arXiv subjects

Marcin Glowacki

Publications and source records attributed to Marcin Glowacki.

At least 19 recordsLinked to original sources

arXiv2026

Two new highly scattered fast radio bursts: evidence for scatter broadening by the circumsource medium

We found two highly scattered Fast Radio Bursts (FRBs) during commissioning of the Commensal Realtime ASKAP Fast Transient COherent (CRACO) backend. FRB 240210D and FRB 240312D have scattering times of $34\pm6$ and $300\pm48$ ms, respectively, when scaled to 1 GHz. FRB 240312D originates near a spiral arm of a face-on galaxy at a redshift of only 0.05. Scintillation from a Milky Way screen constrains the distance of the scattering screen to $\sim 10$ pc from the source. FRB 240312D is therefore the first highly scattered FRB where scattering screens in the host galaxy centre, a background galaxy, or intervening structures can all be excluded, leaving only the circumsource medium. Integral field spectroscopy of the host reveals a Milky Way-like galaxy with a star-formation region at the FRB position. We find refractive scattering in a pulsar wind nebula as the most likely scattering origin. However, the explanation is not completely satisfactory as it requires a fine-tuned orientation. Hence, additional theoretical studies under different FRB progenitor models are needed. From the two FRBs, we calculate a total rate of $R_\mathrm{tot}=210^{+460}_{-180}\,\mathrm{events}\,\mathrm{sky}^{-1}\mathrm{day}^{-1}$ with durations between 55.2 ms and 1 s and above a fluence of 9 Jy ms consistent with the rate of shorter FRBs. This elevated rate suggests that the strong scattering seen in other FRBs likewise does not arise from chance-aligned sightlines, but is instead causally linked to the FRB sources.

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arXiv2026

MIGHTEE-HI: Environmental effects of cosmic filaments on extragalactic HI detections in the COSMOS and XMM-LSS fields

Cosmic filaments have been recognised as influencing galaxy evolution, but their connection to galactic cold gas reservoirs is elusive, particularly at low redshifts. We investigate the influence of filaments on neutral hydrogen (HI) detections in galaxies at $0.02<z<0.09$, using the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) survey in the COSMOS and XMM-LSS fields. We measure the fraction of optical galaxies from the Dark Energy Spectroscopic Instrument (DESI) Survey detected in HI emission as a function of stellar mass, morphology, local density, and the distance to the nearest filament. We find that galaxies closer to filaments have higher stellar masses, higher local densities, and a larger early-type fraction, all of which affect the HI detection. After controlling for these dependencies, filaments have measurable effects on HI detection. Late-type galaxies in low-local density environments show reduced HI detection fractions close to filaments across all stellar mass ranges, suggesting potential gas depletion through ram pressure stripping and cosmic web detachment. Massive early-type galaxies show an enhanced HI detection fraction in filaments compared to the voids, suggesting possible gas replenishment through filamentary accretion or gas-rich mergers. Our results suggest that cosmic filaments influence galactic HI gas reservoirs through various competing processes, whose relative importance varies with stellar mass and local density.

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arXiv2026

MIGHTEE-HI / LADUMA: Investigating the link between baryons and dynamics with 130 resolved HI-selected galaxies

The baryonic Tully-Fisher relation (bTFR) and the radial acceleration relation (RAR) link the observed dynamics in galaxies to that expected from their baryonic mass distributions. The relations' small intrinsic scatters place strong constraints on galaxy formation models, dark matter properties and theories of modified dynamics, yet detailed measurements beyond the very local Universe remain limited. We use 130 purely HI-selected galaxies with resolved HI kinematics and baryonic mass profiles to measure the bTFR and RAR up to $z\approx0.09$. We measure a tight RAR with an acceleration scale $a_0=(1.50\pm0.05)\times10^{-10},{\rm m,s^{-2}}$ and an intrinsic scatter of $0.096\pm0.006$ dex, consistent with local results. We fit the bTFR in the `inverse' direction, conditioning on $M_{\rm bar}$ to mitigate HI flux-related selection effects, measuring a logarithmic slope of $0.27\pm0.01$ (corresponding to a forward slope of $3.72\pm0.16$), with vertical intrinsic scatter $\sigma_\perp\approx0.05$ dex. Fitting the general $\delta$-family of MOND interpolating functions to the RAR, we infer $\delta=4.10^{+1.4}_{-0.68}$, consistent with the value required by Solar System gravitational constraints and a null Wide Binary Test. We find no significant redshift evolution in the RAR acceleration scale for our pure HI-selected sample. However, the bTFR zero-point shows an apparent evolutionary trend that is strongly dependent on the fit direction: the traditional forward fit yields an $8.7\sigma$ preference for $z$ evolution, while for our fiducial inverse fit, this reduces to $3.4\sigma$, within $\approx2\sigma$ of the RAR evolution constraint. This suggests selection effects bias the forward fit; a careful consideration of such effects will be required in future endeavours to robustly measure the redshift evolution of dynamical scaling relations.

