We present the longest-term optical analysis of the AM CVn system KL Dra using ∼ 11 years of monitoring from TESS and wide-field ground-based surveys. The continuous TESS coverage allows us to characterise its frequent outbursts with unprecedented detail, providing the first comprehensive study of an AM CVn during outbursts and enabling detailed modelling of these systems. The superoutbursts in KL Dra generally include a precursor, and are followed by a series of rebrightenings after which a sequence of 3-4 large amplitude normal outbursts is observed. We fit parametric profiles to each superoutburst component (precursor, rise to plateau, plateau, decay), to rebrightenings, and to normal outbursts, which let us quantify every high state feature and investigate correlations with the system’s long term supercyle evolution. Our continuous coverage reveals an average value for the supercycles, superoutbursts and normal outbursts of 60.4 ± 0.1 d, 5.67 ± 0.03 d and 1.17 ± 0.01 d, respectively. The supercycle duration may be correlated with the rebrightenings duration and superoutburst amplitude, and anticorrelated with the plateau length. Within a supercycle, normal outbursts grow in amplitude and duration, and the first normal outburst is usually highly asymmetric, while subsequent normal outbursts are more symmetric. We detected superhumps in TESS superoutbursts but not in the rebrightenings or normal outbursts. We interpret the results within the disc instability model, considering additional effects, such as changes in the donor mass transfer rate.

It has been proposed that radio pulsars can be distinguished from other point-like radio sources in continuum images by their unique interstellar scintillation signatures. Using data from the Australian Square Kilometre Array Pathfinder (ASKAP) Evolutionary Map of the Universe (EMU) survey, we conducted a pilot survey of radio pulsars at high Galactic latitude regions via the variance imaging method. Out of approximately 59,800 compact radio sources detected in a ∼480 square degree survey area, we identified 21 highly variable sources. Among them, 10 are known pulsars, 2 are known radio stars, 1 is a long period transient, 3 are radio star candidates, and the remaining 5 are pulsar candidates. Notably, we discovered two strongly scintillating pulsars: one with a period of 85.707 ms and a dispersion measure (DM) of 19.4 cm–3 pc, and another with a period of 5.492 ms and a DM of 29.5 cm–3 pc. In addition, a third pulsar was discovered in the variance images, with a period of 14.828 ms and a DM of 39.0 cm–3 pc. This source shows a steep radio spectrum and a high degree of circular polarisation. These results underscore the strong potential of variance imaging for pulsar detection in full EMU and future radio continuum surveys planned with Square Kilometre Array (SKA).

Identifying remnant radio-loud active galactic nuclei (AGNs) is challenging due to their diverse morphological and spectral characteristics. Using three-dimensional hydrodynamic simulations of 15 radio galaxies, we investigate how the spectral evolution of remnants depends on progenitor power, active lifetime, environment, and underlying dynamics. The simulations span low-density group and high-density cluster environments re-gridded from smooth-particle-hydrodynamic cosmological simulations. The resulting remnants exhibit a wide range of morphologies, from amorphous structures to double-lobed forms. We find that jet power correlates with the spectral slope. As the remnant lobes evolve, we find surface brightness depends strongly on environment: group remnants are systematically dimmer and more amorphous than cluster remnants, highlighting a potential observational bias against these low-surface-brightness sources. In our models, we estimate that the peak surface brightness of a low-redshift, 50 Myr-old remnant from a low-power progenitor in a 1013 M⊙ group environment should be routinely detectable at the 3σ level with LOFAR, although 20–30% of the emission would remain undetectable within a reasonable integration time. We find young remnants exhibit low-frequency (150–1400 MHz) spectral indices that overlap with active sources, and follow a consistent and established spectral-evolution sequence: significant curvature develops before an ultra-steep low-frequency index . The results presented in this work are intended as a reference point for current and upcoming low-frequency studies of radio remnants.

