, taken from the ROSAT archives. Except for the case of PSR B1821-21, where we identified a possible x-ray counterpart, only upper limits on x-ray flux were obtained. From these results, we conclude that x-ray emission beaming does not follow the same dependence on pulsar period as that of radio emission: while millisecond pulsars have beaming fractions near unity in the radio, x-ray emission is observed only for favorable viewing geometries.

  17. Unraveling the drift behaviour of the remarkable pulsar PSR B0826-34

    NASA Astrophysics Data System (ADS)

    Gupta, Y.; Gil, J.; Kijak, J.; Sendyk, M.

    2004-10-01

    Pulsars with drifting subpulses are thought to be an important key to unlocking the mystery of how radio pulsars work. We present new results from high sensitivity GMRT observations of PSR B0826-34 - a wide profile pulsar that exhibits an interesting but complicated drifting pattern. We provide a model to explain the observed subpulse drift properties of this pulsar, including the apparent reversals of the drift direction. In this model, PSR B0826-34 is close to being an aligned rotator. Using information about the polarization and frequency evolution of the pulse profile, we solve for the emission geometry of this pulsar and show that the angle between the rotation axis and the dipole magnetic axis is less than 5 °. As a result, our line of sight samples a circular path that is entirely within the emission beam. We see evidence for as many as 6 to 7 drifting bands in the main pulse at 318 MHz, which are all part of a circulating system of about 15 spark-associated subpulse emission beams that form, upon averaging, one conal ring of the mean emission. We also see evidence for a second ring of emission, which becomes dominant at higher frequencies (above 1 GHz) due to the nature of the emission geometry. We model the subpulse drift behaviour of this pulsar in detail, providing quantitative treatments of the aliasing problem and various effects of geometry which play an important role. The observed drift rate is an aliased version of the true drift rate which is such that a subpulse drifts to the location of the adjacent subpulse (or a multiple thereof) in about one pulsar period. We show that small variations, of the order of 3-8%, in the mean drift rate are then enough to explain the apparent reversals of drift direction seen in the data. We find the mean circulation time of the drift pattern to be significantly longer than the predictions of the original \\citet{RS75} model and propose an explanation for this, which relates to modified models with temperature

  18. The Vela pulsar in the near-infrared

    NASA Astrophysics Data System (ADS)

    Shibanov, Yu. A.; Koptsevich, A. B.; Sollerman, J.; Lundqvist, P.

    2003-08-01

    We report on the first detection of the Vela pulsar in the near-infrared with the VLT/ISAAC in the Js and H bands. The pulsar magnitudes are Js=22.71+/-0.10 and H=22.04+/-0.16. We compare our results with the available multiwavelength data and show that the dereddened phase-averaged optical spectrum of the pulsar can be fitted with a power law Fnu ~ nu -alpha_nu with alphanu = 0.12+/-0.05, assuming the color excess EB-V=0.055+/-0.005 based on recent spectral fits of the emission of the Vela pulsar and its supernova remnant in X-rays. The negative slope of the pulsar spectrum is different from the positive slope observed over a wide optical range in the young Crab pulsar spectrum. The near-infrared part of the Vela spectrum appears to have the same slope as the phase-averaged spectrum in the high energy X-ray tail, obtained in the 2-10 keV range with the RXTE. Both of these spectra can be fitted with a single power law suggesting their common origin. Because the phase-averaged RXTE spectrum in this range is dominated by the second X-ray peak of the pulsar light curve, coinciding with the second main peak of its optical pulse profile, we suggest that this optical peak can be redder than the first one. We also detect two faint extended structures in the 1.5 = 3.1 arcsec vicinity of the pulsar, projected on and aligned with the south-east jet and the inner arc of the pulsar wind nebula, detected in X-rays with Chandra. We discuss their possible association with the nebula. Based on observations collected at the European Southern Observatory, Paranal, Chile (ESO Programme 66.D-0568).

  19. Pulsar Emission Geometry and Accelerating Field Strength

    NASA Technical Reports Server (NTRS)

    DeCesar, Megan E.; Harding, Alice K.; Miller, M. Coleman; Kalapotharakos, Constantinos; Parent, Damien

    2012-01-01

    The high-quality Fermi LAT observations of gamma-ray pulsars have opened a new window to understanding the generation mechanisms of high-energy emission from these systems, The high statistics allow for careful modeling of the light curve features as well as for phase resolved spectral modeling. We modeled the LAT light curves of the Vela and CTA I pulsars with simulated high-energy light curves generated from geometrical representations of the outer gap and slot gap emission models. within the vacuum retarded dipole and force-free fields. A Markov Chain Monte Carlo maximum likelihood method was used to explore the phase space of the magnetic inclination angle, viewing angle. maximum emission radius, and gap width. We also used the measured spectral cutoff energies to estimate the accelerating parallel electric field dependence on radius. under the assumptions that the high-energy emission is dominated by curvature radiation and the geometry (radius of emission and minimum radius of curvature of the magnetic field lines) is determined by the best fitting light curves for each model. We find that light curves from the vacuum field more closely match the observed light curves and multiwavelength constraints, and that the calculated parallel electric field can place additional constraints on the emission geometry

  20. High Mass X-ray Binary Pulsars

    NASA Astrophysics Data System (ADS)

    Naik, Sachindra

    2016-07-01

    High Mass X-ray Binaries (HMXBs) are interesting objects that provide a wide range of observational probes to the nature of the two stellar components, accretion process, stellar wind and orbital parameters of the systems. Most of the transient HMXBs are found to Be/X-ray binaries (~67%), consisting of a compact object (neutron star) in orbit around the companion Be star. The orbit of the compact object around the Be star is wide and highly eccentric. Be/X-ray binaries are generally quiescent in X-ray emission. The transient X-ray outbursts seen in these objects are known to be due to interaction between the compact object and the circumstellar disk surrounding the Be star. In the recent years, another class of transient HMXBs have been found which have supergiant companions and show shorter X-ray outbursts. X-ray, infrared and optical observations of these HMXBs provide vital information regarding these systems. The timing and broad-band X-ray spectral properties of a few HMXB pulsars, mainly Be/X-ray binary pulsars during regular X-ray outbursts will be discussed.

