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Search Results: 1 - 10 of 312868 matches for " R. T. Edwards "
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Discovery of Eight Recycled Pulsars - The Swinburne Intermediate Latitude Pulsar Survey
R. T. Edwards
Physics , 1999,
Abstract: 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''.
Discovery of Two Relativistic Neutron Star-White Dwarf Binaries
R. T. Edwards,M. Bailes
Physics , 2000, DOI: 10.1086/318893
Abstract: We have discovered two recycled pulsars in relativistic orbits as part of the first high-frequency survey of intermediate Galactic latitudes. PSR J1157-5112 is a 44 ms pulsar and the first recycled pulsar with an ultra-massive (M > 1.14 Mo) white dwarf companion. Millisecond pulsar J1757-5322 is a relativistic circular-orbit system which will coalesce due to the emission of gravitational radiation in less than 9.5 Gyr. Of the ~40 known circular orbit pulsars, J1757-5322 and J1157-5112 have the highest projected orbital velocities. There are now three local neutron-star/white-dwarf binaries that will coalesce in less than a Hubble time, implying a large coalescence rate for these objects in the local Universe. Systems such as J1141-6545 (Kaspi et al. 2000) are potential gamma-ray burst progenitors and dominate the coalescence rate, whilst lighter systems make excellent progenitors of millisecond pulsars with planetary or ultra-low mass companions.
Recycled Pulsars Discovered at High Radio Frequency
R. T. Edwards,M. Bailes
Physics , 2001, DOI: 10.1086/320986
Abstract: We present the timing parameters of nine pulsars discovered in a survey of intermediate Galactic latitudes at 1400 MHz with the Parkes radio telescope. Eight of these pulsars possess small pulse periods and period derivatives thought to be indicative of ``recycling''. Six of the pulsars are in circular binary systems, including two with relatively massive white dwarf companions. We discuss the implications of these new systems for theories of binary formation and evolution. One long-period pulsar (J1410-7404) has a moderately weak magnetic field and an exceedingly narrow average pulse profile, similar to other recycled pulsars.
The frequency-dependence of drifting subpulse patterns
R. T. Edwards,B. W. Stappers
Physics , 2003, DOI: 10.1051/0004-6361:20031326
Abstract: Drifting subpulse patterns in pulsar signals are frequently interpreted in terms of a model in which a rotating ring of sparks on the polar cap gives rise to emission from regions of the magnetsophere connected to the sparks by dipolar magnetic field lines. The spacing of drift-bands in time depends on the circulation rate of the polar cap pattern, but to first order the longitudinal phase dependence of the subpulse modulation should obey a frequency-independent relation determined by the geometrical configuration in a similar manner to the polarization position angle. We present here observations at 272-1380 MHz of PSR B0320+39 and PSR B0809+74, both of which show nearly linear drift in two longitude regions, separated by a region of reduced modulation and accompanied by a large step in the phase of the subpulse pattern. We show that the observation of Bartel et al. (1981) that the subpulse spacing for PSR B0809+74 was 1.8 times greater at 102.5 MHz than at 1720 MHz is most likely an artifact of the phase step, which is only present at high frequencies. The phase steps can be understood as a consequence of observing overlapping offset images of the polar cap spark pattern. We also detected more complicated, frequency-dependent behaviour that would require that the images do not simply differ by rotation about their centers. Detailed modelling of non-axisymmetric refraction or distorted magnetic fields is suggested as a means of pursuing an explanation for this phenomenon.
Drifting Sub-Pulse Analysis Using the Two-Dimensional Fourier Transform
R. T. Edwards,B. W. Stappers
Physics , 2002, DOI: 10.1051/0004-6361:20021067
Abstract: The basic form of drifting sub-pulses is that of a periodicity whose phase depends (approximately linearly) on both pulse longitude and pulse number. As such, we argue that the two-dimensional Fourier transform of the longitude-time data (called the Two-Dimensional Fluctuation Spectrum; 2DFS) presents an ideal basis for studies of this phenomenon. We examine the 2DFS of a pulsar signal synthesized using the parameters of an empirical model for sub-pulse behaviour. We show that the transform concentrates the modulation power to a relatively small area of phase space in the region corresponding to the characteristic frequency of sub-pulses in longitude and pulse number. This property enables the detection of the presence and parameters of drifting sub-pulses with great sensitivity even in data where the noise level far exceeds the instantaneous flux density of individual pulses. The amplitude of drifting sub-pulses is modulated in time by scintillation and pulse nulling and in longitude by the rotating viewing geometry (with an envelope similar to that of the mean pulse profile). In addition, sub-pulse phase as a function of longitude and pulse number can differ from that of a sinusoid due to variations in the drift rate (often associated with nulling) and through the varying rate of traverse of magnetic azimuth afforded by the sight line. These deviations from uniform sub-pulse drift manifest in the 2DFS as broadening of the otherwise delta-function response of a uniform sinusoid. We show how these phase and amplitude variations can be extracted from the complex spectrum.
