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. Pulsar electrodynamics: an unsolved problem

    NASA Astrophysics Data System (ADS)

    Melrose, D. B.; Yuen, R.

    2016-04-01

    > Pulsar electrodynamics is reviewed emphasizing the role of the inductive electric field in an oblique rotator and the incomplete screening of its parallel component by charges, leaving `gaps' with \\Vert \

  3. 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.

  4. 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.

  5. 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.

  6. Spectral Modeling of the Comptonized Continua of Accreting X-Ray Pulsars: Recent Progress

    NASA Astrophysics Data System (ADS)

    Wolff, Michael T.; Becker, P. A.; Marcu, D.; Pottschmidt, K.; Wilms, J.; Wood, K. S.

    2014-01-01

    We are undertaking a program to analyze the X-ray spectra of the accretion flows onto strongly magnetic neutron stars in high mass binary systems such as Her X-1, Cen X-3, and LMC X-4. These accreting pulsars typically have X-ray spectra consisting of broad Comptonized cutoff power-laws. Current theory suggests these X-ray spectra result from the impact of the high-velocity magnetically channeled plasma accretion flows onto the surfaces of the neutron stars. The flows have such high energy density that shocks developing in the plasmas can be radiation-dominated. These X-ray pulsars often, but not always, show cyclotron resonant scattering features implying neutron star surface magnetic field strengths above 10^12 G. Over the past few years a number of studies have reported both positive and negative correlations of the cyclotron line energy centroids with X-ray luminosity in a number of pulsars. However, the detailed analysis of the cyclotron line centroids suffers from the lack of a robust model for the Comptonized X-ray continuum upon which the cyclotron lines are superposed. We discuss in this presentation our progress in developing tools for the analysis of the X-ray spectra formed in these systems. The range of parameter conditions presented by the many known real accreting pulsar systems substantially exceeds that of the limited set of pulsars on which the original analytic model of Becker and Wolff (2007) was validated. In the high temperature optically thick plasmas, the processes of bremsstrahlung emission from the hot plasma, black body emission from a thermal mound near the neutron star surface, and cyclotron emission from electrons in the first Landau excited state, all contribute to the total local photon population in the shock structure. We discuss our strategy for numerically accounting for the relative contribution to the full X-ray spectrum made by each of these physical processes. Solving for the integrated spectrum involves numerical

  7. 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..

  8. 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.

  9. 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)

  10. 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

  11. Pure science and the problem of progress.

    PubMed

    Douglas, Heather

    2014-06-01

    How should we understand scientific progress? Kuhn famously discussed science as its own internally driven venture, structured by paradigms. He also famously had a problem describing progress in science, as problem-solving ability failed to provide a clear rubric across paradigm change--paradigm changes tossed out problems as well as solving them. I argue here that much of Kuhn's inability to articulate a clear view of scientific progress stems from his focus on pure science and a neglect of applied science. I trace the history of the distinction between pure and applied science, showing how the distinction came about, the rhetorical uses to which the distinction has been put, and how pure science came to be both more valued by scientists and philosophers. I argue that the distinction between pure and applied science does not stand up to philosophical scrutiny, and that once we relinquish it, we can provide Kuhn with a clear sense of scientific progress. It is not one, though, that will ultimately prove acceptable. For that, societal evaluations of scientific work are needed.

  12. 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...

  13. 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

  14. [Current progress and problems in oncourology].

    PubMed

    Chakŭrov, S

    2007-01-01

    One of the most serious problems of urology as specialized surgery is the oncological diseases. A large part of the scientific research is dedicated to their basic research, diagnostics and treatment as the results are then presented at the big international forums each year. The new achievements in the investigations of urological diseases excite special interest and mark the stages of the actual progress of the respective science. The overview is a panorama of the newest and at the same time most significant achievements of the science of urology in this field in 2006 presented at the biggest international congresses - the Congress of the European Association of Urology, the Annual Meeting of the American urologists and the Congress of the American Society of Clinical Oncology - ASCO. What is typical is the existence of the large number of researches of the carcinoma of the prostate - an issue on which the urological society focuses its attention quite often. Without any revolutionary breakthroughs being made new scientific proof has been added which considerably enriches our knowledge about this disease and places special focus on the real value and interpretation of the levels of the Prostate Specific Antigen (PSA). What is especially impressive in bladder cancer research is the discovery of a protein element called "survivin", which is of the family of the inhibitors of apoptosis and its level is connected with qualities of the tumors like aggressiveness, recurrence and progression of the disease and mortality rate. The weight of the scientific research in the field of kidney tumors is placed on the basic research of their oncogenesis. After quite a few years of standstill in the area of chemotherapy new drugs like Sunitinib, Sorafenib and Temserolimus are being introduced, some of which even have independent antitumor effect. As far as the testicle tumors are concerned, the necessity of an extensive lymphadenectomy is confirmed. The increased possibilities of

  15. 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.

  16. 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.

  17. 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

  18. 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.

  19. Energy conservation in Kenya: progress, potentials, problems

    SciTech Connect

    Schipper, L.; Hollander, J.M.; Milukas, M.; Alcamo, J.; Meyers, S.; Noll, S.

    1981-09-01

    A study was carried out of the flows of commercial energy in the economy of Kenya. Indications were sought of the extent to which energy conservation, (i.e., increase in efficiency of energy use) has reduced the ratio of energy inputs to economic outputs, in the post-1973 years. An assessment was made of the potential for energy conservation to reduce the growth of Kenyan energy use in the future and of significant barriers to increasing energy efficiency. Consideration was given to the role of government policy and of international assistance in fostering energy conservation in Kenya and other developing countries. The study was performed by analyzing available energy data and statistics from the largest oil companies, the Kenyan electric utility, and the government. These sources were supplemented by conducting personal interviews with personnel of nearly 50 commercial firms in Kenya. Direct consumption of fuel accounts for 94% of the commercial energy use in Kenya, while electricity accounts for 6%. The sectoral division of fuel use is: transportation 53%, industry 21%, energy production 11%, agriculture 9%, buildings and residences 5%, and construction 1%. For electricity the division is: buildings and residences 48%, industry 45%, energy production 4%, agriculture 2%, and construction 1%. Recent progress in conservation is reported.

  20. Recent progress and problems in animal cloning.

    PubMed

    Tsunoda, Y; Kato, Y

    2002-01-01

    It is remarkable that mammalian somatic cell nuclei can form whole individuals if they are transferred to enucleated oocytes. Advancements in nuclear transfer technology can now be applied for genetic improvement and increase of farm animals, rescue of endangered species, and assisted reproduction and tissue engineering in humans. Since July 1998, more than 200 calves have been produced by nuclear transfer of somatic cell nuclei in Japan, but half of them were stillborn or died within several months of parturition. Morphologic abnormalities have also been observed in cloned calves and embryonic stem cell-derived mice. In this review, we discuss the present situation and problems with animal cloning and the possibility for its application to human medicine.

  1. 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.

  2. Hurricane prediction: progress and problem areas.

    PubMed

    Simpson, R H

    1973-09-01

    The subjective approach to hurricane prediction of yesteryear has given way to the automation of many facets of prediction, leaving the forecaster with more time to reason dynamically in making the final adjustments to the official track derived from a hierarchy of computer-generated guidances. The most important task immediately ahead is to develop and apply better diagnostic procedures to help the forecaster identify the guidance sources which are most likely to contain the truth, and to help assure that his final decision will either succeed or fail safely. The ultimate prediction method for both hurricane development and movement will probably need to simulate not only the circulation of the hurricane but the interaction of the cloud clusters in its vortex with the largescale environment. Assuming that this can be effectively done, the most important further handicap will be the problem of describing the initial conditions. The development of a model which will dependably simulate the behavior of the three hurricanes in ten that turn out to be bad actors will not likely become operational in the near future. The most troubling problem in applying such a model-and it would have to be tested for years over a range of many storm types and conditions before becoming fully operational-is that the more complex the model is the more inscrutable the results are and the more difficult it becomes to identify the condition in which computational failure is probable. It would appear, therefore, that engineering approache to prediction and diagnostic procedures of evaluation will dominate the methodology of hurricane forecasting for a number of years to come.

  3. 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 (?)

  4. 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)

  5. Exoplanets around pulsars

    NASA Astrophysics Data System (ADS)

    Kitiashvili, I.; Gusev, A.

    2003-04-01

    Surprise discovery of thrid planets and cometary body (!?) near the pulsar PSR~B1257+12 (Wolszczan and Frail, 1992) posed the problems of describing their moving around pulsar, their origin and early rotation. At the present time the question whether there exist another three pulsars in the planetary systems is under discussion: PSR 0329+54 (1 planet), PSR B1620--26 (1 planet) and PSR 1828--11 (3 planets, Stairs et al., 2000) . It is known the time scale of pulsars is very stable, then in some cases the periodical fluctuation in time of arrival may be provoked motion of planetary bodies, free precession or concerned with the interior of the neutron star. Discovery exoplanets around PSR~B1257+12 gave strong push for search and investigate planets around neutron stars. Dust disks around stars still retain information about the formation processes of the exoplanetary systems as they are formed by collisions of planetesimals or protoplanets.The conventional explanation for the formation gas giant planets, core accretion, presumes that a gaseous envelope collapses upon a roughly 10 M⊕, solid core that was formed by the collisional accumulation of planetary embryos orbiting in a gaseous disk (Boss, 2002). Small protoplanets torque the disk at the Lindblad and corotation resonances, and the resulting back-torque can propel a planet into the star (Ward, 1997). We investigate the equations of the magneto-rotational instability of the Keplerian disk in linear approximation by qualitative and bifurcation methods. The separation of 3-dimensional parameter space of dynamical system by bifurcation surfaces is obtained. The obtained gallery of more ten phase portraits of disk evolution illustrates the various regimes of the planetary systems evolution. Investigation of a matter around young pulsars will allow us to answer about a possibility of birth of planets after explosion of a supernova star.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. MHD/steam electrical power production - Promise, progress and problems

    NASA Astrophysics Data System (ADS)

    Chapman, J. N.; Strom, S. S.; Wu, Y. C. L.

    1980-08-01

    The MHD/Steam Power Plant has promise to burn coal and produce electrical power more efficiently than conventional coal fired plants while producing less environmental intrusion. Problems have been encountered in developing a high temperature air heater (HTAH) using coal exhaust products. Early commercial plants have been proposed that use either a gasifier to produce clean fuel for a separately fired HTAH or use oxygen enrichment to avoid the need for a HTAH. Component development is progressing rapidly but test data is needed at intermediate sizes before a commercial plant can be designed with high confidence of success. Related commercial technology is being adapted for the steam bottoming plant.

  14. 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.

  15. 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

  16. Ensemble Pulsar Time Scale

    NASA Astrophysics Data System (ADS)

    Yin, D. S.; Gao, Y. P.; Zhao, S. H.

    2016-05-01

    Millisecond pulsars can generate another type of time scale that is totally independent of the atomic time scale, because the physical mechanisms of the pulsar time scale and the atomic time scale are quite different from each other. Usually the pulsar timing observational data are not evenly sampled, and the internals between data points range from several hours to more than half a month. What's more, these data sets are sparse. And all these make it difficult to generate an ensemble pulsar time scale. Hence, a new algorithm to calculate the ensemble pulsar time scale is proposed. Firstly, we use cubic spline interpolation to densify the data set, and make the intervals between data points even. Then, we employ the Vondrak filter to smooth the data set, and get rid of high-frequency noise, finally adopt the weighted average method to generate the ensemble pulsar time scale. The pulsar timing residuals represent clock difference between the pulsar time and atomic time, and the high precision pulsar timing data mean the clock difference measurement between the pulsar time and atomic time with a high signal to noise ratio, which is fundamental to generate pulsar time. We use the latest released NANOGRAV (North American Nanohertz Observatory for Gravitational Waves) 9-year data set to generate the ensemble pulsar time scale. This data set is from the newest NANOGRAV data release, which includes 9-year observational data of 37 millisecond pulsars using the 100-meter Green Bank telescope and 305-meter Arecibo telescope. We find that the algorithm used in this paper can lower the influence caused by noises in timing residuals, and improve long-term stability of pulsar time. Results show that the long-term (> 1 yr) frequency stability of the pulsar time is better than 3.4×10-15.

  17. 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.

  18. 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.

  19. 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

  20. 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

  1. 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

  2. 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.

  3. 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.

  4. [Charles Darwin and the problem of evolutionary progress].

    PubMed

    Iordanskiĭ, N N

    2010-01-01

    According to Ch. Darwin's evolutionary theory, evolutionary progress (interpreted as morpho-physiological progress or arogenesis in recent terminology) is one of logical results of natural selection. At the same time, natural selection does not hold any factors especially promoting evolutionary progress. Darwin emphasized that the pattern of evolutionary changes depends on organism nature more than on the pattern of environment changes. Arogenesis specificity is determined by organization of rigorous biological systems - integral organisms. Onward progressive development is determined by fundamental features of living organisms: metabolism and homeostasis. The concept of social Darwinism differs fundamentally from Darwin's ideas about the most important role of social instincts in progress of mankind. Competition and selection play secondary role in socio-cultural progress of human society.

  5. 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

  6. Arecibo Pulsar Highlights

    NASA Astrophysics Data System (ADS)

    Seymour, Andrew

    2016-01-01

    Here we present some of the recent interesting pulsar research that has been conducted from the Arecibo Observatory (AO). Many of these results are only possible because of the unique capabilities of AO's 305 meter telescope. Along with this, we state several possible improvements to AO's capabilities that would aid pulsar studies in the immediate future.

  7. 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.

  8. 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

  9. Gamma ray emission from radio pulsars

    NASA Technical Reports Server (NTRS)

    Romani, Roger W.

    1994-01-01

    While the proposed research received partial funding under this grant, during the term of support substantial progress was made on the development of a new model for the emission of gamma-rays from isolated rotation-powered pulsars. In phase one of the work, we showed how a modified version of the 'outer gap' model of pulsar emission could reproduce the double peaked profiles seen in CGRO pulsar observations. This work also demonstrated the spectrum of gap radiation varies significantly with position in the magnetosphere, and produced approximate computations of the emission from outer magnetosphere gap zones, including primary curvature radiation, gamma - gamma pair production and synchrotron radiation and inverse Compton scattering by the resulting secondary particles. This work was followed in phase two by a more complete treatment of the geometry of the radiation zone, and improved connections with observations at other wavelengths.

  10. 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…

  11. The critical inclination problem — 30 years of progress

    NASA Astrophysics Data System (ADS)

    Jupp, A. H.

    1987-03-01

    The critical inclination problem in artificial satellite theory, first “discovered” 30 years ago, has aroused great interest and provoked much discussion and controversy in the intervening years. It was this problem which essentially provided the seed corn for the development of the theory of the Ideal Resonance Problem (IRP). The latter theory provides good first-approximation solutions to a number of important resonance problems in celestial mechanics. It is not applicable, however, to certain other interesting resonant systems within the solar system. For these resonances a new “fundamental” mathematical model of resonance, in the spirit of the IRP, has recently been formulated and successfully applied. This paper reviews the history of the critical inclination problem and highlights the controversies it has generated over the years. The Problem's strong connection with the IRP is outlined with both thenormal andabnormal forms featuring. Finally, with reference to the critical inclination problem, the essential properties of the newer “fundamental” model are described and compared with the IRP. A strong correspondence is established between recent independent investigations of a variety of resonance problems and earlier work of Andoyer.

  12. 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.

  13. 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.

  14. 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)

  15. 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)

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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

  1. Characteristic Age and True Age of Pulsars

    NASA Astrophysics Data System (ADS)

    Jiang, Long; Zhang, Cheng-Min; Tanni, Ali; Zhao, Hai-Hui

    2013-01-01

    Age of a pulsar is a useful parameter, but it is difficult to get the age from observation. We can only derive the characteristic age from the observed parameters: spin period (P) and period derivative (Ṗ). In this paper, we discussed the relationship between characteristic age and magnetic field of a pulsar. Monte Carlo simulation is also used to support the idea: it is useless to study the magnetic field evolution using characteristic age. From some observation evidences we get that: the characteristic age cannot be used as true age, especially for millisecond pulsar (MSP). The difference between them is also discussed. From the studying of breaking index and MSP's initial spin period (P0), we get the conclusion that: the problem cannot be resolved using different radiation models.

  2. Pulsars and Extreme Physics

    NASA Astrophysics Data System (ADS)

    Bell-Burnell, Jocelyn

    2004-10-01

    Pulsars were discovered 35 years ago. What do we know about them now, and what have they taught us about the extremes of physics? With an average density comparable to that of the nucleus, magnetic fields around 108 T and speeds close to c these objects have stretched our understanding of the behaviour of matter. They serve as extrememly accurate clocks with which to carry out precision experiments in relativity. Created in cataclysmic explosions, pulsars are a (stellar) form of life after death. After half a billion revolutions most pulsars finally die, but amazingly some are born again to yet another, even weirder, afterlife. Pulsar research continues lively, delivering exciting, startling and almost unbelievable results!

  3. 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...

  4. 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

  5. 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.

  6. 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.

  7. 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).

  8. Utilizing Astronomy's Photographic Heritage: Progress, Problems and Challenges

    NASA Astrophysics Data System (ADS)

    Osborn, W.

    This paper critically examines the use in modern research of astronomy's rich store of over one hundred years of photographic observations. The necessary steps to permit such use are summarized, and a few success stories mentioned. The problems that presently cause limited use of - and little interest in - this material by most researchers are discussed. Opinions are offered on how to best meet the challenge of ensuring that the photographic material becomes recognized as an important observational resource.

  9. 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)

  10. 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

  11. 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

  12. 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.

  13. Modern problems of technical progress and methodological support in medicine

    NASA Astrophysics Data System (ADS)

    Novyc'kyy, Victor V.; Lushchyk, Ulyana B.

    2001-06-01

    A rapid development of modern computer technologies gave a powerful incentive to technical progress as a whole and to medical equipment in particular. A range of medical diagnostic computer-based systems has recently appeared. There are various fields these techniques are used in: roentgenology, ultrasound diagnostic, neurophysiology, angiology etc. The advantages of the use of computer interface are undoubted: it gives possibility to enhance the functioning of the system itself, speed up all technological processes, carry out a reliable and easy archivation and exchange the information obtained. But the most important advantage of using PC in diagnostic system lies in an unlimited freedom of use mathematical algorithms and flexible mathematical models for processing information obtained. On the other hand, the absence of clinical techniques for interpretation of the data obtained is an obstacle to the use of software at its full potential. As a result, a close connection of a scientific development of hardware with high-informative techniques for clinical interpretation of the instrumental data obtained has become topical as never before. We see an optimal solution in introducing the interpretation patterns in conjunction with purely numerical computations into mathematical simulations.

  14. 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.

  15. Selected problems in experimental intermediate energy physics. Progress report

    SciTech Connect

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

    1992-09-01

    Objectives of this research program are to investigate forefront problems in experimental intermediate-energy physics, educate students in this field of research, and develop the instrumentation necessary. Generally, this research is designed to search for physical processes that cannot be explained by conventional models of elementary interactions. The program has three major thrusts: strange particle physics, where a strange quark is embedded in the nuclear medium; muon electro-weak decay, which involves a search for a violation of the standard model of the electro-weak interaction; and measurement of the spin-dependent structure function of the neutron. Current research is reported in the following areas: hyperon physics at the AGS, electroproduction of hypernuclei, test of the standard model of electro-weak interactions, spin structure function of nucleons, and instrumentation.

  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. 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

  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. Progress in research on laser damage mechanisms and contamination problem

    NASA Astrophysics Data System (ADS)

    Jitsuno, T.; Murakami, H.; Kato, K.; Sato, E.; Mikami, K.; Motokoshi, S.; Miyanaga, N.; Azechi, H.

    2014-09-01

    In high power laser systems, the laser-induced damage threshold (LIDT) in optical coating is very important parameters for obtaining high performances. Recently, LIDT was found to have strong temperature dependences in the bulk, surface of substrates, and in coatings. These temperature dependences of LIDT were carefully measured, and the damage formation model was constructed regarding to this temperature dependence. To explain this temperature dependence of LIDT, the temperature dependences of the initial electron generation and electron multiplication in the avalanche process were taken into account. On the other hand, LIDT in optical coating is very sensitive to organic contaminations accumulated in coating layers during storage and using condition. This paper also introduces the oil-contamination problem in LFEX laser system for First Ignition scheme in the laser fusion. We have analyzed contaminants and evaluated the effects of the contamination. We also developed new cleaning methods to remove contamination from the coating, and we have succeeded to prevent the degradation in LIDT for the duration of evacuation with Silica-gel in the chamber. The quantitative analysis of contamination on LIDT was made. We have investigated the characteristics of LIDT in dielectric coatings under the controlled contamination with several materials.

  1. 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.

  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. On some electrodynamic properties of binary pulsars

    NASA Astrophysics Data System (ADS)

    Sironi, Lorenzo

    2006-07-01

    respect to the electromagnetic ones and the Lorentz force per unit volume is assumed to be zero outside the pulsar; after showing the main unsolved problems about this model, I will try to examine the origin of the leptons (positrons and electrons) which are expected to fill the pulsar magnetosphere and to continuously stream away from the star through the light cylinder (where co-rotation with the pulsar would mean traveling at the speed of light). Since even the magnetosphere of a single isolated pulsar is not well understood, my approach in considering some hitherto unexplored properties of the joint magnetosphere of a binary pulsar will mainly be qualitative, trying to understand through order-of-magnitude estimates the physical processes involved. First of all I will describe the possibility that, for binary pulsars in which the orbital separation is less than the sum of the light cylinder radii of the stars, the region at the center of the system could show a time-dependent distortion of the two co-rotating magnetospheres which could give origin to an induced electric field. I will then examine the possibility that such a field is quenched by a local production of pairs caused by the electric field itself. After showing that the electric field can not be switched-off by the pairs, I will discuss the possible observational consequences of the production of such a large number of leptons, which will be accelerated by the electric field along the magnetic field lines toward the pulsars and will then radiate their energy via curvature radiation; unfortunately, the small energy flux emitted, together with the rarity of double neutron star systems, will not likely allow us to detect the radiation emitted. Lastly, I will discuss the original idea that the strong induced electric fields could be responsible for the acceleration of cosmic rays whose energy lies between the knee and the ankle of the cosmic ray spectrum. In this case the unsolved problem is the origin for

  6. Braking indices of pulsars obtained in the presence of an effective force

    NASA Astrophysics Data System (ADS)

    Magalhaes, N. S.; Okada, A. S.; Frajuca, C.

    2016-10-01

    Braking indices of pulsars present a scientific challenge as their theoretical calculation is still an open problem. In this paper, we report results of a study regarding such calculation which adapts the canonical model (which admits that pulsars are rotating magnetic dipoles) basically by introducing a compensating component in the energy conservation equation of the system. This component would correspond to an effective force that varies with the first power of the tangential velocity of the pulsar's crust. We test the proposed model using data available and predict braking indices values for different stars. We comment on the high braking index recently measured of the pulsar J1640-4631.

  7. 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.

  8. 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.

  9. 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…

  10. Gamma radiation from radio pulsars

    NASA Technical Reports Server (NTRS)

    Ruderman, Malvin

    1990-01-01

    The probable magnetospheric location and source of the gamma ray emission from some young radiopulsars is discussed. The suggested evolution of this emission as a function of pulsar period gives a diminished gamma-ray luminosity for a more rapidly spinning pre-Crab pulsar. A greatly enhanced one, similar to that of unidentified Cos B sources, is predicted for a slightly slower post-Vela pulsar, followed by a relatively rapid quenching of the gamma-ray luminosity at still longer periods. Possible anomalous exo-magnetospheric pulsed MeV and TeV-PeV radiation from the Crab pulsar is considered.

  11. 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.

  12. 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.

  13. 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.

  14. Pulsar extinction. [astrophysics

    NASA Technical Reports Server (NTRS)

    Sturrock, P. A.; Baker, K.; Turk, J. S.

    1975-01-01

    Radio emission from pulsars, attributed to an instability associated with the creation of electron-positron pairs from gamma rays was investigated. The condition for pair creation therefore lead to an extinction condition. The relevant physical processes were analyzed in the context of a mathematical model, according to which radiation originated at the polar caps and magnetic field lines changed from a closed configuration to an open configuration at the force balance or corotation radius.

  15. Toward an Empirical Theory of Pulsar Emission. XI. Understanding the Orientations of Pulsar Radiation and Supernova “Kicks”

    NASA Astrophysics Data System (ADS)

    Rankin, Joanna M.

    2015-05-01

    Two entwined problems have remained unresolved since pulsars were discovered nearly 50 yr ago: the orientation of their polarized emission relative to the emitting magnetic field and the direction of putative supernova “kicks” relative to their rotation axes. The rotational orientation of most pulsars can be inferred only from the (“fiducial”) polarization angle of their radiation, when their beam points directly at the Earth and the emitting polar fluxtube field is ∥ to the rotation axis. Earlier studies have been unrevealing owing to the admixture of different types of radiation (core and conal, two polarization modes), producing both ∥ or ⊥ alignments. In this paper we analyze some 50 pulsars having three characteristics: core radiation beams, reliable absolute polarimetry, and accurate proper motions (PMs). The “fiducial” polarization angle of the core emission, we then find, is usually oriented ⊥ to the PM direction on the sky. The primary core emission is polarized ⊥ to the projected magnetic field in Vela and other pulsars where X-ray imaging reveals the orientation. This shows that the PMs usually lie ∥ to the rotation axes on the sky. Two key physical consequences then follow: first, to the extent that supernova “kicks” are responsible for pulsar PMs, they are mostly ∥ to the rotation axis; and, second, most pulsar radiation is heavily processed by the magnetospheric plasma such that the lowest altitude “parent” core emission is polarized ⊥ to the emitting field, propagating as the extraordinary (X) mode.

  16. 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.

  17. 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

  18. 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.

  19. 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.

  20. 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.

  1. [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.

  2. [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

  3. 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

  4. Evolution of vaporizing pulsars

    NASA Technical Reports Server (NTRS)

    Mccormick, P.