  1. Pulsar candidates towards Fermi unassociated sources

    NASA Astrophysics Data System (ADS)

    Frail, D. A.; Mooley, K. P.; Jagannathan, P.; Intema, H. T.

    2016-09-01

    We report on a search for steep spectrum radio sources within the 95 per cent confidence error ellipses of the Fermi unassociated sources from the Large Area Telescope (LAT). Using existing catalogues and the newly released Giant Metrewave Radio Telescope all-sky survey at 150 MHz, we identify compact radio sources that are bright at MHz frequencies but faint or absent at GHz frequencies. Such steep spectrum radio sources are rare and constitute a sample of pulsar candidates, selected independently of period, dispersion measure, interstellar scattering and orbital parameters. We find point-like, steep spectrum candidates towards 11 Fermi sources. Based on the gamma-ray/radio positional coincidence, the rarity of such radio sources, and the properties of the 3FGL sources themselves, we argue that many of these sources could be pulsars. They may have been missed by previous radio periodicity searches due to interstellar propagation effects or because they lie in an unusually tight binary. If this hypothesis is correct, then renewed gamma-ray and radio periodicity searches at the positions of the steep spectrum radio sources may reveal pulsations.

  2. Radio Observations of Elongated Pulsar Wind Nebulae

    NASA Astrophysics Data System (ADS)

    Ng, Stephen C.-Y.

    2015-08-01

    The majority of pulsars' rotational energy is carried away by relativistic winds, which are energetic particles accelerated in the magnetosphere. The confinement of the winds by the ambient medium result in synchrotron bubbles with broad-band emission, which are commonly referred to as pulsar wind nebulae (PWNe). Due to long synchrotron cooling time, a radio PWN reflects the integrated history of the system, complementing information obtained from the X-ray and higher energy bands. In addition, radio polarization measurements can offer a powerful probe of the PWN magnetic field structure. Altogether these can reveal the physical conditions and evolutionary history of a system.I report on preliminary results from high-resolution radio observations of PWNe associated with G327.1-1.1, PSRs J1015-5719, B1509-58, and J1549-4848 taken with the Australia Telescope Compact Array (ATCA). Their magnetic field structure and multiwavelength comparison with other observations are discussed.This work is supported by a ECS grant of the Hong Kong Government under HKU 709713P. The Australia Telescope is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO.

  3. Cosmic ray nuclei from extragalactic and galactic pulsars

    NASA Astrophysics Data System (ADS)

    Fang, Ke

    2013-02-01

    In an extragalactic newly-born pulsar, nuclei striped off the star surface can be accelerated to extreme energies and leave the source through dense supernova surroundings. The escaped ultrahigh energy cosmic rays can explain both UHE energy spectral and atmospheric depth observations. In addition, assuming that Galactic pulsars accelerate cosmic rays with the same injection composition, very high energy cosmic rays from local pulsars can meet the flux measurements from above the knee to the ankle, and at the same time, agree with the detected composition trend.

  4. Ultra-Deep searches for pulsars around Sgr A*

    NASA Astrophysics Data System (ADS)

    Eatough, Ralph; Johnston, Simon; Kramer, Michael; Keane, Evan; Shannon, Ryan

    2014-04-01

    Pulsars found closely orbiting the supermassive black hole candidate at the centre of our Galaxy, Sgr A*, could be used to perform the most precise tests of theories of gravity, and to accurately measure the properties of the black hole itself, such as the mass and spin. These measurements can be used to test the no hair theorem and cosmic censorship conjecture in Einsteins theory of General Relativity. The recent discovery of a magnetar in the immediate vicinity of Sgr A* prooves pulsars are indeed present in this region and detectable at lower frequencies than previously thought. We propose to perfom deep searches for such pulsars.

  5. New Energetic Radio Pulsars: An Archival X-Ray Survey

    NASA Technical Reports Server (NTRS)

    2002-01-01

    This ADP grant was to analyze archival X-ray data obtained in the direction of radio pulsars that were recently discovered as part of the Parkes Multibeam Pulsar Search, which was done using the 64-m Parkes radio telescope in Australia. The survey discovered nearly 700 pulsars, of which roughly three dozen were possible candidates for the detection of X-ray emission. Our team looked at 30 of the most interesting candidates. In most cases, there was insufficient data in the archive to conclude anything. However in several cases, there were interesting archival observations. In three cases, a detailed analysis proved scientifically interesting, and two publications have resulted.

  6. A description of HIV prevalence trends in Nigeria from 2001 to 2010: what is the progress, where is the problem?

    PubMed Central

    Bashorun, Adebobola; Nguku, Patrick; Kawu, Issa; Ngige, Evelyn; Ogundiran, Adeniyi; Sabitu, Kabir; Nasidi, Abdulsalam; Nsubuga, Peter

    2014-01-01

    Introduction Nigeria's population of 160 million and estimated HIV prevalence of 3.34% (2011) makes Nigeria the second highest HIV burden worldwide, with 3.2 million people living with HIV (PLHIV). In 2010, US government spent about US$456.5 million on the Nigerian epidemic. Antenatal clinic (ANC) HIV sero-prevalence sentinel survey has been conducted biennially in Nigeria since 1991 to track the epidemic. This study looked at the trends of HIV in Nigeria over the last decade to identify progress and needs. Methods We conducted description of HIV sero-prevalence sentinel cross-sectional surveys conducted among pregnant women attending ANC from 2001 to 2010, which uses consecutive sampling and unlinked-anonymous HIV testing (UAT) in160 sentinel facilities. 36,000 blood samples were collected and tested. We used Epi-Info to determine national and state HIV prevalence and trends. The Estimation and Projection Package with Spectrum were used to estimate/project the burden of infection. Results National ANC HIV prevalence rose from 1.8% (1991) to 5.8% (2001) and dropped to 4.1% (2010). Since 2001, states in the center, and south of Nigeria had higher prevalence than the rest, with Benue and Cross Rivers notable. Benue was highest in 2001 (14%), 2005 (10%), and 2010 (12.7%). Overall, eight states (21.6%) showed increased HIV prevalence while six states (16.2%) had an absolute reduction of at least 2% from 2001 to 2010. In 2010, Nigeria was estimated to have 3.19 million PLHIV, with the general population prevalence projected to drop from 3.34% in 2011 to 3.27% in 2012. Conclusion Examining a decade of HIV ANC surveillance in Nigeria revealed important differences in the epidemic in states that need to be examined further to reveal key drivers that can be used to target future interventions. PMID:25328622

