We present and evaluate the prospects for detecting coherent radio counterparts to gravitational wave (GW) events using Murchison Widefield Array (MWA) triggered observations. The MWA rapid-response system, combined with its buffering mode ($\sim$4 min negative latency), enables us to catch any radio signals produced from seconds prior to hours after a binary neutron star (BNS) merger. The large field of view of the MWA ($\sim$$1\,000\,\textrm{deg}^2$ at 120 MHz) and its location under the high sensitivity sky region of the LIGO-Virgo-KAGRA (LVK) detector network, forecast a high chance of being on-target for a GW event. We consider three observing configurations for the MWA to follow up GW BNS merger events, including a single dipole per tile, the full array, and four sub-arrays. We then perform a population synthesis of BNS systems to predict the radio detectable fraction of GW events using these configurations. We find that the configuration with four sub-arrays is the best compromise between sky coverage and sensitivity as it is capable of placing meaningful constraints on the radio emission from 12.6% of GW BNS detections. Based on the timescales of four BNS merger coherent radio emission models, we propose an observing strategy that involves triggering the buffering mode to target coherent signals emitted prior to, during or shortly following the merger, which is then followed by continued recording for up to three hours to target later time post-merger emission. We expect MWA to trigger on $\sim$$5-22$ BNS merger events during the LVK O4 observing run, which could potentially result in two detections of predicted coherent emission.

In Paper I, we presented an overview of the Southern-sky MWA Rapid Two-metre (SMART) survey, including the survey design and search pipeline. While the combination of MWA’s large field-of-view and the voltage capture system brings a survey speed of ${\sim} 450\, {\textrm{deg}}^{2}\,\textrm{h}^{-1}$, the progression of the survey relies on the availability of compact configuration of the Phase II array. Over the past few years, by taking advantage of multiple windows of opportunity when the compact configuration was available, we have advanced the survey to 75% of the planned sky coverage. To date, about 10% of the data collected thus far have been processed for a first-pass search, where 10 min of observation is processed for dispersion measures out to 250 ${\textrm{pc cm}}^{-3}$, to realise a shallow survey that is largely sensitive to long-period pulsars. The ongoing analysis has led to two new pulsar discoveries, as well as an independent discovery and a rediscovery of a previously incorrectly characterised pulsar, all from ${\sim} 3\% $ of the data for which candidate scrutiny is completed. In this sequel to Paper I, we describe the strategies for further detailed follow-up including improved sky localisation and convergence to timing solution, and illustrate them using example pulsar discoveries. The processing has also led to re-detection of 120 pulsars in the SMART observing band, bringing the total number of pulsars detected to date with the MWA to 180, and these are used to assess the search sensitivity of current processing pipelines. The planned second-pass (deep survey) processing is expected to yield a three-fold increase in sensitivity for long-period pulsars, and a substantial improvement to millisecond pulsars by adopting optimal de-dispersion plans. The SMART survey will complement the highly successful Parkes High Time Resolution Universe survey at 1.2–1.5 GHz, and inform future large survey efforts such as those planned with the low-frequency Square Kilometre Array (SKA-Low).