    1994-01-01

    We construct evolutional scenarios for LMXB's using a simplified stellar model. We discuss the origin and evolution of short-period, low mass binary pulsars with evaporating companions. We suggest that these systems descend from low-mass X-ray binaries and that angular momentum loss mainly due to evaporative wind drives their evolution. We derive limits on the energy and angular momentum carried away by the wind based on the observed low eccentricity. In our model the companion remains near contact, and its quasiadiabatic expansion causes the binary to expand. Short-term oscillations of the orbital period may occur if the Roche-lobe overflow forms an evaporating disk.

  5. Radio pulsar disk electrodynamics

    SciTech Connect

    Michel, F.C.

    1983-03-01

    We outline the macroscopic physics of a disk close to an isolated, magnetized, rotating neutron star. It seems likely that such systems are formed from time to time in the universe. The neutron star acts as a Faraday disk dynamo, and the disk acts as both a load and a neutral sheet, permitting the polar cap current to return to the neutron star and also splitting a dipolar magnetic field into two monopolar halves. Michel and Dessler have proposed that such systems are radio pulsars. The dominant energy loss is from the stellar wind torque (giving a deceleration index n = 7/3), and the next contribution is dissipation in the ''auroral'' zones, where the current returns to the star in a sheet about 5 cm thick. The latter is comparable to the observed radio luminosities and is in reasonable accord with the data. The disk itself may be a source of visible radiation comparable to that in pulsed radiofrequency emission. As the pulsar ages, the disk expands and narrows into a ring, the plausible consequence of which could be cessation of pulsed emission at periods of a few seconds.

  6. Tempo: Pulsar timing data analysis

    NASA Astrophysics Data System (ADS)

    Manchester, R.; Taylor, J.; Peters, W.; Weisberg, J.; Irwin, A.; Wex, N.; Stairs, I.; Demorest, P.; Nice, D.

    2015-09-01

    Tempo analyzes pulsar timing data. Pulse times of arrival (TOAs), pulsar model parameters, and coded instructions are read from one or more input files. The TOAs are fitted by a pulse timing model incorporating transformation to the solar-system barycenter, pulsar rotation and spin-down and, where necessary, one of several binary models. Program output includes parameter values and uncertainties, residual pulse arrival times, chi-squared statistics, and the covariance matrix of the model. In prediction mode, ephemerides of pulse phase behavior (in the form of polynomial expansions) are calculated from input timing models. Tempo is the basis for the Tempo2 (ascl:1210.015) code.

  7. 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.

  8. 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

  9. 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

  10. 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...

  11. 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.

  12. 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.

  13. A millisecond pulsar timing array

    NASA Astrophysics Data System (ADS)

    Hobbs, George; Manchester, Dick; Sarkissian, John; Bailes, Matthew; Bhat, Ramesh; Jenet, Rick; van Straten, Willem; Yardley, Daniel Roger Billing; Burke, Sarah; Oslowski, Stefan; Hotan, Aidan; Champion, David

    2010-10-01

    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 system (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, with four pulsars having rms residuals of less than or about 100 ns and 13 less than 1 microsecond. 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.

  14. A millisecond pulsar timing array

    NASA Astrophysics Data System (ADS)

    Manchester, Dick; Sarkissian, John; Hobbs, George; Bailes, Matthew; Bhat, Ramesh; Jenet, Rick; van Straten, Willem; Yardley, Daniel Roger Billing; Champion, David; Burke, Sarah; Oslowski, Stefan; Hotan, Aidan

    2009-10-01

    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, with three pulsars having rms residuals of less than or about 100 ns and more than half less than 1 microsecond. 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.

  15. A millisecond pulsar timing array

    NASA Astrophysics Data System (ADS)

    Manchester, Dick; Sarkissian, John; Hobbs, George; Bailes, Matthew; Bhat, Ramesh; Hotan, Aidan; Jenet, Rick; van Straten, Willem; Yardley, Daniel Roger Billing; Champion, David; You, Xiaopeng; Burke, Sarah

    2009-04-01

    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, with three pulsars having rms residuals of less than or about 100 ns and more than half less than 1 microsecond. 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.

  16. A millisecond pulsar timing array

    NASA Astrophysics Data System (ADS)

    Manchester, Dick; Verbiest, Joris P. W.; Sarkissian, John; Hobbs, George; Bailes, Matthew; Bhat, Ramesh; Hotan, Aidan; Jenet, Rick; Burke-Spolaor, Sarah; van Straten, Willem; Yardley, Daniel Roger Billing; You, Xiaopeng

    2008-10-01

    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 (PDFB2, PDFB3) and the baseband systems (CPSR2; APSR soon) are used for data recording. With the new instruments and development of an efficient pipeline processing system, we are getting the world's best pulsar timing precision, with four pulsars having rms residuals of less than 200 ns and more than half less than 1 microsecond. 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.

  17. A millisecond pulsar timing array

    NASA Astrophysics Data System (ADS)

    Manchester, Dick; Sarkissian, John; Hobbs, George; Bailes, Matthew; Bhat, Ramesh; Jenet, Rick; van Straten, Willem; Yardley, Daniel Roger Billing; Burke, Sarah; Oslowski, Stefan; Hotan, Aidan; Champion, David

    2010-04-01

    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, with four pulsars having rms residuals of less than or about 100 ns and 13 less than 1 microsecond. 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.

  18. 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.

  19. 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.

  20. 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.

  1. Air pollution control by economic incentives in the U.S.: Policy, problems, and progress

    NASA Astrophysics Data System (ADS)

    Lakhani, Hyder

    1982-01-01

    This paper deals with cost-effectiveness of the economic incentive policies of the bubble concept and offset credits relative to the policy of direct regulations of air emissions. The second section discusses single- and multi-plant bubbles, their adoption across regions and industries, the methods used to control emissions and the extent of savings in costs. We conclude that despite the delay resulting from duplication of review of state implementation plans by both the state and the Environmental Protection Agency, the required technological commands, the requirement to model air quality and the restrictions to permit bubbling only in the attainment areas, the policy is progressing successfully and should be encouraged by eliminating the restrictions. The third section analyzes the policy of emission offset credit, trading, and banking which can permit economic growth in nonattainment areas. It reviews the available literature, which deals only with aggregation of offsets across cities instead of individual offset trades. Progress by individual offset trades is analyzed in terms of the number of offsets, their acceptance across regions, the extent of reductions in emissions, and the classification of the offsets into internal and external trades. Comparison of estimated capital costs and prices of individual offsets with direct regulation costs reveals that the former are economical. We conclude that despite the problems of high tradeoff ratios, the short and uncertain life of the emission offset credits and the technological commands, the policy is progressing successfully and should be encouraged further by relaxing restrictions.

  2. a Surprise from the Pulsar in the Crab Nebula

    NASA Astrophysics Data System (ADS)

    1995-11-01

    century. It thus shows many more spectral details. The analysis of the spectrum required very careful work; as would be expected, it was in particular the effective `subtraction' of the background light from the Crab Nebula that caused the greatest problem. The new, first-ever `clean', high-resolution optical spectrum of a pulsar, is a spectacular scientific result; the corresponding graph and its caption are attached to this Press Release. First of all, the overall shape of the spectrum, i.e. the dependance of the emission from the pulsar on wavelength is now defined with unprecedented accuracy. Theory predicts a straight line; this is well confirmed and the slope of the line can be determined with a precision better than 1 percent. This new measurement has a direct implication for our understanding of the acceleration of energetic particles, close to the surface of the pulsar and also of the structure and intensity of its magnetic field. A Mysterious Feature in the New Spectrum Moreover, for the first time a feature is detected in the spectrum. Close to 5900 A (590 nm), i.e. at a wavelength that corresponds to orange light, a rather wide absorption `dip' (100 A or 10 nm) is apparent in the otherwise featureless spectrum. It goes without saying that the astronomers have checked very carefully whether this feature might not, after all, have an origin outside the pulsar. But the measurements show that this dip is neither due to the Earth's atmosphere, absorption in interstellar space between the pulsar and us, nor absorption in the Crab Nebula around the pulsar. It thus appears firmly established that this feature must arise in the immediate surroundings of the neutron star. What is the cause of this mysterious dip? Unfortunately, the present measurements do not allow a firm interpretation as to its physical nature. Normally the exact wavelength of a spectral feature will indicate the origin, but the observed wavelength does not correspond to any obvious feature in

  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. 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.

  6. 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.

  7. 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

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  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; 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.

  16. 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

  17. Finite-element/progressive-lattice-sampling response surface methodology and application to benchmark probability quantification problems

    SciTech Connect

    Romero, V.J.; Bankston, S.D.

    1998-03-01

    Optimal response surface construction is being investigated as part of Sandia discretionary (LDRD) research into Analytic Nondeterministic Methods. The goal is to achieve an adequate representation of system behavior over the relevant parameter space of a problem with a minimum of computational and user effort. This is important in global optimization and in estimation of system probabilistic response, which are both made more viable by replacing large complex computer models with fast-running accurate and noiseless approximations. A Finite Element/Lattice Sampling (FE/LS) methodology for constructing progressively refined finite element response surfaces that reuse previous generations of samples is described here. Similar finite element implementations can be extended to N-dimensional problems and/or random fields and applied to other types of structured sampling paradigms, such as classical experimental design and Gauss, Lobatto, and Patterson sampling. Here the FE/LS model is applied in a ``decoupled`` Monte Carlo analysis of two sets of probability quantification test problems. The analytic test problems, spanning a large range of probabilities and very demanding failure region geometries, constitute a good testbed for comparing the performance of various nondeterministic analysis methods. In results here, FE/LS decoupled Monte Carlo analysis required orders of magnitude less computer time than direct Monte Carlo analysis, with no appreciable loss of accuracy. Thus, when arriving at probabilities or distributions by Monte Carlo, it appears to be more efficient to expend computer-model function evaluations on building a FE/LS response surface than to expend them in direct Monte Carlo sampling.

  18. Pulsar Astrometry with the VLBA

    NASA Astrophysics Data System (ADS)

    Brisken, W.

    2005-12-01

    Many features of the Very Long Baseline Array (VLBA) contrive to make it the best telescope for pulsar astrometry. The measured proper motions and parallaxes allow distances and transverse velocities to be determined. These in turn provide clues to questions spanning nuclear astrophysics on scales of 10-23 m to the distribution of gas in the Galaxy on scales of 1020 m. Three pulsars are discussed in this paper. Among pulsars, B0950+08 has the most accurate VLBI-determined parallax. B1133+16 has a very high transverse velocity; its radial velocity is discussed. B0656+14 is a thermally detected neutron star. Determination of its distance has allowed its radius to be measured and its association with the Monogem ring supernova remnant (SNR) to be established, allowing a long-standing question in cosmic ray astrophysics to be addressed.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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

  6. 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.

  7. 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

  8. 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.

  9. White Dwarf Pulsars

    NASA Technical Reports Server (NTRS)

    Patterson, Joseph

    1998-01-01

    Work on NAG5-3288 ("White Dwarf Pulsars") has been fully integrated with the identically titled project NAG5-4734. The final report below is the same, since the data analysis and interpretative work are integrated, as are the resulting (previous and in-pipeline) publications. The proposal was designed to study pulse and orbital modulations in candidate DQ Herculis stars. Data on 5 stars were obtained. The best results were obtained on YY Draconis, which exhibited a strongly pulsed hard X-ray flux, and even suggested a transition between one-pole and two-pole emission during the course of the observation. This result is being readied for inclusion in a comprehensive study of YY Draconis. A strong pulsation appeared to be present also in H0857-242, but with a period of - 50 minutes, confusion with the first harmonic of the satellite's orbital frequency is possible. So that result is uncertain and is "on ice". A negative result was obtained on 4UO608-49 (V347 Pup), suggesting either that the X-ray identification is incorrect, or that the source is very transient. Finally, data was obtained on V1432 Aql and WZ Sge, respectively the slowest and fastest of these stars. Combined with the ASCA data, the high-energy data demonstrates the latter to contain a white dwarf rotating with P = 27.87 s (Patterson et al. 1998, PASP, 110, 403). Optical photometry contemporaneous with the X-ray data was obtained of V1432 Aql, in order to study the variations in the eclipse waveform. As anticipated, the width and centroid of the eclipse appeared to vary with the 50-day "supercycle".

  10. 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.

  11. 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.

  12. 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

  13. 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.

  14. Studies in nonlinear problems of energy. Progress report, October 1, 1993--September 30, 1994

    SciTech Connect

    Matkowsky, B.J.

    1994-09-01

    The authors concentrate on modeling, analysis and large scale scientific computation of combustion and flame propagation phenomena, with emphasis on the transition from laminar to turbulent combustion. In the transition process a flame passed through a stages exhibiting increasingly complex spatial and temporal patterns which serve as signatures identifying each stage. Often the transitions arise via bifurcation. The authors investigate nonlinear dynamics, bifurcation and pattern formation in the successive stage of transition. They describe the stability of combustion waves, and transitions to combustion waves exhibiting progressively higher degrees of spatio-temporal complexity. One aspect of this research program is the systematic derivation of appropriate, approximate models from the original models governing combustion. The approximate models are then analyzed. The authors are particularly interested in understanding the basic mechanisms affecting combustion, which is a prerequisite to effective control of the process. They are interested in determining the effects of varying various control parameters, such as Nusselt number, Lewis number, heat release, activation energy, Damkohler number, Reynolds number, Prandtl number, Peclet number, etc. The authors have also considered a number of problems in self-propagating high-temperature synthesis (SHS), in which combustion waves are employed to synthesize advanced materials. Efforts are directed toward understanding fundamental mechanisms. 167 refs.

  15. 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.

  16. 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.

  17. SKA pulsar search: technological challenges and best algorithms development

    NASA Astrophysics Data System (ADS)

    Baffa, C.

    2014-08-01

    One of the key scientific projects of the SKA radio telescope is a large survey for pulsars both in isolated and binary systems. The data rate of the pulsar search engine is expected to reach 0.6TeraSamples/sec. For the purposes of extracting hidden pulses from these streams, we need a complex search strategy which allows us to explore a three dimensional parameter space and it requires approximately 10PetaFlops. This problem is well suited for a parallel computing engine, but the dimensions of SKA bring this problem to a new level of complexity. An up-to-date study shows that this operation would require more than 2000 GPUs. In this report we will present possible mitigation strategies.

  18. 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…

  19. 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.

  20. 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%.

  1. 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

  2. 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.

  3. 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

  4. 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.

  5. 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.

  6. 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.

  7. 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

  8. 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

  9. GLAST 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. 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 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. In particular, the GLAST Large Area Telescope, a successor to EGRET on the Compton Observatory, will provide an excellent complement to H.E.S.S. for the study of the highest-energy emissions powered by neutron stars.

  10. Pulsar discovery by global volunteer computing.

    PubMed

    Knispel, B; Allen, B; Cordes, J M; Deneva, J S; Anderson, D; Aulbert, C; Bhat, N D R; Bock, O; Bogdanov, S; Brazier, A; Camilo, F; Champion, D J; Chatterjee, S; Crawford, F; Demorest, P B; Fehrmann, H; Freire, P C C; Gonzalez, M E; Hammer, D; Hessels, J W T; Jenet, F A; Kasian, L; Kaspi, V M; Kramer, M; Lazarus, P; van Leeuwen, J; Lorimer, D R; Lyne, A G; Machenschalk, B; McLaughlin, M A; Messenger, C; Nice, D J; Papa, M A; Pletsch, H J; Prix, R; Ransom, S M; Siemens, X; Stairs, I H; Stappers, B W; Stovall, K; Venkataraman, A

    2010-09-10

    Einstein@Home aggregates the computer power of hundreds of thousands of volunteers from 192 countries to mine large data sets. It has now found a 40.8-hertz isolated pulsar in radio survey data from the Arecibo Observatory taken in February 2007. Additional timing observations indicate that this pulsar is likely a disrupted recycled pulsar. PSR J2007+2722's pulse profile is remarkably wide with emission over almost the entire spin period; the pulsar likely has closely aligned magnetic and spin axes. The massive computing power provided by volunteers should enable many more such discoveries.

  11. 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.

  12. 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.

  13. The pulsar planet production process

    NASA Technical Reports Server (NTRS)

    Phinney, E. S.; Hansen, B. M. S.

    1993-01-01

    Most plausible scenarios for the formation of planets around pulsars end with a disk of gas around the pulsar. The supplicant author then points to the solar system to bolster faith in the miraculous transfiguration of gas into planets. We here investigate this process of transfiguration. We derive analytic sequences of quasi-static disks which give good approximations to exact solutions of the disk diffusion equation with realistic opacity tables. These allow quick and efficient surveys of parameter space. We discuss the outward transfer of mass in accretion disks and the resulting timescale constraints, the effects of illumination by the central source on the disk and dust within it, and the effects of the widely different elemental compositions of the disks in the various scenarios, and their extensions to globular clusters. We point out where significant uncertainties exist in the appropriate grain opacities, and in the effect of illumination and winds from the neutron star.

  14. 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.

  15. Analyzing the Spectra of Accreting X-Ray Pulsars

    NASA Astrophysics Data System (ADS)

    Wolff, Michael

    This proposal seeks funding for the analysis of accretion-powered X-ray pulsar spectra from NASA/ HEASARC archived X-ray data. Spectral modeling of accreting X-ray pulsars can tell us a great deal about the physical conditions in and near high mass X-ray binary systems. Such systems have accretion flows where plasma is initially channeled from an accretion disk by the strong neutron star magnetic field, eventually falling onto the magnetic polar cap of the neutron star compact object. Many of these accreting X-ray pulsars have X-ray spectra that consist of broad power-law continua with superposed cyclotron resonant scattering features indicating magnetic field strengths above 10^12 G. The energies of these cyclotron line features have recently been shown to vary with X-ray luminosity in a number of sources such as Her X-1 and V 0332+53, a phenomenon not well understood. Another recent development is the relatively new analytic model for the spectral continuum formation in accretion-powered pulsar systems developed by Becker & Wolff. In their formalism the accretion flows are assumed to go through radiation- dominated radiative shocks and settle onto the neutron star surface. The radiation field consists of strongly Comptonized bremsstrahlung emission from the entire plasma, Comptonized cyclotron emission from the de-excitations of Landau-excited electrons in the neutron star magnetic field, and Comptonized black-body emission from a thermal mound near the neutron star surface. We seek to develop the data analysis tools to apply this model framework to the X-ray data from a wide set of sources to make progress characterizing the basic accretion properties (e.g., magnetic field strength, plasma temperatures, polar cap size, accretion rate per unit area, dominance of bulk vs. thermal Comptonization) as well as understanding the variations of the cyclotron line energies with X-ray luminosity. The three major goals of our proposed work are as follows: In the first year

  16. Gamma-Ray Pulsar Revolution

    NASA Astrophysics Data System (ADS)

    Caraveo, Patrizia A.

    2014-08-01

    Isolated neutron stars (INSs) were the first sources identified in the field of high-energy gamma-ray astronomy. In the 1970s, only two sources had been identified, the Crab and Vela pulsars. However, although few in number, these objects were crucial in establishing the very concept of a gamma-ray source. Moreover, they opened up significant discovery space in both the theoretical and phenomenological fronts. The need to explain the copious gamma-ray emission of these pulsars led to breakthrough developments in understanding the structure and physics of neutron star (NS) magnetospheres. In parallel, the 20-year-long chase to understand the nature of Geminga unveiled the existence of a radio-quiet, gamma-ray-emitting INS, adding a new dimension to the INS family. We are living through an extraordinary time of discovery. The current generation of gamma-ray detectors has vastly increased the population of known gamma-ray-emitting NSs. The 100 mark was crossed in 2011, and we are now over 150. The gamma-ray-emitting NS population exhibits roughly equal numbers of radio-loud and radio-quiet young INSs, plus an astonishing, and unexpected, group of isolated and binary millisecond pulsars (MSPs). The number of MSPs is growing so rapidly that they are on their way to becoming the most numerous members of the family of gamma-ray-emitting NSs. Even as these findings have set the stage for a revolution in our understanding of gamma-ray-emitting NSs, long-term monitoring of the gamma-ray sky has revealed evidence of flux variability in the Crab Nebula as well as in the pulsed emission from PSR J2021+4026, challenging a four-decades-old, constant-emission paradigm. Now we know that both pulsars and their nebulae can, indeed, display variable emission.

  17. 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

  18. 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

  19. Newest insights from MHD numerical modeling of Pulsar Wind Nebulae

    NASA Astrophysics Data System (ADS)

    Olmi, B.; Del Zanna, L.; Amato, E.; Bucciantini, N.; Bandiera, R.

    2016-06-01

    Numerical MHD models are considered very successful in accounting for many of the observed properties of Pulsar Wind Nebulae (PWNe), especially those concerning the high energy emission morphology and the inner nebula dynamics. Although PWNe are known to be among the most powerful accelerators in nature, producing particles up to PeV energies, the mechanisms responsible of such an efficient acceleration are still a deep mystery. Indeed, these processes take place in one of the most hostile environment for particle acceleration: the relativistic and highly magnetized termination shock of the pulsar wind. The newest results from numerical simulations of the Crab Nebula, the PWN prototype, will be presented, with special attention to the problem of particle acceleration. In particular it will be shown how a multi-wavelengths analysis of the wisps properties can be used to constrain the particle acceleration mechanisms working at the Crab's termination shock, by identifying the particle acceleration site at the shock front.

  20. 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.

  1. 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).

  2. 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

  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. 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)

  5. Radio-quiet Gamma-ray Pulsars

    NASA Astrophysics Data System (ADS)

    Lin, Lupin Chun-Che

    2016-09-01

    A radio-quiet γ-ray pulsar is a neutron star that has significant γ-ray pulsation but without observed radio emission or only limited emission detected by high sensitivity radio surveys. The launch of the Fermi spacecraft in 2008 opened a new epoch to study the population of these pulsars. In the 2nd Fermi Large Area Telescope catalog of γ-ray pulsars, there are 35 (30 % of the 117 pulsars in the catalog) known samples classified as radio-quiet γ-ray pulsars with radio flux density (S1400) of less than 30 μJy. Accompanying the observations obtained in various wavelengths, astronomers not only have the opportunity to study the emitting nature of radio-quiet γ-ray pulsars but also have proposed different models to explain their radiation mechanism. This article will review the history of the discovery, the emission properties, and the previous efforts to study pulsars in this population. Some particular cases known as Geminga-like pulsars (e.g., PSR J0633+1746, PSR J0007+7303, PSR J2021+4026, and so on) are also specified to discuss their common and specific features.

  6. The "Perseus Arm" Multibeam pulsar survey

    NASA Astrophysics Data System (ADS)

    Lyne, Andrew; Possenti, Andrea; Manchester, Dick; Kramer, Michael; Hobbs, George; McLaughlin, Maura; Burgay, Marta; D'Amico, Nichi; Camilo, Fernando; Stairs, Ingrid; Keith, Michael; Lorimer, Duncan Ross

    2007-04-01

    Given the extremely fruitful results of the completed Parkes Multibeam Pulsar Survey, Parkes Multibeam High Latitude Pulsar Survey, and Parkes Multibeam Intermediate Latitude Swinburne Survey, we have undertaken a new deep search for pulsars, sampling the galactic plane in the direction of the Perseus Arm at galactic coordinates 200 deg pulsar population and in particular improving the knowledge of the poorly known radial distribution of the pulsars in the outer regions of the Galaxy disk. Given the survey parameters and the sky coverage, this search will lead to the discovery of few tens of sources, with a good discovery rate (twice higher than for the two most recent large-scale searches performed at Parkes) and with a favorable ratio of millisecond over longer period pulsars. The requested range of Sidereal Time is complementary to other pulsar projects. We propose to continue this project, concluding the survey observations during this APR07 semester and timing the discovered pulsars.

  7. The "Perseus Arm" Multibeam pulsar survey

    NASA Astrophysics Data System (ADS)

    Lyne, Andrew; Possenti, Andrea; Manchester, Dick; Kramer, Michael; Hobbs, George; McLaughlin, Maura; Burgay, Marta; D'Amico, Nichi; Camilo, Fernando; Stairs, Ingrid; Lorimer, Duncan Ross

    2006-04-01

    Given the extremely fruitful results of the completed Parkes Multibeam Pulsar Survey, Parkes Multibeam High Latitude Pulsar Survey, and Parkes Multibeam Intermediate Latitude Swinburne Survey, we have undertaken a new deep search for pulsars, sampling the galactic plane in the direction of the Perseus Arm at galactic coordinates 200 deg pulsar population and in particular improving the knowledge of the poorly known radial distribution of the pulsars in the outer regions of the Galaxy disk. Given the survey parameters and the sky coverage, this search will lead to the discovery of few tens of sources, with a good discovery rate (twice higher than for the two most recent large-scale searches performed at Parkes) and with a favorable ratio of millisecond over longer period pulsars. The requested range of Sidereal Time is complementary to other pulsar projects. We propose to continue this project and start the timing observations of the discovered pulsars.

  8. The "Perseus Arm" Multibeam pulsar survey

    NASA Astrophysics Data System (ADS)

    Lyne, Andrew; Possenti, Andrea; Manchester, Dick; Kramer, Michael; Hobbs, George; McLaughlin, Maura; Burgay, Marta; D'Amico, Nichi; Camilo, Fernando; Stairs, Ingrid; Lorimer, Duncan Ross

    2006-10-01

    Given the extremely fruitful results of the completed Parkes Multibeam Pulsar Survey, Parkes Multibeam High Latitude Pulsar Survey, and Parkes Multibeam Intermediate Latitude Swinburne Survey, we have undertaken a new deep search for pulsars, sampling the galactic plane in the direction of the Perseus Arm at galactic coordinates 200 deg pulsar population and in particular improving the knowledge of the poorly known radial distribution of the pulsars in the outer regions of the Galaxy disk. Given the survey parameters and the sky coverage, this search will lead to the discovery of few tens of sources, with a good discovery rate (twice higher than for the two most recent large-scale searches performed at Parkes) and with a favorable ratio of millisecond over longer period pulsars. The requested range of Sidereal Time is complementary to other pulsar projects. We propose to continue this project and start the timing observations of the discovered pulsars.