  7. High-precision timing of 42 millisecond pulsars with the European Pulsar Timing Array

    NASA Astrophysics Data System (ADS)

    Desvignes, G.; Caballero, R. N.; Lentati, L.; Verbiest, J. P. W.; Champion, D. J.; Stappers, B. W.; Janssen, G. H.; Lazarus, P.; Osłowski, S.; Babak, S.; Bassa, C. G.; Brem, P.; Burgay, M.; Cognard, I.; Gair, J. R.; Graikou, E.; Guillemot, L.; Hessels, J. W. T.; Jessner, A.; Jordan, C.; Karuppusamy, R.; Kramer, M.; Lassus, A.; Lazaridis, K.; Lee, K. J.; Liu, K.; Lyne, A. G.; McKee, J.; Mingarelli, C. M. F.; Perrodin, D.; Petiteau, A.; Possenti, A.; Purver, M. B.; Rosado, P. A.; Sanidas, S.; Sesana, A.; Shaifullah, G.; Smits, R.; Taylor, S. R.; Theureau, G.; Tiburzi, C.; van Haasteren, R.; Vecchio, A.

    2016-05-01

    We report on the high-precision timing of 42 radio millisecond pulsars (MSPs) observed by the European Pulsar Timing Array (EPTA). This EPTA Data Release 1.0 extends up to mid-2014 and baselines range from 7-18 yr. It forms the basis for the stochastic gravitational-wave background, anisotropic background, and continuous-wave limits recently presented by the EPTA elsewhere. The Bayesian timing analysis performed with TEMPONEST yields the detection of several new parameters: seven parallaxes, nine proper motions and, in the case of six binary pulsars, an apparent change of the semimajor axis. We find the NE2001 Galactic electron density model to be a better match to our parallax distances (after correction from the Lutz-Kelker bias) than the M2 and M3 models by Schnitzeler. However, we measure an average uncertainty of 80 per cent (fractional) for NE2001, three times larger than what is typically assumed in the literature. We revisit the transverse velocity distribution for a set of 19 isolated and 57 binary MSPs and find no statistical difference between these two populations. We detect Shapiro delay in the timing residuals of PSRs J1600-3053 and J1918-0642, implying pulsar and companion masses m_p=1.22_{-0.35}^{+0.5} M_{⊙}, m_c = 0.21_{-0.04}^{+0.06} M_{⊙} and m_p=1.25_{-0.4}^{+0.6} M_{⊙}, m_c = 0.23_{-0.05}^{+0.07} M_{⊙}, respectively. Finally, we use the measurement of the orbital period derivative to set a stringent constraint on the distance to PSRs J1012+5307 and J1909-3744, and set limits on the longitude of ascending node through the search of the annual-orbital parallax for PSRs J1600-3053 and J1909-3744.

  8. Dynamics of Family Economic Hardship and the Progression of Health Problems of Husbands and Wives during the Middle Years: A Perspective from Rural Mid-West

    PubMed Central

    Wickrama, K. A. S.; Kwag, Kyung Hwa; Lorenz, Federick O.; Conger, Rand D.; Surjadi, Florensia F.

    2010-01-01

    Objectives The objective of this study was to investigate the influence of theoretically important dimensions of stability and change in economic hardship during early middle years on decade-long health problems of husbands and wives. Method The study used prospective data collected from 360 middle-aged husbands and wives during a 12-year period. The variables included self-reported economic hardship (22 items), mental and physical health, and physical impairment. Results The results supported the hypothesis that the dynamics of family economic hardship (in terms of stability and change) during the early middle years contribute to subsequent onset of health problems of middle-aged husbands and wives. These health problems, in turn, progress as an interrelated process through intra-health-domain continuities, cross-health-domain proliferations and dyadic associations as they pass through midlife. Discussion A better understanding these processes may aid in the formation and effective implementation of mental and physical health promotion programs for middle-aged husbands and wives. PMID:20682949

  9. ARECIBO PULSAR SURVEY USING ALFA: PROBING RADIO PULSAR INTERMITTENCY AND TRANSIENTS

    SciTech Connect

    Deneva, J. S.; Cordes, J. M.; McLaughlin, M. A.; Lorimer, D. R.; Edel, S.; Kondratiev, V. I.; Nice, D. J.; Crawford, F.; Bhat, N. D. R.; Camilo, F.; Champion, D. J.; Freire, P. C. C.; Hessels, J. W. T.; Jenet, F. A.; Kasian, L.; Kaspi, V. M.; Lazarus, P.; Stairs, I. H.; Kramer, M.; Ransom, S. M.

    2009-10-01

    We present radio transient search algorithms, results, and statistics from the ongoing Arecibo Pulsar ALFA (PALFA) survey of the Galactic plane. We have discovered seven objects through a search for isolated dispersed pulses. All of these objects are Galactic and have measured periods between 0.4 and 4.7 s. One of the new discoveries has a duty cycle of 0.01%, smaller than that of any other radio pulsar. We discuss the impact of selection effects on the detectability and classification of intermittent sources, and compare the efficiencies of periodicity and single-pulse (SP) searches for various pulsar classes. For some cases we find that the apparent intermittency is likely to be caused by off-axis detection or a short time window that selects only a few bright pulses and favors detection with our SP algorithm. In other cases, the intermittency appears to be intrinsic to the source. No transients were found with DMs large enough to require that they originate from sources outside our Galaxy. Accounting for the on-axis gain of the ALFA system, as well as the low gain but large solid-angle coverage of far-out sidelobes, we use the results of the survey so far to place limits on the amplitudes and event rates of transients of arbitrary origin.