We present an overview of the Southern-sky MWA Rapid Two-metre (SMART) pulsar survey that exploits the Murchison Widefield Array’s large field of view and voltage-capture system to survey the sky south of 30$^{\circ}$ in declination for pulsars and fast transients in the 140–170 MHz band. The survey is enabled by the advent of the Phase II MWA’s compact configuration, which offers an enormous efficiency in beam-forming and processing costs, thereby making an all-sky survey of this magnitude tractable with the MWA. Even with the long dwell times employed for the survey (4800 s), data collection can be completed in $<$100 h of telescope time, while still retaining the ability to reach a limiting sensitivity of $\sim$2–3 mJy (at 150 MHz, near zenith), which is effectively 3–5 times deeper than the previous-generation low-frequency southern-sky pulsar survey, completed in the 1990s. Each observation is processed to generate $\sim$5000–8000 tied-array beams that tessellate the full $\sim 610\, {\textrm{deg}^{2}}$ field of view (at 155 MHz), which are then processed to search for pulsars. The voltage-capture recording of the survey also allows a multitude of post hoc processing options including the reprocessing of data for higher time resolution and even exploring image-based techniques for pulsar candidate identification. Due to the substantial computational cost in pulsar searches at low frequencies, the survey data processing is undertaken in multiple passes: in the first pass, a shallow survey is performed, where 10 min of each observation is processed, reaching about one-third of the full-search sensitivity. Here we present the system overview including details of ongoing processing and initial results. Further details including first pulsar discoveries and a census of low-frequency detections are presented in a companion paper. Future plans include deeper searches to reach the full sensitivity and acceleration searches to target binary and millisecond pulsars. Our simulation analysis forecasts $\sim$300 new pulsars upon the completion of full processing. The SMART survey will also generate a complete digital record of the low-frequency sky, which will serve as a valuable reference for future pulsar searches planned with the low-frequency Square Kilometre Array.

We present the pulsar_spectra software repository, an open-source pulsar flux density catalogue and automated spectral fitting software that finds the best spectral model and produces publication-quality plots. The python-based software includes features that enable users in the astronomical community to add newly published spectral measurements to the catalogue as they become available. The spectral fitting software is an implementation of the method described in Jankowski et al. (2018, MNRAS, 473, 4436) which uses robust statistical methods to decide on the best-fitting model for individual pulsar spectra. pulsar_spectra is motivated by the need for a centralised repository for pulsar flux density measurements to make published measurements more accessible to the astronomical community and provide a suite of tools for measuring spectra.

The Murchison Widefield Array (MWA) is a low-frequency aperture array capable of high-time and frequency resolution astronomy applications such as pulsar studies. The large field-of-view of the MWA (hundreds of square degrees) can also be exploited to attain fast survey speeds for all-sky pulsar search applications, but to maximise sensitivity requires forming thousands of tied-array beams from each voltage-capture observation. The necessity of using calibration solutions that are separated from the target observation both temporally and spatially makes pulsar observations vulnerable to uncorrected, frequency-dependent positional offsets due to the ionosphere. These offsets may be large enough to move the source away from the centre of the tied-array beam, incurring sensitivity drops of ${\sim}30{-}50\%$ in Phase II extended array configuration. We analyse these offsets in pulsar observations and develop a method for mitigating them, improving both the source position accuracy and the sensitivity. This analysis prompted the development of a multi-pixel beamforming functionality that can generate dozens of tied-array beams simultaneously, which runs a factor of ten times faster compared to the original single-pixel version. This enhancement makes it feasible to observe multiple pulsars within the vast field of view of the MWA and supports the ongoing large-scale pulsar survey efforts with the MWA. We explore the extent to which ionospheric offset correction will be necessary for the MWA Phase III and the low-frequency square kilometre array (SKA-low).

A new high time resolution observing mode for the Murchison Widefield Array (MWA) is described, enabling full polarimetric observations with up to $30.72\,$ MHz of bandwidth and a time resolution of ${\sim}$ $0.8\,\upmu$ s. This mode makes use of a polyphase synthesis filter to ‘undo’ the polyphase analysis filter stage of the standard MWA’s Voltage Capture System observing mode. Sources of potential error in the reconstruction of the high time resolution data are identified and quantified, with the $S/N$ loss induced by the back-to-back system not exceeding $-0.65\,$ dB for typical noise-dominated samples. The system is further verified by observing three pulsars with known structure on microsecond timescales.

The Murchison Widefield Array (MWA) is an open access telescope dedicated to studying the low-frequency (80–300 MHz) southern sky. Since beginning operations in mid-2013, the MWA has opened a new observational window in the southern hemisphere enabling many science areas. The driving science objectives of the original design were to observe 21 cm radiation from the Epoch of Reionisation (EoR), explore the radio time domain, perform Galactic and extragalactic surveys, and monitor solar, heliospheric, and ionospheric phenomena. All together $60+$ programs recorded 20 000 h producing 146 papers to date. In 2016, the telescope underwent a major upgrade resulting in alternating compact and extended configurations. Other upgrades, including digital back-ends and a rapid-response triggering system, have been developed since the original array was commissioned. In this paper, we review the major results from the prior operation of the MWA and then discuss the new science paths enabled by the improved capabilities. We group these science opportunities by the four original science themes but also include ideas for directions outside these categories.