  9. The "Perseus Arm" Multibeam pulsar survey

    NASA Astrophysics Data System (ADS)

    Lyne, Andrew; Possenti, Andrea; Manchester, Dick; Kramer, Michael; Hobbs, George; McLaughlin, Maura; Burgay, Marta; D'Amico, Nichi; Camilo, Fernando; Stairs, Ingrid; Keith, Michael; Lorimer, Duncan Ross

    2007-10-01

    Given the extremely fruitful results of the completed Parkes Multibeam Pulsar Survey, Parkes Multibeam High Latitude Pulsar Survey, and Parkes Multibeam Intermediate Latitude Swinburne Survey, we have undertaken a new deep search for pulsars, sampling the galactic plane in the direction of the Perseus Arm at galactic coordinates 200 deg pulsar population and in particular improving the knowledge of the poorly known radial distribution of the pulsars in the outer regions of the Galaxy disk. Given the survey parameters and the sky coverage, this search will lead to the discovery of few tens of sources, with a good discovery rate (twice higher than for the two most recent large-scale searches performed at Parkes) and with a favorable ratio of millisecond over longer period pulsars. The requested range of Sidereal Time is complementary to other pulsar projects. We propose to continue this project, concluding the survey observations during this OCT07 semester and timing the discovered pulsars.

  10. 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)

  11. 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.

  12. Pulsar activation by the interstellar medium?

    NASA Technical Reports Server (NTRS)

    Michel, F. Curtis

    1987-01-01

    Recent work suggests that rotating magnetized neutron stars (i.e., pulsar models) trap plasma instead of emitting it. The trapping arises because nonneutral plasma can be stably trapped within such a magnetosphere provided the overall system charge is nonzero. It has been argued that particles from the interstellar medium would discharge this system, thereby presumably reactivating the system as a pulsar. However, radiation pressure either precludes such discharging (requiring an alternative source of ionization) or pulsar magnetic moments must be almost perfectly aligned with the spin axis (a revolutionary alternative). Indeed, the pulsars for which particles could reach the neutron star are those with periods of at least 3 sec. But those periods are where pulsars become inactive, not active. Conceivably, nulling might represent intermittent accretion of the interstellar medium.

  13. Pulsar prospects for the Cherenkov telescope array

    NASA Astrophysics Data System (ADS)

    Hassan, T.; Bonnefoy, S.; López, M.; Mirabal, N.; Barrio, J. A.; Contreras, J. L.; de los Reyes, R.; Wilhelmi, E. O.; Rudak, B.; CTA Consortium

    2012-12-01

    In the last few years, the Fermi-LAT telescope has discovered over a 100 pulsars at energies above 100 MeV, increasing the number of known gamma-ray pulsars by an order of magnitude. In parallel, imaging Cherenkov telescopes, such as MAGIC and VERITAS, have detected for the first time VHE pulsed gamma-rays from the Crab pulsar. Such detections have revealed that the Crab VHE spectrum follows a power-law up to at least 400 GeV, challenging most theoretical models, and opening wide possibilities of detecting more pulsars from the ground with the future Cherenkov Telescope Array (CTA). In this contribution, we study the capabilities of CTA for detecting Fermi pulsars. For this, we extrapolate their spectra with "Crab-like" power-law tails in the VHE range, as suggested by the latest MAGIC and VERITAS results.

  14. 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.

  15. The Parkes Observatory Pulsar Data Archive

    NASA Astrophysics Data System (ADS)

    Hobbs, G.; Miller, D.; Manchester, R. N.; Dempsey, J.; Chapman, J. M.; Khoo, J.; Applegate, J.; Bailes, M.; Bhat, N. D. R.; Bridle, R.; Borg, A.; Brown, A.; Burnett, C.; Camilo, F.; Cattalini, C.; Chaudhary, A.; Chen, R.; D'Amico, N.; Kedziora-Chudczer, L.; Cornwell, T.; George, R.; Hampson, G.; Hepburn, M.; Jameson, A.; Keith, M.; Kelly, T.; Kosmynin, A.; Lenc, E.; Lorimer, D.; Love, C.; Lyne, A.; McIntyre, V.; Morrissey, J.; Pienaar, M.; Reynolds, J.; Ryder, G.; Sarkissian, J.; Stevenson, A.; Treloar, A.; van Straten, W.; Whiting, M.; Wilson, G.

    2011-08-01

    The Parkes pulsar data archive currently provides access to 144044 data files obtained from observations carried out at the Parkes observatory since the year 1991. Around 105 files are from surveys of the sky, the remainder are observations of 775 individual pulsars and their corresponding calibration signals. Survey observations are included from the Parkes 70cm and the Swinburne Intermediate Latitude surveys. Individual pulsar observations are included from young pulsar timing projects, the Parkes Pulsar Timing Array and from the PULSE@Parkes outreach program. The data files and access methods are compatible with Virtual Observatory protocols. This paper describes the data currently stored in the archive and presents ways in which these data can be searched and downloaded.

  16. Possible evidence that pulsars are quark stars

    SciTech Connect

    Xu Renxin

    2008-01-10

    It is a pity that the real state of matter in pulsar-like stars is still not determined confidently because of the uncertainty about cold matter at supranuclear density, even 40 years after the discovery of pulsar. Nuclear matter (related to neutron stars) is one of the speculations for the inner constitution of pulsars even from the Landau's time more than 70 years ago, but quark matter (related to quark stars) is an alternative due to the fact of asymptotic freedom of interaction between quarks as the standard model of particle physics develops since 1960s. Therefore, one has to focus on astrophysical observations in order to answer what the nature of pulsars is. In this presentation, I would like to summarize possible observational evidence/hints that pulsar-like stars could be quark stars, and to address achievable clear evidence for quark stars in the future experiments.

  17. 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

  18. Birth and Evolution of Isolated Radio Pulsars

    NASA Astrophysics Data System (ADS)

    Faucher-Giguère, Claude-André; Kaspi, Victoria M.

    2006-05-01

    We investigate the birth and evolution of Galactic isolated radio pulsars. We begin by estimating their birth space velocity distribution from proper-motion measurements of Brisken and coworkers. We find no evidence for multimodality of the distribution and favor one in which the absolute one-dimensional velocity components are exponentially distributed and with a three-dimensional mean velocity of 380+40-60 km s-1. We then proceed with a Monte Carlo-based population synthesis, modeling the birth properties of the pulsars, their time evolution, and their detection in the Parkes and Swinburne Multibeam surveys. We present a population model that appears generally consistent with the observations. Our results suggest that pulsars are born in the spiral arms, with a galactocentric radial distribution that is well described by the functional form proposed by Yusifov & Küçük, in which the pulsar surface density peaks at radius ~3 kpc. The birth spin period distribution extends to several hundred milliseconds, with no evidence of multimodality. Models that assume the radio luminosities of pulsars to be independent of the spin periods and period derivatives are inadequate, as they lead to the detection of too many old simulated pulsars in our simulations. Dithered radio luminosities proportional to the square root of the spin-down luminosity accommodate the observations well and provide a natural mechanism for the pulsars to dim uniformly as they approach the death line, avoiding an observed pileup on the latter. There is no evidence for significant torque decay (due to magnetic field decay or otherwise) over the lifetime of the pulsars as radio sources (~100 Myr). Finally, we estimate the pulsar birthrate and total number of pulsars in the Galaxy.

  19. 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.

  20. 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.

  1. Properties of the observed recycle radio pulsars

    NASA Astrophysics Data System (ADS)

    Johnston, Simon

    1994-04-01

    Recent searches for pulsars have been highly successful in discovering recycle and binary pulsars, and we now know of approximately 25 recycled pulsars in the Galaxy and approximately 30 in globular cluster systems. These pulsars fall into four classes; those with high-mass stellar companions, with neutron star companions, with low-mass companions, and those whose evolutionary history has been affected by a companion since lost. There are two pulsars known to have high-mass stellar companions. Both systems contain approximately 10 solar mass B-star companions and have high eccentricities (e approximately 0.85). PSR B1259-63 has a spin period of 47 ms and an orbital period in excess of three years. In constrast, PSR J0045-7319 has a spin period close to 1 s and an orbital period of only 50 days. These systems originated from a binary system containing two massive stars. The supernova explosion (SN) creates the pulsar and is also responsible for the observed high eccentricity. There are five pulsars thought to have neutron star companions. All these systems have orbital eccentricities in excess of 0.2, and they fall into two classes. The first class contain the pulsars formed after the first SN, and which have been spun-up to approximately 50 ms periods during the giant phase of their companion star. This also reduces the orbital peirod to 0.3 day and the second SN induces the high eccentricity. The pulsars observed in the second class were born after the second SN and thus have periods more typical of the bulk of pulsars (greater than 250 ms). The bulk of the recycled pulsars have low-mass (probably white dwarf) companions. In general, these pulsars have very fast spin-rates (the 'millisecond' pulsars) and large apparent ages. The observed eccentricities are extremely small (less than 10-5). These pulsars are re-born as millisecond pulsars after accreting matter and angular momentum from their companion stars in their giant phase. The orbit is circularized during

  2. Toward Relativistic Orbit Fitting of Galactic Center Stars and Pulsars

    NASA Astrophysics Data System (ADS)

    Angélil, Raymond; Saha, Prasenjit; Merritt, David

    2010-09-01

    The S stars orbiting the Galactic center black hole reach speeds of up to a few percent the speed of light during pericenter passage. This makes, for example, S2 at pericenter much more relativistic than known binary pulsars and opens up new possibilities for testing general relativity. This paper develops a technique for fitting nearly Keplerian orbits with perturbations from the Schwarzschild curvature, frame dragging, and the black hole spin-induced quadrupole moment, to redshift measurements distributed along the orbit but concentrated around pericenter. Both orbital and light-path effects are taken into account. It turns out that absolute calibration of rest-frame frequency is not required. Hence, if pulsars on orbits similar to the S stars are discovered, the technique described here can be applied without change, allowing the much greater accuracies of pulsar timing to be taken advantage of. For example, pulse timing of 3 μs over 1 hr amounts to an effective redshift precision of 30 cm s-1, enough to measure frame dragging and the quadrupole moment from an S2-like orbit, provided problems like the Newtonian "foreground" due to other masses can be overcome. On the other hand, if stars with orbital periods of order of a month are discovered, the same could be accomplished with stellar spectroscopy from the European Extremely Large Telescope at the level of 1 km s-1.

  3. TOWARD RELATIVISTIC ORBIT FITTING OF GALACTIC CENTER STARS AND PULSARS

    SciTech Connect

    Angelil, Raymond; Saha, Prasenjit; Merritt, David

    2010-09-20

    The S stars orbiting the Galactic center black hole reach speeds of up to a few percent the speed of light during pericenter passage. This makes, for example, S2 at pericenter much more relativistic than known binary pulsars and opens up new possibilities for testing general relativity. This paper develops a technique for fitting nearly Keplerian orbits with perturbations from the Schwarzschild curvature, frame dragging, and the black hole spin-induced quadrupole moment, to redshift measurements distributed along the orbit but concentrated around pericenter. Both orbital and light-path effects are taken into account. It turns out that absolute calibration of rest-frame frequency is not required. Hence, if pulsars on orbits similar to the S stars are discovered, the technique described here can be applied without change, allowing the much greater accuracies of pulsar timing to be taken advantage of. For example, pulse timing of 3 {mu}s over 1 hr amounts to an effective redshift precision of 30 cm s{sup -1}, enough to measure frame dragging and the quadrupole moment from an S2-like orbit, provided problems like the Newtonian 'foreground' due to other masses can be overcome. On the other hand, if stars with orbital periods of order of a month are discovered, the same could be accomplished with stellar spectroscopy from the European Extremely Large Telescope at the level of 1 km s{sup -1}.

  4. 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…

  5. "What the College Has Done for Me": Anzia Yezierska and the Problem of Progressive Education

    ERIC Educational Resources Information Center

    Dayton-Wood, Amy

    2012-01-01

    The literary work of Anzia Yezierska is relevant to the fields of composition, rhetoric, and literacy. Partly in dialogue with the philosophy of John Dewey, it reveals the tensions and conflicts inherent in progressive education, emphasizing how these were viewed through the lens of the immigrant student. Yezierska shows that pedagogical…

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

    PubMed

    Caron, Rosemary M; Serrell, Nancy

    2009-07-01

    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.

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. 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

  12. Arecibo Pulsar and Transient Surveys Using ALFA

    NASA Astrophysics Data System (ADS)

    Cordes, J. M.

    2008-02-01

    A large scale survey for pulsars and transients is being conducted at the Arecibo Observatory using the Arecibo L-band Feed Array (ALFA). Data acquisition so far has been with correlation spectrometers that analyze a 0.1 GHz bandwidth at 1.4 GHz. The 256 frequency channels limit dispersion smearing to 1.2 ms at DMmax = 103 pc cm-3 while the sampling interval of 64 μs equals the dispersion smearing at DM~54 pc cm-3, providing high sensitivity to millisecond pulsars with standard periods out to implied distances of several kpc at low Galactic latitudes. In early 2008, we will use a new set of polyphase filter bank systems that provide the same time and frequency resolutions but over ALFA's full 0.3 GHz bandwidth. Currently the survey covers sky positions within 5° of the Galactic plane that are reachable with Arecibo. Preliminary results are given for some of the discoveries made so far, which include millisecond pulsars, a relativistic binary pulsar, a likely counterpart of a Compton GRO/EGRET gamma-ray source, and transient pulsars (including `RRATs''). We discuss the methodology of the survey, which includes archival of raw survey data at the Cornell Center for Advanced Computing and processing at distributed sites. The survey and follow up observations, which include timing observations, multiwavelength searches for orbital companions in the case of binary pulsars, etc. are organized through the Pulsar-ALFA (PALFA) Consortium. We expect the Galactic plane survey to continue until at least 2010, most likely involving multiple passes on each sky position to optimize detection of variable sources. The ALFA system will also be used to survey intermediate Galactic latitudes for millisecond pulsars, relativistic binaries with large systemic velocities, and runaway pulsars that will escape the Galaxy.

  13. 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.

  14. 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.

  15. Age Discrepancy Throws Pulsar Theories into Turmoil

    NASA Astrophysics Data System (ADS)

    2002-03-01

    Astronomers using the National Science Foundation's Very Large Array (VLA) radio telescope have found a pulsar -- a spinning, superdense neutron star -- that apparently is considerably younger than previously thought. This finding, combined with the discovery in 2000 of a pulsar that was older than previously thought, means that many assumptions astronomers have made about how pulsars are born and age must be reexamined, according to the researchers. Supernova Remnant and Pulsar -- Click on image for larger view Infrared Image of Supernova Remnant; Dashed Line and Arrow Indicate Pulsar's Motion Detected by VLA "We are learning that each individual pulsar is a very complicated object, and we should assume nothing about it," said Bryan Gaensler, of the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA. "Our work makes it more difficult to put pulsars into neat categories, but ultimately will yield new insights into how pulsars are born," he added. The research is reported in the March 10 edition of the Astrophysical Journal Letters. The astronomers studied a pulsar called B1951+32 and a supernova remnant called CTB 80, both nearly 8,000 light-years from Earth. The supernova remnant is the shell of debris from the explosion of a giant star. The explosion resulted from the giant star's catastrophic collapse into the superdense neutron star. By observing the pulsar and the supernova remnant from 1989 to 2000 with the VLA, the scientists were able to measure the movement of the pulsar, which, they found, is moving directly outward from the center of the shell of explosion debris. "We've always felt that, if you see a pulsar and a supernova remnant close together, the pulsar had been born in an explosion at the center of the supernova remnant, but this is the first time that actual observational measurement shows a pulsar moving away from the center of the supernova remnant. It's nice to finally have such an example," said Joshua Migliazzo of the Center for

  16. Parkes Observations of Globular Cluster Pulsars

    NASA Astrophysics Data System (ADS)

    Bailes, M.; Zhu, J.; Richter, S.

    2005-07-01

    Follow-up observations of pulsars from the Swinburne intermediate latitude survey with the Parkes radio telescope have caused us to question the association of PSR B1718-19 with the globular cluster NGC 6342 given the proximity of PSR J1721-1939 to the cluster. We have also found that the millisecond pulsar near the core of NGC 6624 has a large period second derivative, which would change the sign of the first derivative in about 6000 years. This is consistent with the pulsar experiencing a large gravitational perturbation from the cluster core.

  17. 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.

  18. Pulsar reenergization of old supernova remnant shells

    NASA Technical Reports Server (NTRS)

    Shull, J. Michael; Fesen, Robert A.; Saken, Jon M.

    1989-01-01

    The morphology of several unusual composite remnants are suggested to be affected by previously unrecognized interactions between high-velocity pulsars and old SNR shells, and the case of CTB 80 is pointed out as a likely example of such interactions. The interactions generate a new class of 'composite remnants' and furnish a novel method for the derivation of kinematic distances and SNR ages; this technique is noted to be especially useful when the pulsar has a measured spindown age or proper motion. It is predicted that a number of pulsars may interact with 80-100 pc radius 'superbubbles' produced by the combined action of winds and supernovae in OB associations.

  19. 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.

  20. 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

  1. 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.

  2. 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.

  3. 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)…

  4. 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…

  5. 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…

  6. 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

  7. 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.

  8. 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.

  9. Piccard: Pulsar timing data analysis package

    NASA Astrophysics Data System (ADS)

    van Haasteren, Rutger

    2016-10-01

    Piccard is a Bayesian-inference pipeline for Pulsar Timing Array (PTA) data and interacts with Tempo2 (ascl:1210.015) through libstempo. The code is use mainly for single-pulsar analysis and gravitational-wave detection purposes of full Pulsar Timing Array datasets. Modeling of the data can include correlated signals per frequency or modeled spectrum, with uniform, dipolar, quadrupolar, or anisotropic correlations; multiple error bars and EFACs per pulsar; and white and red noise. Timing models can be numerically included, either by using the design matrix (linear timing model), or by calling libstempo for the full non-linear timing model. Many types of samplers are included. For common-mode mitigation, the signals can be reconstructed mitigating arbitrary signals simultaneously.

  10. 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.

  11. 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.

  12. Interactive Database of Pulsar Flux Density Measurements

    NASA Astrophysics Data System (ADS)

    Koralewska, O.; Krzeszowski, K.; Kijak, J.; Lewandowski, W.

    2012-12-01

    The number of astronomical observations is steadily growing, giving rise to the need of cataloguing the obtained results. There are a lot of databases, created to store different types of data and serve a variety of purposes, e. g. databases providing basic data for astronomical objects (SIMBAD Astronomical Database), databases devoted to one type of astronomical object (ATNF Pulsar Database) or to a set of values of the specific parameter (Lorimer 1995 - database of flux density measurements for 280 pulsars on the frequencies up to 1606 MHz), etc. We found that creating an online database of pulsar flux measurements, provided with facilities for plotting diagrams and histograms, calculating mean values for a chosen set of data, filtering parameter values and adding new measurements by the registered users, could be useful in further studies on pulsar spectra.

  13. 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

  14. 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.

  15. Gamma radiation from pulsar magnetospheric gaps

    NASA Technical Reports Server (NTRS)

    Chiang, James; Romani, Roger W.

    1992-01-01

    We investigate the production of gamma rays in two pulsar emission models: the 'polar cap' model and the 'outer cap' model. For the former, we have performed detailed simulations of energetic electrons flowing in the vacuum dipole open field line region. In the outer gap case, we generate light curves for various magnetosphere geometries. Using data from radio and optical observations, we construct models for specific viewing angles appropriate to the Crab and Vela pulsars. Phase-resolved spectra are also computed in the polar cap case and provide signatures for testing the models. The calculations have been extended to include millisecond pulsars, and we have been able to predict fluxes and spectra for populations of recycled pulsars, which are compared to COS B data for globular cluster populations.

  16. VERITAS observations of the Crab pulsar

    NASA Astrophysics Data System (ADS)

    Zitzer, Benjamin; VERITAS Collaboration

    2012-12-01

    The Crab pulsar has been widely studied across the electromagnetic spectrum from radio to gamma-ray energies. The exact nature of the emission processes taking place in the pulsar is a matter of broad debate. Above a few GeV the energy spectrum turns over suddenly. The shape of this cutoff can provide unique insight in to the particle acceleration processes taking place in the pulsar magnetosphere. Here we discuss the detection of pulsed gamma-rays from the Crab Pulsar above 100 GeV with the VERITAS telescopes in the context of measurements made with the Fermi space telescope below 10 GeV. Limits on the level of flux enhancement of emission correlated with giant radio pulses and dispersion due to Lorentz invariance violation effects will also be presented.

  17. Perspectives on Gamma-Ray Pulsar Emission

    NASA Astrophysics Data System (ADS)

    Baring, Matthew G.

    2011-09-01

    Pulsars are powerful sources of radiation across the electromagnetic spectrum. This paper highlights some theoretical insights into non-thermal, magnetospheric pulsar gamma-ray radiation. These advances have been driven by NASA's Fermi mission, launched in mid-2008. The Large Area Telescope (LAT) instrument on Fermi has afforded the discrimination between polar cap and slot gap/outer gap acceleration zones in young and middle-aged pulsars. Altitude discernment using the highest energy pulsar photons will be addressed, as will spectroscopic interpretation of the primary radiation mechanism in the LAT band, connecting to both polar cap/slot gap and outer gap scenarios. Focuses will mostly be on curvature radiation and magnetic pair creation, including population trends that may afford probes of the magnetospheric accelerating potential.

  18. 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.

  19. 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.

  20. 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

  1. The Galactic center pulsar SGR J1745-29

    NASA Astrophysics Data System (ADS)

    Bower, Geoffrey C.

    2014-05-01

    The discovery of the Galactic center pulsar SGR J1745-29 has provided an important new window into plasma processes in the Galactic center (GC) interstellar medium, the population of compact objects in the GC, and the prospects for probing general relativistic effects through timing of a Sgr A* pulsar companion. We discuss here radio observations of the pulsar and how they are providing fresh insights. In particular, our results show that recent pulsar surveys had the sensitivity to detect many pulsars in the GC region without significant losses due to interstellar scattering. This raise the question of why only this pulsar close to Sgr A* has been detected.

  2. 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.

  3. Birth and Evolution of Isolated Radio Pulsars

    NASA Astrophysics Data System (ADS)

    Faucher-Giguère, Claude-André; Kaspi, Victoria M.

    2008-02-01

    We investigate the birth and evolution of isolated radio pulsars using a population synthesis method, modeling the birth properties of the pulsars, their time evolution, and their detection in the Parkes and Swinburne Multibeam (MB) surveys. Together, the Parkes and Swinburne MB surveys [1, 2] have detected nearly 2/3 of the known pulsars and provide a remarkably homogeneous sample to compare with simulations. New proper motion measurements [3, 4] and an improved model of the distribution of free electrons in the interstellar medium, NE2001 [5], also make revisiting these issues particularly worthwhile. We present a simple population model that reproduces the actual observations well, and consider others that fail. We conclude that: pulsars are born in the spiral arms, with the birthrate of 2.8+/-0.5 pulsars/century peaking at a distance ~3 kpc from the Galactic centre, and with mean initial speed of 380-60+40 km s-1 the birth spin period distribution extends to several hundred milliseconds, with no evidence of multimodality, implying that characteristic ages overestimate the true ages of the pulsars by a median factor >2 for true ages <30,000 yr models in which the radio luminosities of the pulsars are random generically fail to reproduce the observed P-Ṗ diagram, suggesting a relation between intrinsic radio luminosity and (P,Ṗ) radio luminosities L~Ė provides a good match to the observed P-Ṗ diagram; for this favored radio luminosity model, we find no evidence for significant magnetic field decay over the lifetime of the pulsars as radio sources (~100 Myr).

  4. 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.

  5. 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.

  6. An update on the pharmacogenomics of metformin: progress, problems and potential.

    PubMed

    Todd, Jennifer N; Florez, Jose C

    2014-03-01

    The increasing prevalence of Type 2 diabetes has emphasized the need to optimize treatment regimens. Metformin, the most widely used oral agent, is recommended as first-line drug therapy by multiple professional organizations. Response to metformin varies significantly at the individual level; this heterogeneity may be explained in part by genetic factors. Understanding these underlying factors may aid with tailoring treatment for individual patients as well as with designing improved Type 2 diabetes therapies. The past 10 years have seen substantial progress in the understanding of the pharmacogenetics of metformin response. The majority of this work has focused on genes involved in the pharmacokinetics of metformin. Owing to the uncertainty surrounding its mechanism of action, studies of pharmacodynamic genetics have been relatively few; genome-wide approaches have the potential to illuminate the molecular details of metformin response. In this review we summarize current knowledge about metformin pharmacogenetics and suggest directions for future investigation.

  7. Progress toward a circulation atlas for application to coastal water siting problems

    NASA Technical Reports Server (NTRS)

    Munday, J. C., Jr.; Gordon, H. H.

    1978-01-01

    Circulation data needed to resolve coastal siting problems are assembled from historical hydrographic and remote sensing studies in the form of a Circulation Atlas. Empirical data are used instead of numerical model simulations to achieve fine resolution and include fronts and convergence zones. Eulerian and Langrangian data are collected, transformed, and combined into trajectory maps and current vector maps as a function of tidal phase and wind vector. Initial Atlas development is centered on the Elizabeth River, Hampton Roads, Virgina.

  8. 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.

  9. 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.

  10. 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.

  11. The Swinburne intermediate-latitude pulsar survey

    NASA Astrophysics Data System (ADS)

    Edwards, R. T.; Bailes, M.; van Straten, W.; Britton, M. C.

    2001-09-01

    We have conducted a survey of intermediate Galactic latitudes using the 13-beam 21-cm multibeam receiver of the Parkes 64-m radio telescope. The survey covered the region enclosed by 5°<|b|<15° and -100°pulsars in the region with flux densities greater than approximately 0.3-1.1mJy. Offline analysis on the 64-node Swinburne workstation cluster resulted in the detection of 170 pulsars of which 69 were new discoveries. Eight of the new pulsars, by virtue of their small spin periods and period derivatives, may be recycled and have been reported elsewhere. The slow pulsars discovered are typical of those already known in the volume searched, being of intermediate to old age. Several pulsars experience pulse nulling and two display very regular drifting subpulses. We discuss the new discoveries and provide timing parameters for the 48 slow pulsars for which we have a phase-connected solution.

  12. 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.