  10. Modelling the response of river systems to environmental change: Progress, problems and prospects for palaeo-environmental reconstructions

    NASA Astrophysics Data System (ADS)

    Van De Wiel, Marco J.; Coulthard, Tom J.; Macklin, Mark G.; Lewin, John

    2011-01-01

    Over the last decade several computational models, and several types of model, have been developed to simulate the response of river systems to environmental change over time scales of decades to millennia: hydrological models, flood inundation models, channel morphology models, channel network models, models of river meandering and river braiding, alluvial stratigraphy models, and landscape evolution models. Each type of model simulates different aspects of a river's response to changes in environmental inputs such as climate and land-use — and to changes in these inputs. And each type of model has its abilities, advantages and limitations. We provide an overview of the different types of model that have been developed, and we evaluate their suitability for testing hypotheses about past environmental conditions, as well as for investigating the response of alluvial river systems to future environmental change. Additionally, we discuss the general issues and problems of computational modelling (e.g. scale and resolution, data availability, process representation, process parameterization, model calibration, non-linearity, and uncertainty), and the extent to which these hamper the usefulness of the models as a tool in environmental landscape studies. Finally, we identify trends in computational modelling research to outline possible future directions of the discipline.

  11. Non-monotonous character of single radio pulsar spin-down

    NASA Astrophysics Data System (ADS)

    Biryukov, A. V.; Beskin, G. M.; Karpov, S. V.

    2011-10-01

    Our paper is dedicated to the problem of anomalous values of braking indices n obs and spin frequency second derivatives ddot ν of isolated radio pulsars. Observations of these objects for over 40 years have shown that in addition to the complex short-term irregular component in the evolution of the pulsars' frequency, secular values of its second derivative are orders of magnitude greater than the predicted theoretical ones, and in a good half of cases—they are even negative. We earlier attributed this behavior of secular values of the second derivative to the presence of a cyclic component in the secular evolution of ν( t), with a characteristic recurrence time of thousands to tens of thousand years. We continue to develop this hypothesis based on a more detailed statistical analysis of the characteristics of 297 isolated radio pulsars: we analyze the model of these objects spin-down, consisting of two components, monotonic and cyclic, and determine their parameters. We demonstrate that the monotonic spin-down component is described by the classical magnetodipolar power law with an braking index of about 3, while the large amplitude of the cyclic component causes a significant variation of the observed spin-down rate (dot ν ) (with respect to magnetodipolar one), and fully determines the anomalous values of ddot ν and n obs. An important consequence of the existence of a cyclic component of the pulsar rotational variations is the difference between their characteristic ages and respective secular values (by about 0.5-5 times). This allows to explainthe observed discrepancy of the characteristic and physical ages of some objects, as well as very large, up to 108 years, characteristic ages of some old pulsars. The paper argues that the cyclic component of the observed spin-down is due to the long-term precession of neutron stars around their magnetic axes, which, in particular, may be driven by the anomalous braking torque. In the model of purely

  12. Production of Gamma-Rays in the Pulsar Wind Nebulae

    NASA Astrophysics Data System (ADS)

    Bednarek, W.; Bartosik, M.

    2004-10-01

    We construct the time dependent hadronic-leptonic radiation model for the high energy processes inside the pulsar wind nebulae (PWNe). This model is based on the hypothesis that heavy nuclei are effi- ciently accelerated in the vicinity of young pulsars. Different energy loss processes of nuclei and accel- erated by them leptons are considered in order to obtain the equilibrium spectra of these particles in- side the nebula at an arbitrary time after the pulsar formation. We calculate the multiwavelength spec- tra from specific PWNe expected from different lep- tonic and hadronic processes. From normalization of the calculated synchrotron spectrum to the observed spectrum at low energies, the expected TeV gamma- ray fluxes from a few PWNe are predicted and its possible detectability by the future TeV telescopes is discussed. Key words: Pulsars: nebulae - radiation mecha- nisms: gamma-rays.

  13. Pulsar timing arrays: the promise of gravitational wave detection.

    PubMed

    Lommen, Andrea N

    2015-12-01

    We describe the history, methods, tools, and challenges of using pulsars to detect gravitational waves. Pulsars act as celestial clocks detecting gravitational perturbations in space-time at wavelengths of light-years. The field is poised to make its first detection of nanohertz gravitational waves in the next 10 years. Controversies remain over how far we can reduce the noise in the pulsars, how many pulsars should be in the array, what kind of source we will detect first, and how we can best accommodate our large bandwidth systems. We conclude by considering the important question of how to plan for a post-detection era, beyond the first detection of gravitational waves. PMID:26564968

  14. Timing and searching millisecond pulsars in globular clusters

    NASA Astrophysics Data System (ADS)

    D'Amico, Nichi; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Kramer, Michael; Sarkissian, John; Lyne, Andrew; Burgay, Marta; Corongiu, Alessandro; Camilo, Fernando; Bailes, Matthew

    2009-10-01

    Timing the dozen pulsars discovered in P303 is ensuring high quality results: (a) the peculiarities (in position or projected acceleration) of all the 5 millisecond pulsars in NGC6752 suggested the presence of non thermal dynamics in the core, perhaps due to black-holes of intermediate mass; (b) the eclipsing pulsar in NGC6397 is a stereotype for studying the late evolution of exotic binaries. We propose to continue our timing project focusing mostly on NGC6752 at 20cm (in order to measure additional parameters useful to constrain the existence of a black-hole) and NGC6397 at 10cm (for studying the eclipse region and the orbital secular evolution). We also request time for performing pilot observations for a new deeper than ever search for millisecond pulsars in a subset of suitable clusters. This revamped search (as well as the requested timing observations) will exploit the new back-ends (APSR and DFB4) now available at Parkes.

  15. Binary pulsar evolution: unveiled links and new species

    NASA Astrophysics Data System (ADS)

    Possenti, Andrea

    2013-03-01

    In the last years a series of blind and/or targeted pulsar searches led to almost triple the number of known binary pulsars in the galactic field with respect to a decade ago. The focus will be on few outliers, which are emerging from the average properties of the enlarged binary pulsar population. Some of them may represent the long sought missing links between two kinds of neutron star binaries, while others could represent the stereotype of new groups of binaries, resulting from an evolutionary path which is more exotic than those considered until recently. In particular, a new class of binaries, which can be dubbed Ultra Low Mass Binary Pulsars (ULMBPs), is emerging from recent data.