Although the spin parameter of dark matter halos is well known to follow a log-normal distribution at fixed epoch, its quantitative redshift evolution - encompassing both the mean and the dispersion - remains only partially explored. Prior studies either lack the mass resolution required to establish reliable evolutionary trends or do not provide analytical relations that enable forward modelling. Using a suite of ΛCDM N-body simulations with controlled resolution across the redshift range 0 ≤ z ≤ 5, we characterise the evolution of the mean and dispersion of the Peebles (λ) and Bullock (λ′) definitions of spin. We find a mild but statistically robust linear evolution for ln λ and a non-monotonic trend with a turnover at z ≈ 1 – 2 for ln λ′, which we verify are unaffected by mass resolution of choice of halo definition. We provide closed-form fitting functions for these trends that allow modellers to draw physically motivated spin values at any redshift within our range of validity. This is a practical, redshift-dependent alternative to the common assumption of a constant spin distribution, and provides a useful input to semi-empirical and semi-analytic models of galaxy formation.

A subset of magnetic stars exhibit periodic radio pulses produced by the coherent electron cyclotron maser mechanism. These pulses are known to exhibit both temporal and spectral variations, which have been attributed to phenomena intrinsic to the stellar magnetosphere. However, in order to fully characterise the radio pulses and use them as magnetospheric probes (as suggested by past studies), it is also important to consider the effects of phenomena extrinsic to the magnetosphere. In this paper, we investigate whether interstellar scintillation could be a relevant mechanism for explaining spectral and temporal variations observed for coherent stellar radio emission. For that, we consider the case of the well-characterised magnetic hot star CUVir. At 400 MHz, coherent radio emission from the star was reported to exhibit a peculiar spectral evolution that remains unexplained. We show that a plausible level of turbulence along the line of sight can produce the observed phenomenon of spectral features. Our analysis shows that diffractive interstellar scintillation can have a strong effect on the observed dynamic spectrum of radio emission from stars, for an assumed size of the emitting region of 0.01r⊙, and that caution should therefore be taken in separating intrinsic and extrinsic features, particularly at low frequencies. These results are preliminary and further work is required to fully model the scintillation of ECME from stars (in particular the change in source location with frequency), and to explore the full range of plausible scintillation parameters. We suggest how further observations may be used to test the interstellar scintillation hypothesis.

The James Webb Space Telescope (JWST) hosts a non-redundant Aperture Masking Interferometer (AMI) in its Near Infrared Imager and Slitless Spectrograph (NIRISS) instrument, providing the only dedicated interferometric facility aboard — magnitudes more precise than any interferometric experiment previously flown. However, the performance of AMI (and other high resolution approaches such as kernel phase) in recovery of structure at high contrasts has not met design expectations. A major contributing factor has been the presence of uncorrected detector systematics, notably charge migration effects in the H2RG sensor, and insufficiently accurate mask metrology. Here we present AMIGO, a data-driven calibration framework and analysis pipeline that forward-models the full JWST AMI system — including its optics, detector physics, and readout electronics — using an end-to-end differentiable architecture implemented in the JAX framework and in particular exploiting the ∂LUX optical modelling package. AMIGO directly models the generation of up-the-ramp detector reads, using an embedded neural sub-module to capture non-linear charge redistribution effects, enabling the optimal extraction of robust observables, for example kernel amplitudes and phases, while mitigating systematics such as the brighter-fatter effect. We demonstrate AMIGO’s capabilities by recovering the AB Dor AC binary from commissioning data with high-precision astrometry, and detecting both HD 206893 B and the inner substellar companion HD 206893 c: a benchmark requiring contrasts approaching 10 magnitudes at separations of only 100mas. These results exceed outcomes from all published pipelines, and re-establish AMI as a viable competitor for imaging at high contrast at the diffraction limit. AMIGO is publicly available as open-source software community resource.

