Impulsive radio signals such as fast radio bursts (FRBs) are imprinted with the signatures of multi-path propagation through ionised media in the form of frequency-dependent temporal broadening of the pulse profile, commonly referred to as scattering. The dominant source of scattering for most FRBs is expected to be within their host galaxies, an assumption which can be tested by examining potential correlations between the scattering properties of the FRBs and global properties of their hosts. Using results from the Commensal Real-time ASKAP Fast Transient (CRAFT) survey, we investigate correlations across a range of host galaxy properties against attributes of the FRB that encode propagation effects: scattering timescale $\tau$, polarisation fractions, and absolute Faraday rotation measure. From 21 host galaxy properties considered, we find three that are correlated with $\tau$, including the stellar surface density (or compactness; Pearson’s p-value p = 0.002 and Spearman’s p = 0.010), the mass-weighted age (Spearman’s p-value p = 0.009), and a weaker correlation with the gas-phase metallicity (Spearman’s $p = 0.017$). Weakly significant correlations are also found with $H\alpha$ equivalent widths and stellar gravitational potential. From 10 000 trials of reshuffled datasets, we expect two strong Spearman’s correlations only 2% of the time and three weaker correlations in 6.6% of cases. Compact host galaxies may have more ionised content which scatters the FRB further. Compact galaxies were also found to correlate with gas-phase metallicity in our sample, while H ii regions along the line-of-sight are also a potential contributing factor. No correlation is seen with host galaxy inclination, which weakens the case for an inclination bias, as previously suggested for samples of localised FRBs. A strong ($p = 0.002$) correlation is found for absolute rotation measure with optical disc axis ratio b/a; greater rotation measures are seen for edge-on host galaxies. Further high-time resolution FRB detections, coupled with localisation and detailed follow-up on their host galaxies, are necessary to corroborate these initial findings and shed further light into the FRB mechanism.

We present microsecond-resolution, coherently dedispersed, polarimetric measurements of 35 fast radio bursts (FRBs) detected during the Commensal Real-time ASKAP Fast Transients (CRAFT) incoherent sum (ICS) survey with the Australian Square Kilometre Array Pathfinder (ASKAP). We find a wide diversity of time–frequency morphology and polarisation properties broadly consistent with those of currently known non-repeating FRBs. The high S/N and fine time-resolution of our data however reveals a wealth of new information. Key results include (i) the distribution of scattering timescales, ${{{\unicode{x03C4}}_\textrm{obs}}}$, is limited purely by instrumental effects, with no downturn at high ${{{\unicode{x03C4}}_\textrm{obs}}}$ as expected from a log-normal distribution; (ii) for the 29 FRBs with known redshift, there is no detectable correlation between ${{{\unicode{x03C4}}_\textrm{obs}}}$ and dispersion measure (DM) fluctuations about the Macquart relation, in contrast to expectations from pulsar scattering–DM relations; (iii) all FRBs probably have multiple components, and at least a large fraction have variable PA, the identification of which is limited by scattering; (iv) at least half of all FRBs exhibit PA microstructure at 200 $\mu{}$s–200 ns timescales, with behaviour most closely resembling a sub-category of Crab main pulses; (v) that there is a break in the FRB circular polarisation distribution at Stokes $V \gtrsim 20$%, which is suggestive of a discrete sub-population.

Fast radio bursts (FRBs) are short, intense radio signals from distant astrophysical sources, and their accurate localisation is crucial for probing their origins and utilising them as cosmological tools. This study focuses on improving the astrometric precision of FRBs discovered by the Australian Square Kilometre Array Pathfinder (ASKAP) by correcting systematic positional errors in the Rapid ASKAP Continuum Survey (RACS), which is used as a primary reference for ASKAP FRB localisation. We present a detailed methodology for refining astrometry in two RACS epochs (RACS-Low1 and RACS-Low3) through crossmatching with the Wide-field Infrared Survey Explorer (WISE) catalogue. The uncorrected RACS-Low1 and RACS-Low3 catalogues had significant astrometric offsets, with all-sky median values of $0.58''$ in RA and $-0.26''$ in Dec. (RACS-Low1) and $0.29''$ in RA and $1.24''$ in Dec. (RACS-Low3), with a substantial and direction-dependent scatter around these values. After correction, the median offset was completely eliminated, and the 68% confidence interval in the all-sky residuals was reduced to $0.2''$ or better for both surveys. By validating the corrected catalogues against other, independent radio surveys, we conclude that the individual corrected RACS source positions are accurate to a 1-$\sigma$ confidence level of $0.3''$ over the bulk of the survey area, degrading slightly to $0.4''$ near the Galactic plane. This work lays the groundwork to extend our corrections to the full RACS catalogue that will enhance future radio observations, particularly for FRB studies.

