ORCID Profile
0000-0003-3294-3081
Current Organisations
Taipei Veterans General Hospital
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National Yang Ming Chiao Tung University - Taipei Campus
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Publisher: Cambridge University Press (CUP)
Date: 04-2009
DOI: 10.1017/S1743921309990421
Abstract: Pulsar timing has proven to be a wonderful tool with which to study neutron stars, providing insights into their ages, distances, proper motions, magnetic field strengths, internal structure, binary histories and evolution, and for tests of General Relativity. Here I describe how to optimise strategies for millisecond pulsar timing to enable the highest timing precision.
Publisher: Elsevier BV
Date: 11-2019
DOI: 10.1016/J.WATRES.2019.114967
Abstract: Characterization of microbial communities using high-throughput licon sequencing is an emerging approach for microbial source tracking of fecal pollution. This study used SourceTracker software to examine temporal and geographical variability of fecal bacterial community profiles to identify pollutant sources in three freshwater catchments in sub-tropical Australia. Fecal bacterial communities from 10 animal species, humans, and composite wastewater s les from six sewage treatment plants were characterized and compared to freshwater s les using Illumina licon sequencing of the V5-V6 regions of the 16S rRNA gene. Source contributions were calculated in SourceTracker using new fecal taxon libraries as well as previously generated libraries to determine the effects of geographic and temporal variability on source assignments. SourceTracker determined 16S rRNA bacterial communites within freshwater s les, shared taxonomic similarities to that of wastewater at low levels (typically <3%). SourceTraker also predicted occasional fecal detection of deer and flying fox sources in the water s les. No significant differences in source contributions were observed within sequences from current and previously characterized fecal s les (P ≥ 0.107). However, significant differences were observed between previously characterized and newly characterized source communities (ANOSIM P ≤ 0.001), which shared <15% community composition. Results suggest temporal instability of fecal taxon libraries among tested sources and highlight continual evaluation of community-based MST using confirmatory qPCR analyses of marker genes.
Publisher: Cambridge University Press (CUP)
Date: 2020
DOI: 10.1017/PASA.2020.19
Abstract: We describe system verification tests and early science results from the pulsar processor (PTUSE) developed for the newly commissioned 64-dish SARAO MeerKAT radio telescope in South Africa. MeerKAT is a high-gain ( ${\\sim}2.8\\,\\mbox{K Jy}^{-1}$ ) low-system temperature ( ${\\sim}18\\,\\mbox{K at }20\\,\\mbox{cm}$ ) radio array that currently operates at 580–1 670 MHz and can produce tied-array beams suitable for pulsar observations. This paper presents results from the MeerTime Large Survey Project and commissioning tests with PTUSE. Highlights include observations of the double pulsar $\\mbox{J}0737{-}3039\\mbox{A}$ , pulse profiles from 34 millisecond pulsars (MSPs) from a single 2.5-h observation of the Globular cluster Terzan 5, the rotation measure of Ter5O, a 420-sigma giant pulse from the Large Magellanic Cloud pulsar PSR $\\mbox{J}0540{-}6919$ , and nulling identified in the slow pulsar PSR J0633–2015. One of the key design specifications for MeerKAT was absolute timing errors of less than 5 ns using their novel precise time system. Our timing of two bright MSPs confirm that MeerKAT delivers exceptional timing. PSR $\\mbox{J}2241{-}5236$ exhibits a jitter limit of $ \\,\\mbox{ns h}^{-1}$ whilst timing of PSR $\\mbox{J}1909{-}3744$ over almost 11 months yields an rms residual of 66 ns with only 4 min integrations. Our results confirm that the MeerKAT is an exceptional pulsar telescope. The array can be split into four separate sub-arrays to time over 1 000 pulsars per day and the future deployment of S-band (1 750–3 500 MHz) receivers will further enhance its capabilities.
Publisher: Springer Science and Business Media LLC
Date: 14-06-2011
Publisher: Cambridge University Press (CUP)
Date: 2016
DOI: 10.1017/PASA.2016.35
Abstract: Here, we present a catalogue of known Fast Radio Burst sources in the form of an online catalogue, FRBCAT. The catalogue includes information about the instrumentation used for the observations for each detected burst, the measured quantities from each observation, and model-dependent quantities derived from observed quantities. To aid in consistent comparisons of burst properties such as width and signal-to-noise ratios, we have re-processed all the bursts for which we have access to the raw data, with software which we make available. The originally derived properties are also listed for comparison. The catalogue is hosted online as a Mysql database which can also be downloaded in tabular or plain text format for off-line use. This database will be maintained for use by the community for studies of the Fast Radio Burst population as it grows.
Publisher: American Astronomical Society
Date: 18-04-2013
Publisher: Oxford University Press (OUP)
Date: 04-2011
Publisher: Oxford University Press (OUP)
Date: 06-1998
Publisher: Oxford University Press (OUP)
Date: 22-11-2010
Publisher: Oxford University Press (OUP)
Date: 21-04-1998
Publisher: American Astronomical Society
Date: 04-05-2012
Publisher: Oxford University Press (OUP)
Date: 17-09-2014
Publisher: American Physical Society (APS)
Date: 05-11-2018
Publisher: American Astronomical Society
Date: 05-06-2017
Publisher: American Astronomical Society
Date: 02-2023
Abstract: In 2018 an ultra–wide-bandwidth low-frequency (UWL) receiver was installed on the 64 m Parkes Radio Telescope, enabling observations with an instantaneous frequency coverage from 704 to 4032 MHz. Here we present the analysis of a 3 yr data set of 35 ms pulsars observed with the UWL by the Parkes Pulsar Timing Array, using wide-band timing methods. The two key differences compared to typical narrowband methods are (1) generation of two-dimensional templates accounting for pulse shape evolution with frequency and (2) simultaneous measurements of the pulse time of arrival (TOA) and dispersion measure (DM). This is the first time that wide-band timing has been applied to a uniform data set collected with a single large fractional bandwidth receiver, for which such techniques were originally developed. As a result of our study, we present a set of profile evolution models and new timing solutions, including initial noise analysis. Precision of our TOA and DM measurements is in the range of 0.005–2.08 μ s and (0.043–14.24) × 10 −4 cm −3 pc, respectively, with 94% of the pulsars achieving a median TOA uncertainty of less than 1 μ s.