  13. Polarized curvature radiation in pulsar magnetosphere

    NASA Astrophysics Data System (ADS)

    Wang, P. F.; Wang, C.; Han, J. L.

    2014-07-01

    The propagation of polarized emission in pulsar magnetosphere is investigated in this paper. The polarized waves are generated through curvature radiation from the relativistic particles streaming along curved magnetic field lines and corotating with the pulsar magnetosphere. Within the 1/γ emission cone, the waves can be divided into two natural wave-mode components, the ordinary (O) mode and the extraordinary (X) mode, with comparable intensities. Both components propagate separately in magnetosphere, and are aligned within the cone by adiabatic walking. The refraction of O mode makes the two components separated and incoherent. The detectable emission at a given height and a given rotation phase consists of incoherent X-mode and O-mode components coming from discrete emission regions. For four particle-density models in the form of uniformity, cone, core and patches, we calculate the intensities for each mode numerically within the entire pulsar beam. If the corotation of relativistic particles with magnetosphere is not considered, the intensity distributions for the X-mode and O-mode components are quite similar within the pulsar beam, which causes serious depolarization. However, if the corotation of relativistic particles is considered, the intensity distributions of the two modes are very different, and the net polarization of outcoming emission should be significant. Our numerical results are compared with observations, and can naturally explain the orthogonal polarization modes of some pulsars. Strong linear polarizations of some parts of pulsar profile can be reproduced by curvature radiation and subsequent propagation effect.

  14. 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.

  15. 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.

  16. Young Pulsar Reveals Clues to Supernova

    NASA Astrophysics Data System (ADS)

    2001-09-01

    Astronomers examined the remnants of a stellar explosion with NASA's Chandra X-ray Observatory and discovered one of the youngest known pulsars. The properties of this pulsar, a neutron star rotating 15 times a second, will enable scientists to better understand how neutron stars are formed in the seconds just before a supernova explosion, and how they pump energy into the space around them for thousands of years after the explosion. A team led by Stephen Murray of the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA studied 3C58, the remains of a supernova observed on Earth in 1181 AD in the constellation Cassiopeia. In addition to a pulsating central source they observed an extended X-ray source surrounding the pulsar thought to be produced by a cloud of high-energy particles about 20 light years across. These results were presented at the "Two Years of Science with Chandra" symposium in Washington, D.C. According to Murray, "Our discovery shows that all pulsars are not born equal. This pulsar is about the same age as the Crab Nebula pulsar, but there is little family resemblance." Murray explained that the 3C58 pulsar, which is now rotating at about half the rate of the Crab pulsar, is rotating almost as fast as it was when it was formed. In contrast, the Crab pulsar was formed spinning much more rapidly and has slowed to about half its initial speed. Conventional theory has assumed that all pulsars were like the Crab, born with rapid rotation and then have spun down considerably. The observations of 3C58, along with Chandra observations by another group of scientists of a pulsar associated with the supernova of 386 AD have cast doubt on that assumption, however. Furthermore, the X-ray power of 3C58 and its surrounding nebula are 20,000 and 1,000 times weaker than the Crab pulsar and its surrounding nebula respectively. One possibility for the low power of 3C58 is that the energy flow from its pulsar is primarily in the form of electromagnetic fields

  17. The imprint of pulsar parameters on the morphology of Pulsar Wind Nebulae

    NASA Astrophysics Data System (ADS)

    Bühler, Rolf; Giomi, Matteo

    2016-11-01

    The morphology of young Pulsar Wind Nebulae (PWN) is largely determined by the properties of the wind injected by the pulsar. We have used a recent parametrization of the wind obtained from force-free electrodynamics simulations of pulsar magnetospheres to simulate nebulae for different sets of pulsar parameters. We performed axisymmetric relativistic magnetohydrodynamics simulations to test the morphology dependence of the nebula on the obliquity of the pulsar and on the magnetization of the pulsar wind. We compare these simulations to the morphology of the Vela and Crab PWN. We find that the morphology of Vela can be reproduced qualitatively if the pulsar obliquity angle is α ≈ 45° and the magnetization of the wind is high (σ0 ≈ 3.0). A morphology similar to the one of the Crab nebula is only obtained for low-magnetization simulations with α ≳ 45°. Interestingly, we find that Kelvin-Helmholtz instabilities produce small-scale turbulences downstream of the reverse shock of the pulsar wind.

  18. Cascading peer dynamics underlying the progression from problem behavior to violence in early to late adolescence.

    PubMed

    Dishion, Thomas J; Véronneau, Marie-Hélène; Myers, Michael W

    2010-08-01

    This study examined the peer dynamics linking early adolescent problem behavior, school marginalization, and low academic performance to multiple indices of late adolescent violence (arrests, parent report, and youth report) in an ethnically diverse sample of 998 males and females. A cascade model was proposed in which early adolescent risk factors assessed at age 11 to 12 predict gang involvement at age 13 to 14, which in turn, predicts deviancy training with friends at age 16 to 17, which then predicts violence by age 18 to 19. Each construct in the model was assessed with multiple measures and methods. Structural equation modeling revealed that the cascade model fit the data well, with problem behavior, school marginalization, and low academic performance significantly predicting gang involvement 2 years later. Gang involvement, in turn, predicted deviancy training with a friend, which predicted violence. The best fitting model included an indirect and direct path between early adolescent gang involvement and later violence. These findings suggest the need to carefully consider peer clustering into gangs in efforts to prevent individual and aggregate levels of violence, especially in youths who may be disengaged, marginalized, or academically unsuccessful in the public school context.

  19. Multisystemic therapy for disruptive behavior problems in youths with autism spectrum disorders: a progress report.

    PubMed

    Wagner, David V; Borduin, Charles M; Kanne, Stephen M; Mazurek, Micah O; Farmer, Janet E; Brown, Rachel M A

    2014-07-01

    Youths with autism spectrum disorders (ASD) often engage in serious disruptive behaviors that interfere with their ability to successfully manage day-to-day responsibilities and contribute to relationship problems with caregivers, peers, and teachers. Effective treatments are needed to address the factors linked with disruptive behavior problems in this population of youths. Multisystemic therapy (MST) is a comprehensive family- and community-based treatment approach that has been effective with other difficult-to-treat populations of youths and holds promise for youths with ASD. In this article, we review the broad range of factors associated with disruptive behaviors among youths with ASD and discuss how MST interventions can be adapted to address those factors. We also present a framework for our adaptation of the MST model for youths with ASD. This framework includes a recently completed pilot study as well as an ongoing efficacy trial that together have served to identify key interventions for our adaptation of the MST model. PMID:24749815

  20. Implantable electrochemical sensors for biomedical and clinical applications: progress, problems, and future possibilities.

    PubMed

    Li, Chang Ming; Dong, Hua; Cao, Xiaodong; Luong, John H T; Zhang, Xueji

    2007-01-01

    Biosensors are of great interest for their ability to monitor clinically important analytes such as blood gases, electrolytes, and metabolites. A classic example is to monitor the dynamics of blood-glucose levels for treating diabetes. However, the current practice, based on a three decade old technology, requires a drop of blood on a test strip, which is in dire need of replacement. The increasing demands and interests in developing implantable glucose sensors for treating diabetes has led to notable progress in this area, and various electrochemical sensors have been developed for intravascular and subcutaneous applications. However, implantations are plagued by biofouling, tissue destruction and infection around the implanted sensors and the response signals must be interpreted in terms of blood or plasma concentrations for clinical utility, rather than tissue fluid levels. This review focuses on the potentials and pitfalls of implantable electrochemical sensors and presents our opinions about future possibilities of such implantable devices with respect to biocompatibility issues, long-term calibration, and other aging effects on the sensors.

  1. Discovery of Eight Recycled Pulsars --- The Swinburne Intermediate Latitude Pulsar Survey

    NASA Astrophysics Data System (ADS)

    Edwards, Russell T.

    We have conducted a pulsar survey of intermediate Galactic latitudes (15deg < |b| < 5deg) at 20 cm. The survey has been highly successful, discovering 58 new pulsars, eight of which are recycled, in only ~14 days of integration time. One pulsar has a very narrow (2deg FWHM) average profile for the pulsar's period (278 ms). The six new recycled binary systems provide valuable information on the formation of white dwarf pulsar binaries. Two systems have massive white dwarf companions (> 0.57 Mo and > 1.2 Mo), while anotherhas a low mass (~0.2 Mo) companion in a 23.3-d orbit, residing the well-known orbital period ``gap''.

  2. 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

  3. Population synthesis of isolated neutron stars with magneto-rotational evolution - II. From radio-pulsars to magnetars

    NASA Astrophysics Data System (ADS)

    Gullón, M.; Pons, J. A.; Miralles, J. A.; Viganò, D.; Rea, N.; Perna, R.

    2015-11-01

    Population synthesis studies constitute a powerful method to reconstruct the birth distribution of periods and magnetic fields of the pulsar population. When this method is applied to populations in different wavelengths, it can break the degeneracy in the inferred properties of initial distributions that arises from single-band studies. In this context, we extend previous works to include X-ray thermal emitting pulsars within the same evolutionary model as radio-pulsars. We find that the cumulative distribution of the number of X-ray pulsars can be well reproduced by several models that, simultaneously, reproduce the characteristics of the radio-pulsar distribution. However, even considering the most favourable magneto-thermal evolution models with fast field decay, lognormal distributions of the initial magnetic field overpredict the number of visible sources with periods longer than 12 s. We then show that the problem can be solved with different distributions of magnetic field, such as a truncated lognormal distribution, or a binormal distribution with two distinct populations. We use the observational lack of isolated neutron stars (NSs) with spin periods P > 12 s to establish an upper limit to the fraction of magnetars born with B > 1015 G (less than 1 per cent). As future detections keep increasing the magnetar and high-B pulsar statistics, our approach can be used to establish a severe constraint on the maximum magnetic field at birth of NSs.

  4. PROGRESS AND PROBLEMS IN THE APPLICATION OF FOCUSED ULTRASOUND FOR BLOOD-BRAIN BARRIER DISRUPTION

    PubMed Central

    Vykhodtseva, Natalia; McDannold, Nathan; Hynynen, Kullervo

    2008-01-01

    Advances in neuroscience have resulted in the development of new diagnostic and therapeutic agents for potential use in the central nervous system (CNS). However, the ability to deliver the majority of these agents to the brain is limited by the blood–brain barrier (BBB), a specialized structure of the blood vessel wall that hampers transport and diffusion from the blood to the brain. Many CNS disorders could be treated with drugs, enzymes, genes, or large-molecule biotechnological products such as recombinant proteins, if they could cross the BBB. This article reviews the problems of the BBB presence in treating the vast majority of CNS diseases and the efforts to circumvent the BBB through the design of new drugs and the development of more sophisticated delivery methods. Recent advances in the development of noninvasive, targeted drug delivery by MRI-guided ultrasound-induced BBB disruption are also summarized. PMID:18511095

  5. 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.

  6. Pulsars, supernovae, and ultrahigh energy cosmic rays

    NASA Astrophysics Data System (ADS)

    Kotera, K.; Fang, K.; Olinto, A. V.; Phinney, E. S.

    2012-12-01

    The acceleration of ultrahigh energy nuclei in fast spinning newborn pulsars can explain the observed spectrum of ultrahigh energy cosmic rays and the trend towards heavier nuclei for energies above 10^{19} eV as indicated by air shower studies reported by the Auger Observatory. By assuming a normal distribution of pulsar birth periods centered at 300 ms, we show that the contribution of extragalactic pulsar births to the ultrahigh energy cosmic ray spectrum naturally gives rise to a contribution to very high energy cosmic rays (VHECRs, between 10^{16} and 10^{18} eV) by Galactic pulsar births. The required injected composition to fit the observed spectrum depends on the absolute energy scale, differing considerably between the energy scale used by Auger and that used by the Telescope Array. Depending on the composition of the cosmic rays that escape the supernova remnant and the diffusion behavior of VHECRs in the Galaxy, the contribution of Galactic pulsar births can also bridge the gap between predictions for cosmic ray acceleration in supernova remnants and the observed spectrum below the ankle. Fast spinning newborn pulsars that could produce UHECRs would be born in supernovae that could present interesting specific radiative features, due to the interaction of the pulsar wind with the surrounding ejecta. The resulting supernova lightcurves could present a high luminosity plateau over a few years, and a bright X-ray and gamma-ray peak around one or two years after the onset of the explosion. If such signatures were observed, they could have important implications both for UHECR astrophysics and for the understanding of core-collapse supernovae.

  7. 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.

  8. 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.

  9. 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

  10. 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.

  11. 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

  12. On tests of general relativity with binary radio pulsars

    NASA Astrophysics Data System (ADS)

    Del Pozzo, W.; Vecchio, A.

    2016-10-01

    The timing of radio pulsars in binary systems provides a superb testing ground of general relativity. Here we propose a Bayesian approach to carry out these tests, and a relevant efficient numerical implementation, that has several conceptual and practical advantages with respect to traditional methods based on least-squares fit that have been used so far: (i) it accounts for the actual structure of the likelihood function - and it is not predicated on the Laplace approximation which is implicitly built in least-squares fit that can potentially bias the inference - (ii) it provides the ratio of the evidences of any two models under consideration as the statistical quantity to compare different theories, and (iii) it allows us to put joint constraints from the monitoring of multiple systems, that can be expressed in terms of ratio of evidences or probability intervals of global (thus not system-dependent) parameters of the theory, if any exists. Our proposed approach optimally exploits the progress in timing of radio pulsars and the increase in the number of observed systems. We demonstrate the power of this framework using simulated data sets that are representative of current observations.

  13. 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.

  14. The Pulsar Search Collaboratory: Discovery and Timing of Five New Pulsars

    NASA Astrophysics Data System (ADS)

    Rosen, R.; Swiggum, J.; McLaughlin, M. A.; Lorimer, D. R.; Yun, M.; Heatherly, S. A.; Boyles, J.; Lynch, R.; Kondratiev, V. I.; Scoles, S.; Ransom, S. M.; Moniot, M. L.; Cottrill, A.; Weaver, M.; Snider, A.; Thompson, C.; Raycraft, M.; Dudenhoefer, J.; Allphin, L.; Thorley, J.; Meadows, B.; Marchiny, G.; Liska, A.; O'Dwyer, A. M.; Butler, B.; Bloxton, S.; Mabry, H.; Abate, H.; Boothe, J.; Pritt, S.; Alberth, J.; Green, A.; Crowley, R. J.; Agee, A.; Nagley, S.; Sargent, N.; Hinson, E.; Smith, K.; McNeely, R.; Quigley, H.; Pennington, A.; Chen, S.; Maynard, T.; Loope, L.; Bielski, N.; McGough, J. R.; Gural, J. C.; Colvin, S.; Tso, S.; Ewen, Z.; Zhang, M.; Ciccarella, N.; Bukowski, B.; Novotny, C. B.; Gore, J.; Sarver, K.; Johnson, S.; Cunningham, H.; Collins, D.; Gardner, D.; Monteleone, A.; Hall, J.; Schweinhagen, R.; Ayers, J.; Jay, S.; Uosseph, B.; Dunkum, D.; Pal, J.; Dydiw, S.; Sterling, M.; Phan, E.

    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 deg2 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.

  15. 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.

  16. 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.

  17. Thermal properties of three Fermi pulsars

    NASA Astrophysics Data System (ADS)

    Danilenko, A.; Karpova, A.; Kirichenko, A.; Shibanov, Y.; Shternin, P.; Zharikov, S.; Zyuzin, D.

    2014-07-01

    We analysed thermal properties of the Fermi pulsars J0357+3205, J1741-2054, and J0633+0632 using data from the XMM-Newton and Chandra archives. The X-ray spectra of all three pulsars can be fitted by sum of thermal and power-law components. For J1741-2054, the thermal component is best described by a blackbody model whose normalization suggests that the thermal emission comes from the bulk of the neutron star surface. The effective temperature of 60 eV, which is rather large for a pulsar as old as J1741-2054, makes it similar to the well-studied pulsar B1055-52, one of ``the three musketeers''. The thermal components of PSRs J0357+3205 and J0633+0632 can be equally well described by blackbody or the hydrogen atmosphere models. In the former case the normalizations suggest hot polar cap as thermal emission origin and only upper limits on the neutron stars surface temperatures can be computed. For the hydrogen atmosphere models, the normalizations are in agreement with emission coming from a substantial part of neutron star surface. Thermal properties of the pulsars are confronted with similar data on other isolated neutron stars and predictions of the neutron star cooling theory.

  18. 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.

  19. 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.

  20. 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.

  1. The Mass of a Millisecond Pulsar

    NASA Astrophysics Data System (ADS)

    Jacoby, B. A.; Hotan, A. W.; Bailes, M.; Ord, S. M.; Kulkarni, S. R.

    2005-12-01

    We report on two years of timing observations of the low-mass binary millisecond pulsar PSR J1909-3744 with the Caltech-Parkes-Swinburne Recorder II (CPSR2), a new instrument that gives unprecedented timing precision. Daily observations give a weighted rms residual of 74 ns. Since their discovery, the masses of the rapidly rotating millisecond pulsars have remained a mystery, with the recycling hypothesis arguing for heavy objects, and the accretion-induced collapse of a white dwarf more consistent with neutron stars less than the Chandrashkar limit. Our data have allowed the measurement of Shapiro delay in this edge-on system, giving the first precise determination of a millisecond pulsar mass, 1.438 ± 0.024 solar masses. The mass of PSR J1909-3744 is at the upper edge of the range observed in mildly recycled pulsars in double neutron star systems, consistent with the the recycling hypothesis. It appears that the production of millisecond pulsars is possible with the accretion of less than 0.2 solar masses.

  2. Probing Microstructure in Interstellar Plasma with Pulsars

    NASA Astrophysics Data System (ADS)

    Backer, Donald

    1999-11-01

    Pulsars provide excellent probes of small structure in the interstellar plasma. The list of observable effects includes dispersion, Faraday rotation, diffraction and refraction. Of great interest recently has been episodes of lensing and dual path propagation when the plasma perturbation has just the right focal length for the pulsar-perturber-earth geometry at a given frequency. I will discuss a recent study of the variable dispersion, refraction and diffraction of the millisecond pulsar B1937+21. This is based mainly on daily observations at 327 and 610 MHz with a pulsar monitoring telescope in Green Bank, WV. Further observations at 820 and 1395 MHz allow us to investigate the limits on dispersion measure determination set by diffraction. Length scales in the medium from 10^10 to 10^15 cm are probed. A second study focuses on a rare event in the Crab pulsar where the dispersion measure jumped by 0.1 pc cm-3 within one week and, prior to the jump, a faint and delayed ghost of the pulsed emission was observed. These phenomena can be explained in terms of a plasma wedge crossing the line of sight. The most likely location of this wedge is in the Rayleigh-Taylor unstable interface between the expanding supernova remains and the pre-supernova stellar wind debris.

  3. Pulsar Radio Emission Mechanisms: The Crab Enigmas

    NASA Astrophysics Data System (ADS)

    Hankins, Timothy

    2012-03-01

    The Crab pulsar, which resulted from a supernova explosion in year 1054 A. D., has been studied intensely over a wide range of wavelengths, yet it continues to reveal new phenomena that challenge explanation. The emission structures in the radio regime are complex and some may be unique among pulsars. The standard models for pulsar geometry and radio emission physics are reviewed briefly. Their predictions are then compared with observations of the Crab pulsar radio emission and the observations are used to critique the theoretical models from an observer's point of view. The models must explain the extremely short and bright nanopulses (0.4 ns duration implying an equivalent brightness temperature of 10^42 K), the wide bandwidths of radio emission (at least 0.02 to 46 GHz), the regular banded nature of the high frequency interpulse emission, the complex polarization structure, and the phases of pulsar rotation where emission occurs. So far no comprehensive model satisfies all of the observational discriminants.

  4. 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.

  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. 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.

  7. 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.

  8. 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"

  9. Target of Opportunity Positioning of Transient X-Ray Pulsars

    NASA Technical Reports Server (NTRS)

    Chakrabarty, Deepto

    2003-01-01

    Our program successfully localized three newly-identified transient X-ray pulsars. XTE J1858+034 is a 221 s pulsar (Takeshima et al. 1998, IAUC 6826), XTE J1946+274 is a 15.8 s pulsar (Takeshima and Chakrabarty 1998, IAUC 7016), and XTE J0111.2-7317 is a 31 s pulsar in the Small Magellanic Cloud (Chakrabarty et al. 1998, IAUC 7048). This last pulsar was a particularly interesting source, and our XTE observations enabled prompt follow-up observations with the ASCA mission (Yokogawa et al. 2000, ApJ. 539, 191).

  10. Spectral indices for radio emission of 228 pulsars

    NASA Astrophysics Data System (ADS)

    Han, Jun; Wang, Chen; Xu, Jun; Han, Jin-Lin

    2016-10-01

    We determine spectral indices of 228 pulsars by using Parkes pulsar data observed at 1.4 GHz, among which 200 spectra are newly determined. The indices are distributed in the range from ‑4.84 to ‑0.46. Together with known pulsar spectra from literature, we tried to find clues to the pulsar emission process. The weak correlations between the spectral index, the spin-down energy loss rate E and the potential drop in the polar gap ΔΨ hint that emission properties are related to the particle acceleration process in a pulsar's magnetosphere.

  11. A LOFAR census of millisecond pulsars

    NASA Astrophysics Data System (ADS)

    Kondratiev, V. I.; Verbiest, J. P. W.; Hessels, J. W. T.; Bilous, A. V.; Stappers, B. W.; Kramer, M.; Keane, E. F.; Noutsos, A.; Osłowski, S.; Breton, R. P.; Hassall, T. E.; Alexov, A.; Cooper, S.; Falcke, H.; Grießmeier, J.-M.; Karastergiou, A.; Kuniyoshi, M.; Pilia, M.; Sobey, C.; ter Veen, S.; van Leeuwen, J.; Weltevrede, P.; Bell, M. E.; Broderick, J. W.; Corbel, S.; Eislöffel, J.; Markoff, S.; Rowlinson, A.; Swinbank, J. D.; Wijers, R. A. M. J.; Wijnands, R.; Zarka, P.

    2016-01-01

    We report the detection of 48 millisecond pulsars (MSPs) out of 75 observed thus far using the LOw-Frequency ARray (LOFAR) in the frequency range 110-188 MHz. We have also detected three MSPs out of nine observed in the frequency range 38-77 MHz. This is the largest sample of MSPs ever observed at these low frequencies, and half of the detected MSPs were observed for the first time atfrequencies below 200 MHz. We present the average pulse profiles of the detected MSPs, their effective pulse widths, and flux densities and compare these with higher observing frequencies. The flux-calibrated, multifrequency LOFAR pulse profiles are publicly available via the European Pulsar Network Database of Pulsar Profiles. We also present average values of dispersion measures (DM) and discuss DM and profile variations. About 35% of the MSPs show strong narrow profiles, another 25% exhibit scattered profiles, and the rest are only weakly detected. A qualitative comparison of the LOFAR MSP profiles with those at higher radio frequencies shows constant separation between profile components. Similarly, the profile widths are consistent with those observed at higher frequencies, unless scattering dominates at the lowest frequencies. This is very different from what is observed for normal pulsars and suggests a compact emission region in the MSP magnetosphere. The amplitude ratio of the profile components, on the other hand, can dramatically change towards low frequencies, often with the trailing component becoming dominant. As previously demonstrated this can be caused by aberration and retardation. This data set enables high-precision studies of pulse profile evolution with frequency, dispersion, Faraday rotation, and scattering in the interstellar medium. Characterising and correcting these systematic effects may improve pulsar-timing precision at higher observing frequencies, where pulsar timing array projects aim to directly detect gravitational waves.

  12. 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.

  13. Double Pulsar: A magnetopause in the double-pulsar binary system

    NASA Astrophysics Data System (ADS)

    Graham-Smith, Francis; McLaughlin, Maura Ann

    2005-02-01

    One of the holy grails of pulsar astronomy was realized last year with the discovery of a double neutron-star binary system in which both stars are visible as radio pulsars. The stars in this highly relativistic system are in a 2.4-hour, mildly eccentric orbit and are separated by only 2.9 light seconds. The wind from one distorts the magnetosphere of the other, forming a comet-like shape similar to the terrestrial magnetosheath. In this article we describe the radio observations of this system, which illuminate the remarkable interactions between the two pulsars. We show how studying these interactions will greatly increase our understanding of pulsar energy budgets, winds and magnetospheric physics.

  14. 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.

  15. Axially symmetric equations for differential pulsar rotation with superfluid entrainment

    NASA Astrophysics Data System (ADS)

    Antonelli, M.; Pizzochero, P. M.

    2016-09-01

    In this article we present an analytical two-component model for pulsar rotational dynamics. Under the assumption of axial symmetry, implemented by a paraxial array of straight vortices that thread the entire neutron superfluid, we are able to project exactly the 3D hydrodynamical problem to a 1D cylindrical one. In the presence of density-dependent entrainment the superfluid rotation is non-columnar: we circumvent this by using an auxiliary dynamical variable directly related to the areal density of vortices. The main result is a system of differential equations that take consistently into account the stratified spherical structure of the star, the dynamical effects of non-uniform entrainment, the differential rotation of the superfluid component and its coupling to the normal crust. These equations represent a mathematical framework in which to test quantitatively the macroscopic consequences of the presence of a stable vortex array, a working hypothesis widely used in glitch models. Even without solving the equations explicitly, we are able to draw some general quantitative conclusions; in particular, we show that the reservoir of angular momentum (corresponding to recent values of the pinning forces), is enough to reproduce the largest glitch observed in the Vela pulsar, provided its mass is not too large.

  16. 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

  17. 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

  18. 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.

  19. 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

  20. [Research progress on standards of commodity classes of Chinese materia medica and discussion on several key problems].