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arXiv2026

Enhanced Astrometry of the Rapid ASKAP Continuum Survey: Mid and High Frequency Epochs

Accurate radio astrometry is essential for reliable cross-identification of sources across wavelengths, precision localisation of transient events, and the construction of stable all-sky reference catalogues. In this work we extend our astrometric correction framework for the Rapid ASKAP Continuum Survey (RACS) to its mid- and high-frequency epochs (RACS-Mid1 and RACS-High1), building on our previous corrections to the low-frequency surveys. Using a hierarchical crossmatching strategy with high-precision external catalogues, we remove large-scale systematic positional errors that were present in the uncorrected data and significantly reduce the residual scatter across the sky. After correction, the median positional offsets are effectively eliminated, and the 68\% confidence interval of the mean residuals of RACS source positions averaged over $~\sim1$~sq.deg. regions is reduced from $\gtrsim 0.4''$ to $\lesssim 0.18''$ over most of the survey area for both epochs. Independent validation against multiple external radio astrometric references confirms that individual corrected RACS source positions are accurate to a 1-$\sigma$ confidence level of $\sim 0.25''$ across the bulk of the sky, with slightly degraded performance within the Galactic plane. While motivated primarily by the need for improved localisation of ASKAP fast radio bursts, these corrections also benefit a wide range of science applications, including transient identification, multiwavelength host association, and studies of Galactic and extragalactic radio populations. Together with our previous work, this establishes RACS as the highest precision arcsecond-resolution all-sky astrometric reference in the southern hemisphere at decimetre wavelengths.

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arXiv2026

A FLASH HI absorption search in compact sources in the pilot ASKAP interplanetary scintillation field

In this pilot study, we use data from the First Large Absorption Survey in HI (FLASH) to search for redshifted HI 21cm absorption at $0.4<z<1$ towards 157 bright radio sources with Interplanetary Scintillation (IPS) measurements at 820MHz in a single field observed with the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope. The ASKAP IPS measurements, which use only 2.5 minutes of observing time in total, allow us to estimate the compactness of these radio sources on sub-arcsecond scales at a frequency within the 712-1000MHz FLASH band. In particular, the Normalised Scintillation Index (NSI) for each source reflects the fraction of the flux density arising from compact components less than 0.1 arcsec in diameter. We find that $18\pm5$% of ASKAP sources with flux densities above 150mJy are highly compact with NSI $\geq0.8$ - implying that at least 80% of their radio emission arises from a single region smaller than about 800pc in size. The compactness of these sources makes them ideal probes for an HI absorption search, since the covering factor for any HI gas clouds along the line of sight is likely to be high. About half of the sources with NSI $\geq0.8$ also have peaked radio spectral energy distributions (SEDs), consistent with previous IPS studies at lower frequencies. These pilot results imply that IPS measurements with ASKAP can provide a simple and powerful tool for identifying uniform samples of compact radio sources at frequencies of a few hundred MHz across large areas of sky. With FLASH, we detect two new HI absorption lines against compact sources in the $\sim30$deg$^2$ region of sky covered by the IPS data; an associated HI line at redshift $z=0.9540$ (with a matching optical redshift) in MRC 2125-237 (NSI = 0.98), and a likely intervening line at $z=0.4632$ towards MRC 2131-241 (NSI = 0.84).

