ORCID Profile
0000-0002-7641-9946
Current Organisation
Australian National University
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Lie Groups, Harmonic and Fourier Analysis | Pure Mathematics | Algebraic and Differential Geometry | Topology
Publisher: Cambridge University Press (CUP)
Date: 2018
DOI: 10.1017/PASA.2018.39
Abstract: The low-frequency polarisation properties of radio sources are poorly studied, particularly in statistical s les. However, the new generation of low-frequency telescopes, such as the Murchison Widefield Array (the precursor for the low-frequency component of the Square Kilometre Array) offers an opportunity to probe the physics of radio sources at very low radio frequencies. In this paper, we present a catalogue of linearly polarised sources detected at 216 MHz, using data from the Galactic and Extragalactic All-sky Murchison Widefield Array survey. Our catalogue covers the Declination range –17° to –37° and 24 h in Right Ascension, at a resolution of around 3 arcminutes. We detect 81 sources (including both a known pulsar and a new pulsar candidate) with linearly polarised flux densities in excess of 18 mJy across a survey area of approximately 6 400 deg 2 , corresponding to a surface density of 1 source per 79 deg 2 . The level of Faraday rotation measured for our sources is broadly consistent with those recovered at higher frequencies, with typically more than an order of magnitude improvement in the uncertainty compared to higher-frequency measurements. However, our catalogue is likely incomplete at low Faraday rotation measures, due to our practice of excluding sources in the region where instrumental leakage appears. The majority of sources exhibit significant depolarisation compared to higher frequencies however, a small sub-s le repolarise at 216 MHz. We also discuss the polarisation properties of four nearby, large-angular-scale radio galaxies, with a particular focus on the giant radio galaxy ESO 422–G028, in order to explain the striking differences in polarised morphology between 216 MHz and 1.4 GHz.
Publisher: Elsevier BV
Date: 02-2008
Publisher: EDP Sciences
Date: 06-2012
Publisher: Oxford University Press (OUP)
Date: 14-11-2017
Publisher: The Open Journal
Date: 13-02-2023
Publisher: American Astronomical Society
Date: 14-01-2015
Publisher: Wiley
Date: 25-08-2022
DOI: 10.1111/INM.13059
Abstract: In the context of pressures faced by the nursing profession including increasing patient acuity and global nursing shortages, the importance of nurse resilience has gained attention in research and practice. Resilience is viewed as a protective factor that enables in iduals to avoid psychological harm and continue in their work. There is limited evidence on the impact of external factors such as work conditions on nurse resilience. This study aimed to explore how external factors influence nurse resilience and to incorporate this knowledge into an updated definition of nurse resilience. As part of a two‐phase mixed methods study, focus groups were conducted to obtain qualitative data to explore nurse's perceptions of resilience and factors they felt affected their resilience. Data analysis identified three main themes derived from 10 subthemes: Perceptions of Resilience, Pressures and Challenges, and Support and Strategies contributed to understanding how external factors can affect nurse resilience. A range of factors emerged including the impact of workplace conditions, organizational philosophy, the performance of managers, and the teams nurses work within, which were not reflected in an earlier definition of nurse resilience derived through a concept analysis. These factors were incorporated in an updated definition of nurse resilience. Understanding resilience in the nursing profession and the external factors that affect it is critical to the development of effective research, policies, interventions, and work environments to protect nurse well‐being, promote nurse retention, and ensure the provision of quality patient care.
Publisher: The Open Journal
Date: 05-06-2021
DOI: 10.21105/JOSS.03067
Publisher: Wiley
Date: 29-03-2020
DOI: 10.1111/INM.12721
Publisher: EDP Sciences
Date: 05-2018
DOI: 10.1051/0004-6361/201732228
Abstract: The polarization properties of radio sources at very low frequencies ( MHz) have not been widely measured, but the new generation of low-frequency radio telescopes, including the Low Frequency Array (LOFAR: a Square Kilometre Array Low pathfinder), now gives us the opportunity to investigate these properties. In this paper, we report on the preliminary development of a data reduction pipeline to carry out polarization processing and Faraday tomography for data from the LOFAR Two-meter Sky Survey (LOTSS) and present the results of this pipeline from the LOTSS preliminary data release region (10 h 45 m –15 h 30 m right ascension, 45°–57° declination, 570 square degrees). We have produced a catalog of 92 polarized radio sources at 150 MHz at 4.′3 resolution and 1 mJy rms sensitivity, which is the largest catalog of polarized sources at such low frequencies. We estimate a lower limit to the polarized source surface density at 150 MHz, with our resolution and sensitivity, of 1 source per 6.2 square degrees. We find that our Faraday depth measurements are in agreement with previous measurements and have significantly smaller errors. Most of our sources show significant depolarization compared to 1.4 GHz, but there is a small population of sources with low depolarization indicating that their polarized emission is highly localized in Faraday depth. We predict that an extension of this work to the full LOTSS data would detect at least 3400 polarized sources using the same methods, and probably considerably more with improved data processing.