    PubMed

    Yang, Guang; Zeng, Yan; Guo, Lan-Ping; Huang, Lu-Qi; Jin, Yan; Zheng, Yu-Guang; Wang, Yong-Yan

    2014-05-01

    Standards of commodity classes of Chinese materia medica is an important way to solve the "Lemons Problem" of traditional Chinese medicine market. Standards of commodity classes are also helpful to rebuild market mechanisms for "high price for good quality". The previous edition of commodity classes standards of Chinese materia medica was made 30 years ago. It is no longer adapted to the market demand. This article researched progress on standards of commodity classes of Chinese materia medica. It considered that biological activity is a better choice than chemical constituents for standards of commodity classes of Chinese materia medica. It is also considered that the key point to set standards of commodity classes is finding the influencing factors between "good quality" and "bad quality". The article also discussed the range of commodity classes of Chinese materia medica, and how to coordinate standards of pharmacopoeia and commodity classes. According to different demands, diversiform standards can be used in commodity classes of Chinese materia medica, but efficacy is considered the most important index of commodity standard. Decoction pieces can be included in standards of commodity classes of Chinese materia medica. The authors also formulated the standards of commodity classes of Notoginseng Radix as an example, and hope this study can make a positive and promotion effect on traditional Chinese medicine market related research.

  1. 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.

  2. 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.

  3. 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...

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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

  10. 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

  11. Single-pulse study of radio pulsars

    NASA Astrophysics Data System (ADS)

    Bilous, Anna V.

    Single pulses provide valuable information about the pulsar magnetosphere, giving more spatial and time resolution than the integrated pulse profiles. Clearly, there are several different types of single pulse emission, however it is still unknown what is the nature or even strict definition of each type. This work aims to shed some light on different kinds of single pulses, making an attempt to constrain some emission theories and trace the possible connection between different types. The thesis consists of following case studies: 1. No apparent correlation was found between giant pulses (GPs) from the Crab pulsar (9 GHz, Green Bank Telescope) and its gamma-ray photons (100 MeV - 5 GeV, Fermi). This result suggests that GPs, at least the ones detected at high radio frequencies, are due to changes in coherence of radio emission rather than an overall increase in the magnetospheric particle density. Also, no apparent correlation was found between Crab GPs (1.5 GHz, Green Bank Telescope) and X-ray photons (1.5 - 4.5 keV, Chandra). 2. We show that single pulses from the millisecond pulsar B182-24A fall into two distinct categories — broad faint pulses, coincident with the peaks of integrated pulse profile and bright narrow GPs on the trailing edges of profile components. Owing to our large fractional bandwidth we were able to prove the hypothesis that the spectra of these GPs consist of separate substantially polarized patches. 3. We present a LOFAR study of single pulses from pulsars B0809+74 and B1133+16 below 90 MHz. We show that the spectral width of bright, low-frequency pulses scales with increasing frequency as Δ f/f ˜ 0.15, at least in the case of PSR B0809+74. This behaviour is consistent with predictions of strong plasma turbulence model. 4. Millisecond pulsar B1744-24A belongs to "windy" binary systems, with unbound material escaping from the companion star and interacting with the pulsar's magnetosphere. B1744-24A appears to emit strong wide single

  12. 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.

  13. 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.

  14. Revisiting the radial distribution of pulsars in the Galaxy

    NASA Astrophysics Data System (ADS)

    Yusifov, I.; Küçük, I.

    2004-08-01

    The high sensitivity Parkes and Swinburne Multibeam pulsar surveys have nearly doubled the number of known pulsars and revealed many more distant pulsars with high dispersion measures. These data allow us to investigate in more detail the statistical parameters and distribution of pulsars, especially in the central regions of the Galaxy, which was almost impossible in previous low-frequency and less-sensitive surveys. To estimate the distances to pulsars we used the new NE2001 Galactic electron density model. We study the Galactic distribution of normal pulsars with 1400 MHz luminosities greater than 0.1 mJy kpc2 refining the shape and parameters of the radial distribution of pulsars. The maximum galactocentric distribution of pulsars is located at 3.2 ± 0.4 kpc and the scale-length of this distribution is 3.8 ± 0.4 kpc for the assumed distances to the Galactic center R⊙=8.5 kpc. The surface density of pulsars near the Galactic center is equal to or slightly higher than that in the solar neighborhood. For observable normal pulsars with luminosities ≥ 0.1 mJy kpc2, we also re-estimate their local surface density and birth-rate: 41 ± 5 pulsars kpc-2 and 4.1 ± 0.5 pulsars kpc-2 Myr-1 respectively. For the total number of potentially observable pulsars in the Galaxy, we obtain (24 ± 3) × 103 and (240 ± 30) × 103 before and after applying beaming correction according the Tauris & Manchester (\\cite{TM98}) beaming model. Within the limits of errors of estimations these results are in close agreement with the results of the previous studies of Lyne et al. (\\cite{lml98}) (hereafter LML98). The dependence of these results on the NE2001 model and recommendations for further improvement of electron density distribution are discussed.

  15. 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.

  16. The Mass of a Millisecond Pulsar

    NASA Astrophysics Data System (ADS)

    Jacoby, B. A.; Hotan, A.; Bailes, M.; Ord, S.; Kulkarni, S. R.

    2005-08-01

    We report on nearly 2 years of timing observations of the low-mass binary millisecond pulsar PSR J1909-3744 with the Caltech-Parkes-Swinburne Recorder II, a new instrument that gives unprecedented timing precision. Daily observations give a weighted rms residual of 74 ns, indicating an extremely low level of systematic error. We have greatly improved on the previous parallax and proper motion measurements of PSR J1909-3744, yielding a distance of 1.14+0.04-0.03 kpc and transverse velocity of 200+7-6 km s-1. The system's orbital eccentricity is just (1.35+/-12)×10-7, the smallest yet recorded. Since their discovery, the masses of the rapidly rotating millisecond pulsars have remained a mystery, with the recycling hypothesis arguing for heavy objects, and the accretion-induced collapse of a white dwarf more consistent with neutron stars less than the Chandrashkar limit. Fortuitously, PSR J1909-3744 is an edge-on system, and our data have allowed the measurement of the range and shape of the Shapiro delay to high accuracy, giving the first precise determination of a millisecond pulsar mass to date, mp=1.438+/-0.024 Msolar. The mass of PSR J1909-3744 is at the upper edge of the range observed in mildly recycled pulsars in double neutron star systems, consistent with the recycling hypothesis. It appears that the production of millisecond pulsars is possible with the accretion of <0.2 Msolar.

  17. 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.

  18. 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.

  19. 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.

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

    NASA Astrophysics Data System (ADS)

    Kaspi, Victoria

    2009-09-01

    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 A11, 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.

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

    NASA Astrophysics Data System (ADS)

    Kaspi, Victoria

    2008-09-01

    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 A10, 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.

  2. 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.

  3. Welfare to Work. States Begin JOBS, but Fiscal and Other Problems May Impede Their Progress. Report to the Committee on Finance, U.S. Senate.

    ERIC Educational Resources Information Center

    General Accounting Office, Washington, DC. Div. of Human Resources.

    The General Accounting Office (GAO) reviewed states' implementation of the Job Opportunities and Basic Skills (JOBS) Training Program. GAO studied states' progress in implementing JOBS, decisions about which welfare recipients to serve and what services to provide, views on implementation problems or difficulties, and the nature and extent to…

  4. 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.

  5. 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

  6. Pulsars at very high energies with HESS-II

    NASA Astrophysics Data System (ADS)

    Giavitto, Gianluca

    Pulsed gamma-rays above 100 GeV, recently discovered from the Crab pulsar by the imaging atmospheric Cherenkov telescopes (IACTs) VERITAS and MAGIC, have demonstrated the possibility of detecting pulsars at very high energies (VHE). In order to clarify the many questions that this unexpected discovery has opened, the detection of more VHE pulsars is now of paramount importance. With an expected threshold below 50 GeV and being the only operating IACT in the Southern Hemisphere, the new 28 m class H.E.S.S. II telescope is in a unique position to observe the pulsar population visible from the Southern Hemisphere. Indeed, several pulsars are promising candidates for VHE emission based on theoretical expectations and on the extrapolation of their Fermi-LAT measured gamma-ray spectra. The selection criteria for candidate pulsars, including the prospects of detection by HESS-II, will be discussed.

  7. 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

  8. A periodically active pulsar giving insight into magnetospheric physics.

    PubMed

    Kramer, M; Lyne, A G; O'Brien, J T; Jordan, C A; Lorimer, D R

    2006-04-28

    PSR B1931+24 (J1933+2421) behaves as an ordinary isolated radio pulsar during active phases that are 5 to 10 days long. However, when the radio emission ceases, it switches off in less than 10 seconds and remains undetectable for the next 25 to 35 days, then switches on again. This pattern repeats quasi-periodically. The origin of this behavior is unclear. Even more remarkably, the pulsar rotation slows down 50% faster when it is on than when it is off. This indicates a massive increase in magnetospheric currents when the pulsar switches on, proving that pulsar wind plays a substantial role in pulsar spin-down. This allows us, for the first time, to estimate the magnetospheric currents in a pulsar magnetosphere during the occurrence of radio emission.

  9. 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.

  10. 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.

  11. Spectral properties and variability of the Vela pulsar wind nebula

    NASA Astrophysics Data System (ADS)

    Rangelov, Blagoy; Kargaltsev, Oleg; Pavlov, George; Klingler, Noel; Kropotina, Julia

    2015-08-01

    The non-thermal emission around young pulsars (seen in radio and X-rays) is known to be synchrotron radiation from a relativistic pulsar wind shocked in the ambient medium. One of the best examples is the Vela pulsar wind nebula (PWN), which shows spectacular structure, such as jets, arcs, knots, and diffuse extended emission, detected with Chandra. The morphology of the Vela PWN is determined by the properties of the pulsar wind and surrounding medium. We will present the results of our multi-year Chandra campaign. We will present our analysis of the variability and spectral properties of the compact nebula and discuss their implications for pulsar wind models and for the interaction of the relativistic pulsar wind with the ambient medium.

  12. 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.

  13. 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.

  14. VizieR Online Data Catalog: Energy distribution in pulsars (Burke-Spolaor+, 2012)

    NASA Astrophysics Data System (ADS)

    Burke-Spolaor, S.; Johnston, S.; Bailes, M.; Bates, S. D.; Bhat, N. D. R.; Burgay, M.; Champion, D. J.; D'Amico, N.; Keith, M. J.; Kramer, M.; Levin, L.; Milia, S.; Possenti, A.; Stappers, B.; van Straten, W.

    2013-04-01

    The initial pulsar set included all pulsars in the med-lat survey region as queried through the online ATNF Pulsar Database (http://www.atnf.csiro.au/research/pulsar/psrcat/). We selected the observation of smallest angular distance within 0.25° to each pulsar, yielding 1159 observations near 1113 pulsars (some had multiple observations at roughly equal distance to the pulsar). We scrutinized the HTRU Fourier and single-pulse search results for each observation (as described in Keith et al., 2010MNRAS.409..619K and Burke-Spolaor et al., 2011MNRAS.416.2465B, respectively) to determine the pulsar's detectability. (1 data file).

  15. 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.

  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. Pulsar and diffuse contributions to observed galactic gamma radiation

    NASA Technical Reports Server (NTRS)

    Harding, A. K.; Stecker, F. W.

    1981-01-01

    The first calculation of a gamma-ray production spectrum from pulsars in the Galaxy, along with a statistical analysis of data on 328 known radio pulsars, are presented. The implications of this point source contribution to the general interpretation of the observed galactic gamma-ray spectrum are indicated. The contributions from diffuse interstellar cosmic-ray induced production mechanisms are then re-examined, concluding that pulsars may be contributing significantly to the galactic gamma-ray emission.

  18. 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.

  19. X-Ray observations of ``γ-ray only'' pulsars

    NASA Astrophysics Data System (ADS)

    de Luca, A.; Marelli, M.; Caraveo, P. A.

    2011-08-01

    Fermi-LAT and AGILE have already detected more than 70 rotation-powered pulsars at GeV energies, opening a new era of pulsar physics. In particular, Fermi has unveiled the existence of a large population of Geminga-like pulsars, γ-ray bright but radio-silent. We used XMM-Newton, Chandra and Swift to study such new, γ-ray selected, pulsar population and to compare its X-ray behaviour with that of the radio pulsars. While radio-loud and radio-quiet pulsars need not to be different objects, their different viewing geometry with respect to the observer does influence the ratio between γ and X-ray emissions. When plotting the distance-indipendent γ to X-ray flux ratios as a function of the pulsars' rotational energy losses, one immediately sees that pulsars with similar energetics have Fγ/FX spanning 3 decades. Such spread, most probably stemming from vastly different geometrical configurations of the X and γ-ray emitting regions, defies any straightforward interpretation of the plot. We find that, on average, radio-quiet pulsars do have higher values of Fγ/FX, implying an intrinsec faintness of their X-ray emission and/or a different geometrical configuration.

  20. 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

  1. 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.

  2. 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*.

  3. Pulsar and diffuse contributions to the observed galactic gamma radiation

    NASA Technical Reports Server (NTRS)

    Harding, A. K.; Stecker, F. W.

    1980-01-01

    With the acquisition of satellite data on the energy spectrum of galactic gamma-radiation, it is clear that such radiation has a multicomponent nature. A calculation of the pulsar gamma ray emission spectrum is used together with a statistical analysis of recent data on 328 known pulsars to make a new determination of the pulsar contribution to galactic gamma ray emission. The contributions from diffuse interstellar cosmic ray induced production mechanisms to the total emission are then reexamined. It is concluded that pulsars may account for a significant fraction of galactic gamma ray emission.

  4. 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.

  5. Are the pulses of the Crab pulsar modulated?

    NASA Astrophysics Data System (ADS)

    Cadez, A.; Galicic, M.

    1996-02-01

    We present the results of optical Crab pulsar observations which were designed to search for short-time variations in pulsar's light-curve. Hubble Space Telescope (High Speed Photometer) data and photometric data obtained at the Asiago 1.82m telescope using a specially designed stroboscopic chopper have been analysed and compared. We find a very weak common modulation with the period of 60 seconds which is consistent with all data sets. Such periodic variations in Crab pulsar's light-curve might reflect the pertained free precession of the young Crab pulsar.

  6. Tackling radio polarization of energetic pulsars

    SciTech Connect

    Craig, H. A.

    2014-08-01

    The traditional, geometrical rotating vector model (RVM) has proved particularly poor at capturing the polarization sweeps of the young energetic and millisecond pulsars detected by Fermi. We augment this model by including finite altitude effects using a swept back vacuum dipole geometry. By further including the effects of orthogonal mode jumps, multiple emission altitudes, open zone growth via y-point lowering, and interstellar scattering, we show that a wide range of departures from RVM can be modeled well while retaining a geometrical picture. We illustrate these effects by fitting six Fermi-detected pulsars (J0023+0923, J1024–0719, J1744–1134, J1057–5226, J1420–6048, and J2124–3358) and we describe how such modeling can improve our understanding of their emission geometry.

  7. 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.

  8. Planets around pulsars - a rare phenomenon?

    NASA Astrophysics Data System (ADS)

    Greaves, J. S.; Holland, W. S.

    1997-12-01

    We have used the new submillimetre camera (SCUBA) at the JCMT to search for dusty disks around nearby millisecond pulsars. Such disks are expected to be the precursors of planets, such as those detected by Wolszczan & Frail around B1257+12. No dust emission was detected in our sample, which is 60% complete for millisecond pulsars within 1 kpc of the Sun (and includes B1257+12). The upper limits on dust masses are only a few Earth masses, assuming large grains, or somewhat higher masses are obtained if the grains are very small. In either case, planetesimals and Earth-mass planets are unlikely to be forming at the present time. An alternative is that rocky planets form rapidly in these systems - the (non)detection rate would imply the process takes less than 3 x 10(8) years.

  9. The nature of pulsar radio emission

    NASA Astrophysics Data System (ADS)

    Dyks, J.; Rudak, B.; Demorest, P.

    2010-01-01

    High-quality averaged radio profiles of some pulsars exhibit double, highly symmetric features both in emission and in absorption. It is shown that both types of feature are produced by a split fan beam of extraordinary-mode curvature radiation that is emitted/absorbed by radially extended streams of magnetospheric plasma. With no emissivity in the plane of the stream, such a beam produces bifurcated emission components (BFCs) when our line of sight passes through the plane. An example of a double component created in this way is present in the averaged profile of the 5-ms pulsar J1012+5307. We show that the component can indeed be very well fitted by the textbook formula for the non-coherent beam of curvature radiation in the polarization state that is orthogonal to the plane of electron trajectory. The observed width of the BFC decreases with increasing frequency at a rate that confirms the curvature origin. Likewise, the double absorption features (double notches) are produced by the same beam of the extraordinary-mode curvature radiation, when it is eclipsed by thin plasma streams. The intrinsic property of curvature radiation to create bifurcated fan beams explains the double features in terms of a very natural geometry and implies the curvature origin of pulsar radio emission. Similarly, the `double conal' profiles of class D result from a cut through a wider stream with finite extent in magnetic azimuth. Therefore, their width reacts very slowly to changes of viewing geometry resulting from geodetic precession. The stream-cut interpretation implies a highly non-orthodox origin of both the famous S-swing of polarization angle and the low-frequency pulse broadening in D profiles. The azimuthal structure of polarization modes in the curvature radiation beam provides an explanation for the polarized `multiple imaging' and the edge depolarization of pulsar profiles.

  10. 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.

  11. 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.

  12. 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.

  13. Braking index of isolated pulsars. II. A novel two-dipole model of pulsar magnetism

    NASA Astrophysics Data System (ADS)

    Hamil, O.; Stone, N. J.; Stone, J. R.

    2016-09-01

    The magnetic dipole radiation model is currently the best approach we have to explain pulsar radiation. However, a most characteristic parameter of the observed radiation, the braking index nobs , shows deviations for all the eight best studied isolated pulsars, from the simple model prediction ndip=3 . The index depends upon the rotational frequency and its first and second time derivatives but also on the assumption that the magnetic dipole moment and inclination angle and the moment of inertia of the pulsar are constant in time. In a recent paper [Phys. Rev. D 91, 063007 (2015)], we showed conclusively that changes in the moment of inertia with frequency alone cannot explain the observed braking indices. Possible observational evidence for the magnetic dipole moment migrating away from the rotational axis at a rate α ˙ ˜0.6 ° per 100 years over the lifetime of the Crab pulsar has been recently suggested by Lyne et al. In this paper, we explore the magnetic dipole radiation model with constant moment of inertia and magnetic dipole moment but variable inclination angle α . We first discuss the effect of the variation of α on the observed braking indices and show they all can be understood. However, no explanation for the origin of the change in α is provided. After discussion of the possible source(s) of magnetism in pulsars, we propose a simple mechanism for the change in α based on a toy model in which the magnetic structure in pulsars consists of two interacting dipoles. We show that such a system can explain the Crab observation and the measured braking indices.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. An optical counterpart to the anomalous X-ray pulsar 4U0142+61.

    PubMed

    Hulleman, F; van Kerkwijk, M H; Kulkarni, S R

    2000-12-01

    The energy source of the anomalous X-ray pulsars (AXPs) is not understood, hence their designation as anomalous. Unlike binary X-ray pulsars, no companions are seen, so the energy cannot be supplied by accretion of matter from a companion star. The loss of rotational energy, which powers radio pulsars, is insufficient to power AXPs. Two models are generally considered: accretion from a large disk left over from the birth process, or decay of a very strong magnetic field (10(15) G) associated with a 'magnetar'. The lack of counterparts at other wavelengths has hampered progress in our understanding of these objects. Here we report deep optical observations of the field around 4U0142+61, which is the brightest AXP in X-rays. The source has no associated supernova remnant, which, together with its spin-down timescale of approximately 10(5) yr (ref. 5), suggests that it may be relatively old. We find an object with peculiar optical colours at the position of the X-ray source, and argue that it is the optical counterpart. The optical emission is too faint to admit the presence of a large accretion disk, but may be consistent with magnetospheric emission from a magnetar.

  2. 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.

  3. 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

  4. 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

  5. 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).

  6. 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.

  7. 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.

  8. 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.

  9. 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).

  10. The Gamma-Ray Luminosity Function of Radio Pulsars

    NASA Technical Reports Server (NTRS)

    Helfand, David J.

    1998-01-01

    This final report is a study of gamma-ray luminosity function of radio pulsars. The goal is to constrain certain parameters in order to address such diverse issues as the high energy emission mechanism in pulsars and the fraction of the Galaxy's gamma ray emission attributable to these objects.

  11. 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.

  12. 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.

  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. 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.

  15. 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.

  16. 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.

  17. Drifting sub-pulses in two newly discovered pulsars

    NASA Astrophysics Data System (ADS)

    Ord, S. M.; Edwards, R.; Bailes, M.

    2001-12-01

    We have detected the rare phenomenon of stable, drifting sub-pulse behaviour in two pulsars discovered in the recent Swinburne intermediate latitude pulsar survey. The pulsars, PSR J1231-47 and PSR J1919+0134, have approximate periods (P) of 1.873 and 1.6039s respectively. Both pulsars have multicomponent profiles, and distinct drifting is observed across them. We have identified a single drift mode in both pulsars: the drift rate for PSR J1231-47 being 5.4(1) ms P-1 and 5.8(2) ms P-1 for PSR 1919+0134. The drifting is linear across the profile with no departure from linearity at the edges within the sensitivity of our observations.

  18. Revealing pulsars hidden in the 2nd Fermi Catalogue

    NASA Astrophysics Data System (ADS)

    Rangelov, Blagoy

    2013-10-01

    We propose a mini-survey of unclassified Fermi sources from the 2FGL catalog. Using an intelligent parameter selection, we have identified a sub-sample that is likely to be dominated by pulsars with some inclusion of high-mass XRBs. We aim to identify 7 new gamma-ray pulsars and their X-ray counterparts, and thus significantly increase the population of pulsars detected in both gamma-rays and X-rays. The existing limited data hint at an intriguing change in the slope of the L(Edot) dependence at log(Edot)=35-36 erg/s. By identifying more pulsars in both gamma- and X-rays, we will be able to confirm the existence of those breaks and investigate their origin. We will also identify new X-ray bright pulsars suitable for detailed study using the prudent snap-shot approach.

  19. Revealing pulsars hidden in the 2nd Fermi Catalogue

    NASA Astrophysics Data System (ADS)

    Kargaltsev, Oleg

    2012-10-01

    We propose a mini-survey of unclassified Fermi sources from the 2FGL catalog. Using an intelligent parameter selection, we have identified a sub-sample that is likely to be dominated by pulsars. We aim to identify 8 new gamma-ray pulsars via their X-ray counterparts and expand the population of pulsars detected in both gamma-rays and X-rays. The existing limited data hint at an intriguing change in the slope of the L(Edot) dependence at Edot=10^35-10^36 erg/s, both in X-rays and gamma-rays. By identifying more pulsars in both gamma- and X-rays, especially at lower Edot, we will be able to confirm the existence of those breaks and investigate their origin. We will also identify new X-ray bright pulsars suitable for detailed study using the prudent snap-shot approach.

  20. Revealing pulsars hidden in the 2nd Fermi Catalogue

    NASA Astrophysics Data System (ADS)

    Pavlov, George

    2012-09-01

    We propose a mini-survey of unclassified Fermi sources from the 2FGL catalogue. Using an intelligent parameter selection, we have identified a sub-sample that is likely to be dominated by pulsars. We aim to identify 8 new gamma-ray pulsars and their X-ray counterparts, and thus significantly increase the population of pulsars detected in both gamma- and X-rays. The existing limited data hint at an intriguing change in the slope of the L(Edot) dependence at Edot~1e35-36 erg/s, both in X-rays and gamma-rays. By identifying more pulsars in both gamma- and X-rays, especially at lower Edot, we will be able to confirm and study such breaks and relationships. We will also find new X-ray bright pulsars suitable for detailed study.

  1. Observations of VHE from the Crab Pulsar with VERITAS

    NASA Astrophysics Data System (ADS)

    Archer, Avery; VERITAS Collaboration

    2015-04-01

    The Crab pulsar has been closely studied across the electromagnetic spectrum from radio to TeV energies. Observations in recent years have challenged the favored models for the highest-energy emission. With 107 hours of observation, VERITAS first observed the Crab pulsar above 120 GeV, well above the expected cut-off of a few GeV. Pulsar modeling demonstrates that magnetosphere of the Crab is opaque to VHE photons, narrowing the possible emission regions within the magnetosphere given recent observations. As of fall 2014, the exposure has been increased to over 200 hours. These new VERITAS results help to further constrain the models, providing improved information about the origin of very high energy emission within the pulsar magnetosphere. Presented here are results of ongoing observations and analysis of the Crab pulsar from 100 GeV up to TeV energies with the VERITAS telescopes in the context of modeling viable emission region models.

  2. The Double Pulsar System J0737-3039

    NASA Astrophysics Data System (ADS)

    Lorimer, D. R.

    The double pulsar system J0737 - 3039 - a 22.7 ms pulsar in a compact 2.4 hr orbit about a 2.7 s pulsar was one of the long-awaited "holy grails" of pulsar astronomy. After only two years of timing, the system is close to surpassing the original Hulse-Taylor binary as a test of general relativity. On-going timing should soon reveal second-order effects in the post-Newtonian parameters. In addition, the observed interactions of the radio beams of the two pulsars provide a unique laboratory for probing neutron star magnetospheres and relativistic winds. Finally, a revised estimate of the cosmic rate of double neutron star mergers including J0737 - 3039 boosts previous estimates by an order of magnitude and suggests a high detection rate for the advanced LIGO gravitational wave detector.

  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. 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

  5. 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.