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arXiv2026

FRB20250613A: a remarkable repeating FRB with apparent millisecond-timescale scattering variations

FRB20250613A is a repeating FRB discovered by the Australian SKA Pathfinder and localised to a low-metallicity dwarf galaxy at a redshift of $z = 0.0987 \pm 0.0001$. FRB 20250613A exhibits a plethora of exotic features that likely overlay the imprint of the circum-burst environment on some intrinsic features of the source. Here we perform a comprehensive analysis of bursts detected by ASKAP, MeerKAT, and the Murriyang Parkes radio telescopes. Bursts during the MeerKAT epoch show a large apparent variance in scattering on timescales of minutes to hours. Polarimetric analysis of the full sample shows spectral depolarisation with variability on timescales of days and changes in rotation measure of $\sim$ 300 rad m$^{-2}$ over days to months. This suggests a highly turbulent magneto-ionised environment. We find significant preference for separations of $\sim$6.8$\pm$0.8 ms in multi-component bursts that we suggest is likely intrinsic to the burst emission mechanism. Finally, we find that a subset of bursts exhibit variations in these propagation effects on burst components separated by just milliseconds, that are difficult to explain by changing sightlines, but plausibly due to non-linear plasma effects in the circum-burst environment caused by the high field strength of the FRB emission. These properties, which demand a nearby turbulent screen of material, are all consistent with the FRB progenitor being embedded in the dense stellar wind of a Be star binary companion, objects which are relatively plentiful in low-mass and low-metallicity galaxies like the FRB20250613A host.

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arXiv2026

MIGHTEE-HI: HI catalogue of 293 sources for the COSMOS field and comparative study of 3-dimensional source finding methods

We present a catalogue of HI sources extracted from the MIGHTEE survey data cubes covering the COSMOS field. The catalogue contains 293 sources in the redshift range of 0.004 < z < 0.093. In addition to HI masses and velocity widths, the catalogue includes optical through near-infrared photometry and inferred stellar masses and star-formation rates. The quantity of sources in the HI catalogue acquired through untargeted source finding is greatly influenced by the source finding methods used. This study therefore also provides a well-characterised expected completeness of the detected sample of galaxies based on their properties, informing of any detection biases, inferred through a comparative study of different source finding algorithms. We have tested the performance of widely-used source finders: PyBDSF, ProFound and SoFiA, along with new source finder LESHI, focusing exclusively on HI source detection rather than source characterisation in the first instance. The source finders were tested by injecting a sample of simulated galaxies divided into narrow bins of mass, inclination and distance into a MeerKAT data cube. The results inform the source finding strategies for the MeerKAT International GigaHertz Tiered Extragalactic Exploration (MIGHTEE) survey, as well as upcoming SKAO surveys.

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arXiv2026

MIGHTEE HI observations of low surface brightness and ultra-diffuse galaxies in the XMM-LSS field

Untargeted neutral hydrogen (HI) surveys are well suited to identifying low surface brightness galaxies (LSBGs) that are gas rich, and they offer a complementary view to optically selected populations. We examined the LSBG population as identified via stellar and gaseous content using the MIGHTEE HI XMM-LSS early science data and the publicly available catalogs of optically identified LSBGs. There is currently little overlap between these datasets, with only three galaxies commonly detected. We performed surface brightness photometry of selected MIGHTEE HI detections to find 29 LSBGs, and 26 of these meet the size requirement (R_eff > 1.5 kpc) to be ultra-diffuse galaxies (UDGs). Furthermore, we extracted HI spectra at the location of all optically identified galaxies, placing upper limits on the HI-to-stellar mass ratio in these systems. While the HI-identified population overall tends toward bluer colors, the HI-identified and the optically selected samples mostly overlap in mean effective surface brightness, effective radii, and color. Although it is not straightforward to discern why the HI-identified LSBGs were missed in optical searches, this work highlights the utility of HI surveys in finding these faint systems. The HI-identified LSBGs are gas rich compared to the general HI-selected population. Furthermore, three out of four HI-selected UDGs with available kinematics show no systematic offset from the baryonic Tully-Fisher relation, although we are biased away from sources with low rotational velocities due to the low spectral resolution of the data. This work demonstrates the utility of HI observations for finding and characterizing the low surface brightness Universe.

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arXiv2026

Detecting HI Absorption in FRB Spectra: Modern Prospects and Scientific Utility

Fast radio bursts (FRBs) emit broadband radio emission that may, in rare cases, encode atomic hydrogen (HI) absorption signals as they traverse the interstellar medium of their host galaxies. Though considered in the early FRB literature, the demanding observational prerequisites and the rarity of suitable events have meant that no thorough search for HI absorption in FRB spectra has yet been undertaken. Here, we present an updated systematic analysis assessing the likelihood of modern facilities to detect such absorption features. As a proof of concept, we search for absorption in the spectrum of the bright ASKAP-localised FRB 20211127I, finding a $3\sigma$ opacity upper limit of 0.51. While this test case offers little constraining power, we find that narrow FRBs with fluences exceeding 20/70/150 Jy ms observed with MeerKAT/ASKAP/DSA can probe opacities below 0.1 - a regime in which absorption detections become physically meaningful. We further highlight that stacking thousands of bursts from hyperactive repeaters with FAST offers a very powerful avenue toward detection. Finally, we discuss the broad scientific potential of such detections, including constraints on extragalactic HI spin temperatures, a means to physically probe the environment surrounding the progenitor, and a path towards disentangling host galaxy contributions to dispersion and scattering.