Publisher: Springer Science and Business Media LLC
Date: 07-1991
DOI: 10.1038/352311A0
Publisher: Oxford University Press (OUP)
Date: 18-07-2013
Publisher: American Astronomical Society
Date: 20-01-2001
DOI: 10.1086/318893
Publisher: American Astronomical Society
Date: 05-2022
Abstract: We report the discovery of a highly circularly polarized, variable, steep-spectrum pulsar in the Australian Square Kilometre Array Pathfinder (ASKAP) Variables and Slow Transients (VAST) survey. The pulsar is located about 1° from the center of the Large Magellanic Cloud, and has a significant fractional circular polarization of ∼20%. We discovered pulsations with a period of 322.5 ms, dispersion measure (DM) of 157.5 pc cm −3 , and rotation measure (RM) of +456 rad m −2 using observations from the MeerKAT and the Parkes telescopes. This DM firmly places the source, PSR J0523−7125, in the Large Magellanic Cloud (LMC). This RM is extreme compared to other pulsars in the LMC (more than twice that of the largest previously reported one). The average flux density of ∼1 mJy at 1400 MHz and ∼25 mJy at 400 MHz places it among the most luminous radio pulsars known. It likely evaded previous discovery because of its very steep radio spectrum (spectral index α ≈ −3, where S ν ∝ ν α ) and broad pulse profile (duty cycle ≳35%). We discuss implications for searches for unusual radio sources in continuum images, as well as extragalactic pulsars in the Magellanic Clouds and beyond. Our result highlighted the possibility of identifying pulsars, especially extreme pulsars, from radio continuum images. Future large-scale radio surveys will give us an unprecedented opportunity to discover more pulsars and potentially the most distant pulsars beyond the Magellanic Clouds.
Publisher: American Astronomical Society
Date: 28-12-2010
Publisher: Oxford University Press (OUP)
Date: 19-09-2011
Publisher: American Astronomical Society
Date: 08-2022
Abstract: We present a targeted search for continuous gravitational waves (GWs) from 236 pulsars using data from the third observing run of LIGO and Virgo (O3) combined with data from the second observing run (O2). Searches were for emission from the l = m = 2 mass quadrupole mode with a frequency at only twice the pulsar rotation frequency (single harmonic) and the l = 2, m = 1, 2 modes with a frequency of both once and twice the rotation frequency (dual harmonic). No evidence of GWs was found, so we present 95% credible upper limits on the strain litudes h 0 for the single-harmonic search along with limits on the pulsars’ mass quadrupole moments Q 22 and ellipticities ε . Of the pulsars studied, 23 have strain litudes that are lower than the limits calculated from their electromagnetically measured spin-down rates. These pulsars include the millisecond pulsars J0437−4715 and J0711−6830, which have spin-down ratios of 0.87 and 0.57, respectively. For nine pulsars, their spin-down limits have been surpassed for the first time. For the Crab and Vela pulsars, our limits are factors of ∼100 and ∼20 more constraining than their spin-down limits, respectively. For the dual-harmonic searches, new limits are placed on the strain litudes C 21 and C 22 . For 23 pulsars, we also present limits on the emission litude assuming dipole radiation as predicted by Brans-Dicke theory.
Publisher: Oxford University Press (OUP)
Date: 16-06-2023
Abstract: PSR J1757−1854 is one of the most relativistic double neutron star binary systems known in our Galaxy, with an orbital period of $P_\\text{b}=4.4\\, \\text{h}$ and an orbital eccentricity of e = 0.61. As such, it has promised to be an outstanding laboratory for conducting tests of relativistic gravity. We present the results of a 6-yr c aign with the 100-m Green Bank and 64-m Parkes radio telescopes, designed to capitalize on this potential. We identify secular changes in the profile morphology and polarization of PSR J1757−1854, confirming the presence of geodetic precession and allowing the constraint of viewing geometry solutions consistent with General Relativity. We also update PSR J1757−1854’s timing, including new constraints of the pulsar’s proper motion, post-Keplerian parameters, and component masses. We conclude that the radiative test of gravity provided by PSR J1757−1854 is fundamentally limited to a precision of 0.3 per cent due to the pulsar’s unknown distance. A search for pulsations from the companion neutron star is also described, with negative results. We provide an updated evaluation of the system’s evolutionary history, finding strong support for a large kick velocity of $w\\ge 280\\, \\rm{km\\,s}^{-1}$ following the second progenitor supernova. Finally, we reassess PSR J1757−1854’s potential to provide new relativistic tests of gravity. We conclude that a 3-σ constraint of the change in the projected semimajor axis ($\\dot{x}$) associated with Lense–Thirring precession is expected no earlier than 2031. Meanwhile, we anticipate a 3-σ measurement of the relativistic orbital deformation parameter δθ as soon as 2026.
