Willem van Straten

A Radio-loud Magnetar in X-ray Quiescence

As part of a survey for radio pulsars with the Parkes 64 m telescope, we have discovered PSR J1622-4950, a pulsar with a 4.3 s rotation period. Follow-up observations show that the pulsar has the highest inferred surface magnetic field of the known radio pulsars (B {approx}3 x 10{sup 14} G), and it exhibits significant timing noise and appears to have an inverted spectrum. Unlike the vast majority of the known pulsar population, PSR J1622-4950 appears to switch off for many hundreds of days and even in its on-state exhibits extreme variability in its flux density. Furthermore, the integrated pulse profile changes shape with epoch. All of these properties are remarkably similar to the only two magnetars previously known to emit radio pulsations. The position of PSR J1622-4950 is coincident with an X-ray source that, unlike the other radio pulsating magnetars, was found to be in quiescence. We conclude that our newly discovered pulsar is a magnetar-the first to be discovered via its radio emission.

High time resolution observations of the Vela pulsar

We present high time resolution observations of single pulses from the Vela pulsar (PSR B0833-45) made with a baseband recording system at observing frequencies of 660 and 1413 MHz. We have discovered two startling features in the 1413 MHz single-pulse data. The first is the presence of giant micropulses that are confined to the leading edge of the pulse profile. One of these pulses has a peak flux density in excess of 2500 Jy, more than 40 times the integrated pulse peak. The second new result is the presence of a large-amplitude Gaussian component on the trailing edge of the pulse profile. This component can exceed the main pulse in intensity but is switched on only relatively rarely. Fluctuation spectra reveal a possible periodicity in this feature of 140 pulse periods. Unlike the rest of the profile, this component has low net polarization and emits predominantly in the orthogonal mode. This feature appears to be unique to the Vela pulsar. We have also detected microstructure in the Vela pulsar for the first time. These same features are present in the 660 MHz data. We suggest that the full width of the Vela pulse profile might be as large as 10 ms but that the conal edges emit only rarely.

PuMa-II: a wide band pulsar machine for the westerbork synthesis radio telescope

The Pulsar Machine II (PuMa-II) is the new flexible pulsar processing back-end system at the Westerbork Synthesis Radio Telescope (WSRT), specifically designed to take advantage of the upgraded WSRT. The instrument is based on a computer cluster running the Linux operating system, with minimal custom hardware. A maximum of 160 MHz analog bandwidth sampled as 8 × 20 MHz subbands with 8-bit resolution can be recorded on disks attached to separate computer nodes. Processing of the data is done in the additional 32 nodes allowing near real time coherent dedispersion for most pulsars observed at the WSRT. This has doubled the bandwidth for pulsar observations in general, and has enabled the use of coherent dedispersion over a bandwidth 8 times larger than was previously possible at the WSRT. PuMa-II is one of the widest bandwidth coherent dedispersion machines currently in use and has a maximum time resolution of 50 ns. The system is now routinely used for high-precision pulsar timing studies, polarization studies, single pulse work, and a variety of other observational work.The Pulsar Machine II (PuMa II) is the new flexible pulsar processing backend system at the Westerbork Synthesis Radio Telescope (WSRT), specifically designed to take advantage of the upgraded WSRT. The instrument is based on a computer cluster running the Linux operating system, with minimal custom hardware. A maximum of 160 MHz analogue bandwidth sampled as 8×20 MHz subbands with 8-bit resolution can be recorded on disks attached to separate computer nodes. Processing of the data is done in the additional 32-nodes allowing near real time coherent dedispersion for most pulsars observed at the WSRT. This has doubled the bandwidth for pulsar observations in general, and has enabled the use of coherent dedispersion over a bandwidth eight times larger than was previously possible at the WSRT. PuMa II is one of the widest bandwidth coherent dedispersion machines currently in use and has a maximum time resolution of 50ns. The system is now routinely used for high precision pulsar timing studies, polarization studies, single pulse work and a variety of other observational work.

Gravitational-wave cosmology across 29 decades in frequency

Quantum fluctuations of the gravitational field in the early Universe, amplified by inflation, produce a primordial gravitational-wave background across a broad frequency band. We derive constraints on the spectrum of this gravitational radiation, and hence on theories of the early Universe, by combining experiments that cover 29 orders of magnitude in frequency. These include Planck observations of cosmic microwave background temperature and polarization power spectra and lensing, together with baryon acoustic oscillations and big bang nucleosynthesis measurements, as well as new pulsar timing array and ground-based interferometer limits. While individual experiments constrain the gravitational-wave energy density in specific frequency bands, the combination of experiments allows us to constrain cosmological parameters, including the inflationary spectral index n_t and the tensor-to-scalar ratio r. Results from individual experiments include the most stringent nanohertz limit of the primordial background to date from the Parkes Pulsar Timing Array, Ω_(GW)(f) < 2.3 × 10^(−10). Observations of the cosmic microwave background alone limit the gravitational-wave spectral index at 95% confidence to n_t ≲ 5 for a tensor-to-scalar ratio of r = 0.11. However, the combination of all the above experiments limits n_t < 0.36. Future Advanced LIGO observations are expected to further constrain n_t < 0.34 by 2020. When cosmic microwave background experiments detect a nonzero r, our results will imply even more stringent constraints on n_t and, hence, theories of the early Universe.