We report the design and functionality of the Murchison Widefield Array Particle Detector Array (MWA PDA), an array of eight particle scintillation detectors deployed to Inyarrimanha Ilgari Bundara, the Murchison Radio-astronomy Observatory (MRO). The purpose of the instrument is to identify cosmic ray extensive air showers (EAS) occurring over the core of the MWA radio telescope, and generate a trigger to allow radio data on the event to be captured and analysed. The system also acts as a pathfinder for a much larger instrument to be deployed in the core of the low-frequency component of the Square Kilometre Array, SKA-Low, by the SKA’s ultra-high-energy particles science working group. Here, we describe the instrument and associated infrastructure, which has been verified to comply with the strict radio-frequency emissions requirements of the MRO, and was deployed in November 2024. We present calibration data, which demonstrates the ability of each detector to identify individual atmospheric muons at the expected rate, and we characterise the temperature dependence of the system. We describe a sample of 35,500 EAS identified using multi-detector coincidence over a 13-day period, and show how the detector data can be used to reconstruct the arrival directions and approximate energies of these events. We conclude that the PDA can reliably trigger on and reconstruct EAS contained within the ∼ 103 × 90m2 core region, arriving within 20° of zenith, at primary cosmic ray energies above ∼ 4PeV. We have also verified that the detector array can generate triggers, allowing the capture of radio data from the MWA correlator for offline analysis.

We present the discovery of two intersecting radio shells, likely radio relics, surrounding a compact galaxy group dominated by a massive elliptical galaxy. The shells present as partial, edge-brightened rings with diameters of ∼240′′ (∼720 kpc) each and resemble a pair of odd radio circles. The central galaxy, WISEA J184105.19–654753.8, which shows signs of interactions, is radio bright, has a stellar mass of 3.1×1011 M⊙ (for a redshift of zphot ∼ 0.18) and is located in the intersect region. The double radio shell system, which we refer to as ORC J1841–6547, also known as ORC 6, was detected in 944 MHz radio continuum images obtained with Phased Array Feeds on the Australian Square Kilometre Array Pathfinder (ASKAP). The more prominent, north-western shell may be associated with an X-ray detection, while the weaker, south-eastern shell has no counterpart at non-radio wavelength. We propose outwards moving shocks from galaxy mergers driving into the intragroup medium, re-energising relic radio lobes, as a possible formation scenario for the observed radio shells. We conclude that at least some ORCs are shock-energised relics in the outskirts of galaxy groups, which originate during the merger evolution of the brightest group galaxy.

We present the characterisation, including a photometric redshift (photo-z) analysis, of the optical counterparts (CTPs) to over 45 000 bright (S856 MHz ≥ 30 mJy) compact radio sources, identified across all ASKAP First Large Absorption Survey in Hi (FLASH) fields observed up to April 2025. These sources constitute a large, homogeneous population of background continuum sightlines specifically selected to enable statistical studies of cold gas at intermediate redshifts of 0.42 ≤ z ≤ 1. As spectroscopic redshift measurements are not available for the majority of these candidate absorbers, we estimate photo-zs for the CTPs of all FLASH continuum sources cross-matched to the tenth data release of the DESI Legacy Imaging Surveys (LS10). Using these estimates, we establish the redshift distribution and find that approximately 13% of continuum sources lie at z < 0.42 (foreground), 35% within the detectability range of FLASH (‘in-band’), and 52% at z > 1 (background). We examine the subset of FLASH continuum sources with CTPs in the eROSITA X-ray survey, providing additional insight into their AGN content, multiwavelength properties, and environments. Finally, we discuss how this information can be used as a statistical prior to aid in distinguishing between associated and intervening Hi absorption systems and estimating the total comoving absorption path length of the survey, establishing a framework for incorporating redshift-based priors in future large radio absorption surveys. We release a catalogue of LS10 counterparts to FLASH continuum sources, providing photo-z estimates, associated uncertainties, and measures of redshift degeneracies.