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arXiv2026

I can see your halo: Constraining the Milky Way halo DM with FRB population studies

Fast radio bursts (FRBs) probe the electron column density along the line of sight and hence can be used to probe foreground structures. One such structure is the Galactic halo. In this work, we use a total of 98 high Galactic latitude ($|b| > 20^\circ$) FRBs detected by ASKAP, Parkes, DSA and FAST with 32 associated redshifts to constrain the dispersion measure (DM) contribution from the Galactic halo. We simultaneously fit unknown FRB population parameters, which show correlations with the Galactic halo but are not completely degenerate. We primarily use an isotropic model for the halo, but find no evidence favouring a particular halo model. We find DM$_{\rm MW,halo}$=$68^{+27}_{-24}$pc/cm$^3$, which is in agreement with other results within the literature. Previous constraints on DM$_{\rm MW,halo}$ with FRBs have used a few, low-DM FRBs. However, this is highly subject to fluctuations between different lines of sight, and hence using a larger number of sightlines as we do is more likely to be representative of the true average contribution. Nevertheless, we show that individual FRBs can still skew the data significantly and hence will be important in the future for more precise results.

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arXiv2025

The Distribution of Atomic Hydrogen in the Host Galaxies of FRBs

We probe the atomic hydrogen (HI) emission from the host galaxies of fast radio bursts (FRBs) to investigate the emerging trend of disturbance and asymmetry in the population. Quadrupling the sample size, we detect 16 out of 17 new hosts in HI, with the single non-detection arising in a galaxy known to be transitioning towards quiescence. With respect to typical local Universe galaxies, FRB hosts are generally massive in HI ($M_{HI}>10^9 M_\odot$), which aligns with previous studies reporting that FRB hosts also tend to have high stellar masses and are star-forming. However, they span a broad range of other HI derived properties. Using visual inspection alongside various asymmetry metrics, we identify six unambiguously settled host galaxies, demonstrating for the first time that a disturbed HI morphology is not a universal feature of FRB host galaxies. However, we find another six that show clear signs of disturbance, one borderline case, and three which require deeper or more targeted observations to reach a conclusion; this brings the confirmed ratio of disturbed-to-settled FRB hosts to 11:6. Given that roughly a 1:1 ratio is expected for random background galaxies of similar type, our observed ratio yields a p-value of 0.222. Therefore, we conclude that contrary to earlier indications, there is no statistically significant excess of HI disturbance in this sample of FRB host galaxies with respect to the general galaxy population, and hence we find no evidence for a fundamental connection between FRB progenitor formation and merger-induced star formation activity.

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arXiv2025

The Low-mass Dwarf Host Galaxy of Nonrepeating FRB 20230708A

We present Very Large Telescope/X-Shooter spectroscopy for the host galaxies of 12 fast radio bursts (FRBs) detected by the Australian SKA Pathfinder observed through the ``Fast and Unbiased FRB Host Galaxy (FURBY)" Large Programme at the European Southern Observatory, which imposes strict selection criteria on the included FRBs and their host galaxies to produce a homogeneous and well-defined sample. We describe the data reduction and analysis of these spectra and report their redshifts, line-emission fluxes, and derived host properties. From the present sample, this paper focuses on the faint host of FRB ($m_R = 22.53 \pm 0.02$) identified at low redshift ($z=0.1050$). This indicates an intrinsically very low-luminosity galaxy ($L \approx 10^8 L_\odot$), making it the lowest-luminosity nonrepeating FRB host to date by a factor of $\sim 3$, and slightly dimmer than the lowest-luminosity host for repeating FRBs. Our SED fitting analysis reveals a low stellar mass ($M_* \approx 10^{8.0} M_\odot$), low star formation rate (${\rm SFR} \approx 0.04 M_\odot \rm yr^{-1}$), and very low metallicity ($12+\log(\text{O}/\text{H})\sim(8.0-8.3)$), distinct from the more massive galaxies ($\log(M/M_\odot) \sim 10$) that are commonly identified for non-repeating FRBs. Its discovery demonstrates that FRBs can arise in among the faintest, metal-poor galaxies of the universe. In turn, this suggests that at least one FRB progenitor channel must include stars (or their remnants) created in very low metallicity environments. This indicates better prospects for detecting FRBs from the high-$z$ universe where young, low-mass galaxies proliferate.