The Murchison Widefield Array is a low-frequency Square Kilometre Array precursor located at the Murchison Radio-astronomy Observatory in Western Australia. Primarily designed as an imaging telescope, but with a flexible signal path, the capabilities of this telescope have recently been extended to include off-line incoherent and tied-array beam formation using recorded antenna voltages. This has provided the capability for high-time and frequency resolution observations, including a pulsar science program. This paper describes the algorithms and pipeline that we have developed to form the tied-array beam products from the summation of calibrated signals of the antenna elements, and presents example polarimetric profiles for PSRs J0437-4715 and J1900-2600 at 185 MHz.

Polarimetric studies of pulsars at low radio frequencies provide important observational insights into the pulsar emission mechanism and beam models, and probe the properties of the magneto-ionic interstellar medium (ISM). Aperture arrays are the main form of next-generation low-frequency telescopes, including the Murchison Widefield Array (MWA). These require a distinctly different approach to data processing (e.g. calibration and beamforming) compared to traditional dish antennas. As the second paper of this series, we present a verification of the MWA’s pulsar polarimetry capability, using two bright southern pulsars, PSRs J0742–2822 and J1752–2806. Our observations simultaneously cover multiple frequencies (76–313 MHz) and were taken at multiple zenith angles (ZA) during a single night for each pulsar. We show that the MWA can be reliably calibrated for ZA ≲45° and frequencies ≲270 MHz. We present the polarimetric profiles for PSRs J0742–2822 and J1752–2806 at frequencies lower than 300 MHz for the first time, along with an analysis of the linear polarisation degree and pulse profile evolution with frequency. For PSR J0742–2822, the measured degree of linear polarisation shows a rapid decrease at low frequencies, in contrast with the generally expected trend, which can be attributed to depolarisation effects from small-scale, turbulent, magneto-ionic ISM components. This effect has not been widely explored for pulsars in general and will be further investigated in future work.

The Murchison Widefield Array, and its recently developed Voltage Capture System, facilitates extending the low-frequency range of pulsar observations at high-time and -frequency resolution in the Southern Hemisphere, providing further information about pulsars and the ISM. We present the results of an initial time-resolved census of known pulsars using the Murchison Widefield Array. To significantly reduce the processing load, we incoherently sum the detected powers from the 128 Murchison Widefield Array tiles, which yields ~10% of the attainable sensitivity of the coherent sum. This preserves the large field-of-view (~450 deg2 at 185 MHz), allowing multiple pulsars to be observed simultaneously. We developed a WIde-field Pulsar Pipeline that processes the data from each observation and automatically folds every known pulsar located within the beam. We have detected 50 pulsars to date, 6 of which are millisecond pulsars. This is consistent with our expectation, given the telescope sensitivity and the sky coverage of the processed data (~17 000 deg2). For 10 pulsars, we present the lowest frequency detections published. For a subset of the pulsars, we present multi-frequency pulse profiles by combining our data with published profiles from other telescopes. Since the Murchison Widefield Array is a low-frequency precursor to the Square Kilometre Array, we use our census results to forecast that a survey using the low-frequency component of the Square Kilometre Array Phase 1 can potentially detect around 9 400 pulsars.

