Many short gamma-ray bursts (GRBs) originate from binary neutron star mergers, and there are several theories that predict the production of coherent, prompt radio signals either prior, during, or shortly following the merger, as well as persistent pulsar-like emission from the spin-down of a magnetar remnant. Here we present a low frequency (170–200 MHz) search for coherent radio emission associated with nine short GRBs detected by the Swift and/or Fermi satellites using the Murchison Widefield Array (MWA) rapid-response observing mode. The MWA began observing these events within 30–60 s of their high-energy detection, enabling us to capture any dispersion delayed signals emitted by short GRBs for a typical range of redshifts. We conducted transient searches at the GRB positions on timescales of 5 s, 30 s, and 2 min, resulting in the most constraining flux density limits on any associated transient of 0.42, 0.29, and 0.084 Jy, respectively. We also searched for dispersed signals at a temporal and spectral resolution of 0.5 s and 1.28 MHz, but none were detected. However, the fluence limit of 80–100 Jy ms derived for GRB 190627A is the most stringent to date for a short GRB. Assuming the formation of a stable magnetar for this GRB, we compared the fluence and persistent emission limits to short GRB coherent emission models, placing constraints on key parameters including the radio emission efficiency of the nearly merged neutron stars ( $\epsilon_r\lesssim10^{-4}$ ), the fraction of magnetic energy in the GRB jet ( $\epsilon_B\lesssim2\times10^{-4}$ ), and the radio emission efficiency of the magnetar remnant ( $\epsilon_r\lesssim10^{-3}$ ). Comparing the limits derived for our full GRB sample (along with those in the literature) to the same emission models, we demonstrate that our fluence limits only place weak constraints on the prompt emission predicted from the interaction between the relativistic GRB jet and the interstellar medium for a subset of magnetar parameters. However, the 30-min flux density limits were sensitive enough to theoretically detect the persistent radio emission from magnetar remnants up to a redshift of $z\sim0.6$ . Our non-detection of this emission could imply that some GRBs in the sample were not genuinely short or did not result from a binary neutron star merger, the GRBs were at high redshifts, these mergers formed atypical magnetars, the radiation beams of the magnetar remnants were pointing away from Earth, or the majority did not form magnetars but rather collapse directly into black holes.

Therecently discovered massive binary system Apep is the most powerful synchrotron emitter among the known Galactic colliding-wind binaries. This makes this particular system of great interest to investigate stellar winds and the non-thermal processes associated with their shocks. This source was detected at various radio bands, and in addition the wind-collision region was resolved by means of very-long baseline interferometric observations. We use a non-thermal emission model for colliding-wind binaries to derive physical properties of this system. The observed morphology in the resolved maps allows us to estimate the system projection angle on the sky to be $\psi \approx 85^\circ$ . The observed radio flux densities also allow us to characterise both the intrinsic synchrotron spectrum of the source and its modifications due to free–free absorption in the stellar winds at low frequencies; from this, we derive mass–loss rates of the stars of $\dot{M}_\mathrm{WN} \approx 4\times10^{-5}\;\mathrm{M}_\odot\,\mathrm{yr}^{-1}$ and $\dot{M}_\mathrm{WC} \approx 2.9\times10^{-5}\;\mathrm{M}_\odot\,\mathrm{yr}^{-1}$ . Finally, the broadband spectral energy distribution is calculated for different combinations of the remaining free parameters, namely the intensity of the magnetic field and the injected power in non-thermal particles. We show that the degeneracy of these two parameters can be solved with observations in the high-energy domain, most likely in the hard X-rays but also possibly in $\gamma$ -rays under favourable conditions.