  6. Rotation powered pulsars in the x-rays

    NASA Astrophysics Data System (ADS)

    Arumugasamy, Prakash

    The dissertation focuses on the study of rotation-powered pulsars, the primary observational manifestation of neutron stars. These objects are powerful sources of electromagnetic radiation and relativistic particles whose emission is provided by the loss of pulsar rotational energy. Understanding the evolution of pulsars, which happens over billion year timescales, requires detection and study of pulsars at different stages of evolution. I present detailed X-ray analyses of pulsars at four distinct stages of evolution and compare their emission behavior with that of other pulsars expected to be in similar evolutionary stages. I also show key characteristics of the pulsars that make them unique in their group. I start with a young and energetic pulsar, PSR J2022+3842 (characteristic age tauc ≈ 9 kyr, spin-down power E = 3 x 1037 erg s-1), with powerful non-thermal emission. X-ray timing of the pulsar revealed double-peaked X-ray profile with a period twice the previously established value. Our analysis allowed us to update the pulsar's spin-down power and X-ray efficiency using the correct timing results, which brought the pulsar more in-line with other young X-ray pulsars. I also provide the phase-dependent behavior of the pulsar's non-thermal emission. Pulsars with true ages, often substituted by characteristic age, below tauc ˜100 kyr are considered young and ones with tau c ≥ 1 Myr are considered old, with the 'middle-aged' pulsars in the middle. My next pulsar is a tauc = 1.8 Myr old J1836+5925 (E = 1 x 1034 erg s-1), which is perhaps the brightest X-ray source among the oldest pulsars still observable in the gamma-rays. Detailed timing and spectral analyses show strong evidence of an absorption feature (perhaps an electron cyclotron line) in the pulsar's spectrum. Characterizing its thermal emission might have important implications for the neutron star cooling models. Moving another two orders of magnitude up in tauc, we arrive at one of the oldest known

  7. 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.

  8. Theory of Pulsar Action as Revealed by PSR B1931+24 (the "intermittent Pulsar")

    NASA Astrophysics Data System (ADS)

    Michel, F. Curtis

    2010-03-01

    The intermittent pulsar B1931+24 is observed to be ON for about a week at a time and OFF for about a month in between. Compared to its period of about 0.8 seconds, each interval is effectively "forever". The more popular theories are based on an old model that suggests that pulsars cannot be OFF, but are fundamentally doomed to be active at all times. The alternative theory which has had less attention is just the opposite and in its simplest form suggests that the pulsar could instead be OFF at all times. We now know that the later is not true owing to magnetic pair production (ApJ, 383, 808, 1991), which additionally explains coherent radio emission as being due to particle bunching. An obvious explanation of B1931+24 (and others are known) is that pulsars can become "stuck" in between these limiting states. If this is true, the obvious conclusion is that in the OFF state it has no currents to/from the neutron star and is being slowed purely from magnetic dipole radiation (n=3, in the simplest limit, although there may be corrections from change in inclination).

  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}⊙ ) 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. A search for fast gamma-ray pulsars with OSSE

    NASA Technical Reports Server (NTRS)

    Hertz, P.; Grove, J. E.; Grabelsky, D. A.; Matz, S. M.

    1995-01-01

    Pulsar mode data from the Oriented Scintillation Spectrometer Experiment (OSSE) onboard the Compton Gamma Ray Observatory (CGRO), with time resolution between 125 microsecs and 8 ms, have been analyzed for the presence of short-period gamma-ray pulsations. Observations of known point sources (including SN 1987A, SN 1993J, GRO J0422+32, and several pulsars) and of regions where higher densities of pulsars are expected (including the Galactic center, the Galactic plane and arms, and the Large Magellanic Cloud) are included in the study. Both isolated pulsars and pulsars in close binary systems are searched for; in the latter case, the quadratic coherence recovery technique is used to correct for broadening of the pulsar signal from orbital motion. No new gamma-ray pulsars have been detected. Upper limits on the pulsed gamma-ray flux from isolated pulsars in the 50-210 keV energy range of OSSE are between 0.2 x 10(exp -3) and 2.0 x 10(exp -3) photons/s/sq cm for pulse periods between 250 microsecs and 0.5 s. Upper limits on the pulsed flux from binary pulsars are between 1.5 x 10(exp -3) and 6.4 x 10(exp -3) photons/s/sq cm for the same energy band and pulse period range. We estimate that, in the Galaxy, there are fewer than approximately 125 isolated pulsars similar to PSR B1509-58 with radiation peaks in the OSSE band but undetected in the radio and X-rays bands.

  12. 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.

  13. Accretion X-ray ms pulsar as a probe of NS EOS

    NASA Astrophysics Data System (ADS)

    Zhang, Shu; Ji, Long

    2016-07-01

    Equation state of NS is one of the core sciences for future mission. Regarding to the possible probes, apart from the bursting ms pulsars for which the relation between the spinning light curve and the mass/radius of NS is well established theoretically, the accretion X-ray ms pulsars are the potential alternatives. However, the emission mechanism of the latter is more complicated since one has to account for the corona on top of the NS surface which provides Comptonizations that mix/distort the black body underneath. Thus disentangling the model components between the black body and the Comptonization becomes a big challenge in case of relating the spinning light curve to the mass/radius of NS. This problem is hard to be handled even with a powerful telescope owning a very large detection area. X-ray polarimetry shows us a new insight on model discrimination, and we take the accretion X-ray ms pulsar XTEJ1751-305 as an example to show how this issue could be addressed with a polarization telescope.

  14. 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.

  15. 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.

  16. Axion mass limits from pulsar x rays

    SciTech Connect

    Morris, D.E.

    1984-12-01

    Axions thermally emitted by a neutron star would be converted into x rays in the strong magnetic field surrounding the star. An improvement in the observational upper limit of pulsed x rays from the Vela pulsar (PSR 0833-45) by a factor of 12 would constrain the axion mass M/sub a/ < 2 x 10/sup -3/eV if the core is non-superfluid and at temperature T/sub c/ greater than or equal to 2 x 10/sup 8/K. If the core is superfluid throughout, an improvement factor of 240 would be needed to provide the same constraint on the axion mass, while in the absence of superfluidity, an improvement factor of 200 could constrain M/sub a/ < 6 x 10/sup -4/eV. A search for modulated hard x rays from PSR 1509-58 or other young pulsars at presently attainable sensitivities may enable the setting of an upper limit for the axion mass. Observation of hard x rays from a very young hot pulsar with T/sub c/ greater than or equal to 7 x 10/sup 8/K could set a firm bound on the axion mass, since neutron superfluidity is not expected above this temperature. The remaining axion mass range 6 x 10/sup -4/eV > M/sub a/ > 10/sup -5/eV (the cosmological lower bound) can be covered by an improved Sikivie type laboratory cavity detector for relic axions constituting the galactic halo. 48 refs.

  17. 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.

  18. 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.

  19. Ultraviolet Pulsations from X-Ray Pulsars

    NASA Astrophysics Data System (ADS)

    Bless, Robert

    1991-07-01

    We propose to obtain high-speed photometry at ultraviolet wavelengths of all the pulsing X-ray heated stellar atmospheres of the companion stars to the neutron stars in the binaries and to create list of X-ray pulsars with optical pulsations that can be further observed for such purposes as determining the mass ratios of the binary system. Revision History: Prepared for future cycles submission-- BJW 4/24/92; Cycle 3 to cycle 2; PRISM to SINGLE-- BJW 8/27/92;

  20. 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.

  1. 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.

  2. 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

  3. 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.

  4. 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.

  5. 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

  6. ON DETECTING MILLISECOND PULSARS AT THE GALACTIC CENTER

    SciTech Connect

    Macquart, Jean-Pierre

    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.

  7. A Search for Radio Pulsars at High Galactic Latitude

    NASA Astrophysics Data System (ADS)

    Jacoby, B. A.

    We have completed a search for radio pulsars using the Parkes 64-m telescope, covering about 4500 square degrees between 15 deg and 30 deg from the Galactic plane. Each pointing was observed for 265 s with the 13-beam multibeam system at a frequency of 1374 MHz. The signal from each beam was processed by a 96-channel filterbank and sampled every 125 us, with a bandwidth of 288 MHz. This strategy affords rapid sky coverage and good sensitivity to pulsars with periods as short as 1 ms, whose existence would constrain the neutron star equation of state. Data were analyzed using the workstation cluster at the Swinburne Centre for Astrophysics and Supercomputing. This effort has yielded 26 new pulsars, including seven recycled pulsars. Taken together with the previous Swinburne Intermediate Latitude Pulsar Survey, a total of 95 new pulsars were found over nearly 7500 square degrees of sky between 5 deg and 30 deg from the plane of the Galaxy. This large sample of newly discovered objects contains no young pulsars.

  8. 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.

    2016-11-01

    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 maximize 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.

  9. Properties of pulsars with short and long periods

    NASA Astrophysics Data System (ADS)

    Loginov, A. A.; Malov, I. F.

    2015-11-01

    A comparative analysis has been conducted for the timescale on which the observed radio emission of pulsars is switched off (nulling fraction), the polarization parameters, and the residual deviations in the pulse arrival times for pulsars with periods P >0.1 s and P <0.1 s. For the former group of pulsars, the greater the energy injected into the magnetosphere from internal layers of the neutron star, the smaller the nulling fraction; in the latter group, nullings are not observed at all. Mode switches are also observed only in pulsarswith long pulse-to-pulse intervals ( P >1 s), and in many objects they are correlatedwith the presence of nullings. The degree of polarization grows with decreasing period, and is systematically higher in objects with P <0.1 s than in long-period pulsars. The relative deviations of the pulse arrival times are, on average, appreciably smaller for pulsars with P >0.1 s. The observed differences in the parameters of pulsars with short and long periods can be understood if the radiation of pulsars with P <0.1 s is generated near the light cylinder.

  10. 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?

  11. 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.

  12. 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

  13. 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.

  14. PULSAR OBSERVATIONS OF EXTREME SCATTERING EVENTS

    SciTech Connect

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

    2015-08-01

    Extreme scattering events (ESEs) in the interstellar medium (ISM) were first observed in regular flux measurements of compact extragalactic sources. They are characterized by a flux variation over a period of weeks, suggesting the passage of a “diverging plasma lens” across the line of sight (LOS). Modeling the refraction of such a lens indicates that the structure size must be of the order of AU and the electron density of the order of 10s of cm{sup −3}. Similar structures have been observed in measurements of pulsar intensity scintillation and group delay. Here we report observations of two ESEs, showing increases in both intensity scintillation and dispersion made with the Parkes Pulsar Timing Array. These allow us to make more complete models of the ESE, including an estimate of the “outer-scale” of the turbulence in the plasma lens. These observations clearly show that the ESE structure is fully turbulent on an AU scale. They provide some support for the idea that the structures are extended along the LOS, such as would be the case for a scattering shell. The dispersion measurements also show a variety of AU scale structures that would not be called ESEs, yet involve electron density variations typical of ESEs and likely have the same origin.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. Pulsar coherent de-dispersion system of Urumqi Observatory

    NASA Astrophysics Data System (ADS)

    Liyong, Liu; Esamdin, Ali; Jin, Zhang

    Pulsar coherent de-dispersion experiment has been carried by using the 25-m Nanshan radio telescope of Urumqi Observatory It uses a dual polarization receiver operating at 18cm and a VLBI back-end Mark5A The data processing system is based on a C program on Linux and a 4-node Beowulf cluster A high quality data acquisition system and a cluster with more processors are needed to build an on-line pulsar coherent de-dispersion system in future Key words Astronomical instrument Pulsar Coherent de-dispersion Parallel computing Cluster Mark5A

  20. Pulsar Coherent De-dispersion Experiment at Urumqi Observatory

    NASA Astrophysics Data System (ADS)

    Liu, Li-Yong; Ali, Esamdin; Zhang, Jin

    2006-12-01

    A Pulsar coherent de-dispersion experiment has been carried out using the 25-m Nanshan radio telescope at Urumqi Observatory. It uses a dual polarization receiver operating at 18 cm and a VLBI back-end: Mark5A, the minimum sampling time is 5 ns. The data processing system is based on a C program on Linux and a 4-node Beowulf cluster. A high quality data acquisition system and a cluster with more processors are needed to build an on-line pulsar coherent de-dispersion system in future. The main directions for the instrument are studies of pulsar timing, scintillation monitoring, etc.

  1. Gravitational waves from pulsars with measured braking index

    NASA Astrophysics Data System (ADS)

    de Araujo, José C. N.; Coelho, Jaziel G.; Costa, Cesar A.

    2016-09-01

    We study the putative emission of gravitational waves (GWs) in particular for pulsars with measured braking index. We show that the appropriate combination of both GW emission and magnetic dipole brakes can naturally explain the measured braking index, when the surface magnetic field and the angle between the magnetic dipole and rotation axes are time dependent. Then we discuss the detectability of these very pulsars by aLIGO and the Einstein Telescope. We call attention to the realistic possibility that aLIGO can detect the GWs generated by at least some of these pulsars, such as Vela, for example.

  2. 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.

  3. Coherent Network Analysis for Continuous Gravitational Wave Signals in a Pulsar Timing Array: Pulsar Phases as Extrinsic Parameters

    NASA Astrophysics Data System (ADS)

    Wang, Yan; Mohanty, Soumya D.; Jenet, Fredrick A.

    2015-12-01

    Supermassive black hole binaries are one of the primary targets of gravitational wave (GW) searches using pulsar timing arrays (PTAs). GW signals from such systems are well represented by parameterized models, allowing the standard Generalized Likelihood Ratio Test (GLRT) to be used for their detection and estimation. However, there is a dichotomy in how the GLRT can be implemented for PTAs: there are two possible ways in which one can split the set of signal parameters for semi-analytical and numerical extremization. The straightforward extension of the method used for continuous signals in ground-based GW searches, where the so-called pulsar phase parameters are maximized numerically, was addressed in an earlier paper. In this paper, we report the first study of the performance of the second approach where the pulsar phases are maximized semi-analytically. This approach is scalable since the number of parameters left over for numerical optimization does not depend on the size of the PTA. Our results show that for the same array size (9 pulsars), the new method performs somewhat worse in parameter estimation, but not in detection, than the previous method where the pulsar phases were maximized numerically. The origin of the performance discrepancy is likely to be in the ill-posedness that is intrinsic to any network analysis method. However, the scalability of the new method allows the ill-posedness to be mitigated by simply adding more pulsars to the array. This is shown explicitly by taking a larger array of pulsars.

  4. 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…

  5. 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…

  6. The Effects of Spacing and Birth Order on Problem-Solving Competence of Preschool Children. Progress Report.

    ERIC Educational Resources Information Center

    McGillicuddy-DeLisi, Ann V.; Sigel, Irving

    This study investigates the impact of family configuration and parent education-income level on parental beliefs, the relationship between these beliefs and actual parental practices, and the effect of parental practices on children's problem-solving abilities. One hundred twenty intact families participated in the study. Forty families consisted…

  7. The High Time Resolution Universe Pulsar Survey - XII. Galactic plane acceleration search and the discovery of 60 pulsars

    NASA Astrophysics Data System (ADS)

    Ng, C.; Champion, D. J.; Bailes, M.; Barr, E. D.; Bates, S. D.; Bhat, N. D. R.; Burgay, M.; Burke-Spolaor, S.; Flynn, C. M. L.; Jameson, A.; Johnston, S.; Keith, M. J.; Kramer, M.; Levin, L.; Petroff, E.; Possenti, A.; Stappers, B. W.; van Straten, W.; Tiburzi, C.; Eatough, R. P.; Lyne, A. G.

    2015-07-01

    We present initial results from the low-latitude Galactic plane region of the High Time Resolution Universe pulsar survey conducted at the Parkes 64-m radio telescope. We discuss the computational challenges arising from the processing of the terabyte-sized survey data. Two new radio interference mitigation techniques are introduced, as well as a partially coherent segmented acceleration search algorithm which aims to increase our chances of discovering highly relativistic short-orbit binary systems, covering a parameter space including potential pulsar-black hole binaries. We show that under a constant acceleration approximation, a ratio of data length over orbital period of ≈0.1 results in the highest effectiveness for this search algorithm. From the 50 per cent of data processed thus far, we have redetected 435 previously known pulsars and discovered a further 60 pulsars, two of which are fast-spinning pulsars with periods less than 30 ms. PSR J1101-6424 is a millisecond pulsar whose heavy white dwarf (WD) companion and short spin period of 5.1 ms indicate a rare example of full-recycling via Case A Roche lobe overflow. PSR J1757-27 appears to be an isolated recycled pulsar with a relatively long spin period of 17 ms. In addition, PSR J1244-6359 is a mildly recycled binary system with a heavy WD companion, PSR J1755-25 has a significant orbital eccentricity of 0.09 and PSR J1759-24 is likely to be a long-orbit eclipsing binary with orbital period of the order of tens of years. Comparison of our newly discovered pulsar sample to the known population suggests that they belong to an older population. Furthermore, we demonstrate that our current pulsar detection yield is as expected from population synthesis.

  8. Application of Millisecond Pulsar Timing to the Long-Term Stability of Clock Ensembles

    NASA Technical Reports Server (NTRS)

    Foster, Roger S.; Matsakis, Demetrios N.

    1996-01-01

    We review the application of millisecond pulsars to define a precise long-term standard and positional reference system in a nearly inertial reference frame. We quantify the current timing precision of the best millisecond pulsars and define the required precise time and time interval (PTTI) accuracy and stability to enable time transfer via pulsars. Pulsars may prove useful as independent standards to examine decade-long timing stability and provide an independent natural system within which to calibrate any new, perhaps vastly improved atomic time scale. Since pulsar stability appears to be related to the lifetime of the pulsar, the new millisecond pulsar J173+0747 is projected to have a 100-day accuracy equivalent to a single HP5071 cesium standard. Over the last five years, dozens of new millisecond pulsars have been discovered. A few of the new millisecond pulsars may have even better timing properties.

  9. 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.

  10. 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.

  11. 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.

  12. Pulsar timing arrays: the promise of gravitational wave detection

    NASA Astrophysics Data System (ADS)

    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.

  13. Pulsar radiation in post-Maxwellian vacuum nonlinear electrodynamics

    NASA Astrophysics Data System (ADS)

    Denisov, V. I.; Shvilkin, B. N.; Sokolov, V. A.; Vasili'ev, M. I.

    2016-08-01

    The effects of nonlinear vacuum electrodynamics are most clearly pronounced in a strong electromagnetic field close to Schwinger limit. Electromagnetic fields of such intensity can be obtained in laboratory conditions only on very few extreme laser facilities and during a short time interval. At the same time, the astrophysical compact objects with a strong electromagnetic field such as pulsars and magnetars are the best suited to study the effects of nonlinear vacuum electrodynamics. We present analytical calculations for pulsar proper radiation in parametrized post-Maxwellian nonlinear vacuum electrodynamics. Based on the obtained solutions, the effect of nonlinear vacuum corrections to pulsar spin down is being investigated. The analysis of torque functions show that the nonlinear vacuum electrodynamics corrections to the electromagnetic radiation for some pulsars may be comparable to the energy loss by gravitational radiation.

  14. Pulsar Science with the Green Bank 43 m Telescope

    NASA Astrophysics Data System (ADS)

    Mickaliger, M. B.; McLaughlin, M. A.; Lorimer, D. R.; Langston, G.; Bilous, A. V.; Kondratiev, V. I.; Ransom, S. M.; Crawford, F.

    2011-08-01

    The 43 m telescope at the NRAO site in Green Bank, WV has recently been outfitted with a clone of the Green Bank Ultimate Pulsar Processing Instrument (GUPPI [1]) backend, making it very useful for a number of pulsar related studies in frequency ranges 800-1600 MHz and 220-440 MHz. Some of the recent science being done with it include: monitoring of the Crab pulsar, a blind search for transient sources, pulsar searches of targets of opportunity, and an all-sky mapping project. For the Crab monitoring project, regular observations are searched for giant pulses (GPs), which are then correlated with γ-ray photons from the Fermi spacecraft. Data from the all-sky mapping project are first run through a pipeline that does a blind transient search, looking for single pulses over a DM range of 0-500 pc cm-3. These projects are made possible by MIT Lincoln Labs.

  15. 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

  16. 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.

  17. Ab Initio Pulsar Magnetosphere: The Role of General Relativity

    NASA Astrophysics Data System (ADS)

    Philippov, Alexander A.; Cerutti, Benoît; Tchekhovskoy, Alexander; Spitkovsky, Anatoly

    2015-12-01

    It has recently been demonstrated that self-consistent particle-in-cell simulations of low-obliquity pulsar magnetospheres in flat spacetime show weak particle acceleration and no pair production near the poles. We investigate the validity of this conclusion in a more realistic spacetime geometry via general-relativistic particle-in-cell simulations of the aligned pulsar magnetosphere with pair formation. We find that the addition of the frame-dragging effect makes the local current density along the magnetic field larger than the Goldreich–Julian value, which leads to unscreened parallel electric fields and the ignition of a pair cascade. When pair production is active, we observe field oscillations in the open field bundle, which could be related to pulsar radio emission. We conclude that general-relativistic effects are essential for the existence of the pulsar mechanism in low-obliquity rotators.

  18. 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)

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. AB INITIO PULSAR MAGNETOSPHERE: THE ROLE OF GENERAL RELATIVITY

    SciTech Connect

    Philippov, Alexander A.; Cerutti, Benoit; Spitkovsky, Anatoly; Tchekhovskoy, Alexander

    2015-12-20

    It has recently been demonstrated that self-consistent particle-in-cell simulations of low-obliquity pulsar magnetospheres in flat spacetime show weak particle acceleration and no pair production near the poles. We investigate the validity of this conclusion in a more realistic spacetime geometry via general-relativistic particle-in-cell simulations of the aligned pulsar magnetosphere with pair formation. We find that the addition of the frame-dragging effect makes the local current density along the magnetic field larger than the Goldreich–Julian value, which leads to unscreened parallel electric fields and the ignition of a pair cascade. When pair production is active, we observe field oscillations in the open field bundle, which could be related to pulsar radio emission. We conclude that general-relativistic effects are essential for the existence of the pulsar mechanism in low-obliquity rotators.

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. 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.

  10. An Eccentric Binary Millisecond Pulsar in the Galactic Plane

    NASA Technical Reports Server (NTRS)

    Champion, David J.; Ransom, Scott M.; Lazarus, Patrick; Camilo, Fernando; Bassa, Cess; Kaspi, Victoria M.; Nice, David J.; Freire, Paulo C. C.; Stairs, Ingrid H.; vanLeeuwen, 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, Ismael; Deneva, Julia S.; Faucher-Giguere, Claude-Andre; Gaensler, Bryan M.; Han, JinLin; Jenet, Fredrick A.; Kasian, Laura

    2008-01-01

    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.) 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 Solar Mass, an unusually high value.

  11. 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.

  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. 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

  15. Magnetic pair creation transparency in gamma-ray pulsars

    SciTech Connect

    Story, Sarah A.; Baring, Matthew G. E-mail: baring@rice.edu

    2014-07-20

    Magnetic pair creation, γ → e {sup +} e {sup –}, has been at the core of radio pulsar paradigms and central to polar cap models of gamma-ray pulsars for over three decades. The Fermi gamma-ray pulsar population now exceeds 140 sources and has defined an important part of Fermi's science legacy, providing rich information for the interpretation of young energetic pulsars and old millisecond pulsars. Among the population characteristics well established is the common occurrence of exponential turnovers in their spectra in the 1-10 GeV range. These turnovers are too gradual to arise from magnetic pair creation in the strong magnetic fields of pulsar inner magnetospheres. By demanding insignificant photon attenuation precipitated by such single-photon pair creation, the energies of these turnovers for Fermi pulsars can be used to compute lower bounds for the typical altitude of GeV band emission. This paper explores such pair transparency constraints below the turnover energy and updates earlier altitude bound determinations that have been deployed in various Fermi pulsar papers. For low altitude emission locales, general relativistic influences are found to be important, increasing cumulative opacity, shortening the photon attenuation lengths, and also reducing the maximum energy that permits escape of photons from a neutron star magnetosphere. Rotational aberration influences are also explored, and are found to be small at low altitudes, except near the magnetic pole. The analysis presented in this paper clearly demonstrates that including near-threshold physics in the pair creation rate is essential to deriving accurate attenuation lengths and escape energies. The altitude bounds are typically in the range of 2-7 stellar radii for the young Fermi pulsar population, and provide key information on the emission altitude in radio quiet pulsars that do not possess double-peaked pulse profiles. The bound for the Crab pulsar is at a much higher altitude, with the

  16. VizieR Online Data Catalog: ATNF Pulsar Catalogue (Manchester+, 2005)

    NASA Astrophysics Data System (ADS)

    Manchester, R. N.; Hobbs, G. B.; Teoh, A.; Hobbs, M.

    2016-05-01

    The catalogue is a compilation of the principal observed parameters of pulsars, including positions, timing parameters, pulse widths, flux densities, proper motions, distances, and dispersion, rotation, and scattering measures. It also lists the orbital elements of binary pulsars, and some commonly used parameters derived from the basic measurements. The catalogue includes all published rotation-powered pulsars, including those detected only at high energies. It also includes Anomalous X-ray Pulsars (AXPs) and Soft Gamma-ray Repeaters (SGRs) for which coherent pulsations have been detected. However, it excludes accretion-powered pulsars such as Her X-1 and the recently discovered X-ray millisecond pulsars. (2 data files).

  17. On high frequency Cherenkov-type radiation in pulsar magnetospheric electron-positron plasma

    NASA Astrophysics Data System (ADS)

    Machabeli, G.; Chkheidze, N.

    2014-12-01

    Emission process of a charged particle propagating in a medium with a curved magnetic field is considered. This mechanism combines features of conventional Cherenkov and curvature emission. Thus, presence of a medium with the index of refraction larger than the unity is essential for the emission. In the present paper the generation of high frequency radiation by the mentioned mechanism is considered. The generated waves are vacuum-like electromagnetic waves and may leave the medium directly. Consequently, this emission mechanism may be important for the problem of pulsar X-ray and gamma-ray emission generation.

  18. Is Jupiter's magnetosphere like a pulsar's or earth's?

    NASA Technical Reports Server (NTRS)

    Kennel, C. F.; Coroniti, F. V.

    1974-01-01

    The application of pulsar physics to determine the magnetic structure in the planet Jupiter outer magnetosphere is discussed. A variety of theoretical models are developed to illuminate broad areas of consistency and conflict between theory and experiment. Two possible models of Jupiter's magnetosphere, a pulsar-like radial outflow model and an earth-like convection model, are examined. A compilation of the simple order of magnitude estimates derivable from the various models is provided.

  19. PULSE@Parkes (Pulsar Student Exploration at Parkes)

    NASA Astrophysics Data System (ADS)

    Hobbs, George; Chapman, Jessica M.; Hollow, Robert; Amy, Shaun

    2007-10-01

    We propose to have secondary school students from NSW government schools use the Parkes radio telescope in a remote observing mode to observe and analyse pulsar data. The data will later become part of the GLAST mission support observations and the P456 Pulsar Timing Array project. This trial program will allow us to develop technical methods and the educational pedagogy for future student access of ATNF telescopes including ASKAP and eventually the SKA.