Population studies show that greater red and processed meat consumption increases colorectal cancer risk, whereas dietary fibre is protective. In rats, resistant starches (a dietary fibre component) oppose colonocyte DNA strand breaks induced by high red meat diets, consistent with epidemiological data. Protection appears to be through SCFA, particularly butyrate, produced by large bowel carbohydrate fermentation. Arabinoxylans are important wheat fibre components and stimulate large bowel carbohydrate SCFA production. The present study aimed to determine whether an arabinoxylan-rich fraction (AXRF) from wheat protected colonocytes from DNA damage and changed colonic microbial composition in pigs fed with a diet high (30 %) in cooked red meat for 4 weeks. AXRF was primarily fermented in the caecum, as indicated by higher tissue and digesta weights and higher caecal (but not colonic) acetate, propionate and total SCFA concentrations. Protein fermentation product concentrations (caecal p-cresol and mid- and distal colonic phenol) were lower in pigs fed with AXRF. Colonocyte DNA damage was lower in pigs fed with AXRF. The microbial profiles of mid-colonic mucosa and adjacent digesta showed that bacteria affiliating with Prevotella spp. and Clostridial cluster IV were more abundant in both the mucosa and digesta fractions of pigs fed with AXRF. These data suggest that, although AXRF was primarily fermented in the caecum, DNA damage was reduced in the large bowel, occurring in conjunction with lower phenol concentrations and altered microbial populations. Further studies to determine the relationships between these changes and the lowering of colonocyte DNA damage are warranted.

This study was conducted to investigate effects of disodium fumarate (DF) on fermentation characteristics and microbial populations in the rumen of Hu sheep fed on high-forage diets. Two complementary feeding trials were conducted. In Trial 1, six Hu sheep fitted with ruminal cannulae were randomly allocated to a 2 × 2 cross-over design involving dietary treatments of either 0 or 20 g DF daily. Total DNA was extracted from the fluid- and solid-associated rumen microbes, respectively. Numbers of 16S rDNA gene copies associated with rumen methanogens and bacteria, and 18S rDNA gene copies associated with rumen protozoa and fungi were measured using real-time PCR, and expressed as proportion of total rumen bacteria 16S rDNA. Ruminal pH decreased in the DF group compared with the control (P < 0.05). Total volatile fatty acids increased (P < 0.001), but butyrate decreased (P < 0.01). Addition of DF inhibited the growth of methanogens, protozoa, fungi and Ruminococcus flavefaciens in fluid samples. Both Ruminococcus albus and Butyrivibrio fibrisolvens populations increased (P < 0.001) in particle-associated samples. Trial 2 was conducted to investigate the adaptive response of rumen microbes to DF. Three cannulated sheep were fed on basal diet for 2 weeks and continuously for 4 weeks with supplementation of DF at a level of 20 g/day. Ruminal samples were collected every week to analyze fermentation parameters and microbial populations. No effects of DF were observed on pH, acetate and butyrate (P > 0.05). Populations of methanogens and R. flavefaciens decreased in the fluid samples (P < 0.001), whereas addition of DF stimulated the population of solid-associated Fibrobacter succinogenes. Population of R. albus increased in the 2nd to 4th week in fluid-associated samples and was threefold higher in the 4th week than control week in solid samples. Analysis of denaturing gradient gel electrophoresis fingerprints revealed that there were significant changes in rumen microbiota after adding DF. Ten of 15 clone sequences from cut-out bands appearing in both the 2nd and the 4th week were 94% to 100% similar to Prevotella-like bacteria, and four sequences showed 95% to 98% similarity to Selenomonas dianae. Another 15 sequences were obtained from bands, which appeared in the 4th week only. Thirteen of these 15 sequences showed 95% to 99% similarity to Clostridium sp., and the other two showed 95% and 100% similarity to Ruminococcus sp. In summary, the microorganisms positively responding to DF addition were the cellulolytic bacteria, R. albus, F. succinogenes and B. fibrisolvens as well as proteolytic bacteria, B. fibrisolvens, P. ruminicola and Clostridium sp.

The methanol multi-beam (MMB) survey has produced the largest and most complete catalogue of Galactic 6.7-GHz methanol masers to date. 6.7-GHz methanol masers are exclusively associated with high-mass star formation, and as such provide invaluable insight into the Galactic distribution and properties of high-mass star formation regions. I present the statistical properties of the MMB catalogue and, through the calculation of kinematic distances, investigate the resolution of distance ambiguities and explore the Galactic distribution.