Recent ground-based deep observations of the Universe have discovered large populations of massive quiescent galaxies at $z\sim3\!-\!5$ . With the launch of the James Webb Space Telescope (JWST), the on-board Near-Infrared Spectrograph (NIRSpec) instrument will provide continuous $0.6\!-\!5.3\,\unicode{x03BC}\,\mathrm{m}$ spectroscopic coverage of these galaxies. Here we show that NIRSpec/CLEAR spectroscopy is ideal to probe the completeness of photometrically selected massive quiescent galaxies such as the ones presented by Schreiber et al. (2018b, A&A, 618, A85). Using a subset of the Schreiber et al. (2018b, A&A, 618, A85) sample with deep Keck/MOSFIRE spectroscopy presented by Esdaile J., et al. (2021b, ApJ, 908, L35), we perform a suite of mock JWST/NIRSpec observations to determine optimal observing strategies to efficiently recover the star formation histories (SFHs), element abundances, and kinematics of these massive quiescent galaxies. We find that at $z\sim3$ , medium resolution G235M/FL170LP NIRSpec observations could recover element abundances at an accuracy of ${\sim}15\%$ , which is comparable to local globular clusters. Mimicking ZFOURGE COSMOS photometry, we perform mock spectrophotometric fitting with Prospector to show that the overall shape of the SFHs of our mock galaxies can be recovered well, albeit with a dependency on the number of non-parametric SFH bins. We show that deep high-resolution G235H/FL170LP integral field spectroscopy with a $S/N\sim7$ per spaxel is required to constrain the rotational properties of our sample at $>\!2\sigma$ confidence. Thus, through optimal grism/filter choices, JWST/NIRSpec slit and integral field spectroscopy observations would provide tight constraints to galaxy evolution in the early Universe.

Most applications of Bayesian Inference for parameter estimation and model selection in astrophysics involve the use of Monte Carlo techniques such as Markov Chain Monte Carlo (MCMC) and nested sampling. However, these techniques are time-consuming and their convergence to the posterior could be difficult to determine. In this study, we advocate variational inference as an alternative to solve the above problems, and demonstrate its usefulness for parameter estimation and model selection in astrophysics. Variational inference converts the inference problem into an optimisation problem by approximating the posterior from a known family of distributions and using Kullback–Leibler divergence to characterise the difference. It takes advantage of fast optimisation techniques, which make it ideal to deal with large datasets and makes it trivial to parallelise on a multicore platform. We also derive a new approximate evidence estimation based on variational posterior, and importance sampling technique called posterior-weighted importance sampling for the calculation of evidence, which is useful to perform Bayesian model selection. As a proof of principle, we apply variational inference to five different problems in astrophysics, where Monte Carlo techniques were previously used. These include assessment of significance of annual modulation in the COSINE-100 dark matter experiment, measuring exoplanet orbital parameters from radial velocity data, tests of periodicities in measurements of Newton’s constant G, assessing the significance of a turnover in the spectral lag data of GRB 160625B, and estimating the mass of a galaxy cluster using weak gravitational lensing. We find that variational inference is much faster than MCMC and nested sampling techniques for most of these problems while providing competitive results. All our analysis codes have been made publicly available.

This review of Aboriginal astronomy and navigation brings together accounts from widely dispersed places in Western Australia, from Noongar Country in the south-west, through to the Eastern Goldfields, the Pilbara, the Kimberley and the Central Deserts. Information for this review has been taken from the literature and non-conventional sources, including artist statements of paintings. The intention for the review is that the scope is traditional, pre-European settlement understandings, but post-settlement records of oral accounts, and later articulation by Aboriginal peoples, are necessarily relied upon. In large part, the Western Australian accounts reflect understandings reported for other states. For example, star maps were used for teaching routes on the ground, but available accounts do not evidence that star maps were used in real-time navigation. The narratives or dreamings that differ most from those of other states explain creation of night-sky objects and landforms on Earth, events including thunder, or they address social behaviour.

We present a software package for single-dish data processing of spacecraft signals observed with VLBI-equipped radio telescopes. The Spacecraft Doppler tracking (SDtracker) software allows one to obtain topocentric frequency detections with a sub-Hz precision and reconstructed and residual phases of the carrier signal of any spacecraft or landing vehicle at any location in the Solar System. These data products are estimated using the ground-based telescope’s highly stable oscillator as a reference, without requiring an a priori model of the spacecraft dynamics nor the downlink transmission carrier frequency. The software has been extensively validated in multiple observing campaigns of various deep space missions and is compatible with the raw sample data acquired by any standard VLBI radio telescope worldwide. In this paper, we report the numerical methodology of SDtracker, the technical operations for deployment and usage, and a summary of use cases and scientific results produced since its initial release.

