We detect and characterise extended, diffuse radio emission from galaxy clusters at 168 MHz within the Epoch of Reionization 0-h field: a $45^{\circ} \times 45^{\circ}$ region of the southern sky centred on R. A.${}= 0^{\circ}$, decl.${}=-27^{\circ}$. We detect 29 sources of interest; a newly detected halo in Abell 0141; a newly detected relic in Abell 2751; 4 new halo candidates and a further 4 new relic candidates; and a new phoenix candidate in Abell 2556. Additionally, we find nine clusters with unclassifiable, diffuse steep-spectrum emission as well as a candidate double relic system associated with RXC J2351.0-1934. We present measured source properties such as their integrated flux densities, spectral indices ($\alpha$, where $S_\nu \propto \nu^\alpha$), and sizes where possible. We find several of the diffuse sources to have ultra-steep spectra including the halo in Abell 0141, if confirmed, showing $\alpha \leq -2.1 \pm 0.1$ with the present data making it one of the steepest-spectrum haloes known. Finally, we compare our sample of haloes with previously detected haloes and revisit established scaling relations of the radio halo power ($P_{1.4}$) with the cluster X-ray luminosity ($L_{\textrm{X}}$) and mass ($M_{500}$). We find that the newly detected haloes and candidate haloes are consistent with the $P_{1.4}$–$L_{\textrm{X}}$ and $P_{1.4}$–$M_{500}$ relations and see an increase in scatter in the previously found relations with increasing sample size likely caused by inhomogeneous determination of $P_{1.4}$ across the full halo sample. We show that the MWA is capable of detecting haloes and relics within most of the galaxy clusters within the Planck catalogue of Sunyaev–Zel’dovich sources depending on exact halo or relic properties.

We present the results of our extensive binary orbital motion corrected pulsation search for 13 low-mass X-ray binaries. These selected sources exhibit burst oscillations in X-rays with frequencies ranging from 45 to 1 122 Hz and have a binary orbital period varying from 2.1 to 18.9 h. We first determined episodes that contain weak pulsations around the burst oscillation frequency by searching all archival Rossi X-ray Timing Explorer data of these sources. Then, we applied Doppler corrections to these pulsation episodes to discard the smearing effect of the binary orbital motion and searched for recovered pulsations at the second stage. Here we report 75 pulsation episodes that contain weak but coherent pulsations around the burst oscillation frequency. Furthermore, we report eight new episodes that show relatively strong pulsations in the binary orbital motion corrected data.

In this paper, we describe the system design and capabilities of the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope at the conclusion of its construction project and commencement of science operations. ASKAP is one of the first radio telescopes to deploy phased array feed (PAF) technology on a large scale, giving it an instantaneous field of view that covers $31\,\textrm{deg}^{2}$ at $800\,\textrm{MHz}$. As a two-dimensional array of 36$\times$12 m antennas, with baselines ranging from 22 m to 6 km, ASKAP also has excellent snapshot imaging capability and 10 arcsec resolution. This, combined with 288 MHz of instantaneous bandwidth and a unique third axis of rotation on each antenna, gives ASKAP the capability to create high dynamic range images of large sky areas very quickly. It is an excellent telescope for surveys between 700 and $1800\,\textrm{MHz}$ and is expected to facilitate great advances in our understanding of galaxy formation, cosmology, and radio transients while opening new parameter space for discovery of the unknown.

The remnant phase of a radio galaxy begins when the jets launched from an active galactic nucleus are switched off. To study the fraction of radio galaxies in a remnant phase, we take advantage of a $8.31$ deg$^2$ subregion of the GAMA 23 field which comprises of surveys covering the frequency range 0.1–9 GHz. We present a sample of 104 radio galaxies compiled from observations conducted by the Murchison Widefield Array (216 MHz), the Australia Square Kilometer Array Pathfinder (887 MHz), and the Australia Telescope Compact Array (5.5 GHz). We adopt an ‘absent radio core’ criterion to identify 10 radio galaxies showing no evidence for an active nucleus. We classify these as new candidate remnant radio galaxies. Seven of these objects still display compact emitting regions within the lobes at 5.5 GHz; at this frequency the emission is short-lived, implying a recent jet switch off. On the other hand, only three show evidence of aged lobe plasma by the presence of an ultra-steep-spectrum ($\alpha<-1.2$) and a diffuse, low surface brightness radio morphology. The predominant fraction of young remnants is consistent with a rapid fading during the remnant phase. Within our sample of radio galaxies, our observations constrain the remnant fraction to $4\%\lesssim f_{\mathrm{rem}} \lesssim 10\%$; the lower limit comes from the limiting case in which all remnant candidates with hotspots are simply active radio galaxies with faint, undetected radio cores. Finally, we model the synchrotron spectrum arising from a hotspot to show they can persist for 5–10 Myr at 5.5 GHz after the jets switch of—radio emission arising from such hotspots can therefore be expected in an appreciable fraction of genuine remnants.