Publisher: Elsevier BV
Date: 02-2022
DOI: 10.1016/J.JCJD.2021.04.008
Abstract: Mixed methods were used to evaluate a group self-management education intervention to address type 1 diabetes (T1D)-specific barriers to physical activity (PA). We evaluated the acceptability of study resources and procedures. Consenting participants from a quantitative evaluation (n=70) were invited to participate in 1 of 5 focus groups. Interviews explored the acceptability of procedures across the randomized controlled trial schedule, acceptability of the intervention/control workshops and resources and the perceived effectiveness of the intervention/control on participant outcomes. The use and helpfulness of intervention take-home resources, Facebook data and fidelity coding were also examined to inform other aspects of intervention acceptability. Twenty-one focus group participants from control or intervention arms participated in 1 of the 5 focus groups. Participants were 46±10 years of age about half were female and had been living with T1D for 23±16 years. Study procedures were widely accepted however, randomization and some aspects of the questionnaire were of concern to a small number of participants. Group education was acceptable and preferred, but participants expressed ambivalence toward the private Facebook group. Control participants indicated that basic information on PA guidelines and hypoglycemia risk are not currently being provided in standard care. Fidelity assessment confirmed the intervention was delivered consistently and was facilitated using behaviours and communication skills based on social cognitive theory. Future definitive evaluation of this promising intervention should utilize a blinded randomized controlled trial study design. Alterations to the control workshop are required to better reflect standard care in Australia. Our qualitative findings suggest that group education can be an acceptable and preferred method of education in T1D management for PA.
Publisher: EDP Sciences
Date: 2017
Publisher: Oxford University Press (OUP)
Date: 19-01-2016
Publisher: Cambridge University Press (CUP)
Date: 2020
DOI: 10.1017/PASA.2020.20
Abstract: The low-frequency linearly polarised radio source population is largely unexplored. However, a renaissance in low-frequency polarimetry has been enabled by pathfinder and precursor instruments for the Square Kilometre Array. In this second paper from the POlarised GaLactic and Extragalactic All-Sky MWA Survey-the POlarised GLEAM Survey, or POGS-we present the results from our all-sky MWA Phase I Faraday Rotation Measure survey. Our survey covers nearly the entire Southern sky in the Declination range $-82^\\circ$ to $+30^\\circ$ at a resolution between around three and seven arcminutes (depending on Declination) using data in the frequency range 169−231 MHz. We have performed two targeted searches: the first covering 25 489 square degrees of sky, searching for extragalactic polarised sources the second covering the entire sky South of Declination $+30^\\circ$ , searching for known pulsars. We detect a total of 517 sources with 200 MHz linearly polarised flux densities between 9.9 mJy and 1.7 Jy, of which 33 are known radio pulsars. All sources in our catalogues have Faraday rotation measures in the range $-328.07$ to $+279.62$ rad m −2 . The Faraday rotation measures are broadly consistent with results from higher-frequency surveys, but with typically more than an order of magnitude improvement in the precision, highlighting the power of low-frequency polarisation surveys to accurately study Galactic and extragalactic magnetic fields. We discuss the properties of our extragalactic and known-pulsar source population, how the sky distribution relates to Galactic features, and identify a handful of new pulsar candidates among our nominally extragalactic source population.
Publisher: MDPI AG
Date: 29-11-2018
Abstract: The technique of Faraday tomography is a key tool for the study of magnetised plasmas in the new era of broadband radio-polarisation observations. In particular, observations at metre wavelengths provide significantly better Faraday depth accuracies compared to traditional centimetre-wavelength observations. However, the effect of Faraday depolarisation makes the polarised signal very challenging to detect at metre wavelengths (MHz frequencies). In this work, Faraday tomography is used to characterise the Faraday rotation properties of polarised sources found in data from the LOFAR Two-Metre Sky Survey (LoTSS). Of the 76 extragalactic polarised sources analysed here, we find that all host a radio-loud AGN (Active Galactic Nucleus). The majority of the sources (∼64%) are large FRII radio galaxies with a median projected linear size of 710 kpc and median radio luminosity at 144 MHz of 4 × 10 26 W Hz − 1 (with ∼13% of all sources having a linear size Mpc). In several cases, both hotspots are detected in polarisation at an angular resolution of ∼20″ . One such case allowed a study of intergalactic magnetic fields on scales of 3.4 Mpc. Other detected source types include an FRI radio galaxy and at least eight blazars. Most sources display simple Faraday spectra, but we highlight one blazar that displays a complex Faraday spectrum, with two close peaks in the Faraday dispersion function.