  16. Timing and searching millisecond pulsars in globular clusters

    NASA Astrophysics Data System (ADS)

    D'Amico, Nichi; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Kramer, Michael; Sarkissian, John; Lyne, Andrew; Burgay, Marta; Corongiu, Alessandro; Camilo, Fernando; Bailes, Matthew; van Straten, Willem

    2010-04-01

    Timing the dozen pulsars discovered in P303 is ensuring high quality results: (a) the peculiarities (in position or projected acceleration) of all the 5 millisecond pulsars in NGC6752 suggested the presence of non thermal dynamics in the core, perhaps due to black-holes of intermediate mass; (b) the eclipsing pulsar in NGC6397 is a stereotype for studying the late evolution of exotic binaries. We propose to continue our timing project focusing mostly on NGC6752 at 20cm (in order to measure additional parameters useful to constrain the existence of a black-hole) and NGC6397 at 10cm (for studying the eclipse region and the orbital secular evolution). We also request time for performing observations for a new deeper than ever search for millisecond pulsars in a subset of suitable clusters. This revamped search (as well as the requested timing observations) will exploit the new back-ends (APSR and DFB4) now available at Parkes.

  17. Pulsar Pair Cascades in a Distorted Magnetic Dipole Field

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.; Muslimov, Alex G.

    2010-01-01

    We investigate the effect of a distorted neutron star dipole magnetic field on pulsar pair cascade multiplicity and pair death lines. Using a simple model for a distorted dipole field that produces an offset polar cap (PC), we derive the accelerating electric field above the PC in space-charge-limited flow. We find that even a modest azimuthally asymmetric distortion can significantly increase the accelerating electric field on one side of the PC and, combined with a smaller field line radius of curvature, leads to larger pair multiplicity. The death line for producing pairs by curvature radiation moves downward in the P-P-dot diagram, allowing high pair multiplicities in a larger percentage of the radio pulsar population. These results could have important implications for the radio pulsar population, high energy pulsed emission, and the pulsar contribution to cosmic ray positrons.

  18. An axisymmetric magnetohydrodynamic model for the Crab pulsar wind bubble

    NASA Technical Reports Server (NTRS)

    Begelman, Mitchell C.; Li, Zhi-Yun

    1992-01-01

    We extend Kennel and Coroniti's (1984) spherical magnetohydrodynamic models for the Crab Nebula to include the pinching effect of the toroidal magnetic field. Since the bulk nebular flow is likely to be very submagnetosonic, a quasi-static treatment is possible. We show that the pinching effect can be responsible for the observed elongation of the pulsar wind bubble, as indicated by the surface brightness contours of optical synchrotron radiation. From the observed elongation we estimate a value for sigma, the ratio of Poynting flux to plasma kinetic energy flux in the free pulsar wind, which is consistent with previous results from spherical models. Using the inferred magnetic field configuration inside the pulsar wind bubble, combined with the observed dimensions of the X-ray nebula, we are able to constrain the particle distribution function. We conclude that, for a power-law injection function, the maximum energy has to be much larger in the pulsar equatorial region than in the polar region.

  19. Fast pulsars, strange stars: An opportunity in radio astronomy

    SciTech Connect

    Glendenning, N.K.

    1990-07-15

    The world's data on radio pulsars is not expected to represent the underlying pulsar population because of a search bias against detection of short periods, especially below 1 ms. Yet pulsars in increasing numbers with periods right down to this limit have been discovered suggesting that there may be even shorter ones. If pulsars with periods below 1/2 ms were found, the conclusion that the confined hadronic phase of nucleons and nuclei is only metastable would be almost inescapable. The plausible ground state in that event is the deconfined phase of (3-flavor) strange-quark-matter. From the QCD energy scale this is as likely a ground state as the confined phase. We show that strange matter as the ground state is not ruled out by any known fact, and most especially not by the fact that the universe is in the confined phase. 136 refs.

  20. Chandler wobble and free core nutation of single pulsar

    NASA Astrophysics Data System (ADS)

    Gusev, A.

    2011-10-01

    PSR B1828-11 has long-term, highly periodic and correlated variations pulse shape and of the rate of slow-down with period variations approximately 1000, 500 and 250 days (Stairs et al., 2000). There are three potential explanations of pulses time-of-arrival from pulsar concerned with the interior of the neutron star, planetary bodies, free precession and nutation. We use the Hamiltonian canonical method of Getino et al. (1999) for the dynamically symmetrical pulsar consisting of the rigid crust, elliptical liquid outer core and solid inner core of PSR B1828-11. Correctly extending theory of differential rotation of a pulsar, we investigated dependence on Chandler wobble period, Inner Chandler Wobble, retrograde Free Core Nutation and prograde Free Inner Core Nutation from ellipticity of inner crystal core, outer liquid core and total pulsar.

  1. The radio luminosity distribution of pulsars in 47 Tucanae

    NASA Astrophysics Data System (ADS)

    McConnell, D.; Deshpande, A. A.; Connors, T.; Ables, J. G.

    2004-03-01

    We have used the Australia Telescope Compact Array to seek the integrated radio flux from all the pulsars in the core of the globular cluster 47 Tucanae. We have detected an extended region of radio emission and have calibrated its flux against the flux distribution of the known pulsars in the cluster. We find the total 20-cm radio flux from the pulsars in the cluster to be S= 2.0 +/- 0.3 mJy. This implies the lower limit to the radio luminosity distribution to be minL1400= 0.4 mJy kpc2 and the size of the observable pulsar population to be N<~ 30.

  2. Pulsars in the Classroom: Suggested Exercises for Lab or Homework

    ERIC Educational Resources Information Center

    Gordon, Kurtiss J.

    1978-01-01

    Exercises for introductory to intermediate level college students are proposed. Observations of pulsars can be used to illustrate the phenomena of dispersion and Faraday rotation of radio waves, and to illustrate the differential rotation of the galaxy. (BB)

  3. Pulsar H(alpha) Bowshocks probe Neutron Star Physics

    NASA Astrophysics Data System (ADS)

    Romani, Roger W.