Publisher: Cambridge University Press (CUP)
Date: 09-2017
DOI: 10.1017/S1743921318000467
Abstract: Radio pulsars have been responsible for many astonishing astrophysical and fundamental physics breakthroughs since their discovery 50 years ago. In this review I will discuss many of the highlights, most of which were only possible because of the provision of large-scale observing facilities. The next 50 years of pulsar astronomy can be very bright, but only if our governments properly plan and fund the infrastructure necessary to enable future discoveries. Being a small sub-field of astronomy places an onus on the pulsar community to have an open-source/open access approach to data, software, and major observing facilities to enable new groups to emerge to keep the field vibrant.
Publisher: American Astronomical Society
Date: 30-08-2010
Publisher: Oxford University Press (OUP)
Date: 21-08-1998
Publisher: Oxford University Press (OUP)
Date: 24-12-2017
Publisher: American Astronomical Society
Date: 29-06-2023
Abstract: Pulsar timing arrays aim to detect nanohertz-frequency gravitational waves (GWs). A background of GWs modulates pulsar arrival times and manifests as a stochastic process, common to all pulsars, with a signature spatial correlation. Here we describe a search for an isotropic stochastic gravitational-wave background (GWB) using observations of 30 millisecond pulsars from the third data release of the Parkes Pulsar Timing Array (PPTA), which spans 18 yr. Using current Bayesian inference techniques we recover and characterize a common-spectrum noise process. Represented as a strain spectrum h c = A ( f / 1 yr − 1 ) α , we measure A = 3.1 − 0.9 + 1.3 × 10 − 15 and α = −0.45 ± 0.20, respectively (median and 68% credible interval). For a spectral index of α = −2/3, corresponding to an isotropic background of GWs radiated by inspiraling supermassive black hole binaries, we recover an litude of A = 2.04 − 0.22 + 0.25 × 10 − 15 . However, we demonstrate that the apparent signal strength is time-dependent, as the first half of our data set can be used to place an upper limit on A that is in tension with the inferred common-spectrum litude using the complete data set. We search for spatial correlations in the observations by hierarchically analyzing in idual pulsar pairs, which also allows for significance validation through randomizing pulsar positions on the sky. For a process with α = −2/3, we measure spatial correlations consistent with a GWB, with an estimated false-alarm probability of p ≲ 0.02 (approx. 2 σ ). The long timing baselines of the PPTA and the access to southern pulsars will continue to play an important role in the International Pulsar Timing Array.
Publisher: American Astronomical Society
Date: 29-06-2023
Abstract: The noise in millisecond pulsar (MSP) timing data can include contributions from observing instruments, the interstellar medium, the solar wind, solar system ephemeris errors, and the pulsars themselves. The noise environment must be accurately characterized in order to form the null hypothesis from which signal models can be compared, including the signature induced by nanohertz-frequency gravitational waves (GWs). Here we describe the noise models developed for each of the MSPs in the Parkes Pulsar Timing Array (PPTA) third data release, which have been used as the basis of a search for the isotropic stochastic GW background. We model pulsar spin noise, dispersion measure variations, scattering variations, events in the pulsar magnetospheres, solar wind variability, and instrumental effects. We also search for new timing model parameters and detected Shapiro delays in PSR J0614−3329 and PSR J1902−5105. The noise and timing models are validated by testing the normalized and whitened timing residuals for Gaussianity and residual correlations with time. We demonstrate that the choice of noise models significantly affects the inferred properties of a common-spectrum process. Using our detailed models, the recovered common-spectrum noise in the PPTA is consistent with a power law with a spectral index of γ = 13/3, the value predicted for a stochastic GW background from a population of supermassive black hole binaries driven solely by GW emission.
Publisher: Oxford University Press (OUP)
Date: 07-12-2017
Publisher: American Astronomical Society
Date: 07-08-2018
Publisher: Elsevier BV
Date: 03-2010
Publisher: American Association for the Advancement of Science (AAAS)
Date: 18-10-2013
Abstract: Gravitational waves, predicted by General Relativity, are expected to be produced when very massive bodies, such as black holes, merge together. Shannon et al. (p. 334 ) used data from the Parkes Pulsar Timing Array project to estimate the gravitational wave background produced by pairs of supermassive black holes (those with masses between 10 6 and 10 11 that of the Sun) in merging galaxies. The results can be used to test models of the supermassive black hole population.
Publisher: Oxford University Press (OUP)
Date: 21-12-2012
Publisher: Oxford University Press (OUP)
Date: 08-1999
Publisher: American Astronomical Society
Date: 03-2022
Abstract: We report the discovery of two Black Widow millisecond pulsars in the globular cluster (GC) M28 with the MeerKAT telescope. PSR J1824−2452M (M28M) is a 4.78 ms pulsar in a 5.82 hr orbit, and PSR J1824−2452N (M28N) is a 3.35 ms pulsar in a 4.76 hr orbit. Both pulsars have dispersion measures near 119.30 pc cm −3 and have low-mass companion stars (∼0.01–0.03 M ⊙ ) that do not cause strong radio eclipses or orbital variations. Including these systems, there are now five known black widow pulsars in M28. The pulsar searches were conducted as a part of an initial phase of MeerKAT’s GC census (within the TRAPUM Large Survey Project). These faint discoveries demonstrate the advantages of MeerKAT’s survey sensitivity over previous searches, and we expect to find additional pulsars in continued searches of this cluster.