Publisher: MDPI AG
Date: 27-03-2019
Abstract: The Galactic magnetic field is an integral constituent of the interstellar medium (ISM), and knowledge of its structure is crucial to understanding Galactic dynamics. The Rotation Measures (RM) of extragalactic (EG) sources have been the basis of comprehensive Galactic magnetic field models. Polarised extended emission (XE) is also seen along lines of sight through the Galactic disk, and also displays the effects of Faraday rotation. Our aim is to investigate and understand the relationship between EG and XE RMs near the Galactic plane, and to determine how the XE RMs, a hitherto unused resource, can be used as a probe of the large-scale Galactic magnetic field. We used polarisation data from the Canadian Galactic Plane Survey (CGPS), observed near 1420 MHz with the Dominion Radio Astrophysical Observatory (DRAO) Synthesis Telescope. We calculated RMs from a linear fit to the polarisation angles as a function of wavelength squared in four frequency channels, for both the EG sources and the XE. Across the CGPS area, 55 ∘ ℓ 193 ∘ , − 3 ∘ b 5 ∘ , the RMs of the XE closely track the RMs of the EG sources, with XE RMs about half the value of EG-source RMs. The exceptions are places where large local HII complexes heavily depolarise more distant emission. We conclude that there is valuable information in the XE RM dataset. The factor of 2 between the two types of RM values is close to that expected from a Burn slab model of the ISM. This result indicates that, at least in the outer Galaxy, the EG and XE sources are likely probing similar depths, and that the Faraday rotating medium and the synchrotron emitting medium have similar variation with galactocentric distance.
Publisher: Oxford University Press (OUP)
Date: 28-06-2023
Abstract: We use data from the pilot observations of the EMU/POSSUM surveys to study the ‘missing supernova remnant (SNR) problem’, the discrepancy between the number of Galactic SNRs that have been observed, and the number that are estimated to exist. The Evolutionary Map of the Universe (EMU) and the Polarization Sky Survey of the Universe’s Magnetism (POSSUM) are radio sky surveys that are conducted using the Australian Square Kilometre Array Pathfinder (ASKAP). We report on the properties of seven known SNRs in the joint Galactic pilot field, with an approximate longitude and latitude of 323° ≤ l ≤ 330° and −4° ≤ b ≤ 2°, respectively, and identify 21 SNR candidates. Of these, four have been previously identified as SNR candidates, three were previously listed as a single SNR, 13 have not been previously studied, and one has been studied in the infrared. These are the first discoveries of Galactic SNR candidates with EMU/POSSUM and, if confirmed, they will increase the SNR density in this field by a factor of 4. By comparing our SNR candidates to the known Galactic SNR population, we demonstrate that many of these sources were likely missed in previous surveys due to their small angular size and/or low surface brightness. We suspect that there are SNRs in this field that remain undetected due to limitations set by the local background and confusion with other radio sources. The results of this paper demonstrate the potential of the full EMU/POSSUM surveys to uncover more of the missing Galactic SNR population.
Publisher: Wiley
Date: 09-02-2021
DOI: 10.1111/JAN.14763
Publisher: EDP Sciences
Date: 10-2021
DOI: 10.1051/0004-6361/202141071
Abstract: Context. Faraday tomography of a field centred on the extragalactic point source 3C 196 with the LOw Frequency ARray (LOFAR) revealed an intertwined structure of diffuse polarised emission with straight depolarisation canals and tracers of the magnetised and multi-phase interstellar medium (ISM), such as dust and line emission from atomic hydrogen (HI). Aims. This study aims at extending the multi-tracer analysis of LOFAR data to three additional fields in the surroundings of the 3C 196 field. For the first time, we study the three-dimensional structure of the LOFAR emission by determining the distance to the depolarisation canals. Methods. We used the rolling Hough transform to compare the orientation of the depolarisation canals with that of the filamentary structure seen in HI, and based on starlight and dust polarisation data, with that of the plane-of-the-sky magnetic field. Stellar parallaxes from Gaia complemented the starlight polarisation with the corresponding distances. Results. Faraday tomography of the three fields shows a rich network of diffuse polarised emission at Faraday depths between − 10 and + 15 rad m −2 . A complex system of straight depolarisation canals resembles that of the 3C 196 field. The depolarisation canals align both with the HI filaments and with the magnetic field probed by dust. The observed alignment suggests that an ordered magnetic field organises the multiphase ISM over a large area (~20°). In one field, two groups of stars at distances below and above 200 pc, respectively, show distinct magnetic field orientations. These are both comparable with the orientations of the depolarisation canals in the same field. We conclude that the depolarisation canals likely trace the same change in the magnetic field as probed by the stars, which corresponds to the edge of the Local Bubble.