Mid- and far-infrared (IR) photometric and spectroscopic observations are fundamental to a full understanding of the dust-obscured Universe and the evolution of both star formation and black hole accretion in galaxies. In this work, using the specifications of the SPace Infrared telescope for Cosmology and Astrophysics (SPICA) as a baseline, we investigate the capability to study the dust-obscured Universe of mid- and far-IR photometry at 34 and $70\, {\rm{\mu }}\mathrm{m}$ and low-resolution spectroscopy at $17{-}36\, {\rm{\mu }}\mathrm{m}$ using the state-of-the-art Spectro-Photometric Realisations of Infrared-selected Targets at all-z (Spritz) simulation. This investigation is also compared to the expected performance of the Origins Space Telescope and the Galaxy Evolution Probe. The photometric view of the Universe of a SPICA-like mission could cover not only bright objects (e.g. $L_{IR}>10^{12}\,{\rm L}_{\odot}$ ) up to ${z}=10$ , but also normal galaxies ( $L_{IR}<10^{11}\,{\rm L}_{\odot}$ ) up to $\textit{z}\sim4$ . At the same time, the spectroscopic observations of such mission could also allow us to estimate the redshifts and study the physical properties for thousands of star-forming galaxies and active galactic nuclei by observing the polycyclic aromatic hydrocarbons and a large set of IR nebular emission lines. In this way, a cold, 2.5-m size space telescope with spectro-photometric capability analogous to SPICA, could provide us with a complete three-dimensional (i.e. images and integrated spectra) view of the dust-obscured Universe and the physics governing galaxy evolution up to $\textit{z}\sim4$ .

The Rapid ASKAP Continuum Survey (RACS) is the first large sky survey using the Australian Square Kilometre Array Pathfinder (ASKAP), covering the sky south of $+41^\circ$ declination. With ASKAP’s large, instantaneous field of view, ${\sim}31\,\mathrm{deg}^2$ , RACS observed the entire sky at a central frequency of 887.5 MHz using 903 individual pointings with 15 minute observations. This has resulted in the deepest radio survey of the full Southern sky to date at these frequencies. In this paper, we present the first Stokes I catalogue derived from the RACS survey. This catalogue was assembled from 799 tiles that could be convolved to a common resolution of $25^{\prime\prime}$ , covering a large contiguous region in the declination range $\delta=-80^{\circ}$ to $+30^\circ$ . The catalogue provides an important tool for both the preparation of future ASKAP surveys and for scientific research. It consists of $\sim$ 2.1 million sources and excludes the $|b|<5^{\circ}$ region around the Galactic plane. This provides a first extragalactic catalogue with ASKAP covering the majority of the sky ( $\delta<+30^{\circ}$ ). We describe the methods to obtain this catalogue from the initial RACS observations and discuss the verification of the data, to highlight its quality. Using simulations, we find this catalogue detects 95% of point sources at an integrated flux density of $\sim$ 5 mJy. Assuming a typical sky source distribution model, this suggests an overall 95% point source completeness at an integrated flux density $\sim$ 3 mJy. The catalogue will be available through the CSIRO ASKAP Science Data Archive (CASDA).

At relatively high frequencies, highly sensitive grating sidelobes occur in the primary beam patterns of low frequency aperture arrays (LFAA) such as the Murchison Widefield Array (MWA). This occurs when the observing wavelength becomes comparable to the dipole separation for LFAA tiles, which for the MWA occurs at ${\sim}300$ MHz. The presence of these grating sidelobes has made calibration and image processing for 300 MHz MWA observations difficult. This work presents a new calibration and imaging strategy which employs existing techniques to process two example 300 MHz MWA observations. Observations are initially calibrated using a new 300 MHz sky-model which has been interpolated from low frequency and high frequency all-sky surveys. Using this 300 MHz model in conjunction with the accurate MWA tile primary beam model, we perform sky-model calibration for the two example observations. After initial calibration a self-calibration loop is performed by all-sky imaging each observation. We mask the main lobe of the all-sky image, and perform a sky-subtraction by estimating the masked image visibilities. We then image the main lobe of the sky-subtracted visibilities, which results in high dynamic range images of the two example observations. These images have been convolved with a Gaussian to a resolution of $2.4$ arcminutes, with a maximum sensitivity of ${{\sim}}31\,\textrm{mJy/beam}$ . The calibration and imaging strategy demonstrated in this work opens the door to performing science at 300 MHz with the MWA, which was previously an inaccessible domain. With this paper we release the code described below and the cross-matched catalogue along with the code to produce a sky-model in the range 70–1 400 MHz.