Publisher: Cambridge University Press (CUP)
Date: 2001
DOI: 10.1071/AS01006
Abstract: Digital signal processing is one of many valuable tools for suppressing unwanted signals or inter-ference. Building hardware processing engines seems to be the way to best implement some classes of interference suppression but is, unfortunately, expensive and time-consuming, especially if several miti-gation techniques need to be compared. Simulations can be useful, but are not a substitute for real data. CSIRO’s Australia Telescope National Facility has recently commenced a ‘software radio telescope’ project designed to fill the gap between dedicated hardware processors and pure simulation. In this approach, real telescope data are recorded coherently, then processed offline. This paper summarises the current contents of a freely available database of base band recorded data that can be used to experiment with signal processing solutions. It includes data from the following systems: single dish, multi-feed receiver single dish with reference antenna and an array of six 22 m antennas with and without a reference antenna. Astronomical sources such as OH masers, pulsars and continuum sources subject to interfering signals were recorded. The interfering signals include signals from the US Global Positioning System (GPS) and its Russian equivalent (GLONASS), television, microwave links, a low-Earth-orbit satellite, various other transmitters, and signals leaking from local telescope systems with fast clocks. The data are available on compact disk, allowing use in general purpose computers or as input to laboratory hardware prototypes.
Publisher: Oxford University Press (OUP)
Date: 21-07-2008
Publisher: Oxford University Press (OUP)
Date: 10-2000
Publisher: Cambridge University Press (CUP)
Date: 2020
DOI: 10.1017/PASA.2020.11
Abstract: We describe 14 yr of public data from the Parkes Pulsar Timing Array (PPTA), an ongoing project that is producing precise measurements of pulse times of arrival from 26 millisecond pulsars using the 64-m Parkes radio telescope with a cadence of approximately 3 weeks in three observing bands. A comprehensive description of the pulsar observing systems employed at the telescope since 2004 is provided, including the calibration methodology and an analysis of the stability of system components. We attempt to provide full accounting of the reduction from the raw measured Stokes parameters to pulse times of arrival to aid third parties in reproducing our results. This conversion is encapsulated in a processing pipeline designed to track provenance. Our data products include pulse times of arrival for each of the pulsars along with an initial set of pulsar parameters and noise models. The calibrated pulse profiles and timing template profiles are also available. These data represent almost 21 000 h of recorded data spanning over 14 yr. After accounting for processes that induce time-correlated noise, 22 of the pulsars have weighted root-mean-square timing residuals of $ \\!\\!1\\,\\mu\\text{s}$ in at least one radio band. The data should allow end users to quickly undertake their own gravitational wave analyses, for ex le, without having to understand the intricacies of pulsar polarisation calibration or attain a mastery of radio frequency interference mitigation as is required when analysing raw data files.
Publisher: Oxford University Press (OUP)
Date: 17-02-2014
DOI: 10.1093/MNRAS/STU067
Publisher: Oxford University Press (OUP)
Date: 02-09-2011
Publisher: American Astronomical Society
Date: 20-05-2008
DOI: 10.1086/529576
Publisher: American Astronomical Society
Date: 20-08-1997
DOI: 10.1086/304462
Publisher: Oxford University Press (OUP)
Date: 09-03-2016
DOI: 10.1093/MNRAS/STW175
Publisher: Springer Science and Business Media LLC
Date: 02-1993
DOI: 10.1038/361613A0
Publisher: American Association for the Advancement of Science (AAAS)
Date: 11-11-2022
Abstract: Fast radio bursts (FRBs) are millisecond-time-scale bursts of coherent radio emission that are luminous enough to be detectable at cosmological distances. In this Review, I describe the discovery of FRBs, subsequent advances in understanding them, and future prospects. Thousands of potentially observable FRBs reach Earth every day, which likely originate from highly magnetic and/or rapidly rotating neutron stars in the distant Universe. Some FRBs repeat, with this subclass often occurring in highly magnetic environments. Two repeating FRBs exhibit cyclic activity windows, consistent with an orbital period. One nearby FRB was emitted by a Galactic magnetar during an x-ray outburst. The host galaxies of some FRBs have been located, providing information about the host environments and the total baryonic content of the Universe.
Publisher: American Astronomical Society
Date: 27-03-2019
Publisher: American Astronomical Society
Date: 08-2021
Publisher: Oxford University Press (OUP)
Date: 12-2012
Publisher: American Astronomical Society
Date: 20-06-2014
Publisher: Oxford University Press (OUP)
Date: 21-07-2014
Publisher: Oxford University Press (OUP)
Date: 04-04-2012
Publisher: Oxford University Press (OUP)
Date: 06-2011
Publisher: American Association for the Advancement of Science (AAAS)
Date: 02-11-2007
Abstract: Pulsar surveys offer a rare opportunity to monitor the radio sky for impulsive burst-like events with millisecond durations. We analyzed archival survey data and found a 30-jansky dispersed burst, less than 5 milliseconds in duration, located 3° from the Small Magellanic Cloud. The burst properties argue against a physical association with our Galaxy or the Small Magellanic Cloud. Current models for the free electron content in the universe imply that the burst is less than 1 gigaparsec distant. No further bursts were seen in 90 hours of additional observations, which implies that it was a singular event such as a supernova or coalescence of relativistic objects. Hundreds of similar events could occur every day and, if detected, could serve as cosmological probes.