Publisher: American Astronomical Society
Date: 04-2021
Abstract: Faraday rotation provides a valuable tracer of magnetic fields in the interstellar medium catalogs of Faraday rotation measures provide key observations for studies of the Galactic magnetic field. We present a new catalog of rotation measures derived from the Canadian Galactic Plane Survey, covering a large region of the Galactic plane spanning 52° l 192°, −3° b 5°, along with northern and southern latitude extensions around l ≈ 105°. We have derived rotation measures for 2234 sources (4 of which are known pulsars), 75% of which have no previous measurements, over an area of approximately 1300 deg 2 . These new rotation measures increase the measurement density for this region of the Galactic plane by a factor of 2.
Publisher: EDP Sciences
Date: 03-2019
DOI: 10.1051/0004-6361/201834777
Abstract: Faraday tomography allows us to map diffuse polarized synchrotron emission from our Galaxy and use it to interpret the magnetic field in the interstellar medium (ISM). We have applied Faraday tomography to 60 observations from the LOFAR Two-meter Sky Survey (LOTSS) and produced a Faraday depth cube mosaic covering 568 square degrees at high Galactic latitudes, at 4.′3 angular resolution and 1 rad m −2 Faraday depth resolution, with a typical noise level of 50–100 μ Jy per point spread function (PSF) per rotation measure spread function (RMSF 40–80 mK RMSF −1 ). While parts of the images are strongly affected by instrumental polarization, we observed diffuse polarized emission throughout most of the field, with typical brightness between 1 and 6 K RMSF −1 , and Faraday depths between − 7 and +25 rad m −2 . We observed many new polarization features, some up to 15° in length. These include two regions with very uniformly structured, linear gradients in the Faraday depth we measured the steepness of these gradients as 2.6 and 13 rad m −2 deg −1 . We also observed a relationship between one of the gradients and an H I filament in the local ISM. Other ISM tracers were also checked for correlations with our polarization data and none were found, but very little signal was seen in most tracers in this region. We conclude that the LOTSS data are very well suited for Faraday tomography, and that a full-scale survey with all the LOTSS data has the potential to reveal many new Galactic polarization features and map out diffuse Faraday depth structure across the entire northern hemisphere.
Publisher: MDPI AG
Date: 06-07-2020
Abstract: The Square Kilometre Array (SKA) will answer fundamental questions about the origin, evolution, properties, and influence of magnetic fields throughout the Universe. Magnetic fields can illuminate and influence phenomena as erse as star formation, galactic dynamics, fast radio bursts, active galactic nuclei, large-scale structure, and dark matter annihilation. Preparations for the SKA are swiftly continuing worldwide, and the community is making tremendous observational progress in the field of cosmic magnetism using data from a powerful international suite of SKA pathfinder and precursor telescopes. In this contribution, we revisit community plans for magnetism research using the SKA, in light of these recent rapid developments. We focus in particular on the impact that new radio telescope instrumentation is generating, thus advancing our understanding of key SKA magnetism science areas, as well as the new techniques that are required for processing and interpreting the data. We discuss these recent developments in the context of the ultimate scientific goals for the SKA era.
Publisher: American Astronomical Society
Date: 25-07-2023
Abstract: Faraday rotation measures (RMs) have been used for many studies of cosmic magnetism, and in most cases having more RMs is beneficial for those studies. This has lead to the development of RM surveys that have produced large catalogs, as well as meta-catalogs collecting RMs from many different publications. However, it has been difficult to take full advantage of all of these RMs, as the in idual catalogs have been published in many different places, and in many different formats. In addition, the polarization spectra used to determine these RMs are rarely published, limiting the ability to reanalyze data as new methods or additional observations become available. We propose a standard convention for RM catalogs, RMTable2023, and a standard for source-integrated polarized spectra of radio sources, PolSpectra2023. These standards are intended to maximize the value and utility of these data for researchers and to make them easier to access. To demonstrate the use of the RMTable2023 standard, we have produced a consolidated catalog of 55,819 RMs collected from 42 published catalogs.