The cosmic evolution of the chemical elements from the Big Bang to the present time is driven by nuclear fusion reactions inside stars and stellar explosions. A cycle of matter recurrently re-processes metal-enriched stellar ejecta into the next generation of stars. The study of cosmic nucleosynthesis and this matter cycle requires the understanding of the physics of nuclear reactions, of the conditions at which the nuclear reactions are activated inside the stars and stellar explosions, of the stellar ejection mechanisms through winds and explosions, and of the transport of the ejecta towards the next cycle, from hot plasma to cold, star-forming gas. Due to the long timescales of stellar evolution, and because of the infrequent occurrence of stellar explosions, observational studies are challenging, as they have biases in time and space as well as different sensitivities related to the various astronomical methods. Here, we describe in detail the astrophysical and nuclear-physical processes involved in creating two radioactive isotopes useful in such studies, $^{26}\mathrm{Al}$ and $^{60}\mathrm{Fe}$ . Due to their radioactive lifetime of the order of a million years, these isotopes are suitable to characterise simultaneously the processes of nuclear fusion reactions and of interstellar transport. We describe and discuss the nuclear reactions involved in the production and destruction of $^{26}\mathrm{Al}$ and $^{60}\mathrm{Fe}$ , the key characteristics of the stellar sites of their nucleosynthesis and their interstellar journey after ejection from the nucleosynthesis sites. This allows us to connect the theoretical astrophysical aspects to the variety of astronomical messengers presented here, from stardust and cosmic-ray composition measurements, through observation of $\gamma$ rays produced by radioactivity, to material deposited in deep-sea ocean crusts and to the inferred composition of the first solids that have formed in the Solar System. We show that considering measurements of the isotopic ratio of $^{26}\mathrm{Al}$ to $^{60}\mathrm{Fe}$ eliminate some of the unknowns when interpreting astronomical results, and discuss the lessons learned from these two isotopes on cosmic chemical evolution. This review paper has emerged from an ISSI-BJ Team project in 2017–2019, bringing together nuclear physicists, astronomers, and astrophysicists in this inter-disciplinary discussion.

Curiously, our Universe was born in a low entropy state, with abundant free energy to power stars and life. The form that this free energy takes is usually thought to be gravitational: the Universe is almost perfectly smooth, and so can produce sources of energy as matter collapses under gravity. It has recently been argued that a more important source of low-entropy energy is nuclear: the Universe expands too fast to remain in nuclear statistical equilibrium, effectively shutting off nucleosynthesis in the first few minutes, providing leftover hydrogen as fuel for stars. Here, we fill in the astrophysical details of this scenario and seek the conditions under which a Universe will emerge from early nucleosynthesis as almost-purely iron. In so doing, we identify a hitherto-overlooked character in the story of the origin of the second law: matter–antimatter asymmetry.

The RAD@home RGB-maker Tool is a python-based web application that enables citizen science research through collaboration using open-source technology. The tool fetches FITS image data from NASA SkyView and generates false colour images in Red-Green-Blue channels with contour. This helps in the basic multi-wavelength understanding and characterization of extragalactic objects, and further analysis along with reporting of potential new discoveries in a uniform format. Students from Universities or science-graduate citizens gain skills in RGB-C image analysis and identify unique features in objects via either one-day online-weekend events or week-long in-person training. Trained citizen scientists in turn are part of rare discoveries such as the jet-galaxy interaction system RAD12. The tool has been successfully used by thousands of citizen scientists in India since its launch on 26th January 2021 and has demonstrated the potential during IAU symposium 375 to be part of citizen science efforts with international participants.