In Einstein’s special theory of relativity, all observers measure the speed of light, c, to be the same. However, this refers to the round-trip speed, where a clock at the origin times the outward and return trip of light reflecting off a distant mirror. Measuring the one-way speed of light is fraught with issues of clock synchronisation, and, as long as the average speed of light remains c, the speeds on the outward and return legs could be different. One objection to this anisotropic speed of light is that views of the distant universe would be different in different directions, especially with regard to the ages of observed objects and the smoothness of the Cosmic Microwave Background. In this paper, we explore this in the Milne universe, the limiting case of a Friedmann–Robertson–Walker universe containing no matter, radiation, or dark energy. Given that this universe is empty, it can be mapped onto flat Minkowski space-time and so can be explored in terms of the one-way speed of light. The conclusion is that the presence of an anisotropic speed of light leads to anisotropic time dilation effects, and hence observers in the Milne universe would be presented with an isotropic view of the distant cosmos.

One of the basic parameters of a charge coupled device (CCD) camera is its gain, that is, the number of detected electrons per output Analogue to Digital Unit (ADU). This is normally determined by finding the statistical variances from a series of flat-field exposures with nearly constant levels over substantial areas, and making use of the fact that photon (Poisson) noise has variance equal to the mean. However, when a CCD has been installed in a spectroscopic instrument fed by numerous optical fibres, or with an echelle format, it is no longer possible to obtain illumination that is constant over large areas. Instead of making do with selected small areas, it is shown here that the wide variation of signal level in a spectroscopic ‘flat-field’ can be used to obtain accurate values of the CCD gain, needing only a matched pair of exposures (that differ in their realisation of the noise). Once the gain is known, the CCD readout noise (in electrons) is easily found from a pair of bias frames. Spatial stability of the image in the two flat-fields is important, although correction of minor shifts is shown to be possible, at the expense of further analysis.

The past few decades have seen the burgeoning of wide-field, high-cadence surveys, the most formidable of which will be the Legacy Survey of Space and Time (LSST) to be conducted by the Vera C. Rubin Observatory. So new is the field of systematic time-domain survey astronomy; however, that major scientific insights will continue to be obtained using smaller, more flexible systems than the LSST. One such example is the Gravitational-wave Optical Transient Observer (GOTO) whose primary science objective is the optical follow-up of gravitational wave events. The amount and rate of data production by GOTO and other wide-area, high-cadence surveys presents a significant challenge to data processing pipelines which need to operate in near-real time to fully exploit the time domain. In this study, we adapt the Rubin Observatory LSST Science Pipelines to process GOTO data, thereby exploring the feasibility of using this ‘off-the-shelf’ pipeline to process data from other wide-area, high-cadence surveys. In this paper, we describe how we use the LSST Science Pipelines to process raw GOTO frames to ultimately produce calibrated coadded images and photometric source catalogues. After comparing the measured astrometry and photometry to those of matched sources from PanSTARRS DR1, we find that measured source positions are typically accurate to subpixel levels, and that measured L-band photometries are accurate to $\sim50$ mmag at $m_L\sim16$ and $\sim200$ mmag at $m_L\sim18$. These values compare favourably to those obtained using GOTO’s primary, in-house pipeline, gotophoto, in spite of both pipelines having undergone further development and improvement beyond the implementations used in this study. Finally, we release a generic ‘obs package’ that others can build upon, should they wish to use the LSST Science Pipelines to process data from other facilities.

We present a radio and X-ray analysis of the galaxy cluster SPT-CL J2032–5627. Investigation of public data from the Australian Square Kilometre Array Pathfinder (ASKAP) at 943 MHz shows two previously undetected radio relics at either side of the cluster. For both relic sources, we utilise archival Australia Telescope Compact Array (ATCA) data at 5.5 GHz in conjunction with the new ASKAP data to determine that both have steep integrated radio spectra ( $\ensuremath{{\alpha_\mathrm{SE} = -1.52 \pm 0.10}}$ and $\ensuremath{{\alpha_\mathrm{NW,full} = -1.18 \pm 0.10}}$ for the southeast and northwest relic sources, respectively). No shock is seen in XMM-Newton observations; however, the southeast relic is preceded by a cold front in the X-ray–emitting intra-cluster medium. We suggest the lack of a detectable shock may be due to instrumental limitations, comparing the situation to the southeast relic in Abell 3667. We compare the relics to the population of double relic sources and find that they are located below the current power–mass scaling relation. We present an analysis of the low-surface brightness sensitivity of ASKAP and the ATCA, the excellent sensitivity of both allow the ability to find heretofore undetected diffuse sources, suggesting these low-power radio relics will become more prevalent in upcoming large-area radio surveys such as the Evolutionary Map of the Universe.