Publisher: MDPI AG
Date: 23-10-2018
Abstract: Faraday tomography, the study of the distribution of extended polarized emission by strength of Faraday rotation, is a powerful tool for studying magnetic fields in the interstellar medium of our Galaxy and nearby galaxies. The strong frequency dependence of Faraday rotation results in very different observational strengths and limitations for different frequency regimes. I discuss the role these effects take in Faraday tomography below 1 GHz, emphasizing the 100–200 MHz band observed by the Low Frequency Array and the Murchison Widefield Array. With that theoretical context, I review recent Faraday tomography results in this frequency regime, and discuss expectations for future observations.
Publisher: MDPI AG
Date: 26-10-2018
DOI: 10.20944/PREPRINTS201810.0637.V1
Abstract: The technique of Faraday tomography is a key tool for the study of magnetised plasmas in the new era of broadband radio polarisation observations. In particular, observations at metre-wavelengths provide significantly better Faraday depth accuracies compared to traditional cm-wavelength observations. However, the effect of Faraday depolarisation makes the polarised signal very challenging to detect at metre wavelengths (MHz frequencies). In this work, Faraday tomography is used to characterise the Faraday rotation properties of polarised sources found in data from the LOFAR Two-Metre Sky Survey (LoTSS). Of the 76 extragalactic polarised sources analysed here, we find that all host a radio-loud AGN. The majority of the sources (& sim %) are large FRII radio galaxies with a median projected linear size of 710 kpc and median radio luminosity at 144 MHz of 4 & times 10^26 W/Hz. In several cases, both hotspots are detected in polarisation at an angular resolution of & sim ". One such case allowed a study of intergalactic magnetic fields on scales of 3.4 Mpc. Other detected source types include an FRI radio galaxy and at least 8 blazars. Most sources display simple Faraday spectra, however, we highlight one blazar that displays a complex Faraday spectrum, with two close peaks in the Faraday dispersion function.
Publisher: American Astronomical Society
Date: 25-01-2011
Publisher: Oxford University Press (OUP)
Date: 14-09-2023
Publisher: American Astronomical Society
Date: 23-07-2012
Publisher: American Astronomical Society
Date: 03-2022
Abstract: Understanding how the Galactic magnetic field threads the multiphase interstellar medium (ISM) remains a considerable challenge, as different magnetic field tracers probe dissimilar phases and field components. We search for evidence of a common magnetic field shared between the ionized and neutral ISM by comparing 1.4 GHz radio continuum polarization and H i line emission from the Galactic Arecibo L -Band Feed Array Continuum Transit Survey (GALFACTS) and Galactic Arecibo L -Band Feed Array H i (GALFA-H i ) survey, respectively. We compute the polarization gradient of the continuum emission and search for associations with diffuse/translucent H i structures. The polarization gradient is sensitive to changes in the integrated product of the thermal electron density and line-of-sight field strength ( B ∥ ) in warm ionized gas, while narrow H i structures highlight the plane-of-sky field orientation in cold neutral gas. We identified one region in the high Galactic latitude Arecibo sky, G216+26 centered on ( ℓ , b ) ∼ (216°, +26°), containing filaments in the polarization gradient that are aligned with narrow H i structures roughly parallel to the Galactic plane. We present a comparison of multiphase observations and magnetic field tracers of this region, demonstrating that the warm ionized and cold neutral media are connected likely via a common magnetic field. We quantify the physical properties of a polarization gradient filament associated with H α emission, measuring a line-of-sight field strength B ∥ = 6 ± 4 μ G and a plasma beta β = 2.1 − 2.1 + 3.1 . We discuss the lack of widespread multiphase magnetic field alignments and consider whether this region is associated with a short-timescale or physically rare phenomenon. This work highlights the utility of multitracer analyses for understanding the magnetized ISM.
Publisher: Cambridge University Press (CUP)
Date: 08-2015
DOI: 10.1017/S1743921314011727
Abstract: We present a study of the Milky Way halo magnetic field, determined from observations of Faraday rotation measure (RM) of extragalactic radio sources (EGS) in Galactic longitude range 100°–117° within 30° of the Galactic plane. We find negative median RMs in both the northern and southern Galactic hemispheres for | b | °, outside the latitude range where the disk field dominates. This suggest that the halo magnetic field towards the outer Galaxy does not reverse direction across the mid-plane. An azimuthal magnetic field at heights 0.8−2 kpc above/below the Galactic plane between the local and the Perseus spiral arm can reproduce the observed trend of RM against Galactic latitude. We propose that the Milky Way could have a halo magnetic field similar to that observed in M51.
Location: No location found
Location: Canada
Start Date: 2013
End Date: 12-2018
Amount: $315,000.00
Funder: Australian Research Council
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