Unlike most web-based citizen science programmes, RAD@home citizen scientists are trained in an interactive manner, both online and in person. This Collaboratory model can alleviate various geo-political and socio-economic constraints on the growth of people in underdeveloped regions which is in synergy with mandates of the IAU Office of Astronomy for Development. Owing to its Inter-University collaboratory design, supported by over 30 research institutions, it can attempt to convert the ‘Big Data Problem’ into a ‘Big Data Prospect’ by direct training and involving citizens in discoveries from multi-telescope data. Using the RAD-RGB-maker web-tool, e-astronomers learn the basics of multi-wavelength (UV-optical-IR-radio) extragalactic astronomy and create preliminary discovery reports of unusual radio sources thus becoming Co-Investigator in follow-up observations and publications (e.g. Discovery of RAD12). International expansion of RAD@home has been initiated during the recent IAU symposium 375 through its Educational and Outreach programme.

We performed photo-polarimetry observations for the blazar BL Lacertae (BL Lac) in 2020 to 2021, in which BL Lac showed historical outburst. As a result, we obtained microvariability with a timescale about five minutes and wavelength dependence of polarization degree and angle. These results indicate multiple emission regions and turbulent magnetic field structure.

Blazars are the most numerous type of observed high-energy gamma-ray emitters. However, their emission mechanisms and population properties are still not well-understood. Crucial to this understanding are their cosmological redshifts, which are often not easy to obtain. This presents a great challenge to the next-generation ground-based observatory for very-high-energy gamma rays, the Cherenkov Telescope Array (CTA), which aims to detect a large number of distant blazars to study their intrinsic emission properties and to place tight constraints on the extragalactic background light density, amongst others. The successful investigation of these subjects needs a precise redshift determination. Motivated by these challenges, the CTA redshift task force initiated more than 3 years ago a spectroscopic observing program using some of the largest optical and infrared telescopes to measure the redshifts of a large fraction of blazars that are likely to be detected with CTA. In this proceedings, we give an overview of the CTA redshift task force, discuss some of the difficulties associated with measuring the redshifts of blazars and present our sample selection and observing strategies. We end the proceedings with reporting selected results from the program, the on-going collaborative efforts and our plans for the future.

This report presents the results of optical polarimetric observations carried out with 6-m and 1-m telescopes at SAO RAS. The study of the blazar S5 0716+714 radiation showed the presence of a period of the variability of brightness and polarization vector variations on scales of ∼1.5 hours, constant on a long time scale; multi-colour monitoring of BL Lac polarization before, during and after the flare demonstrates the difference in the patterns of polarization vector variability depending on the wavelength. Several geometrical models and physical descriptions are discussed.

Particle-in-Cell simulations can provide a possible answer to an important key issue for astrophysical plasma jets; namely on how a toroidal magnetic field affects the evolution of pair and electron-ion jets. We show that Weibel, mushroom, and kinetic Kelvin-Helmhotz instabilities excited at the linear stage, generate a quasi-steady x-component of the electric field which accelerates and decelerates electrons. We observe significant differences in the structure of the strong electromagnetic fields that are driven by the kinetic instabilities with the pair jet. We find that the two different jet compositions (e± and e– - i+) generate different instability modes respectively. Moreover, the magnetic field in the non-linear stage generated by different instabilities is dissipated and reorganized into new topologies. A 3D magnetic field topology depiction indicates possible reconnection sites in the non-linear stage where the particles are significantly accelerated by the dissipation of the magnetic field associated to a possible reconnection manifestation.

We present a new algorithm for the identification and physical characterization of current sheets and reconnection sites as well as the update of post-reconnection particles spectra in 2D and 3D large scale relativistic magnetohydrodynamic simulations. Lagrangian particles, which follow the fluid, are used to sample plasma parameters before entering the reconnection sites that form during the evolution of the different configurations considered. With the sampled parameters and a subgrid model based on results of Particle-in-Cell simulations we introduced in the PLUTO code an algorithm able to describe the post-reconnection spectra associated to the non-thermal component.

We present and briefly discuss results of several studies of the source J2102+6015 with tentatively defined redshift z = 4.575 which demonstrates unusual properties in imaging and astrometric VLBI observations. Its properties might be considered as indications on the supermassive black hole binary which can be considered as a so far rare example of a high-redshift source of known electromagnetic and, possibly, predictable gravitational wave emissions.