    2014-08-01

    We propose a KOALA/AAOmega study of southern pulsar bow shocks. These rare, Balmer-dominated, non-radiative shocks provide an ideal laboratory to study the interaction of the relativistic pulsar wind with the ISM. We will cover H(alpha) at high spectral resolution to measure the kinematics of the upstream ISM and the post-shock flow, while the blue channel measures the Balmer decrement and probes for a faint cooling component. These data, with MHD models, allow us to extract the 3D flow geometry and the orientation and asymmetry of the pulsar wind. These data can also measure the pulsar spindown power, thus estimating the neutron star moment of inertia and effecting a fundamental test of dense matter physics.

  4. Pulsar timing sensitivity to very-low-frequency gravitational waves

    SciTech Connect

    Jenet, Fredrick A.; Armstrong, J. W.; Tinto, Massimo

    2011-04-15

    We compute the sensitivity, constrained by instrumental, propagation, and other fundamental noises, of pulsar timing to very-low-frequency gravitational waves (GWs). Reaching predicted GW signal strengths will require suppression of time-of-arrival fluctuations caused by interstellar plasma turbulence and a reduction of white rms timing noise to < or approx. 100 ns. Assuming negligible intrinsic pulsar rotational noise, perfect time transfer from time standard to observatory, and stable pulse profiles, the resulting single-pulsar signal-to-noise ratio=1 sensitivity is limited by terrestrial time standards at h{sub rms}{approx}2x10{sup -16} [f/ (1 cycle/year)]-1/2 for f<3x10{sup -8} Hz, where f is the Fourier frequency and a bandwidth of 1 cycle/(10 years) is assumed. Since this sensitivity is comparable to predicted GW signal levels, a reliable detection will require substantial signal-to-noise ratio improvement via pulsar timing array.

  5. Finding (Or Not) New Gamma-Ray Pulsars with GLAST

    SciTech Connect

    Ransom, Scott M.; /NRAO, Charlottesville

    2011-11-29

    Young energetic pulsars will likely be the largest class of Galactic sources observed by GLAST, with many hundreds detected. Many will be unknown as radio pulsars, making pulsation detection dependent on radio and/or x-ray observations or on blind periodicity searches of the gamma-rays. Estimates for the number of pulsars GLAST will detect in blind searches have ranged from tens to many hundreds. I argue that the number will be near the low end of this range, partly due to observations being made in a scanning as opposed to a pointing mode. This paper briefly reviews how blind pulsar searches will be conducted using GLAST, what limits these searches, and how the computations and statistics scale with various parameters.

  6. Future Gamma-Ray Observations of Pulsars and their Environments

    NASA Technical Reports Server (NTRS)

    Thompson, David J.

    2006-01-01

    Pulsars and pulsar wind nebulae seen at gamma-ray energies offer insight into particle acceleration to very high energies under extreme conditions. Pulsed emission provides information about the geometry and interaction processes in the magnetospheres of these rotating neutron stars, while the pulsar wind nebulae yield information about high-energy particles interacting with their surroundings. During the next decade, a number of new and expanded gamma-ray facilities will become available for pulsar studies, including Astro-rivelatore Gamma a Immagini LEggero (AGILE) and Gamma-ray Large Area Space Telescope (GLAST) in space and a number of higher-energy ground-based systems. This review describes the capabilities of such observatories to answer some of the open questions about the highest-energy processes involving neutron stars.

  7. Giant pulsar glitches and the inertia of neutron star crusts

    NASA Astrophysics Data System (ADS)

    Delsate, T.; Chamel, N.; Gürlebeck, N.; Fantina, A. F.; Pearson, J. M.; Ducoin, C.

    2016-07-01

    Giant pulsar frequency glitches as detected in the emblematic Vela pulsar have long been thought to be the manifestation of a neutron superfluid permeating the inner crust of a neutron star. However, this superfluid has been recently found to be entrained by the crust, and as a consequence it does not carry enough angular momentum to explain giant glitches. The extent to which pulsar-timing observations can be reconciled with the standard vortex-mediated glitch theory is studied considering the current uncertainties on dense-matter properties. To this end, the crustal moment of inertia of glitching pulsars is calculated employing a series of different unified dense-matter equations of state.

  8. Spin-down of radio millisecond pulsars at genesis.

    PubMed

    Tauris, Thomas M

    2012-02-01

    Millisecond pulsars are old neutron stars that have been spun up to high rotational frequencies via accretion of mass from a binary companion star. An important issue for understanding the physics of the early spin evolution of millisecond pulsars is the impact of the expanding magnetosphere during the terminal stages of the mass-transfer process. Here, I report binary stellar evolution calculations that show that the braking torque acting on a neutron star, when the companion star decouples from its Roche lobe, is able to dissipate >50% of the rotational energy of the pulsar. This effect may explain the apparent difference in observed spin distributions between x-ray and radio millisecond pulsars and help account for the noticeable age discrepancy with their young white dwarf companions. PMID:22301314

  9. Pulsar timing sensitivity to very-low-frequency gravitational waves

    NASA Astrophysics Data System (ADS)

    Jenet, Fredrick A.; Armstrong, J. W.; Tinto, Massimo

    2011-04-01

    We compute the sensitivity, constrained by instrumental, propagation, and other fundamental noises, of pulsar timing to very-low-frequency gravitational waves (GWs). Reaching predicted GW signal strengths will require suppression of time-of-arrival fluctuations caused by interstellar plasma turbulence and a reduction of white rms timing noise to ≲100ns. Assuming negligible intrinsic pulsar rotational noise, perfect time transfer from time standard to observatory, and stable pulse profiles, the resulting single-pulsar signal-to-noiseratio=1 sensitivity is limited by terrestrial time standards at hrms˜2×10-16[f/(1cycle/year)]-1/2 for f<3×10-8Hz, where f is the Fourier frequency and a bandwidth of 1 cycle/(10 years) is assumed. Since this sensitivity is comparable to predicted GW signal levels, a reliable detection will require substantial signal-to-noise ratio improvement via pulsar timing array.