Pulse-to-pulse intensity modulation and drifting subpulses in recycled pulsars
R. T. Edwards,B. W. Stappers
Physics , 2003, DOI: 10.1051/0004-6361:20030716
Abstract: We report the detection of pulse-to-pulse periodic intensity modulations, in observations of recycled pulsars. Even though the detection of individual pulses was generally not possible due to their low flux density and short duration, through the accumulation of statistics over sequences of 10^5--10^6 pulses we were able to determine the presence and properties of the pulse-to-pulse intensity variations of six pulsars. In most cases we found that the modulation included a weak, broadly quasi-periodic component. For two pulsars the sensitivity was high enough to ascertain that the modulation phase apparently varies systematically across the profile, indicating that the modulation appears as drifting subpulses. We detected brighter than average individual pulses in several pulsars, with energies up to 2--7 times higher than the mean, similar to results from normal pulsars. We were sensitive to giant pulses of a rate of occurrence equal to (and in many instances much lower than) that of PSR B1937+21 at 1400 MHz (~30 times lower than at 430 MHz), but none were detected, indicating that the phenomenon is rare in recycled pulsars.
Scaling Properties of Paths on Graphs
R. Edwards,E. Foxall,T. J. Perkins
Mathematics , 2013,
Abstract: Let $G$ be a directed graph on finitely many vertices and edges, and assign a positive weight to each edge on $G$. Fix vertices $u$ and $v$ and consider the set of paths that start at $u$ and end at $v$, self-intersecting in any number of places along the way. For each path, sum the weights of its edges, and then list the path weights in increasing order. The asymptotic behaviour of this sequence is described, in terms of the structure and type of strongly connected components on the graph. As a special case, for a Markov chain the asymptotic probability of paths obeys either a power law scaling or a weaker type of scaling, depending on the structure of the transition matrix. This generalizes previous work by Mandelbrot and others, who established asymptotic power law scaling for special classes of Markov chains.
The Schr?dinger Functional and Non-Perturbative Improvement
R. G. Edwards,U. M. Heller,T. R. Klassen
Physics , 1997, DOI: 10.1016/S0920-5632(97)00918-3
Abstract: After describing the Schr\"odinger functional for standard and improved gluon and quark actions we present results for the non-perturbative clover coefficients of the SW quark action coupled to the Wilson plaquette action for $\beta \geq 5.7$, as well as the L\"uscher-Weisz one-loop tadpole improved gauge action, both in the quenched approximation.
The Effectiveness of Non-Perturbative O(a) Improvement in Lattice QCD
R. G. Edwards,U. M. Heller,T. R. Klassen
Physics , 1997, DOI: 10.1103/PhysRevLett.80.3448
Abstract: The ALPHA collaboration has determined the O(a) improved Wilson quark action for lattice spacings $a\leq 0.1$ fm, in the quenched approximation. We extend this result to coarser lattices, $a\leq 0.17$ fm, and calculate the hadron spectrum on them. The large range of lattice spacings obtained by combining our results with earlier ones on finer lattices, allow us to present a convincing demonstration of the efficiency of non-perturbative O(a) improvement. We find that scaling violations of the hadron masses studied drop from 30-40% for the unimproved Wilson action on the coarsest lattice to only 2-3%.
Accurate Scale Determinations for the Wilson Gauge Action
R. G. Edwards,U. M. Heller,T. R. Klassen
Physics , 1997, DOI: 10.1016/S0550-3213(98)80003-5
Abstract: Accurate determinations of the physical scale of a lattice action are required to check scaling and take the continuum limit. We present a high statistics study of the static potential for the SU(3) Wilson gauge action on coarse lattices ($5.54 \leq \beta \leq 6.0$). Using an improved analysis procedure we determine the string tension and the Sommer scale $r_0$ (and related quantities) to 1% accuracy, including all systematic errors. Combining our results with earlier ones on finer lattices, we present parameterizations of these quantities that should be accurate to about 1% for $5.6 \leq \beta \leq 6.5$. We estimate the $\La$-parameter of quenched QCD to be $\La_\MSb = 247(16)$ MeV.
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