Publisher: Wiley
Date: 09-1995
Publisher: American Astronomical Society
Date: 05-04-2018
Publisher: Oxford University Press (OUP)
Date: 11-10-2009
Publisher: Oxford University Press (OUP)
Date: 24-04-2012
Publisher: Oxford University Press (OUP)
Date: 10-2018
Publisher: Cambridge University Press (CUP)
Date: 2023
DOI: 10.1017/PASA.2023.36
Abstract: We present the third data release from the Parkes Pulsar Timing Array (PPTA) project. The release contains observations of 32 pulsars obtained using the 64-m Parkes “Murriyang” radio telescope. The data span is up to 18 years with a typical cadence of 3 weeks. This data release is formed by combining an updated version of our second data release with ∼ 3 years of more recent data primarily obtained using an ultra-wide-bandwidth receiver system that operates between 704 and 4032 MHz. We provide calibrated pulse profiles, flux-density dynamic spectra, pulse times of arrival, and initial pulsar timing models. We describe methods for processing such wide-bandwidth observations, and compare this data release with our previous release.
Publisher: American Astronomical Society
Date: 19-12-2018
Publisher: American Astronomical Society
Date: 07-1996
DOI: 10.1086/177427
Publisher: American Astronomical Society
Date: 12-03-2020
Publisher: Oxford University Press (OUP)
Date: 02-09-2011
Publisher: Oxford University Press (OUP)
Date: 14-06-2010
Publisher: Oxford University Press (OUP)
Date: 20-11-2014
Publisher: Cambridge University Press (CUP)
Date: 08-2012
DOI: 10.1017/S1743921312024404
Abstract: We present the results from nearly three years of monitoring of the variations in dispersion measure (DM) along the line-of-sight to 11 millisecond pulsars using the Giant Metrewave Radio Telescope (GMRT). These results demonstrate accuracies of single epoch DM estimates of the order of 5 × 10 −4 cm −3 pc. A preliminary comparison with the Parkes Pulsar Timing Array (PPTA) data shows that the measured DM fluctuations are comparable. We show effects of DM variations due to the solar wind and solar corona and compare with the existing models.
Publisher: Oxford University Press (OUP)
Date: 14-12-2021
Abstract: Radio-loud magnetars display a wide variety of radio-pulse phenomenology seldom seen among the population of rotation-powered pulsars. Spectropolarimetry of the radio pulses from these objects has the potential to place constraints on their magnetic topology and unveil clues about the magnetar radio emission mechanism. Here, we report on eight observations of the magnetar Swift J1818.0–1607 taken with the Parkes Ultra-Wideband Low receiver covering a wide frequency range from 0.7 to 4 GHz over a period of 5 months. The magnetar exhibits significant temporal profile evolution over this period, including the emergence of a new profile component with an inverted spectrum, two distinct types of radio emission mode switching, detected during two separate observations, and the appearance and disappearance of multiple polarization modes. These various phenomena are likely a result of ongoing reconfiguration of the plasma content and electric currents within the magnetosphere. Geometric fits to the linearly polarized position angle indicate we are viewing the magnetar at an angle of ∼99○ from the spin axis, and its magnetic and rotation axes are misaligned by ∼112○. While conducting these fits, we found the position angle swing had reversed direction on MJD 59062 compared to observations taken 15 d earlier and 12 d later. We speculate this phenomena may be evidence the radio emission from this magnetar originates from magnetic field lines associated with two co-located magnetic poles that are connected by a coronal loop.
Publisher: Springer Science and Business Media LLC
Date: 1992
DOI: 10.1038/355213B0
Publisher: Cambridge University Press (CUP)
Date: 2017
DOI: 10.1017/PASA.2017.39
Abstract: The Molonglo Observatory Synthesis Telescope (MOST) is an 18000 m 2 radio telescope located 40 km from Canberra, Australia. Its operating band (820–851 MHz) is partly allocated to telecommunications, making radio astronomy challenging. We describe how the deployment of new digital receivers, Field Programmable Gate Array-based filterbanks, and server-class computers equipped with 43 Graphics Processing Units, has transformed the telescope into a versatile new instrument (UTMOST) for studying the radio sky on millisecond timescales. UTMOST has 10 times the bandwidth and double the field of view compared to the MOST, and voltage record and playback capability has facilitated rapid implementaton of many new observing modes, most of which operate commensally. UTMOST can simultaneously excise interference, make maps, coherently dedisperse pulsars, and perform real-time searches of coherent fan-beams for dispersed single pulses. UTMOST operates as a robotic facility, deciding how to efficiently target pulsars and how long to stay on source via real-time pulsar folding, while searching for single pulse events. Regular timing of over 300 pulsars has yielded seven pulsar glitches and three Fast Radio Bursts during commissioning. UTMOST demonstrates that if sufficient signal processing is applied to voltage streams, innovative science remains possible even in hostile radio frequency environments.
Publisher: Springer Science and Business Media LLC
Date: 06-1996
DOI: 10.1038/381584A0
Publisher: Oxford University Press (OUP)
Date: 09-03-2012
Publisher: Cambridge University Press (CUP)
Date: 09-2017
DOI: 10.1017/S1743921317010651
Abstract: The initial results from timing observations of PSR J1141–6545, a relativistic pulsar-white dwarf binary system, are presented. Predictions from the timing baseline hint at the most stringent test of gravity by an asymmetric binary yet. The timing precision has been hindered by the dramatic variations of the pulse profile due to geodetic precession, a pulsar glitch and red timing noise. Methods to overcome such timing irregularities are briefly presented along with preliminary results from the test of the General Theory of Relativity (GR) from this pulsar.