Post-red and post-asymptotic giant stars in binary systems with main sequence companions, have periods in the range ∼50-2000 days, eccentricities as high as 0.6 and are surrounded by a circumbinary disc. Their orbital separations are small enough that the system must have gone through Roche lobe overflow when the primary was a full blown giant; Roche lobe overflow between a giant and a more compact companion tend to lead to a common envelope inspiral, leaving a circular orbit with periods much shorter than observed in these systems. In this first work in a series we explore to what extent a high mass ratio, q ≡ M2/M1, can lead to wider orbital separations, by carrying out a series of 3D, hydrodynamical CE binary interaction simulations with the smoothed particle hydrodynamics code PHANTOM. The giant is a 0.88 M⊙, 90 R⊙, red giant branch star and the companions have a range of masses such that q = 0.68 − 1.5. While larger q values result in wider post-CE separations, the upper limit we predict is only ∼ 50 R⊙, smaller than the observed range. The pre-CE mass transfer phase is longer for larger companion masses and around q ≳ 1 the nature of the CE inspiral changes significantly, showing greater stability, as predicted by analytical theory. However, this phase is not converged with respect to simulation resolution and it is expected that a higher resolution would lead to even more stability and a longer pre-inspiral phase. Despite more material flowing through the L2 and L3 Lagrange points for higher q values, with the potential for the formation of a circumbinary disc structure in this way, we conclude that, for our parameters, circumbinary discs are more likely to form from fall back of leftover bound envelope. Fall-back times are short (a few × 100 years) and fall-back discs extend between 0.5 and 5 au (outside the binary orbit), at which point the discs are likely to spread farther on short timescales via viscous torques. These discs have characteristics in line with those observed.

Following long periods of quiescence, low-mass X-ray binaries can exhibit intense X-ray outbursts triggered by instabilities within the accretion disk. These outbursts can sometimes be detected in optical wavelengths before being detected in X-ray, acting as an early onset warning and enabling a deep study of accretion disk properties informed by the lag between optical and X-ray rise. We explore the potential of Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST) to detect these outbursts early through optical observations. We evaluate the capabilities of LSST based on currently planned survey cadence, filter-specific depth, and other observational factors that affect early detection. We develop and apply an extended metric to assess outburst detectability and recovery fraction. We find that despite inherent potential for early detection of XRB outbursts, the currently planned survey strategy makes it challenging to detect early onset of XRBs. Lastly, we demonstrate how this estimate can be used to infer the wider LMXB population in the Galaxy as the LSST progresses.

The increasing field of view of radio telescopes and improved data processing capabilities have led to a surge in the detection of Fast Radio Bursts (FRBs). The discovery rate of FRBs is already a few per day and is expected to increase rapidly with new surveys coming online. The growing number of events necessitates prioritized follow-up due to limited multi-wavelength resources, requiring rapid and automated classification. In this study, we introduce Frabjous, a deep learning framework for an automated morphology classifier with an aim towards enabling the prompt follow-up of anomalous and intriguing FRBs, and a comprehensive statistical analysis of FRB morphologies. Deep learning models require a large training set of each FRB archetype, however, publicly available data lacks sufficient samples for most FRB types. In this paper, we build a simulation framework for generating realistic examples of FRBs and train a network based on a combination of simulated and real data starting with the CHIME/FRB catalog. Applying our framework to the first CHIME/FRB catalog, we achieve an overall classification accuracy of approximately 55%, well over a random multiclass classification rate of 20% with five balanced classes during training. While this falls short of desirable performance, we critically discuss the limitations of our approach and propose potential avenues for improvement. Future work should explore strategies to augment training datasets and broaden the scope of FRB morphological studies, aiming for more accurate and reliable classification results.

The discovery of the galaxy ring known as the Council of Giants (CoG) highlights the need to explain such structures in the Local Universe. In the first paper of this series, we presented HINORA – a code to locate (ring-like) structures in 3D point sets – and used it to identify the CoG in the most complete observations of the Local Volume. Here, in Part II, we apply the same method to cosmological simulations to quantify the possible existence of such objects in the $\rm \Lambda$CDM model of structure formation. We analyse DM-only simulations with random and constrained initial conditions, selecting regions that reproduce the properties of the Local Group and Volume, respectively. In order to use the same selection criteria as previously done for observations, we relate K-band luminosities to halo masses through semi-empirical relations. After confirming that the selected regions from the simulations match the observed mass function and density of the Local Universe, we use HINORA to search for ring-like structures in them. We find that the existence of CoGs in $\rm \Lambda$CDM simulations is a rather unusual phenomenon. The observed CoG represents an anomaly of more than 2.7$\sigma$ from what is expected in the distribution of massive galaxies in $\rm \Lambda$CDM. These results hint that the CoG could either be a rare chance configuration or the imprint of physical processes at intermediate scales that standard DM-only simulations fail to capture.