We have found a class of circular radio objects in the Evolutionary Map of the Universe Pilot Survey, using the Australian Square Kilometre Array Pathfinder telescope. The objects appear in radio images as circular edge-brightened discs, about one arcmin diameter, that are unlike other objects previously reported in the literature. We explore several possible mechanisms that might cause these objects, but none seems to be a compelling explanation.

Precise measurement of the fundamental parameters of stellar systems, including mass and radius, depends critically on how well the stellar distances are known. Astrometry from space provides parallax measurements of unprecented accuracy, from which distances can be derived, initially from the Hipparcos mission, with a further refinement of that analysis provided by van Leeuwen in 2007. The publication of the Gaia DR2 catalogue promises a dramatic improvement in the available data. We have recalculated the dynamical masses of a sample of 1 700 close visual binary stars using Gaia DR2 and compared the results with masses derived from both the original and enhanced Hipparcos data. We show the van Leeuwen analysis yields results close to those of Gaia DR2, but the latter are significantly more accurate. We consider the impact of the Gaia DR2 parallaxes on our understanding of the sample of visual binaries.

We have realised a simple prototype system to perform searches for short timescale optical transients, utilising the novel drift scan imaging technique described by Tingay (2020). We used two coordinated and aligned cameras, with an overlap field of view of approximately 3.7 deg$^2$, to capture over $34\,000 \times 5$ second images during approximately 24 h of observing. The system is sensitive to optical transients, due to an effective exposure time per pixel of 21 ms, brighter than a V magnitude of 6.6. In our 89.7 deg$^2$ h of observations, we find no candidate astronomical transients, giving an upper limit to the rate of these transients of 0.8 per deg$^2$ per day, competitive with other experiments of this type. The system is triggered by reflections from satellites and various instrumental effects, which are easily identifiable due to the two camera system. The next step in the development of this promising technique is to move to a system with larger apertures and wider fields of view.

The Galactic TeV ${\gamma}$ -ray source ${\mathrm{HESS\,J}1804{-}216}$ is currently an unidentified source. In an attempt to unveil its origin, we present here the most detailed study of interstellar gas using data from the Mopra Southern Galactic Plane CO Survey, 7- and 12-mm wavelength Mopra surveys and Southern Galactic Plane Survey of HI. Several components of atomic and molecular gas are found to overlap ${\mathrm{HESS\,J}1804{-}216}$ at various velocities along the line of sight. The CS(1-0) emission clumps confirm the presence of dense gas. Both correlation and anti-correlation between the gas and TeV ${\gamma}$ -ray emission have been identified in various gas tracers, enabling several origin scenarios for the TeV ${\gamma}$ -ray emission from ${\mathrm{HESS\,J}1804{-}216}$ . For a hadronic scenario, ${\mathrm{SNR\,G}8.7{-}0.1}$ and the progenitor supernova remnant (SNR) of ${\mathrm{PSR\,J}1803{-}2137}$ require cosmic ray (CR) enhancement factors of ${\mathord{\sim} 50}$ times the solar neighbour CR flux value to produce the TeV ${\gamma}$ -ray emission. Assuming an isotropic diffusion model, CRs from both these SNRs require a slow diffusion coefficient, as found for other TeV SNRs associated with adjacent ISM gas. The morphology of gas located at 3.8 kpc (the dispersion measure distance to ${\mathrm{PSR\,J}1803{-}2137}$ ) tends to anti-correlate with features of the TeV emission from ${\mathrm{HESS\,J}1804{-}216}$ , making the leptonic scenario possible. Both pure hadronic and pure leptonic scenarios thus remain plausible.

The diatomic free radical methylidyne (CH) is an important tracer of the interstellar medium, and the study of it was critical to our earliest understanding of star formation. Although it is detectable across the electromagnetic spectrum, observations at radio frequencies allow for a study of the kinematics of the diffuse and dense gas in regions of new star formation. There is only two published (single-dish) detections of the low-frequency hyperfine transitions between 700 and 725 MHz, despite the precise frequencies being known. These low-frequency transitions are of particular interest as they are shown in laboratory experiments to be more sensitive to magnetic fields than their high-frequency counterparts (with more pronounced Zeeman splitting). In this work, we take advantage of the radio quiet environment and increased resolution of the Australian Square Kilometre Array Pathfinder (ASKAP) over previous searches to make a pilot interferometric search for CH at 724.7883 MHz (the strongest of the hyperfine transitions) in RCW 38. We found the band is clean of radio frequency interference, but we did not detect the signal from this transition to a five-sigma sensitivity limit of 0.09 Jy, which corresponds to a total column density upper limit of 1.9 $\times 10^{18}$ cm–2 for emission and 1.3 $\times 10^{14}$ cm–2 for absorption with an optical depth limit of 0.95. Achieved within 5 h of integration, this column density sensitivity should have been adequate to detect the emission or absorption in RCW 38, if it had similar properties to the only previous reported detections in W51.