A suite of domain-specific visual languages for scientific software application modelling

Many advances in science now require sophisticated scientific software applications that facilitate data and computationally intensive experiments. However, the effective utilization of existing computational power e.g., grid and cloud platforms depends on the capabilities of scientists to implement parallel, scalable code for such experiments. Currently, tools aimed at supporting scientists are either very limited to specific domains, or require significant development using low-level code. We describe our work towards a more end user-friendly scientific applications development process, notations and toolset. We introduce a scientific application designer intended for use primarily by scientists to enable them in describing workflow, processes, entities, formulae, computation and ultimately realization code for different computing platforms. This is achieved via a set of integrated, domain-specific visual and textual languages (DSVLs). A Web-based modeling tool supports definition of new DSVLs and modeling of these applications. We are currently extending our tool to support generation of multi-core and GPU implementations, and visualization of results.

Toward an Empirical Theory of Pulsar Emission. XII. Exploring the Physical Conditions in Millisecond Pulsar Emission Regions

The five-component profile of the 2.7 ms pulsar J0337+1715 appears to exhibit the best example to date of a core/double-cone emission-beam structure in a millisecond pulsar (MSP). Moreover, three other MSPs, the binary pulsars B1913+16, B1953+29, and J1022+1001, seem to exhibit core/single-cone profiles. These configurations are remarkable and important because it has not been clear whether MSPs and slow pulsars exhibit similar emission-beam configurations, given that they have considerably smaller magnetospheric sizes and magnetic field strengths. MSPs thus provide an extreme context for studying pulsar radio emission. Particle currents along the magnetic polar flux tube connect processes just above the polar cap through the radio-emission region to the light-cylinder and the external environment. In slow pulsars, radio-emission heights are typically about 500 km around where the magnetic field is nearly dipolar, and estimates of the physical conditions there point to radiation below the plasma frequency and emission from charged solitons by the curvature process. We are able to estimate emission heights for the four MSPs and carry out a similar estimation of physical conditions in their much lower emission regions. We find strong evidence that MSPs also radiate by curvature emission from charged solitons.

Pulsar Applications of the Caltech Parkes Swinburne Baseband Processing System

The Caltech-Parkes-Swinburne Recorder (CPSR) was installed at the Parkes Radio-telescope in August of 1998. It is capable of continuously two-bit quadrature-sampling a 20 MHz bandpass in two polarizations, though other configurations are possible. Since its successful installation, over 17 Terabytes of observational data have been recorded. These data were processed using the Swinburne Baseband Processing System (SBPS), a suite of data management and reduction software executed using a Beowulf-style cluster of high-performance workstations. A description of CPSR and SBPS is presented herein, followed by a brief presentation of some results from the past year of observations, and an outline of possible future uses of the system.

Polarization study of the pulsars in the globular cluster 47 Tucanae

By investigating the linearly polarized component of a pulsar signal at different radio frequencies it is possible to derive constraints on the parallel component of the magnetic field along the line of sight (los) to the pulsar. In this work we have measured the polarimetric properties of 18 known pulsars in the globular cluster 47 Tucanae and we report for the first time the rotation measure (RM) for 13 of them. Our study led to the discovery of a gradient in the RM values of the pulsars across the cluster. This indicates the presence of significant variations in the magnetic field across the very small angular scales beween the pulsars in 47 Tucanae. We discuss the hypotheses that the magnetic field responsible for the gradient is located inside the globular cluster or in the Galactic disk in the direction of the cluster. However, deeper observations with the MeerKAT and/or the SKA1 radio telescopes are necessary to discriminate among the hypotheses.

Tracking dispersion measure variations of timing array pulsars with the GMRT

We present the results from nearly three years of monitoring of thevariations in dispersion measure (DM) along the line-of-sight to 11millisecond pulsars using the Giant Metrewave Radio Telescope (GMRT).These results demonstrate accuracies of single epoch DM estimates of theorder of 5 {\times} 10

The Parkes Pulsar Backends

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