Eccentric millisecond pulsar + helium white dwarf (MSP + He WD) systems have attracted increasing attention, with the rotationally delayed accretion-induced collapse (RD-AIC) scenario proposed as a possible formation channel. Given the similarity between the formation channels of He WDs and subdwarf B (sdB) stars, eccentric MSP + sdB binaries could also exist in the Galaxy, though none have been detected so far. Theoretical predictions of their properties would greatly aid in their discovery. Here, within the RD-AIC framework, I present predictions for their orbital parameters, including MSP mass, secondary mass, eccentricity, and orbital period. Based on two detailed binary population synthesis calculations, I estimate their Galactic birth rate to be $(0.67$–$1.5)\times10^\mathrm{-4}\mathrm{yr^\mathrm{-1}}$. Then, a very conservative upper limit for their total number in the Galaxy is 15 000, implying that the most optimistic fraction of eccentric MSP + sdB systems among all MSP + sdB populations could reach up to 55%. These systems are relatively young, with ages on the order of a few hundred Myr, and should therefore be found in relatively young environments. Furthermore, most MSPs in such eccentric binaries have masses below 1.5 M$_{\odot}$. I also briefly discuss their potential future applications in various astrophysical contexts.

The rest-frame ultraviolet (UV) spectra of star-forming galaxies are increasingly important as they become one of the primary windows to probe the physical properties of cosmic dawn (z > 8) galaxies with the JamesWebb Space Telescope. However, the systematic discrepancies between UV and optical gas-phase metallicity measurements remain poorly understood in the local universe, partly due to challenges in achieving precise comparisons between UV and optical spectra for the same objects. In this work, we introduce a novel method that leverages the He ii λ1640 and He ii λ4686 nebular emission lines to achieve accurate aperture and reddening corrections between UV and optical spectra. Here we apply this method to three nearby Blue Compact Dwarf (BCD) galaxies. Our results demonstrate that this approach enables precise measurements, with electron temperatures (Te) derived from UV and optical spectra exhibiting closer agreement compared to previous studies, and O/H abundance agreeing within 0.1 dex. However, two BCDs appear to have lower UV-based electron temperatures Te 1666 < Te 4363, in contrast to expectations from the temperature fluctuation model. We consider a variety of possible explanations for these unphysical temperatures – differential dust attenuation, aperture differences, and spatial extent of emission lines – but no suitable cause is identified. These findings suggest a complex gaseous environment associated with star formation, and underscore the need for additional observations to further investigate the nature of He ii nebular emission and address the systematic issues between UV and optical nebular properties. Nonetheless, the close empirical agreement of these results indicates that UV- and optical-based nebular temperature and abundance measurements can be reliably compared within 0.1 dex, providing a solid foundation for evolutionary studies from the local Universe to cosmic dawn.

We report the discovery of an intervening 21 cm absorption line at z = 0.882 towards the z = 1.284 quasar PKS 0405–385, identified in the First Large Absorption Survey in H i (FLASH). This quasar once displayed the most rapid known intraday variability at radio frequencies, from which it earned the title of ‘the smallest radio quasar’. Although its size was revised upwards soon after based on updated scattering theory, PKS 0405–385 remains an important probe of Galactic plasma, and now also of intervening gas discovered through H i absorption. We present new long-slit spectroscopy spanning both PKS 0405–385 and the candidate host of the intervening H i gas. We identify Mg ii and Fe ii absorption lines in this spectrum consistent with the redshift of the intervening H i, as well as two additional, independent metal-line systems at z = 0.907 and z = 0.966, but we cannot accurately pinpoint the host(s) of this intervening gas in current data. We revisit the radio variability of PKS 0405–385 in light of advances in scintillation theory, as well as extended monitoring with the Australia Telescope Compact Array and the Australian SKA Pathfinder, and find a revised linear size ≥ 0.3 pc, but no new evidence of repeating intraday variability.