Publisher: Cambridge University Press (CUP)
Date: 2013
Abstract: A ‘pulsar timing array’ (PTA), in which observations of a large s le of pulsars spread across the celestial sphere are combined, allows investigation of ‘global’ phenomena such as a background of gravitational waves or instabilities in atomic timescales that produce correlated timing residuals in the pulsars of the array. The Parkes Pulsar Timing Array (PPTA) is an implementation of the PTA concept based on observations with the Parkes 64-m radio telescope. A s le of 20 ms pulsars is being observed at three radio-frequency bands, 50 cm (~700 MHz), 20 cm (~1400 MHz), and 10 cm (~3100 MHz), with observations at intervals of two to three weeks. Regular observations commenced in early 2005. This paper describes the systems used for the PPTA observations and data processing, including calibration and timing analysis. The strategy behind the choice of pulsars, observing parameters, and analysis methods is discussed. Results are presented for PPTA data in the three bands taken between 2005 March and 2011 March. For 10 of the 20 pulsars, rms timing residuals are less than 1 μs for the best band after fitting for pulse frequency and its first time derivative. Significant ‘red’ timing noise is detected in about half of the s le. We discuss the implications of these results on future projects including the International Pulsar Timing Array and a PTA based on the Square Kilometre Array. We also present an ‘extended PPTA’ data set that combines PPTA data with earlier Parkes timing data for these pulsars.
Publisher: American Astronomical Society
Date: 11-03-2019
Publisher: American Astronomical Society
Date: 10-10-2001
DOI: 10.1086/322772
Publisher: American Astronomical Society
Date: 02-1995
DOI: 10.1086/175230
Publisher: Oxford University Press (OUP)
Date: 18-01-2013
DOI: 10.1093/MNRAS/STS662
Publisher: American Astronomical Society
Date: 23-08-2010
Publisher: Oxford University Press (OUP)
Date: 09-03-2016
DOI: 10.1093/MNRAS/STW109
Publisher: Oxford University Press (OUP)
Date: 08-06-2012
Publisher: IEEE
Date: 02-2009
Publisher: Oxford University Press (OUP)
Date: 11-12-1996
Publisher: American Astronomical Society
Date: 10-09-1997
DOI: 10.1086/304563
Publisher: American Astronomical Society
Date: 20-05-1997
DOI: 10.1086/304041
Publisher: American Association for the Advancement of Science (AAAS)
Date: 05-07-2013
Abstract: It has been uncertain whether single, short, and bright bursts of radio emission that have been observed are celestial or terrestrial in origin. Thornton et al. (p. 53 see the Perspective by Cordes ) report the detection of four nonrepeating radio transient events with millisecond duration in data from the 64-meter Parkes radio telescope in Australia. The properties of these radio bursts indicate that they had their origin outside our galaxy, but it is not possible to tell what caused them. Because the intergalactic medium affects the characteristics of the bursts, it will be possible to use them to study its properties.
Publisher: Oxford University Press (OUP)
Date: 21-02-2010
Publisher: Cambridge University Press (CUP)
Date: 2011
DOI: 10.1071/AS10021
Abstract: dspsr is a high-performance, open-source, object-oriented, digital signal processing software library and application suite for use in radio pulsar astronomy. Written primarily in C++, the library implements an extensive range of modular algorithms that can optionally exploit both multiple-core processors and general-purpose graphics processing units. After over a decade of research and development, dspsr is now stable and in widespread use in the community. This paper presents a detailed description of its functionality, justification of major design decisions, analysis of phase-coherent dispersion removal algorithms, and demonstration of performance on some contemporary microprocessor architectures.
Publisher: IOP Publishing
Date: 03-2007
DOI: 10.1086/513572
Publisher: Oxford University Press (OUP)
Date: 29-08-2015
DOI: 10.1093/MNRAS/STV508
Publisher: Oxford University Press (OUP)
Date: 21-09-2021
Abstract: We report on a timing programme of 74 young pulsars that have been observed by the Parkes 64-m radio telescope over the past decade. Using modern Bayesian timing techniques, we have measured the properties of 124 glitches in 52 of these pulsars, of which 74 are new. We demonstrate that the glitch s le is complete to fractional increases in spin frequency greater than $\\Delta \\nu ^{90{{\\ \\rm per\\ cent}}}_{\\mathrm{ g}}/\\nu \\approx 8.1 \\times 10^{-9}$ . We measure values of the braking index, n, in 33 pulsars. In most of these pulsars, their rotational evolution is dominated by episodes of spin-down with n & 10, punctuated by step changes in the spin-down rate at the time of a large glitch. The step changes are such that, averaged over the glitches, the long-term n is small. We find a near one-to-one relationship between the interglitch value of n and the change in spin-down of the previous glitch ided by the interglitch time interval. We discuss the results in the context of a range of physical models.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 25-09-2015
Abstract: Gravitational waves are expected to be generated by the interaction of the massive bodies in black-hole binary systems. As gravitational waves distort spacetime, it should be possible to verify their existence as they interfere with the pulses emitted by millisecond pulsars. However, after monitoring 24 pulsars with the Parkes radio telescope for 12 years, Shannon et al. found no detectable variation in pulsar records. This nondetection result indicates that a new detection strategy for gravitational waves is needed. Science , this issue p. 1522
Publisher: Springer Science and Business Media LLC
Date: 07-1991
DOI: 10.1038/352219A0
Publisher: Oxford University Press (OUP)
Date: 03-05-2018
Publisher: Springer Science and Business Media LLC