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arXiv2025

HI asymmetries in spatially resolved SIMBA galaxies

We present a study of the neutral atomic hydrogen (HI) content of spatially resolved, low-redshift galaxies in the SIMBA cosmological simulations. We create synthetic HI data cubes designed to match observations from the Apertif Medium-Deep HI imaging survey, and follow an observational approach to derive the HI size-mass relation. The HI size-mass relation for SIMBA is in broad agreement with the observed relation to within 0.1 dex, but SIMBA galaxies are slightly smaller than expected at fixed HI mass. We quantify the HI spectral ($A_{\mathrm{flux}}$) and morphological ($A_{\mathrm{mod}}$) asymmetries of the galaxies and motivate standardizing the relative spatial resolution when comparing values in a sample that spans several orders of magnitude in HI mass. Galaxies are classified into three categories (isolated, interacted, or merged) based on their dynamical histories over the preceding ~2 Gyr to contextualize disturbances in their HI reservoirs. We determine that the interacted and merged categories have higher mean asymmetries than the isolated category, with a larger separation between the categories' $A_{\mathrm{mod}}$ distributions than between their $A_{\mathrm{flux}}$ distributions. For the interacted and merged categories, we find an inverse correlation between baryonic mass and $A_{\mathrm{mod}}$ that is not observed between baryonic mass and $A_{\mathrm{flux}}$. These results, coupled with the weak correlation found between $A_{\mathrm{flux}}$ and $A_{\mathrm{mod}}$, highlight the limitations of only using $A_{\mathrm{flux}}$ to infer the HI distributions of spatially unresolved HI detections.

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arXiv2025

Mapping the Spatial Distribution of Fast Radio Bursts within their Host Galaxies

We present deep optical and near-infrared observations of the host galaxies of 34 fast radio bursts (FRBs) detected by the Commensal Real-time ASKAP Fast Transient (CRAFT) survey on the Australian SKA Pathfinder (ASKAP) to compare the locations of FRBs relative to their host light distributions. Incorporating three additional FRBs from the literature, for a total of four repeating and 33 apparently non-repeating FRBs, we determine their projected galactocentric offsets and find a median of $ 4.2^{+5.7}_{-2.5}$ kpc ($1.0^{+1.5}_{-0.6}r_e$). We model their host surface brightness profiles and develop synthetic spatial distributions of their globular clusters based on host properties. We calculate the likelihood the observed location of each FRB is consistent with the smooth light of its host galaxy, residual (primarily spiral) substructure, or globular cluster distributions. The majority of FRBs favor locations within the disks of their galaxies, while only 11$\pm$5\% favor a globular cluster origin, primarily those with galactocentric offsets $\gtrsim3r_e$. At $z<0.15$, where spiral structure is apparent in 86\% of our sample of FRB hosts, we find $\approx 20-46\%$ of FRBs favor an association with spiral arms. Assuming FRBs derive from magnetars, our results support multiple formation channels with the majority of progenitors associated with massive stars and a minority formed through dynamical channels. However, the moderate fraction of FRBs associated with spiral structure indicates that high star formation efficiency of the youngest and most massive stars is not a predominant driver in the production of FRB progenitors.

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arXiv2025

The galaxy-halo connection of disc galaxies over six orders of magnitude in stellar mass