  10. Finding (or not) New Gamma-ray Pulsars with GLAST

    SciTech Connect

    Ransom, Scott M.

    2007-07-12

    Young energetic pulsars will likely be the largest class of Galactic sources observed by GLAST, with many hundreds detected. Many will be unknown as radio pulsars, making pulsation detection dependent on radio and/or x-ray observations or on blind periodicity searches of the gamma-rays. Estimates for the number of pulsars GLAST will detect in blind searches have ranged from tens to many hundreds. I argue that the number will be near the low end of this range, partly due to observations being made in a scanning as opposed to a pointing mode. This paper briefly reviews how blind pulsar searches will be conducted using GLAST, what limits these searches, and how the computations and statistics scale with various parameters.

  11. GLAST LAT And Pulsars: What Do We Learn from Simulations?

    SciTech Connect

    Razzano, Massimiliano; Harding, Alice K.; /NASA, Goddard

    2007-10-24

    Gamma-ray pulsars are among the best targets for the Large Area Telescope (LAT) aboard the GLAST mission. The higher sensitivity, time and energy resolution of the LAT will provide data of fundamental importance to understand the physics of these fascinating objects. Powerful tools for studying the LAT capabilities for pulsar science are the simulation programs developed within the GLAST Collaboration. Thanks to these simulations it is possible to produce a detailed distribution of gamma-ray photons in energy and phase that can be folded through the LAT Instrument Response Functions (IRFs). Here we present some of the main interesting results from the simulations developed to study the discovery potential of the LAT. In particular we will focus on the capability of the LAT to discover new radio-loud gamma-ray pulsars, on the discrimination between Polar Cap and Outer Gap models, and on the LAT pulsar sensitivity.

  12. Nanohertz gravitational wave searches with interferometric pulsar timing experiments.

    PubMed

    Tinto, Massimo

    2011-05-13

    We estimate the sensitivity to nano-Hertz gravitational waves of pulsar timing experiments in which two highly stable millisecond pulsars are tracked simultaneously with two neighboring radio telescopes that are referenced to the same timekeeping subsystem (i.e., "the clock"). By taking the difference of the two time-of-arrival residual data streams we can exactly cancel the clock noise in the combined data set, thereby enhancing the sensitivity to gravitational waves. We estimate that, in the band (10(-9)-10(-8))  Hz, this "interferometric" pulsar timing technique can potentially improve the sensitivity to gravitational radiation by almost 2 orders of magnitude over that of single-telescopes. Interferometric pulsar timing experiments could be performed with neighboring pairs of antennas of the NASA's Deep Space Network and the forthcoming large arraying projects. PMID:21668135

  13. An eccentric binary millisecond pulsar in the galactic plane.

    PubMed

    Champion, David J; Ransom, Scott M; Lazarus, Patrick; Camilo, Fernando; Bassa, Cees; Kaspi, Victoria M; Nice, David J; Freire, Paulo C C; Stairs, Ingrid H; van Leeuwen, Joeri; Stappers, Ben W; Cordes, James M; Hessels, Jason W T; Lorimer, Duncan R; Arzoumanian, Zaven; Backer, Don C; Bhat, N D Ramesh; Chatterjee, Shami; Cognard, Ismaël; Deneva, Julia S; Faucher-Giguère, Claude-André; Gaensler, Bryan M; Han, Jinlin; Jenet, Fredrick A; Kasian, Laura; Kondratiev, Vlad I; Kramer, Michael; Lazio, Joseph; McLaughlin, Maura A; Venkataraman, Arun; Vlemmings, Wouter

    2008-06-01

    Binary pulsar systems are superb probes of stellar and binary evolution and the physics of extreme environments. In a survey with the Arecibo telescope, we have found PSR J1903+0327, a radio pulsar with a rotational period of 2.15 milliseconds in a highly eccentric (e = 0.44) 95-day orbit around a solar mass (M(middle dot in circle)) companion. Infrared observations identify a possible main-sequence companion star. Conventional binary stellar evolution models predict neither large orbital eccentricities nor main-sequence companions around millisecond pulsars. Alternative formation scenarios involve recycling a neutron star in a globular cluster, then ejecting it into the Galactic disk, or membership in a hierarchical triple system. A relativistic analysis of timing observations of the pulsar finds its mass to be 1.74 +/- 0.04 M solar symbol, an unusually high value. PMID:18483399

  14. Pulsar timing and the Fermi and AGILE missions

    NASA Astrophysics Data System (ADS)

    Johnston, Simon; Possenti, Andrea; Manchester, Dick; Hobbs, George; Keith, Michael; Romani, Roger W.; Thompson, David J.; Thorsett, Stephen; Roberts, Mallory; Weltevrede, Patrick

    2010-10-01

    We request time to observe 170 pulsars on a regular basis in order to provide accurate ephemerides necessary for the detection of gamma-ray pulsars with the Fermi and AGILE satellites. The main science goals are to increase the number of known gamma-ray pulsars (both radio loud and radio quiet), to determine accurate pulse profiles, to characterise their high energy spectra and phase resolved spectroscopy of the brightest pulsars. In the radio, the observations will also allow us to find glitches, characterise timing noise, investigate dispersion and rotation measure variability and enhance our knowledge of single pulse phenomenology. To date, we are (co-)authors on 27 papers arising from the collaboration and P574 data. The data have contributed to the PhD theses of Lucas Guillemot and Damien Parent from the Bordeaux Fermi group (submitted mid 2009) and Kyle Watters from Stanford.