  20. Escaping radio emission from pulsars: Possible role of velocity shear

    SciTech Connect

    Mahajan, S.M. |; Machabeli, G.Z.; Rogava, A.D. |

    1997-01-01

    It is demonstrated that the velocity shear, intrinsic to the e{sup +}e{sup {minus}} plasma present in the pulsar magnetosphere, can efficiently convert the nonescaping longitudinal Langmuir waves (produced by some kind of a beam or stream instability) into propagating (escaping) electromagnetic waves. It is suggested that this shear induced transformation may be the basic mechanism needed for the eventual generation of the observed pulsar radio emission.

  1. Spin-powered Pulsars in the CTA Era

    NASA Astrophysics Data System (ADS)

    Romani, Roger W.

    2016-04-01

    What can CTA do for the study of isolated and binary neutron stars? Are the recent Crab observations the vanguard of numerous strong pulsed detections in the CTA era? Will the typical pulsar show only the tail of the Fermi spectrum? Or will we be tantalized by a handful of new unusual sources? I review our current HE picture and suggest that pulsar binaries represent a new TeV frontier.

  2. A millisecond pulsar in an extremely wide binary system

    NASA Astrophysics Data System (ADS)

    Bassa, C. G.; Janssen, G. H.; Stappers, B. W.; Tauris, T. M.; Wevers, T.; Jonker, P. G.; Lentati, L.; Verbiest, J. P. W.; Desvignes, G.; Graikou, E.; Guillemot, L.; Freire, P. C. C.; Lazarus, P.; Caballero, R. N.; Champion, D. J.; Cognard, I.; Jessner, A.; Jordan, C.; Karuppusamy, R.; Kramer, M.; Lazaridis, K.; Lee, K. J.; Liu, K.; Lyne, A. G.; McKee, J.; Osłowski, S.; Perrodin, D.; Sanidas, S.; Shaifullah, G.; Smits, R.; Theureau, G.; Tiburzi, C.; Zhu, W. W.

    2016-08-01

    We report on 22 yr of radio timing observations of the millisecond pulsar J1024-0719 by the telescopes participating in the European Pulsar Timing Array (EPTA). These observations reveal a significant second derivative of the pulsar spin frequency and confirm the discrepancy between the parallax and Shklovskii distances that has been reported earlier. We also present optical astrometry, photometry and spectroscopy of 2MASS J10243869-0719190. We find that it is a low-metallicity main-sequence star (K7V spectral type, [M/H] = -1.0, Teff = 4050 ± 50 K) and that its position, proper motion and distance are consistent with those of PSR J1024-0719. We conclude that PSR J1024-0719 and 2MASS J10243869-0719190 form a common proper motion pair and are gravitationally bound. The gravitational interaction between the main-sequence star and the pulsar accounts for the spin frequency derivatives, which in turn resolves the distance discrepancy. Our observations suggest that the pulsar and main-sequence star are in an extremely wide (Pb > 200 yr) orbit. Combining the radial velocity of the companion and proper motion of the pulsar, we find that the binary system has a high spatial velocity of 384 ± 45 km s-1 with respect to the local standard of rest and has a Galactic orbit consistent with halo objects. Since the observed main-sequence companion star cannot have recycled the pulsar to millisecond spin periods, an exotic formation scenario is required. We demonstrate that this extremely wide-orbit binary could have evolved from a triple system that underwent an asymmetric supernova explosion, though find that significant fine-tuning during the explosion is required. Finally, we discuss the implications of the long period orbit on the timing stability of PSR J1024-0719 in light of its inclusion in pulsar timing arrays.

  3. The LOFAR pilot surveys for pulsars and fast radio transients

    NASA Astrophysics Data System (ADS)

    Coenen, Thijs; van Leeuwen, Joeri; Hessels, Jason W. T.; Stappers, Ben W.; Kondratiev, Vladislav I.; Alexov, A.; Breton, R. P.; Bilous, A.; Cooper, S.; Falcke, H.; Fallows, R. A.; Gajjar, V.; Grießmeier, J.-M.; Hassall, T. E.; Karastergiou, A.; Keane, E. F.; Kramer, M.; Kuniyoshi, M.; Noutsos, A.; Osłowski, S.; Pilia, M.; Serylak, M.; Schrijvers, C.; Sobey, C.; ter Veen, S.; Verbiest, J.; Weltevrede, P.; Wijnholds, S.; Zagkouris, K.; van Amesfoort, A. S.; Anderson, J.; Asgekar, A.; Avruch, I. M.; Bell, M. E.; Bentum, M. J.; Bernardi, G.; Best, P.; Bonafede, A.; Breitling, F.; Broderick, J.; Brüggen, M.; Butcher, H. R.; Ciardi, B.; Corstanje, A.; Deller, A.; Duscha, S.; Eislöffel, J.; Fender, R.; Ferrari, C.; Frieswijk, W.; Garrett, M. A.; de Gasperin, F.; de Geus, E.; Gunst, A. W.; Hamaker, J. P.; Heald, G.; Hoeft, M.; van der Horst, A.; Juette, E.; Kuper, G.; Law, C.; Mann, G.; McFadden, R.; McKay-Bukowski, D.; McKean, J. P.; Munk, H.; Orru, E.; Paas, H.; Pandey-Pommier, M.; Polatidis, A. G.; Reich, W.; Renting, A.; Röttgering, H.; Rowlinson, A.; Scaife, A. M. M.; Schwarz, D.; Sluman, J.; Smirnov, O.; Swinbank, J.; Tagger, M.; Tang, Y.; Tasse, C.; Thoudam, S.; Toribio, C.; Vermeulen, R.; Vocks, C.; van Weeren, R. J.; Wucknitz, O.; Zarka, P.; Zensus, A.

    2014-10-01

    We have conducted two pilot surveys for radio pulsars and fast transients with the Low-Frequency Array (LOFAR) around 140 MHz and here report on the first low-frequency fast-radio burst limit and the discovery of two new pulsars. The first survey, the LOFAR Pilot Pulsar Survey (LPPS), observed a large fraction of the northern sky, ~ 1.4 × 104 deg2, with 1 h dwell times. Each observation covered ~75 deg2 using 7 independent fields formed by incoherently summing the high-band antenna fields. The second pilot survey, the LOFAR Tied-Array Survey (LOTAS), spanned ~600 deg2, with roughly a 5-fold increase in sensitivity compared with LPPS. Using a coherent sum of the 6 LOFAR "Superterp" stations, we formed 19 tied-array beams, together covering 4 deg2 per pointing. From LPPS we derive a limit on the occurrence, at 142 MHz, of dispersed radio bursts of < 150 day-1 sky-1, for bursts brighter than S> 107 Jy for the narrowest searched burst duration of 0.66 ms. In LPPS, we re-detected 65 previously known pulsars. LOTAS discovered two pulsars, the first with LOFAR or any digital aperture array. LOTAS also re-detected 27 previously known pulsars. These pilot studies show that LOFAR can efficiently carry out all-sky surveys for pulsars and fast transients, and they set the stage for further surveying efforts using LOFAR and the planned low-frequency component of the Square Kilometer Array. http://www.astron.nl/pulsars/lofar/surveys/lotas/

  4. Population Studies of Radio and Gamma-Ray Pulsars

    NASA Technical Reports Server (NTRS)

    Harding, Alice K; Gonthier, Peter; Coltisor, Stefan

    2004-01-01

    Rotation-powered pulsars are one of the most promising candidates for at least some of the 40-50 EGRET unidentified gamma-ray sources that lie near the Galactic plane. Since the end of the EGRO mission, the more sensitive Parkes Multibeam radio survey has detected mere than two dozen new radio pulsars in or near unidentified EGRET sources, many of which are young and energetic. These results raise an important question about the nature of radio quiescence in gamma-ray pulsars: is the non-detection of radio emission a matter of beaming or of sensitivity? The answer is very dependent on the geometry of the radio and gamma-ray beams. We present results of a population synthesis of pulsars in the Galaxy, including for the first time the full geometry of the radio and gamma-ray beams. We use a recent empirically derived model of the radio emission and luminosity, and a gamma-ray emission geometry and luminosity derived theoretically from pair cascades in the polar slot gap. The simulation includes characteristics of eight radio surveys of the Princeton catalog plus the Parkes MB survey. Our results indicate that EGRET was capable of detecting several dozen pulsars as point sources, with the ratio of radio-loud to radio-quiet gamma-ray pulsars increasing significantly to about ten to one when the Parkes Survey is included. Polar cap models thus predict that many of the unidentified EGRET sources could be radio-loud gamma- ray pulsars, previously undetected as radio pulsars due to distance, large dispersion and lack of sensitivity. If true, this would make gamma-ray telescopes a potentially more sensitive tool for detecting distant young neutron stars in the Galactic plane.

  5. Towards robust gravitational wave detection with pulsar timing arrays

    NASA Astrophysics Data System (ADS)

    Cornish, Neil J.; Sampson, Laura

    2016-05-01

    Precision timing of highly stable millisecond pulsars is a promising technique for the detection of very low frequency sources of gravitational waves. In any single pulsar, a stochastic gravitational wave signal appears as an additional source of timing noise that can be absorbed by the noise model, and so it is only by considering the coherent response across a network of pulsars that the signal can be distinguished from other sources of noise. In the limit where there are many gravitational wave sources in the sky, or many pulsars in the array, the signals produce a unique tensor correlation pattern that depends only on the angular separation between each pulsar pair. It is this distinct fingerprint that is used to search for gravitational waves using pulsar timing arrays. Here we consider how the prospects for detection are diminished when the statistical isotropy of the timing array or the gravitational wave signal is broken by having a finite number of pulsars and a finite number of sources. We find the standard tensor-correlation analysis to be remarkably robust, with a mild impact on detectability compared to the isotropic limit. Only when there are very few sources and very few pulsars does the standard analysis begin to fail. Having established that the tensor correlations are a robust signature for detection, we study the use of "sky scrambles" to break the correlations as a way to increase confidence in a detection. This approach is analogous to the use of "time slides" in the analysis of data from ground-based interferometric detectors.

  6. High-energy flux evolution of Pulsar Wind Nebulae

    SciTech Connect

    Mattana, F.; Falanga, M.; Goetz, D.

    2008-12-24

    The very high energy {gamma}-ray spectra of Pulsar Wind Nebulae are interpreted as due to inverse Compton scattering of ultrarelativistic electrons on the ambient photons, whereas their X-ray spectra are due to synchrotron emission. We investigate the relation between the {gamma}- and X-ray emission and the pulsars' spin-down luminosity and characteristic age. We find that the {gamma}-to X-ray flux ratio of the nebulae is inversely proportional to the spin-down luminosity ({proportional_to}E{sup -1.9}) and to the characteristic age ({proportional_to}{tau}{sub c}{sup 2.2}) of the parent pulsar. We interpret these results as due to the evolution of the electron energy distribution and the nebular dynamics, supporting the idea of so-called relic pulsar wind nebulae. These empirical relations provide a new tool to classify unidentified diffuse {gamma}-ray sources and to estimate the spin-down luminosity and characteristic age for four rotation powered pulsars with no detected pulsation from the X- and {gamma}--ray properties of the associated pulsar wind nebulae.

  7. Be/X-Ray Pulsar Binary Science with LOFT

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, Colleen A.

    2011-01-01

    Accretion disks are ubiquitous in astronomical sources. Accretion powered pulsars are a good test bed for accretion disk physics, because unlike for other objects, the spin of the neutron star is directly observable allowing us to see the effects of angular momentum transfer onto the pulsar. The combination of a sensitive wide-field monitor and the large area detector on LOFT will enable new detailed studies of accretion powered pulsars which I will review. RXTE observations have shown an unusually high number of Be/X-ray pulsar binaries in the SMC. Unlike binaries in the Milky Way, these systems are all at the same distance, allowing detailed population studies using the sensitive LOFT WFM, potentially providing connections to star formation episodes. For Galactic accreting pulsar systems, LOFT will allow measurement of spectral variations within individual pulses, mapping the accretion column in detail for the first time. LOFT will also provide better constraints on magnetic fields in accreting pulsars, allowing measurements of cyclotron features, observations of transitions into the centrifugal inhibition regime, and monitoring of spin-up rate vs flux correlations. Coordinated multi-wavelength observations are crucial to extracting the best science from LOFT from these and numerous other objects.

  8. XMM-Newton Observations of Four Millisecond Pulsars

    NASA Technical Reports Server (NTRS)

    Zavlin, Vyacheslav E.

    2005-01-01

    I present an analysis of the XMM-Newton observations of four millisecond pulsars, J0437-4715, J2124-3358, J1024-0719, and J0034-0534. The new data provide strong evidence of thermal emission in the X-ray flux detected from the first three objects. This thermal component is best interpreted as radiation from pulsar polar caps covered with a nonmagnetic hydrogen atmosphere. A nonthermal power-law component, dominating at energies E greater than or equal to 3 keV, can also be present in the detected X-ray emission. For PSR J0437-4715, the timing analysis reveals that the shape and pulsed fraction of the pulsar light curves are energy dependent. This, together with the results obtained from the phase-resolved spectroscopy, supports the two-component (thermal plus nonthermal) interpretation of the pulsar's X-ray radiation. Highly significant pulsations have been found in the X-ray flux of PSRs 52124-3358 and 51024-0719. For PSR 50034-0534, a possible X-ray counterpart of the radio pulsar has been suggested. The inferred properties of the detected thermal emission are compared with predictions of radio pulsar models.

  9. Physics of radio emission in gamma-ray pulsars

    NASA Astrophysics Data System (ADS)

    Petrova, S. A.

    2016-04-01

    > Propagation of radio emission in a pulsar magnetosphere is reviewed. The effects of polarization transfer, induced scattering and reprocessing to high energies are analysed with a special emphasis on the implications for the gamma-ray pulsars. The possibilities of the pulsar plasma diagnostics based on the observed radio pulse characteristics are also outlined. As an example, the plasma number density profiles obtained from the polarization data for the Vela and the gamma-ray millisecond pulsars J1446-4701, J1939+2134 and J1744-1134 are presented. The number densities derived tend to be the highest/lowest when the radio pulse leads/lags the gamma-ray peak. In the PSR J1939+2134, the plasma density profiles for the main pulse and interpulse appear to fit exactly the same curve, testifying to the origin of both radio components above the same magnetic pole and their propagation through the same plasma flow in opposite directions. The millisecond radio pulse components exhibiting flat position angle curves are suggested to result from the induced scattering of the main pulse by the same particles that generate gamma rays. This is believed to underlie the wide-sense radio/gamma-ray correlation in the millisecond pulsars. The radio quietness of young gamma-ray pulsars is attributed to resonant absorption, whereas the radio loudness to the radio beam escape through the periphery of the open field line tube.

  10. X-Ray States of Redback Millisecond Pulsars

    NASA Astrophysics Data System (ADS)

    Linares, M.

    2014-11-01

    Compact binary millisecond pulsars with main-sequence donors, often referred to as "redbacks," constitute the long-sought link between low-mass X-ray binaries and millisecond radio pulsars and offer a unique probe of the interaction between pulsar winds and accretion flows. We present a systematic study of eight nearby redbacks, using more than 100 observations obtained with Swift's X-ray Telescope. We distinguish between three main states: pulsar, disk, and outburst states. We find X-ray mode switching in the disk state of PSR J1023+0038 and XSS J12270-4859, similar to what was found in the other redback that showed evidence for accretion: rapid, recurrent changes in X-ray luminosity (0.5-10 keV, L X), between (6-9) × 1032 erg s-1 (disk-passive state) and (3-5) × 1033 erg s-1 (disk-active state). This strongly suggests that mode switching—which has not been observed in quiescent low-mass X-ray binaries—is universal among redback millisecond pulsars in the disk state. We briefly explore the implications for accretion disk truncation and find that the inferred magnetospheric radius in the disk state of PSR J1023+0038 and XSS J12270-4859 lies outside the light cylinder. Finally, we note that all three redbacks that have developed accretion disks have relatively high L X in the pulsar state (>1032 erg s-1).

  11. ON THE POLAR CAP CASCADE PAIR MULTIPLICITY OF YOUNG PULSARS

    SciTech Connect

    Timokhin, A. N.; Harding, A. K.

    2015-09-10

    We study the efficiency of pair production in polar caps of young pulsars under a variety of conditions to estimate the maximum possible multiplicity of pair plasma in pulsar magnetospheres. We develop a semi-analytic model for calculation of cascade multiplicity which allows efficient exploration of the parameter space and corroborate it with direct numerical simulations. Pair creation processes are considered separately from particle acceleration in order to assess different factors affecting cascade efficiency, with acceleration of primary particles described by recent self-consistent non-stationary model of pair cascades. We argue that the most efficient cascades operate in the curvature radiation/synchrotron regime, the maximum multiplicity of pair plasma in pulsar magnetospheres is ∼few × 10{sup 5}. The multiplicity of pair plasma in magnetospheres of young energetic pulsars weakly depends on the strength of the magnetic field and the radius of curvature of magnetic field lines and has a stronger dependence on pulsar inclination angle. This result questions assumptions about very high pair plasma multiplicity in theories of pulsar wind nebulae.

  12. 1974: the discovery of the first binary pulsar

    NASA Astrophysics Data System (ADS)

    Damour, Thibault

    2015-06-01

    The 1974 discovery, by Russell A Hulse and Joseph H Taylor, of the first binary pulsar, PSR B1913+16, opened up new possibilities for the study of relativistic gravity. PSR B1913+16, as well as several other binary pulsars, provided direct observational proof that gravity propagates at the velocity of light and has a quadrupolar structure. Binary pulsars also provided accurate tests of the strong-field regime of relativistic gravity. General relativity has passed all of the binary pulsar tests with flying colors. The discovery of binary pulsars also had very important consequences for astrophysics, leading to accurate measurement of neutron star masses, improved understanding of the possible evolution scenarios for the co-evolution of binary stars, and proof of the existence of binary neutron stars emitting gravitational waves for hundreds of millions of years, before coalescing in catastrophic events radiating intense gravitational wave signals, and probably also leading to important emissions of electromagnetic radiation and neutrinos. This article reviews the history of the discovery of the first binary pulsar, and describes both its immediate impact and its longer-term effect on theoretical and experimental studies of relativistic gravity.

  13. Developing Precision Pulsar Timing Capability for the DSN

    NASA Astrophysics Data System (ADS)

    Majid, Walid A.; Kuiper, T. B.; Lazio, J.; Monroe, R.; Preston, R. A.; Spolaor, S.; Teitelbaum, L.; Trinh, J.

    2014-01-01

    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 are currently developing 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 pilot observations scheduled later this year. This research was performed at the Jet Propulsion Laboratory, California Institute of Technology, under the Research and Technology Development Program, under a contract with the National Aeronautics and Space Administration.

  14. Pulsar emission at the bottom end of the electromagnetic spectrum

    NASA Astrophysics Data System (ADS)

    Kondratiev, Vladislav; LOFAR Pulsar Working Group

    2013-03-01

    Pulsars are arguably the only astrophysical sources whose emission spans the entire electromagnetic spectrum, from decameter radio wavelengths to TeV energies. The LOw Frequency ARray (LOFAR) offers the unique possibility to study pulsars over a huge fractional bandwidth in the bottom 4 octaves of the radio window, from 15-240 MHz. Here we present a LOFAR study of pulsar single pulses, focussing specifically on the bright nearby pulsar B0809+74. We show that the spectral width of bright low-frequency pulses can be as narrow as 1 MHz and scales with increasing frequency as Δ f/f c ~ 0.15, at least in the case of the PSR B0809+74. This appears to be intrinsic to the pulsar, as opposed to being due to propagation effects. If so, this behavior is consistent with predictions by the strong plasma turbulence model of pulsar radio emission. We also present other observed properties of the single pulses and discuss their relation to other single-pulse phenomena like giant pulses.

  15. Pulsar timing noise from superfluid turbulence

    NASA Astrophysics Data System (ADS)

    Melatos, Andrew; Link, Bennett

    2014-01-01

    Shear-driven turbulence in the superfluid interior of a neutron star exerts a fluctuating torque on the rigid crust, causing the rotational phase to walk randomly. The phase fluctuation spectrum is calculated analytically for incompressible Kolmogorov turbulence and is found to be red; the half-power point is set by the observed spin-down rate, the crust-superfluid lag and the dynamical response time of the superfluid. Preliminary limits are placed on the latter quantities using selected time- and frequency-domain data. It is found that measurements of the normalization and slope of the power spectrum are reproduced for reasonable choices of the turbulence parameters. The results point preferentially to the neutron star interior containing a turbulent superfluid rather than a turbulent Navier-Stokes fluid. The implications for gravitational wave detection by pulsar timing arrays are discussed briefly.

  16. Tests of gravitational symmetries with radio pulsars

    NASA Astrophysics Data System (ADS)

    Shao, LiJing; Wex, Norbert

    2016-09-01

    Symmetries play important roles in modern theories of physical laws. In this paper, we review several experimental tests of important symmetries associated with the gravitational interaction, including the universality of free fall for self-gravitating bodies, time-shift symmetry in the gravitational constant, local position invariance and local Lorentz invariance of gravity, and spacetime translational symmetries. Recent experimental explorations for post-Newtonian gravity are discussed, of which, those from pulsar astronomy are highlighted. All of these tests, of very different aspects of gravity theories, at very different length scales, favor to very high precision the predictions of the strong equivalence principle (SEP) and, in particular, general relativity which embodies SEP completely. As the founding principles of gravity, these symmetries are motivated to be promoted to even stricter tests in future.

  17. The Optical Spectrum of the Geminga Pulsar

    NASA Technical Reports Server (NTRS)

    Martin, Christopher; Halpern, Jules P.; Schiminovich, David; Oliversen, Ronald (Technical Monitor)

    2001-01-01

    We obtained an optical spectrum of the isolated pulsar Geminga at the Keck Observatory. The optical object is at the limit of spectroscopic capability of any telescope, with a continuum flux that is approx. 0.5% of the dark sky on Mauna Kea. With particular attention paid to the dominant systematics of sky subtraction in our observing and analysis methods, we attained approx. 0.1% systematics in heavily binned spectra. The resulting spectrum spanning 3700 - 8000 A has a flat power-law shape f(sub nu) proportional to nu(exp -0.8) and a broad dip over 6300 - 6500 A. Thermal radiation cannot explain the optical spectrum of Geminga. The dominant component can be modeled as either electron synchrotron emission and ion (proton) cyclotron absorption, or ion cyclotron emission, the latter in a 10(exp 11) G magnetic field.

  18. SN 1054: A pulsar-powered supernova?

    NASA Astrophysics Data System (ADS)

    Li, Shao-Ze; Yu, Yun-Wei; Huang, Yan

    2015-11-01

    The famous ancient supernova SN 1054 could have been too bright to be explained in the “standard” radioactive-powered supernova scenario. As an alternative attempt, we demonstrate that the spin-down of the newly born Crab pulsar could provide a sufficient energy supply to make SN 1054 visible at daytime for 23 days and at night for 653 days, where a one-zone semi-analytical model is employed. Our results indicate that SN 1054 could be a “normal” cousin of magnetar-powered superluminous supernovae. Therefore, SN 1054-like supernovae could be a probe to uncover the properties of newly born neutron stars, which provide initial conditions for studies on neutron star evolutions.

  19. Possible radio emission mechanism for pulsars

    NASA Technical Reports Server (NTRS)

    Kovalev, Y. A.

    1979-01-01

    A mathematical model is presented and discussed as a possible mechanism to describe radio emission from pulsars. The model determines that the magnetic field in the neutron proton electron (npe) layer of a neutron star results from a quasistationary eddy current of superconducting and normal protons relative to normal electrons, which generates radio emission by the Josephson effect. The radiation propagates in the magnetically active medium, from the optically thick npe layer to the magnetosphere through breaks in the crust. As a result, hot radio spots form on the surface of the star, and a radiation pattern forms near the magnetic poles, the cross section of which gives the observed pulse structure. Due to the specific properties of the mechanism, variations of the quasistationary current are converted to amplitude frequency variations of the radiation spectrum. Variations of the fine structure of the spectrum pulse amplitude and spectral index, as well as their correlation are discussed.

  20. Using Nanobiotechnology to circumvent the "Nonpoint" problem in nonpoint source pollution: Possibilities, challenges, and progress to date

    NASA Astrophysics Data System (ADS)

    Sharma, Dr; Meyer, Dr; Luo, Dr; Regan, Dr; Walter, Dr

    2009-04-01

    Applying the power of nanoscale technology to answer landscape-scale questions constitutes an exciting new frontier in science and engineering. In this project, we are exploring a possible method of reducing the "nonpoint" problem associated with nonpoint source (NPS) pollution, a problem that has hampered agricultural sustainability and water quality protection for decades. We are developing superparamagnetic polylactic acid (PLA) microspheres incorporating DNA "nanobarcodes" as potential tracers. The eventual goal of this project is to develop technologies for identifying and characterizing different flowpaths at field and watershed scales by using multiple sets of polymer microspheres, each coded with unique DNA sequences, of which there are essentially limitless combinations, i.e., many flowpaths can be uniquely coded. Our ultimate vision is to have the capacity of introducing microsphere-encapsulated DNA at different points in a watershed and collecting these microspheres elsewhere in the watershed; using quantitative, real-time polymerase chain reaction targeted at the specific DNA, we would be able to determine the hydrological linkages and transport times between the collection point(s) and the points of DNA introduction. The potential advantages of this nanotechnology strategy compared to conventional tracers are the elimination of background interferences, the ability to segregate superimposed flowpaths through the design of strictly unique DNA tracers and the biodegradability of the tracers. This presentation highlights recent advances, new challenges, and potential applications for this tracer technology.

  1. [How to slow the progression of kidney damage today. Chronic kidney disease: an important personal, family and social problem].