Date: 1990
DOI: 10.1038/343240A0
Publisher: Oxford University Press (OUP)
Date: 22-09-2015
Publisher: Oxford University Press (OUP)
Date: 11-04-1996
Publisher: Oxford University Press (OUP)
Date: 21-05-2013
DOI: 10.1093/MNRAS/STT721
Publisher: American Astronomical Society
Date: 20-10-1995
DOI: 10.1086/309725
Publisher: American Astronomical Society
Date: 25-11-2020
Publisher: Oxford University Press (OUP)
Date: 02-03-2019
Publisher: American Astronomical Society
Date: 22-05-2017
Publisher: Oxford University Press (OUP)
Date: 25-07-2014
Publisher: Oxford University Press (OUP)
Date: 19-05-2010
Publisher: American Astronomical Society
Date: 10-07-1995
DOI: 10.1086/309565
Publisher: American Astronomical Society
Date: 17-12-2019
Publisher: Oxford University Press (OUP)
Date: 02-12-2021
Abstract: Dedicated surveys using different detection pipelines are being carried out at multiple observatories to find more fast radio bursts (FRBs). Understanding the efficiency of detection algorithms and the survey completeness function is important to enable unbiased estimation of the underlying FRB population properties. One method to achieve end-to-end testing of the system is by injecting mock FRBs in the live data stream and searching for them blindly. Mock FRB injection is particularly effective for machine-learning-based classifiers, for which analytic characterization is impractical. We describe a first-of-its-kind implementation of a real-time mock FRB injection system at the upgraded Molonglo Observatory Synthesis Telescope (UTMOST) and present our results for a set of 20 000 mock FRB injections. The injections have yielded clear insight into the detection efficiencies and have provided a survey completeness function for pulse width, fluence, and dispersion measure (DM). Mock FRBs are recovered with uniform efficiency over the full range of injected DMs however, the recovery fraction is found to be a strong function of the width and signal-to-noise ratio (SNR). For low widths (≲20 ms) and high SNR (≳9) the recovery is highly effective with recovery fractions exceeding 90 per cent. We find that the presence of radio-frequency interference causes the recovered SNR values to be systematically lower by up to 20 per cent compared to the injected values. We find that wider FRBs become increasingly hard to recover for the machine-learning-based classifier employed at UTMOST. We encourage other observatories to implement live injection set-ups for similar testing of their surveys.
Publisher: American Astronomical Society
Date: 07-1996
DOI: 10.1086/177473
Publisher: Springer Science and Business Media LLC
Date: 1993
DOI: 10.1038/361047A0
Publisher: American Astronomical Society
Date: 03-2001
DOI: 10.1086/319154
Publisher: American Astronomical Society
Date: 02-04-2019
Publisher: Oxford University Press (OUP)
Date: 03-05-2018
Publisher: Oxford University Press (OUP)
Date: 11-04-2016
Publisher: AIP
Date: 2011
DOI: 10.1063/1.3615067
Publisher: Oxford University Press (OUP)
Date: 14-09-2010
Publisher: Oxford University Press (OUP)
Date: 22-12-2012
DOI: 10.1093/MNRAS/STS486
Publisher: American Astronomical Society
Date: 06-1992
DOI: 10.1086/171379
Publisher: American Astronomical Society
Date: 18-06-2020
Publisher: Oxford University Press (OUP)
Date: 12-2009
Publisher: AIP
Date: 2011
DOI: 10.1063/1.3615068
Publisher: Springer Science and Business Media LLC
Date: 02-2016
DOI: 10.1038/NATURE17140
Abstract: In recent years, millisecond-duration radio signals originating in distant galaxies appear to have been discovered in the so-called fast radio bursts. These signals are dispersed according to a precise physical law and this dispersion is a key observable quantity, which, in tandem with a redshift measurement, can be used for fundamental physical investigations. Every fast radio burst has a dispersion measurement, but none before now have had a redshift measurement, because of the difficulty in pinpointing their celestial coordinates. Here we report the discovery of a fast radio burst and the identification of a fading radio transient lasting ~6 days after the event, which we use to identify the host galaxy we measure the galaxy's redshift to be z = 0.492 ± 0.008. The dispersion measure and redshift, in combination, provide a direct measurement of the cosmic density of ionized baryons in the intergalactic medium of ΩIGM = 4.9 ± 1.3 per cent, in agreement with the expectation from the Wilkinson Microwave Anisotropy Probe, and including all of the so-called 'missing baryons'. The ~6-day radio transient is largely consistent with the radio afterglow of a short γ-ray burst, and its existence and timescale do not support progenitor models such as giant pulses from pulsars, and supernovae. This contrasts with the interpretation of another recently discovered fast radio burst, suggesting that there are at least two classes of bursts.
Publisher: Oxford University Press (OUP)
Date: 24-10-2013
Publisher: Oxford University Press (OUP)
Date: 03-2018
DOI: 10.1093/MNRAS/STV753
Publisher: American Association for the Advancement of Science (AAAS)
Date: 31-01-2020
Abstract: Radio pulsars in short-period eccentric binary orbits can be used to study both gravitational dynamics and binary evolution. The binary system containing PSR J1141-6545 includes a massive white dwarf (WD) companion that formed before the gravitationally bound young radio pulsar. We observed a temporal evolution of the orbital inclination of this pulsar that we infer is caused by a combination of a Newtonian quadrupole moment and Lense-Thirring (LT) precession of the orbit resulting from rapid rotation of the WD. LT precession, an effect of relativistic frame dragging, is a prediction of general relativity. This detection is consistent with an evolutionary scenario in which the WD accreted matter from the pulsar progenitor, spinning up the WD to a period of <200 seconds.