(Abridged) The relations between stellar ($M_\ast$), gas ($M_{\rm gas}$), baryonic ($M_{\rm bar} = M_\ast + M_{\rm gas}$), and dark matter halo mass ($M_{200}$) provide unique constraints on galaxy formation and cosmology. The shape of the relations constrains how galaxies regulate their growth through gas accretion, star formation, and feedback; their scatter probes the stochasticity of galaxy assembly. Here, we assemble a sample of 49 nearby gas-rich dwarf and massive disc galaxies with unmatched ancillary data. We obtain their gas kinematics and derive their dark matter properties through rotation curve decomposition. Our sample allows us to study the galaxy-halo connection across nearly six orders of magnitude in $M_\ast$. We find that the $M_{\rm gas}-M_{200}$ relation rises monotonically, with galaxies having around 4 per cent of the average cosmological baryon fraction in cold gas. Contrastingly, the $M_\ast-M_{200}$ relation shows a more complex behaviour. A particularly interesting finding is that of a population of baryon-deficient' dwarfs (BDDs) with stellar masses $\sim 1-1.5$ orders of magnitude lower than expected from current models. Yet, baryon-rich galaxies also exist, and we find a large spread in the baryon retention fraction across our galaxies. We compare our findings with semi-analytic and hydrodynamical galaxy formation simulations. While the simulations broadly reproduce most observed features, they struggle to match the BDDs and do not capture the diversity in baryon fractions. Understanding these differences will shed new light on how feedback regulates galaxy formation. Finally, we study the dark matter halo concentration-mass relation. We find that below $M_{200} \sim 10^{11}\,M_\odot$, the concentrations are systematically lower than expected. We discuss whether these results stem from the influence of baryonic physics or the environment.

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arXiv2025

MIGHTEE-HI: The radial acceleration relation with resolved stellar mass measurements

The radial acceleration relation (RAR) is a fundamental relation linking baryonic and dark matter in galaxies by relating the observed acceleration derived from dynamics to the one estimated from the baryonic mass. This relation exhibits small scatter, thus providing key constraints for models of galaxy formation and evolution -- allowing us to map the distribution of dark matter in galaxies -- as well as models of modified dynamics. However, it has only been extensively studied in the very local Universe with largely heterogeneous samples. We present a new measurement of the RAR, utilising a homogeneous sample of 19 HI-selected galaxies out to $z=0.08$. We introduce a novel approach of measuring resolved stellar masses using spectral energy distribution (SED) fitting across 10 photometric bands to determine the resolved mass-to-light ratio, which we show is essential for measuring the acceleration due to baryons in the low-acceleration regime. Our results reveal a tight RAR with a low-acceleration power-law slope of $\sim 0.5$, consistent with previous studies. Adopting a spatially varying mass-to-light ratio yields the tightest RAR with an intrinsic scatter of only $0.045 \pm 0.022$ dex, highlighting the importance of resolved stellar mass measurements in accurately characterising the gravitational contribution of the baryons in low-mass, gas-rich galaxies. We also find the first tentative evidence for redshift evolution in the acceleration scale, but more data will be required to confirm this. Adopting a more general MOND interpolating function, we find that our results ameliorate the tension between previous RAR analyses, the Solar System quadrupole and wide-binary test.

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arXiv2025

A depolarisation census of ASKAP fast radio bursts

Fast radio bursts (FRBs) are luminous, dispersed pulses of extra-galactic origin. The physics of the emission mechanism, the progenitor environment, and their origin are unclear. Some repeating FRBs are observed to have frequency-dependent exponential suppression in linear polarisation fraction. This has been attributed to multipath propagation in a surrounding complex magneto-ionic environment. The magnitude of depolarisation can be quantified using the parameter $\rm \sigma^{\prime}_{RM}$, which can be used to model the magneto-ionic complexity of the medium. In addition to depolarisation, some repeating sources (in particular those with active magneto-ionic environments) have been identified to have co-located persistent radio sources (PRS). Searches for depolarisation of non-repeating sources are challenging due to the limited bandwidth of most FRB detection systems used to detect one-off bursts. However, even with a limited bandwidth, such depolarisation can be identified if it lies within the $\rm \sigma^{\prime}_{RM}$ sensitivity window of the telescope. In this paper, we present a search for depolarisation in $12$ one-off FRBs detected by the Australian SKA Pathfinder. We report on the first strongly depolarised FRB detected by ASKAP (FRB$~$20230526A) and a marginal detection of depolarisation in a second. We also report constraints on the presence of a PRS coincident with FRB$~$20230526A using observations obtained with the Australia Telescope Compact Array. We use this to study the relationship between $\rm \sigma^{\prime}_{RM}$ and PRS luminosity. Our investigation supports a scenario in which repeaters and non-repeaters share a common origin and where non-repeaters represent an older population relative to repeating FRBs.

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arXiv2025

Enhanced Astrometry of the Rapid ASKAP Continuum Survey for Precise Localisation of Fast Radio Bursts

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.

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