  15. Pulsar timing and the Fermi and AGILE missions

    NASA Astrophysics Data System (ADS)

    Johnston, Simon; Possenti, Andrea; Manchester, Dick; Hobbs, George; Keith, Michael; Romani, Roger W.; Thompson, David J.; Thorsett, Stephen; Roberts, Mallory; Weltevrede, Patrick

    2010-04-01

    We request time to observe 170 pulsars on a regular basis in order to provide accurate ephemerides necessary for the detection of gamma-ray pulsars with the Fermi and AGILE satellites. The main science goals are to increase the number of known gamma-ray pulsars (both radio loud and radio quiet), to determine accurate pulse profiles, to characterise their high energy spectra and phase resolved spectroscopy of the brightest pulsars. In the radio, the observations will also allow us to find glitches, characterise timing noise, investigate dispersion and rotation measure variability and enhance our knowledge of single pulse phenomenology. To date, we are (co-)authors on 20 papers arising from the collaboration and P574 data. The data have contributed to the PhD theses of Lucas Guillemot and Damien Parent from the Bordeaux Fermi group (submitted mid 2009).

  16. Pulsar Timing and the Fermi and AGILE missions

    NASA Astrophysics Data System (ADS)

    Shannon, Ryan; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Hobbs, George; Keith, Michael; Romani, Roger W.; Thompson, David J.; Roberts, Mallory; Weltevrede, Patrick; Kerr, Matthew; Petroff, Emily; Brook, Paul

    2013-10-01

    We request time to observe 170 pulsars on a regular basis in order to provide accurate ephemerides necessary for the detection of gamma-ray pulsars with the Fermi and AGILE satellites. The main science goals are to increase the number of known gamma-ray pulsars (both radio loud and radio quiet), to determine accurate pulse profiles, to characterise their high energy spectra and phase resolved spectroscopy of the brightest pulsars. In the radio, the observations will also allow us to find glitches, characterise timing noise, investigate dispersion and rotation measure variability and enhance our knowledge of single pulse phenomenology. To date, we are (co-)authors on 43 papers arising from the collaboration and P574 data. The data have contributed to the PhD theses of Lucas Guillemot and Damien Parent from the Bordeaux Fermi group and Kyle Watters from Stanford. Currently five students have active projects using the radio datasets.

  17. Pulsar timing and the Fermi and AGILE missions

    NASA Astrophysics Data System (ADS)

    Weltevrede, Patrick; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Kramer, Michael; Hobbs, George; Keith, Michael; Romani, Roger W.; Thompson, David J.; Thorsett, Stephen; Roberts, Mallory

    2009-10-01

    We request time to observe 160 pulsars on a regular basis in order to provide accurate ephemerides necessary for the detection of gamma-ray pulsars with the Fermi and AGILE satellites. The main science goals are to increase the number of known gamma-ray pulsars (both radio loud and radio quiet), to determine accurate pulse profiles, to characterise their high energy spectra and phase resolved spectroscopy of the brightest pulsars. In the radio, the observations will also allow us to find glitches, characterise timing noise, investigate dispersion and rotation measure variability and enhance our knowledge of single pulse phenomenology. To date, we are (co-)authors on 2 Agile papers, 4 Fermi papers, 3 radio papers and authors on 3 papers in submission. The data are contributing to the PhD theses of Lucas Guillemot and Damien Parent from the Bordeaux Fermi group.

  18. Pulsar Timing and the Fermi and AGILE missions

    NASA Astrophysics Data System (ADS)

    Shannon, Ryan; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Hobbs, George; Keith, Michael; Romani, Roger W.; Thompson, David J.; Thorsett, Stephen; Roberts, Mallory; Weltevrede, Patrick

    2011-04-01

    We request time to observe 170 pulsars on a regular basis in order to provide accurate ephemerides necessary for the detection of gamma-ray pulsars with the Fermi and AGILE satellites. The main science goals are to increase the number of known gamma-ray pulsars (both radio loud and radio quiet), to determine accurate pulse profiles, to characterise their high energy spectra and phase resolved spectroscopy of the brightest pulsars. In the radio, the observations will also allow us to find glitches, characterise timing noise, investigate dispersion and rotation measure variability and enhance our knowledge of single pulse phenomenology. To date, we are (co-)authors on 27 papers arising from the collaboration and P574 data. The data have contributed to the PhD theses of Lucas Guillemot and Damien Parent from the Bordeaux Fermi group (submitted mid 2009) and Kyle Watters from Stanford.

  19. Pulsar Timing and the Fermi and AGILE missions

    NASA Astrophysics Data System (ADS)

    Shannon, Ryan; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Hobbs, George; Keith, Michael; Romani, Roger W.; Thompson, David J.; Thorsett, Stephen; Roberts, Mallory; Weltevrede, Patrick

    2011-10-01

    We request time to observe 170 pulsars on a regular basis in order to provide accurate ephemerides necessary for the detection of gamma-ray pulsars with the Fermi and AGILE satellites. The main science goals are to increase the number of known gamma-ray pulsars (both radio loud and radio quiet), to determine accurate pulse profiles, to characterise their high energy spectra and phase resolved spectroscopy of the brightest pulsars. In the radio, the observations will also allow us to find glitches, characterise timing noise, investigate dispersion and rotation measure variability and enhance our knowledge of single pulse phenomenology. To date, we are (co-)authors on 27 papers arising from the collaboration and P574 data. The data have contributed to the PhD theses of Lucas Guillemot and Damien Parent from the Bordeaux Fermi group (submitted mid 2009) and Kyle Watters from Stanford.

  20. Pulsar Timing and the Fermi and AGILE missions

    NASA Astrophysics Data System (ADS)

    Shannon, Ryan; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Hobbs, George; Keith, Michael; Romani, Roger W.; Thompson, David J.; Thorsett, Stephen; Roberts, Mallory; Weltevrede, Patrick

    2012-04-01

    We request time to observe 170 pulsars on a regular basis in order to provide accurate ephemerides necessary for the detection of gamma-ray pulsars with the Fermi and AGILE satellites. The main science goals are to increase the number of known gamma-ray pulsars (both radio loud and radio quiet), to determine accurate pulse profiles, to characterise their high energy spectra and phase resolved spectroscopy of the brightest pulsars. In the radio, the observations will also allow us to find glitches, characterise timing noise, investigate dispersion and rotation measure variability and enhance our knowledge of single pulse phenomenology. To date, we are (co-)authors on 27 papers arising from the collaboration and P574 data. The data have contributed to the PhD theses of Lucas Guillemot and Damien Parent from the Bordeaux Fermi group (submitted mid 2009) and Kyle Watters from Stanford.