Spectral-line results from a new cryogenic phased array feed (cryoPAF) on the Murriyang telescope at Parkes are presented. This array offers a significant improvement in field of view, aperture efficiency, bandwidth, chromaticity and survey speed compared with conventional horn-fed receivers. We demonstrate this with measurements of sky calibrators and observations of 21-cm neutral hydrogen (HI) in the Large Magellanic Cloud (LMC) and the nearby galaxy NGC 6744. Within 0.3 deg of the optical axis, the ratio of system temperature to dish aperture efficiency (Tsys/ηd) is 25 K and the ratio with beam efficiency (Tsys/ηmb) is 21 K (at 1.4 GHz). For the previously measured Tsys = 17 K, respective efficiency values ηd ≈ 0.7 and ηmb ≈ 0.8 are derived. Our HI observational results are in good agreement with previous results, although detailed comparison with multibeam observations of the LMC suggests that the earlier observations may have missed an extended component of low-column-density gas (∼ 8 × 1018 cm−2). We use the cryoPAF zoom-band and wideband data to make a preliminary investigation of whether the large number of simultaneous beams (72) permits the use of novel data reduction methods to reduce the effects of foreground/background continuum contamination and radio-frequency interference (RFI). We also investigate if these methods can better protect against signal loss for the detection of faint, extended cosmological signals such as HI intensity maps. Using robust higher-order singular value decomposition (SVD) techniques, we find encouraging results for the detection of both compact and extended sources, including challenging conditions with high RFI occupancy and significant sky continuum structure. Examples are shown that demonstrate that 3D SVD techniques offer a significant improvement in noise reduction and signal capture compared with more traditional layered 2D techniques.

We report diffuse extended radio-continuum emission spatially coinciding with the IR source, WISEA J094409.17$-$751012.8, and a semi-variable star, V687 Carinae. We use 944 MHz radio data from the large-scale Evolutionary Map of the Universe (EMU) survey to analyse this diffuse emission (EMU J094412$-$751016), which we nickname ‘Anglerfish’. We investigate if the spatially correlated infrared (IR) source, WISEA J094409.17$-$751012.8, is physically related to Anglerfish. The IR colours of WISEA J094409.17$-$751012.8 are indicative of an elliptical galaxy, raising the possibility that Anglerfish may belong to the newly discovered class of extragalactic radio sources known as Odd Radio Circles (ORCs) with WISEA J094409.17$-$751012.8 as the host galaxy. We also investigate the possibility that Anglerfish is physically related to the star, V687 Carinae, and whether it may be a remnant from a previous epoch of stellar mass-loss. We determine that a physical association between the radio emission and the star is unlikely due to the star’s weak stellar winds compared to the theoretical expansion velocity of the ‘shell’. It is possible that Anglerfish may be a Galactic high-latitude supernova remnant; however, we find that the observed size and luminosity are not consistent with this scenario. We also investigate the ORC scenario, which we deem the most likely scenario based on the Anglerfish’s observed properties such as size, brightness, lack of other frequency detections, and possible host galaxy identification. We therefore propose Anglerfish as an ORC candidate, but note that additional radio and optical observations are vital to further constrain the properties and confirm this classification.

Flying on board the James Webb Space Telescope (JWST) above Earth’s turbulent atmosphere, the Aperture Masking Interferometer (AMI) on the NIRISS instrument is the highest-resolution infrared interferometer ever placed in space. However, its performance was found to be limited by non-linear detector systematics, particularly charge migration – or the Brighter-Fatter Effect. Conventional interferometric Fourier observables are degraded by non-linear transformations in the image plane, with the consequence that the inner working angle and contrast limits of AMI were seriously compromised. Building on the end-to-end differentiable model & calibration code , we here present a regularised maximum-likelihood image reconstruction framework , which can deconvolve AMI images either in the image plane or from calibrated Fourier observables, achieving high angular resolution and contrast over a wider field of view than conventional interferometric limits. This modular code by default includes regularisation by maximum entropy, and total variation defined with $l_1$ or $l_2$ metrics. We present imaging results from dorito for three benchmark imaging datasets: the volcanoes of Jupiter’s moon Io, the colliding-wind binary dust nebula WR 137 and the archetypal Seyfert 2 active galactic nucleus NGC 1068. In all three cases, we recover images consistent with the literature at diffraction-limited resolutions. The performance, limitations, and future opportunities enabled by amigo for AMI imaging (and beyond) are discussed.