    PubMed

    Locatelli, Francesco; Tucci, Benedetta; Del Vecchio, Lucia

    2012-01-01

    The number of patients with chronic kidney disease (CKD) is increasing worldwide like an unstoppable tsunami. This causes considerable suffering for patients and families and places a severe economic burden also on society, especially when the patient reaches the stage of being in need of renal replacement therapy. Accordingly, a program of prevention and treatment of CKD at its earlier stages is of great importance, also in view of the fact that the general population is getting older and older and is more frequently affected by comorbidities such as hypertension, diabetes, obesity and cardiovascular disease. All these factors increase the likelihood of the development and worsening of CKD. In the meantime, nephrologists have developed new and better strategies to halt or at least slow the progression of CKD. These are based on the prescription to quit smoking and on dietary interventions guaranteeing an adequate calorie, protein, phosphate and sodium intake together with the correction of metabolic acidosis through either the supplementation of sodium bicarbonate or the choice of basic proteins. The treatment of hypertension and proteinuria (when detectable) by means of RAS inhibitors is another important strategy, where partial correction of anemia and statin use may be of help. Other treatments have not proven to be effective or their introduction into clinical practice is still far away.

  2. Gamma-ray connection of Pulsars-Pulsar Wind Nebulae: From GeV to TeV energies

    NASA Astrophysics Data System (ADS)

    López-Coto, Rubén; de Ona Wilhelmi, Emma

    2015-08-01

    Pulsars are the remnants of massive star explosions and Pulsar Wind Nebulae (PWNe) are the bubbles of relativistic particles and magnetic field surrounding pulsars. The acceleration in PWNe is produced when the pulsar's relativistic wind interacts with its surrounding medium and particles are accelerated at the shock region. The non-thermal photon emission ranges from the radio to the very-high-energy (VHE) range and it is believed to be originated in synchrotron, curvature and inverse Compton processes.So far, pulsars and PWNe represent the largest population of identified GeV and TeV sources. In this contribution, we will describe the recent measurements on young PWNe such as the Crab whose inverse Compton peak was recently accurately determined. We will also discuss the origin of the GeV gamma-ray flares and their non-detection at any other wavelength, together with the recent reports of pulsed emission up to TeV energies. This result evidences the extreme acceleration of electrons in the surrounding of the Crab pulsar, up to Lorenz factors of 5 × 106. We will also put in context the recent discovery of VHE pulsed emission from the Vela pulsar. We will discuss the case of the inefficient pulsar at the center of 3C 58, a PWN discovered by Fermi at GeV energies and by MAGIC at TeV. In addition, we will also present population studies comparing several properties of the central engine such as age or spin-down power with the gamma-ray luminosity of their surrounding PWNe. We will finally show the measurement prospects for this kind of sources with the future Cherenkov Telescope Array.

  3. Youngest Radio Pulsar Revealed with Green Bank Telescope

    NASA Astrophysics Data System (ADS)

    2002-04-01

    Astronomers using the National Science Foundation's (NSF) newly commissioned Robert C. Byrd Green Bank Telescope (GBT) have detected remarkably faint radio signals from an 820 year-old pulsar, making it the youngest radio-emitting pulsar known. This discovery pushes the boundaries of radio telescope sensitivity for discovering pulsars, and will enable scientists to conduct observations that could lead to a better understanding of how these stars evolve. The Robert C. Byrd Green Bank Telescope Robert C. Byrd Green Bank Telescope "Important questions about pulsars may be answered by long-term monitoring of objects such as the one we just detected," said Fernando Camilo of Columbia University in New York City. "Young pulsars are particularly rare, and being able to study such a young one at radio wavelengths provides an outstanding opportunity to learn critical facts about their evolution and workings." The results of this research, based on observations conducted on February 22-23, 2002, were accepted for publication in the Astrophysical Journal Letters. Scientists have long suspected that a pulsar - a rapidly spinning, superdense neutron star - was born when a giant star ended its life in a cataclysmic supernova explosion observed in late summer of 1181, as suggested by Japanese and Chinese historical records. For the past 20 years, astronomers have searched this supernova remnant (3C58), located 10,000 light-years away in the constellation Cassiopeia, for the telltale pulsations of a newly born pulsar. Late in 2001, data from NASA's Chandra X-ray satellite confirmed its existence, but it remained an elusive quarry for radio telescopes. "We believed from historical records and certainly knew from recent X-ray observations that this star was there," Camilo remarked, "but despite many attempts, no one had been able to find any radio pulsations from it because the signals are, it turns out, incredibly weak." For comparison, this pulsar's radio emission is some 250

  4. Pulsars as Celestial Beacons to Detect the Motion of the Earth

    NASA Astrophysics Data System (ADS)

    Ruggiero, Matteo Luca; Capolongo, Emiliano; Tartaglia, Angelo

    In order to show the principle viability of a recently proposed relativistic positioning method based on the use of pulsed signals from sources at infinity, we present an application example reconstructing the world line of an idealized Earth in the reference frame of distant pulsars. The method considers the null four-vectors built from the period of the pulses and the direction cosines of the propagation from each source. Starting from a simplified problem (a receiver at rest) we have been able to calibrate our procedure, evidencing the influence of the uncertainty on the arrival times of the pulses as measured by the receiver, and of the numerical treatment of the data. The most relevant parameter turns out to be the accuracy of the clock used by the receiver. Actually, the uncertainty used in the simulations combines the accuracy of the clock and the fluctuations in the sources. As an evocative example the method has then been applied to the case of an ideal observer moving as a point on the surface of the Earth. The input has been the simulated arrival times of the signals from four pulsars at the location of the Parkes radiotelescope in Australia. Some substantial simplifications have been made both excluding the problems of visibility due to the actual size of the planet, and the behavior of the sources. A rough application of the method to a three-day run gives a correct result with a poor accuracy. The accuracy is then enhanced to the order of a few hundred meters if a continuous set of data is assumed. The method could actually be used for navigation across the solar system and be based on artificial sources, rather than pulsars. The viability of the method, whose additional value is in the self-sufficiency, i.e. independence from any control from other operators, has been confirmed.

  5. Ten Years Timing of Millisecond Pulsars at Kalyazin

    NASA Astrophysics Data System (ADS)

    Ilyasov, Yu. P.; Oreshko, V. V.

    2006-08-01

    Precise timing of millisecond binary pulsars has been started at Kalyazin radio astronomical observatory since 1995. (Tver' region, Russia). Binary pulsars: J0613-02, J1020+10, J1640+22, J1643-12, J1713+07, J2145-07 and isolated millisecond pulsar B1937+21 have been included among the Kalayazin Pulsar Timing Array (KPTA). The Backer's pulsar B1937+21 is being monitored at Kalyazin observatory (0.6 GHz) and Kashima space research centre of the National Institute of Communication Technology (NICT, Japan) (2.2 GHz) simultaneously from 1996, as well. .At Kalyazin pulsars are observed at 0.6 GHz by a full steerable 64-m dish radio telescope RT-64 of the Special Research Bureau of the Moscow Power Engineering Institute. Filter-bank receiver of PRAO Lebedev Physical Institute is used for observations in two circular polarizations by 80 channels per each. Bandwidth per channel is 40 kHz, so total band is 3.2 MHz and time resolution is about 10 μs per channel. Now a perfect data base of pulses Time of Arrival (TOA) are collected with refer to the Solar system barycenter for about 10 years period. Main aim is: a) to study Pulsar Time and to establish a long-term standard of time based on pulsars ensemble as space long life clock alternative to atomic standards; b) to detect gravitational waves extremely low frequency belong to the Gravity Wave Background - GWB. After ten years monitoring of B1937+21 its timing noise is looking as "white phase noise" with RMS about 1.8 μs.( Fractional instability is about 6.10^-15). After these data and timing results of binary pulsar J1640+22 gravitational natural GWB upper limit should be reduced till to less than Ω[g]h^2 <10^-7-10^ -9 . Secular changes of DM toward millisecond pulsar B1937+21 was revealed after long time two frequency timing observations (Kalyazin -0,6 and Kashima -2.3).

  6. Glitch event observed in the pulsar PSR J1740-3015

    NASA Astrophysics Data System (ADS)

    Jankowski, Fabian; Bailes, Matthew; Barr, Ewan; Bateman, Timothy; Bhandari, Shivani; Caleb, Manisha; Campbell-Wilson, Duncan; Farah, Wael; Flynn, Chris; Green, Anne; Hunstead, Richard; Jameson, Andrew; Keane, Evan; Krishnan, Vivek Venkatraman; Parthasarathy, Aditya; Straten, Willem van

    2016-05-01

    As part of the UTMOST project at the recently refurbished Molonglo Observatory Synthesis radio Telescope (MOST) near Canberra, Australia, we carry out a pulsar timing programme in which we observe a large number of pulsars with up to daily cadence.

  7. TIMING AND INTERSTELLAR SCATTERING OF 35 DISTANT PULSARS DISCOVERED IN THE PALFA SURVEY

    SciTech Connect

    Nice, D. J.; Altiere, E.; Farrington, D.; Popa, L.; Wang, Y.; Bogdanov, S.; Camilo, F.; Cordes, J. M.; Brazier, A.; Chatterjee, S.; Hessels, J. W. T.; Kaspi, V. M.; Lyne, A. G.; Stappers, B. W.; Ransom, S. M.; Sanpa-arsa, S.; Allen, B.; Bhat, N. D. R.; Champion, D. J.; Crawford, F.; and others

    2013-07-20

    We have made extensive observations of 35 distant slow (non-recycled) pulsars discovered in the ongoing Arecibo PALFA pulsar survey. Timing observations of these pulsars over several years at Arecibo Observatory and Jodrell Bank Observatory have yielded high-precision positions and measurements of rotation properties. Despite being a relatively distant population, these pulsars have properties that mirror those of the previously known pulsar population. Many of the sources exhibit timing noise, and one underwent a small glitch. We have used multifrequency data to measure the interstellar scattering properties of these pulsars. We find scattering to be higher than predicted along some lines of sight, particularly in the Cygnus region. Finally, we present XMM-Newton and Chandra observations of the youngest and most energetic of the pulsars, J1856+0245, which has previously been associated with the GeV-TeV pulsar wind nebula HESS J1857+026.

  8. A Survey for Millisecond Pulsars and Fast Transients in the Large Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Crawford, Fronefield; Lorimer, D.; Ridley, J.; Madden, J.

    2013-01-01

    We report on a new survey for radio pulsars in the Large Magellanic Cloud (LMC) using the Parkes 64-m telescope. The survey uses the 1400 MHz multibeam receiver and the Berkeley Parkes Swinburne Recorder (BPSR) high-resolution backend. This survey has unprecedented sensitivity to millisecond pulsars and short-duration transients in the LMC. The goals of the survey include discovering new source populations (including the first extragalactic millisecond pulsar), probing the high-end of the pulsar luminosity function, and investigating how star formation differences between the LMC and the Milky Way affect the LMC pulsar population. To date about 20% of the survey area has been observed, and those data have been searched for single pulses and partially searched for accelerated pulsars over a wide range of trial dispersions. We have discovered three new pulsars in the survey so far, and we have several new millisecond pulsar candidates and transient sources that await confirmation.

  9. Glitch event observed in the pulsar PSR J1740-3015

    NASA Astrophysics Data System (ADS)

    Jankowski, Fabian; Bailes, Matthew; Barr, Ewan; Bateman, Timothy; Bhandari, Shivani; Briggs, Frank; Caleb, Manisha; Campbell-Wilson, Duncan; Flynn, Chris; Green, Anne; Hunstead, Richard; Jameson, Andrew; Keane, Evan; Krishnan, Vivek Venkatraman; Straten, Willem van

    2015-11-01

    At the recently refurbished Molonglo Observatory Synthesis radio Telescope (MOST) near Canberra, Australia, we carry out a pulsar timing programme in which we observe a large number of pulsars with up to daily cadence.

  10. Method of vibrational control in the problem of stabilization of chemical reactors. Progress report, July 1, 1981-June 30, 1982

    SciTech Connect

    Meerkov, S.M.

    1982-03-01

    The results obtained during the second year of the three years study of vibrational control application to the problem of stabilization of chemical reactors are presented. The main objective was the development of a nonlinear approach to analytical and numerical investigation of the properties of chemical reactors with oscillating parameters. This objective was achieved and the following results were obtained. Nonlinear vibrational control theory was applied to two types of chemical reactors, the Catalytic Reactor and Continuous Stirred Tank Reactor. It was shown that introduction of sufficiently fast oscillations results in a decrease of the negative slope part (unstable area) of the reactor steady state characteristic. Consequently, the steady states, corresponding to larger productivity, are stabilized. A simulation program was developed and the numerical investigation of reactors with oscillating parameters was carried out. Experiments with the program showed that: the averaged description yields an adequate precision if epsilon = 1/T/sub r/..omega.. approx. = 0.16 (..omega.. is the frequency of introduced vibrations and T/sub r/ is the rise time of the system without vibrations); and the admissible vibrations could result in an increase in productivity of the reactor by a factor of 2/3. On the basis of numerical simulations, the following phenomena were discovered: stabilization of unstable steady states by small and slow oscillations; enlargement of the attraction domain of stable steady states due to medium amplitude and frequency oscillations; and destruction of limit cycles by any types of oscillations. None of these phenomena has theoretical explanations. A basis of vibrational control theory for distributed parameter systems was established. This opened the possibility for vibrational control applications to chemical reactors described by partial differential equation.

  11. X-RAY OBSERVATIONS OF HIGH-B RADIO PULSARS

    SciTech Connect

    Olausen, S. A.; Kaspi, V. M.; Zhu, W. W.; Vogel, J. K.; Lyne, A. G.; Espinoza, C. M.; Stappers, B. W.; Manchester, R. N.; McLaughlin, M. A.

    2013-02-10

    The study of high-magnetic-field pulsars is important for examining the relationships between radio pulsars, magnetars, and X-ray-isolated neutron stars (XINSs). Here, we report on X-ray observations of three such high-magnetic-field radio pulsars. We first present the results of a deep XMM-Newton observation of PSR J1734-3333, taken to follow up on its initial detection in 2009. The pulsar's spectrum is well fit by a blackbody with a temperature of 300 {+-} 60 eV, with bolometric luminosity L{sub bb}=2.0{sub -0.7}{sup +2.2} Multiplication-Sign 10{sup 32} erg s{sup -1}{approx}0.0036 E-dot for a distance of 6.1 kpc. We detect no X-ray pulsations from the source, setting a 1{sigma} upper limit on the pulsed fraction of 60% in the 0.5-3 keV band. We compare PSR J1734-3333 to other rotation-powered pulsars of similar age and find that it is significantly hotter, supporting the hypothesis that the magnetic field affects the observed thermal properties of pulsars. We also report on XMM-Newton and Chandra observations of PSRs B1845-19 and J1001-5939. We do not detect either pulsar, setting 3{sigma} upper limits on their blackbody temperatures of 48 and 56 eV, respectively. Despite the similarities in rotational properties, these sources are significantly cooler than all but one of the XINSs, which we attribute to the two groups having been born with different magnetic fields and hence evolving differently.

  12. Study of frame tie between planetary ephemerids and ICRF with millisecond and young pulsars

    NASA Astrophysics Data System (ADS)

    Wang, Jingbo; Hobbs, George; Coles, William

    2016-07-01

    The positions of pulsar can be measured by pulsar timing technology and VLBI astrometry with high precision. They can be used to tie between referece frame based on solar system ephemerids and distant quasars with high accuracy. In this paper, we have collect the pulsar positions with VLBI measurement and obtain the pulsar timing position form Nanshan and Parkes data archive. We derive the rotation matrix between JPL DE and ICRF reference frame.

  13. High-Altitude Emission from Pulsar Slot Gaps: The Crab Pulsar

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.; Stern, Julie V.; Dyks, Jaroslaw; Frackowiak, Michal

    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-altitudes in the unscreened electric field of the slot gap reach radiation-reaction limited Lorentz factors of approx. 2 x 10(exp 7), while electron-positron pairs from lower-altitude cascades flow along field lines interior to the slot gap. The curvature, synchrotron and inverse Compton radiation of both primary electrons and pairs produce a broad spectrum of emission from infra-red to GeV energies. Both primaries and pairs undergo cyclotron resonant absorption of radio photons, allowing them to maintain significant pitch angles. Synchrotron radiation from pairs with a power-law energy spectrum from gamma = 10(exp 2) - 10(exp 5), dominate the spectrum up to approx. 10 MeV. Synchrotron and curvature radiation of primaries dominates from 10 MeV up to a few GeV. We examine the energy-dependent pulse profiles and phase-resolved spectra for parameters of the Crab pulsar as a function of magnetic inclination alpha and viewing angle zeta, comparing to broad-band data. In most cases, the pulse profiles are dominated by caustics on trailing field lines. We also explore the relation of the high-energy and the radio profiles, as well as the possibility of caustic formation in the radio cone emission. We find that the Crab pulsar profiles and spectrum can be reasonably well reproduced by a model with alpha = 45deg and zeta approx. 100deg or 80deg. This model predicts that the slot gap emission below 200 MeV will exhibit correlations in time and phase with the radio emission.

  14. A Large-Area Survey for Radio Pulsars at High Galactic Latitudes

    NASA Astrophysics Data System (ADS)

    Jacoby, B. A.; Bailes, M.; Ord, S. M.; Edwards, R. T.; Kulkarni, S. R.

    2009-07-01

    We have completed a survey for pulsars at high Galactic latitudes with the 64 m Parkes radio telescope. Observing with the 13 beam multibeam receiver at a frequency of 1374 MHz, we covered ~4150 square degrees in the region -100° <= l <= 50°, 15° <= |b| <= 30° with 7232 pointings of 265 s each, thus extending the Swinburne Intermediate Latitude Pulsar Survey a further 15° on either side of the Galactic plane. The signal from each beam was processed by a 96 channel × 3 MHz × 2 polarization filterbank, with the detected power in the two polarizations of each frequency channel summed and digitized with 1 bit sampling every 125 μs, giving good sensitivity to millisecond pulsars with low or moderate dispersion measure. The resulting 2.4 TB data set was processed using standard pulsar search techniques with the workstation cluster at the Swinburne Centre for Astrophysics and Supercomputing. This survey resulted in the discovery of 26 new pulsars including seven binary and/or millisecond pulsars, and redetected 36 previously known pulsars. We describe the survey methodology and results, and present timing solutions for the 19 newly discovered slow pulsars, as well as for nine slow pulsars discovered the Swinburne Intermediate Latitude Pulsar Survey that had no previous timing solutions. Even with a small sampling interval, 1374 MHz center frequency, and a large mid-latitude survey volume we failed to detect any very rapidly spinning pulsars. Evidently, such "submillisecond" pulsars are rare.

  15. Pulsars above 10 GeV: Fermi LAT Observations and Questions

    NASA Technical Reports Server (NTRS)

    Thomson, Dave

    2012-01-01

    The success of the Fermi Large Area Telescope in studying gamma-ray pulsars offers hints about future work above 10 GeV. The infrastructure for discovering pulsars will be similar between LAT and any future telescope. Some of the Fermi LAT results suggest intriguing questions about the future of high-energy pulsar studies.

  16. Newly Commissioned Green Bank Telescope Bags New Pulsars

    NASA Astrophysics Data System (ADS)

    2002-01-01

    Astronomers using the National Science Foundation's newly commissioned Robert C. Byrd Green Bank Telescope (GBT) have discovered a windfall of three previously undetected millisecond pulsars in a dense cluster of stars in the Milky Way Galaxy. The Green Bank Telescope The Robert C. Byrd Green Bank Telescope "This globular cluster, known as Messier 62, has been very well studied, and it would have been an exciting discovery to find just one new pulsar. The fact that we were able to detect three new pulsars at one time is simply remarkable," said Bryan Jacoby, a graduate student at the California Institute of Technology who led the research team. Results of the discovery were recently announced in an International Astronomical Union Circular. Jacoby and his colleague Adam Chandler, also a graduate student at Caltech, used the GBT to search for new pulsars in addition to the three already known in this cluster. Their research was part of the GBT's Early Science Program, which allows scientific investigations during the testing and commissioning of the telescope. The researchers used the Berkeley-Caltech Pulsar Machine, a new instrument whose development was overseen by Donald Backer at the University of California at Berkeley, to process the signals from the GBT and record them for later analysis. After their data were analyzed, the researchers discovered the telltale signatures of three additional pulsars and their white dwarf companion stars. Pulsars are rapidly rotating neutron stars that emit intense beams of radio waves along their misaligned magnetic axes. When these beams intersect the Earth, we see the pulsar flash on and off. Due to their exquisitely steady rotation, pulsars allow astronomers to study the basic laws of physics and the ways in which these dense clusters and exotic stellar systems are formed. Astronomers study globular clusters because they are among the oldest building blocks of our Galaxy. With their very dense stellar populations, these

  17. Pulsar glitches: The crust may be enough

    NASA Astrophysics Data System (ADS)

    Piekarewicz, J.; Fattoyev, F. J.; Horowitz, C. J.

    2014-07-01

    Background: Pulsar glitches—the sudden spin-up in the rotational frequency of a neutron star—suggest the existence of an angular-momentum reservoir confined to the inner crust of the neutron star. Large and regular glitches observed in the Vela pulsar have originally constrained the fraction of the stellar moment of inertia that must reside in the solid crust to about 1.4%. However, crustal entrainment—which until very recently has been ignored—suggests that in order to account for the Vela glitches, the fraction of the moment of inertia residing in the crust must increase significantly; to about 7-9 %. This indicates that the required angular momentum reservoir may exceed that which is available in the crust. Purpose: We explore the possibility that uncertainties in the equation of state provide enough flexibility for the construction of models that predict a large crustal thickness and consequently a large crustal moment of inertia. Methods: Moments of inertia—both total and crustal—are computed in the slow-rotation approximation using a relativistic mean-field formalism to generate the equation of state of neutron-star matter. Results: We compute the fractional moment of inertia of neutron stars of various masses using a representative set of relativistic mean-field models. Given that analytic results suggest that the crustal moment of inertia is sensitive to the transition pressure at the crust-core interface, we tune the parameters of the model to maximize the transition pressure, while still providing an excellent description of nuclear observables. In this manner we are able to obtain fractional moments of inertia as large as 7% for neutron stars with masses below 1.6 solar masses. Conclusions: We find that uncertainties in the equation of state of neutron-rich matter are large enough to accommodate theoretical models that predict large crustal moments of inertia. In particular, we find that if the neutron-skin thickness of Pb208 falls within the

  18. Physical processes in eclipsing pulsars: Eclipse mechanisms and diagnostics

    NASA Technical Reports Server (NTRS)

    Thompson, C.; Blandford, R. D.; Evans, Charles R.; Phinney, E. S.

    1994-01-01

    We investigate how the radio emission of a pulsar interacts with plasma derived from a stellar companion. Various physical mechanisms that can cause radio pulse eclipse are discussed, and predictions are made for the polarization properties of the emergent radio wave. We consider eclipses by a wind from the stellar companion, by a stellar magnetosphere, or by material entrained in the pulsar wind. Eclipses due to refraction require either a relatively high plasma density or a sharp edge to the plasma distribution. The conditions that must prevail for free-free absorption to be effective in eclipsing a radio beam are also outlined. Pulse smearing may be important at higher frequencies; related eclipse mechanisms include pulse spreading due to a rapidly changing electron column, and scattering by Langmuir turbulence. The high brightness temperature radio beam can generate its own plasma turbulence via a number of nonlinear parametric instabilities, such as the instability associated with stimulated Raman scattering. When the plasma turbulence is heavily damped, the radio bean can still undergo induced Compton scattering. Stimulated scattering effects such as these are very sensitive to the presence of narrow-band substructure in the pulsar radio emission. Finally, we consider the possibility that plasma derived from a stellar companion may mix with the relativistic pulsar wind and cause cyclotron absorption at low radio frequencies. Even if the cyclotron optical depth is small, fluctuations in the emergent polarization of the radio beam on the timescale of a few seconds are a very sensitive probe of the spatial structure of the magnetic field in the pulsar wind. The current observational properties of two known eclipsing pulsar systems, PSR 1957+20 and PSR 1744-24A, are used to construct tentative eclipse models. The favored model for PSR 1957+20 is cyclotron or synchrotron absorption by plasma embedded in the pulsar wind combined with pulse smearing at high

  19. Searches for Pulsars at the Center of the Galaxy

    NASA Astrophysics Data System (ADS)

    Majid, Walid

    2015-08-01

    Pulsars are highly magnetized, rapidly rotating neutron stars that emit a beam of electromagnetic radiation that could be detected at Earth, if the emission beam is pointing toward the Earth, analogous to the way a lighthouse can be seen when the light is pointed in the direction of the observer. Pulsars within the central parsec of our Galaxy is expected to make excellent probes of not only the environment of the supermassive black hole at the center of the galaxy, but also in the case of pulsar/black hole binary systems expected in this region, of their own rich environment dominated by relativistic gravity effects. In this presentation I will give an overview of why it is important to search for pulsars in the center of the galaxy, and a summary of previous and ongoing efforts to survey this region with radio telescopes. I will describe the difficulties encountered with current surveys and prospects for detection of perhaps hundreds of pulsars in this region with new generations of radio telescopes now under construction.

  20. THE GALACTIC POPULATION OF YOUNG {gamma}-RAY PULSARS

    SciTech Connect

    Watters, Kyle P.; Romani, Roger W. E-mail: rwr@astro.stanford.edu

    2011-02-01

    We have simulated a Galactic population of young pulsars and compared with the Fermi LAT sample, constraining the birth properties, beaming and evolution of these spin-powered objects. Using quantitative tests of agreement with the distributions of observed spin and pulse properties, we find that short birth periods P{sub 0} {approx} 50 ms and {gamma}-ray beams arising in the outer magnetosphere, dominated by a single pole, are strongly preferred. The modeled relative numbers of radio-detected and radio-quiet objects agrees well with the data. Although the sample is local, extrapolation to the full Galaxy implies a {gamma}-ray pulsar birthrate 1/(59 yr). This is shown to be in good agreement with the estimated Galactic core collapse rate and with the local density of OB star progenitors. We give predictions for the numbers of expected young pulsar detections if Fermi LAT observations continue 10 years. In contrast to the potentially significant contribution of unresolved millisecond pulsars, we find that young pulsars should contribute little to the Galactic {gamma}-ray background.