Four swamp buffaloes (Bubalus bubalis) and four crossbred Bos indicus x B. taurus cattle, fistulated at the rumen and abomasum or duodenum, were offered rice straw with mineral supplements in two experiments. In Expt 1, the straw was supplemented with 5% of leaf of Leucaena leucocephala, and in Expt 2 with either urea or urea with sunflower meal and rice grain. Intake of supplements of urea or urea/sunflower/rice respectively was 935 and 681 g/kg offered in buffaloes and 566 and 789 in cattle.

Buffaloes ruminated longer than cattle (Expt 1, 635 v. 452 min/day; Expt 2, 626 v. 466 min/day, P < 0·01). In Expt 1, voluntary intake and frequency of ‘A’ sequence forestomach contractions of both species was not affected by species, but buffaloes had a greater (P < 0·05) contraction force in the rumen and omasum, lower rate of ‘B’ sequence rumen contractions, and faster (P < 0·001) rate of gastrointestinal passage than cattle. In Expt 2, voluntary intake of both species was similar, and addition of concentrates did not affect voluntary roughage consumption, nor in situ rate of digestion of rice straw. Rate and predicted extent of digestion of dietary materials did not differ between species in Expt 1, despite lower concentrations of ammonia in rumen fluid in cattle than buffaloes; however in Expt 2, the rate of digestion of rice straw was higher (p < 0·05) and predicted extent of digestion was 14–20% (P < 0·05) lower in buffaloes. Digestibility of cell wall constituents was lower (P < 0·05) in buffaloes than in cattle in both experiments, but in Expt 2, provision of concentrates reduced (P < 0·01) the proportion of digestible cell wall constituents digested in the forestomach of buffaloes, but not of cattle.

The results of the first complete survey for 6668-MHz CH3OH and 6035-MHz excited-state OH masers in the Small and Large Magellanic Clouds are presented. A new 6668-MHz CH3OH maser in the Large Magellanic Cloud has been detected towards the star-forming region N 160a, together with a new 6035-MHz excited-state OH maser detected towards N 157a. We also re-observed the previously known 6668-MHz CH3OH masers and the single known 6035-MHz OH maser. Neither maser transition was detected above ~0.13 Jy in the Small Magellanic Cloud. All observations were initially made using the CH3OH Multibeam (MMB) survey receiver on the 64-m Parkes radio telescope as part of the overall MMB project. Accurate positions were measured with the Australia Telescope Compact Array (ATCA). In a comparison of the star formation maser populations in the Magellanic Clouds and our Galaxy, the LMC maser populations are demonstrated to be smaller than their Milky Way counterparts. CH3OH masers are under-abundant by a factor of ~50, whilst OH and H2O masers are a factor of ~10 less abundant than our Galaxy.

A new 7-beam methanol multibeam receiver is being used to survey the Galaxy for newly forming massive stars, that are pinpointed by strong methanol maser emission at 6.668 GHz. The receiver, jointly constructed by Jodrell Bank Observatory (JBO) and the Australia Telescope National Facility (ATNF), was successfully commissioned at Parkes in January 2006. The Parkes-Jodrell survey of the Milky Way for methanol masers is two orders of magnitude faster than previous systematic surveys using 30-m class dishes, and is the first systematic survey of the entire Galactic plane. The first 53 days of observations with the Parkes telescope have yielded 518 methanol sources, of which 218 are new discoveries. We present the survey methodology as well as preliminary results and analysis.

A new 7-beam methanol multibeam receiver was successfully commissioned at Parkes Observatory in January 2006, and has begun surveying the Milky Way for newly forming massive stars, that are pinpointed by strong methanol maser emission at 6.7 GHz. The receiver was jointly constructed by Jodrell Bank Observatory and the Australia Telescope National Facility for use on the Parkes and Lovell Telescopes. The whole galactic plane is being surveyed within latitudes ±2°, with a velocity resolution of 0.1 km s−1 and a 5-σ sensitivity of ~0.7 Jy. Altogether 200 days of observing will be required.