The First Large Absorption Survey in H i (FLASH) is a large-area radio survey for neutral hydrogen in and around galaxies in the intermediate redshift range $0.4\lt z\lt1.0$, using the 21-cm H i absorption line as a probe of cold neutral gas. The survey uses the ASKAP radio telescope and will cover 24,000 deg$^2$ of sky over the next five years. FLASH breaks new ground in two ways – it is the first large H i absorption survey to be carried out without any optical preselection of targets, and we use an automated Bayesian line-finding tool to search through large datasets and assign a statistical significance to potential line detections. Two Pilot Surveys, covering around 3000 deg$^2$ of sky, were carried out in 2019-22 to test and verify the strategy for the full FLASH survey. The processed data products from these Pilot Surveys (spectral-line cubes, continuum images, and catalogues) are public and available online. In this paper, we describe the FLASH spectral-line and continuum data products and discuss the quality of the H i spectra and the completeness of our automated line search. Finally, we present a set of 30 new H i absorption lines that were robustly detected in the Pilot Surveys, almost doubling the number of known H i absorption systems at $0.4\lt z\lt1$. The detected lines span a wide range in H i optical depth, including three lines with a peak optical depth $\tau\gt1$, and appear to be a mixture of intervening and associated systems. Interestingly, around two-thirds of the lines found in this untargeted sample are detected against sources with a peaked-spectrum radio continuum, which are only a minor (5–20%) fraction of the overall radio-source population. The detection rate for H i absorption lines in the Pilot Surveys (0.3 to 0.5 lines per 40 deg$^2$ ASKAP field) is a factor of two below the expected value. One possible reason for this is the presence of a range of spectral-line artefacts in the Pilot Survey data that have now been mitigated and are not expected to recur in the full FLASH survey. A future paper in this series will discuss the host galaxies of the H i absorption systems identified here.

With wide-field phased array feed technology, the Australian Square Kilometre Array Pathfinder (ASKAP) is ideally suited to search for seemingly rare radio transient sources that are difficult to discover previous-generation narrow-field telescopes. The Commensal Real-time ASKAP Fast Transient (CRAFT) Survey Science Project has developed instrumentation to continuously search for fast radio transients (duration $\lesssim$ 1 s) with ASKAP, with a particular focus on finding and localising fast radio bursts (FRBs). Since 2018, the CRAFT survey has been searching for FRBs and other fast transients by incoherently adding the intensities received by individual ASKAP antennas, and then correcting for the impact of frequency dispersion on these short-duration signals in the resultant incoherent sum (ICS) in real time. This low-latency detection enables the triggering of voltage buffers, which facilitates the localisation of the transient source and the study of spectro-polarimetric properties at high time resolution. Here we report the sample of 43 FRBs discovered in this CRAFT/ICS survey to date. This includes 22 FRBs that had not previously been reported: 16 FRBs localised by ASKAP to $\lesssim 1$ arcsec and 6 FRBs localised to $\sim 10$ arcmin. Of the new arcsecond-localised FRBs, we have identified and characterised host galaxies (and measured redshifts) for 11. The median of all 30 measured host redshifts from the survey to date is $z=0.23$. We summarise results from the searches, in particular those contributing to our understanding of the burst progenitors and emission mechanisms, and on the use of bursts as probes of intervening media. We conclude by foreshadowing future FRB surveys with ASKAP using a coherent detection system that is currently being commissioned. This will increase the burst detection rate by a factor of approximately ten and also the distance to which ASKAP can localise FRBs.

We examine the energy distribution of the fast radio burst (FRB) population using a well-defined sample of 63 FRBs from the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope, 28 of which are localised to a host galaxy. We apply the luminosity-volume ($V/V_{\mathrm{max}}$) test to examine the distribution of these transient sources, accounting for cosmological and instrumental effects, and determine the energy distribution for the sampled population over the redshift range $0.01 \lesssim z \lesssim 1.02$. We find the distribution between $10^{23}$ and $10^{26}$ J Hz$^{-1}$ to be consistent with both a pure power-law with differential slope $\gamma=-1.96 \pm 0.15$, and a Schechter function with $\gamma = -1.82 \pm 0.12$ and downturn energy $E_\mathrm{max} \sim 6.3 \, \times 10^{25}$ J Hz$^{-1}$. We identify systematic effects which currently limit our ability to probe the luminosity function outside this range and give a prescription for their treatment. Finally, we find that with the current dataset, we are unable to distinguish between the evolutionary and spectral models considered in this work.

Fast radio burst (FRB) science primarily revolves around two facets: the origin of these bursts and their use in cosmological studies. This work follows from previous redshift–dispersion measure (z–DM) analyses in which we model instrumental biases and simultaneously fit population parameters and cosmological parameters to the observed population of FRBs. This sheds light on both the progenitors of FRBs and cosmological questions. Previously, we have completed similar analyses with data from the Australian Square Kilometer Array Pathfinder (ASKAP) and the Murriyang (Parkes) Multibeam system. In this manuscript, we use 119 FRBs with 29 associated redshifts by additionally modelling the Deep Synoptic Array (DSA) and the Five-hundred-metre Aperture Spherical radio Telescope (FAST). We also invoke a Markov chain Monte Carlo (MCMC) sampler and implement uncertainty in the Galactic DM contributions. The latter leads to larger uncertainties in derived model parameters than previous estimates despite the additional data and indicate that precise measurements of DM$_\textrm{ISM}$ will be important in the future. We provide refined constraints on FRB population parameters and derive a new constraint on the minimum FRB energy of log $E_{\mathrm{min}}$(erg)=39.47$^{+0.54}_{-1.28}$ which is significantly higher than bursts detected from strong repeaters. This result likely indicates a low-energy turnover in the luminosity function or may alternatively suggest that strong repeaters have a different luminosity function to single bursts. We also predict that FAST will detect 25–41% of their FRBs at $z \gtrsim 2$ and DSA will detect 2–12% of their FRBs at $z \gtrsim 1$.

Determining amino acid sequences of protein molecules is one of the most important issues in molecular biology. These sequences determine protein structure and functionality. Unfortunately, direct biochemical methods for reading amino acid sequences can be used for reading short sequences only. This is the reason, which makes peptide assembly algorithms an important complement of these methods. In this paper, a genetic algorithm solving the problem of short amino acid sequence assembly is presented. The algorithm has been tested in computational experiment and compared with an existing tabu search method for the same problem. The results clearly show that the genetic algorithm outperformed the tabu search approach.