Publisher: Oxford University Press (OUP)
Date: 24-10-2014
Publisher: Cambridge University Press (CUP)
Date: 2022
DOI: 10.1017/PASA.2022.19
Abstract: MeerTime is a five-year Large Survey Project to time pulsars with MeerKAT, the 64-dish South African precursor to the Square Kilometre Array. The science goals for the programme include timing millisecond pulsar (MSPs) to high precision ( ${ } 1 \\unicode{x03BC} \\mathrm{s}$ ) to study the Galactic MSP population and to contribute to global efforts to detect nanohertz gravitational waves with the International Pulsar Timing Array (IPTA). In order to plan for the remainder of the programme and to use the allocated time most efficiently, we have conducted an initial census with the MeerKAT ‘ L -band’ receiver of 189 MSPs visible to MeerKAT and here present their dispersion measures, polarisation profiles, polarisation fractions, rotation measures, flux density measurements, spectral indices, and timing potential. As all of these observations are taken with the same instrument (which uses coherent dedispersion, interferometric polarisation calibration techniques, and a uniform flux scale), they present an excellent resource for population studies. We used wideband pulse portraits as timing standards for each MSP and demonstrated that the MeerTime Pulsar Timing Array (MPTA) can already contribute significantly to the IPTA as it currently achieves better than $1\\,\\unicode{x03BC}\\mathrm{s}$ timing accuracy on 89 MSPs (observed with fortnightly cadence). By the conclusion of the initial five-year MeerTime programme in 2024 July, the MPTA will be extremely significant in global efforts to detect the gravitational wave background with a contribution to the detection statistic comparable to other long-standing timing programmes.
Publisher: Oxford University Press (OUP)
Date: 11-08-1997
Publisher: American Association for the Advancement of Science (AAAS)
Date: 09-12-2016
Abstract: Fast radio bursts (FRBs) are powerful flashes of astronomical radio waves that last just milliseconds and whose origins are a matter of debate. Ravi et al. discovered a FRB that is exceptionally bright (see the Perspective by Kaspi). This allowed them to measure how the polarization of the signal varies with wavelength (Faraday rotation). Combining this with the time delay of the flash at different wavelengths revealed the mean magnetic field along the line of sight. Assuming that the FRB originates from a colocated galaxy, the results constrain the intergalactic magnetic field and will inform models of galaxy formation and cosmology. Science , this issue p. 1249 see also p. 1230
Publisher: American Astronomical Society
Date: 20-10-1998
DOI: 10.1086/306282
Publisher: Oxford University Press (OUP)
Date: 02-10-2017
Publisher: Oxford University Press (OUP)
Date: 05-12-2011
Publisher: Oxford University Press (OUP)
Date: 18-11-2015
Publisher: American Astronomical Society
Date: 20-10-2005
DOI: 10.1086/444447
Publisher: Oxford University Press (OUP)
Date: 03-2001
Publisher: Elsevier BV
Date: 02-2023
Publisher: Oxford University Press (OUP)
Date: 21-07-2008
Publisher: Oxford University Press (OUP)
Date: 09-12-2014
Publisher: AIP
Date: 2008
DOI: 10.1063/1.2900282
Publisher: Oxford University Press (OUP)
Date: 03-11-2011
Publisher: Oxford University Press (OUP)
Date: 04-1997
Publisher: Springer Science and Business Media LLC
Date: 08-1993
DOI: 10.1038/364603A0
Publisher: IOP Publishing
Date: 06-04-2010
Publisher: American Physical Society (APS)
Date: 12-06-2008
Publisher: American Association for the Advancement of Science (AAAS)
Date: 06-03-2009
Abstract: The double pulsar J0737-3039A/B is a unique system with which to test gravitational theories in the strong-field regime. However, the accuracy of such tests will be limited by knowledge of the distance and relative motion of the system. Here we present very long baseline interferometry (VLBI) observations which reveal that the distance to PSR J0737-3039A/B is \\batchmode \\documentclass[fleqn,10pt,legalpaper]{article} \\usepackage{amssymb} \\usepackage{amsfonts} \\usepackage{amsmath} \\pagestyle{empty} \\begin{document} \\(1150_{-160}^{+220}\\) \\end{document} parsecs, more than double previous estimates, and confirm its low transverse velocity (∼9 kilometers per second). Combined with a decade of pulsar timing, these results will allow tests of gravitational radiation emission theories at the 0.01% uncertainty level, putting stringent constraints on theories that predict dipolar gravitational radiation. They also allow insight into the system's formation and the source of its high-energy emission.
Publisher: IOP Publishing
Date: 06-04-2010
Publisher: Oxford University Press (OUP)
Date: 17-08-2017
Publisher: American Astronomical Society
Date: 08-11-2012
Publisher: American Astronomical Society
Date: 26-08-2008
DOI: 10.1086/592401
Publisher: American Astronomical Society
Date: 02-1995
DOI: 10.1086/187766
Publisher: Oxford University Press (OUP)
Date: 27-05-2014
DOI: 10.1093/MNRAS/STU804
Publisher: American Astronomical Society
Date: 27-07-2015
Publisher: Oxford University Press (OUP)
Date: 12-2015
Publisher: American Astronomical Society
Date: 30-07-2009
Publisher: AIP
Date: 2011
DOI: 10.1063/1.3615087
Publisher: American Astronomical Society
Date: 22-08-2016
Publisher: American Astronomical Society
Date: 08-01-2013
Publisher: Oxford University Press (OUP)
Date: 09-2001
Publisher: American Association for the Advancement of Science (AAAS)
Date: 23-09-2011
Abstract: Timing observations of a millisecond pulsar reveal a planet that is far denser than any known planet.
Publisher: American Physical Society (APS)
Date: 31-03-2016
Publisher: Springer Science and Business Media LLC
Date: 07-2001
DOI: 10.1038/35084015
Location: Taiwan, Province of China
Location: Taiwan, Province of China
No related grants have been discovered for Matthew Bailes.