arXiv subjects

A. C. Bradley

Publications and source records attributed to A. C. Bradley.

8 recordsLinked to original sources

arXiv2026

The MeerKAT 1.3 GHz Survey of the Large Magellanic Cloud

We present a radio-continuum survey of the LMC using the MeerKAT telescope, describe the full-Stokes products included in the first data release, and highlight some initial results. The observations are centred at 1.3 GHz with a bandwidth of 0.8 GHz. The imaging products comprise six fields of view, each encompassing $\sim$5$^\circ$ $\times$ 5$^\circ$ with the resulting images achieving a resolution of 8". The median broad-band Stokes~I image root-mean-square noise value is $\sim$11 $μ$Jy beam$^{-1}$. The survey enables a variety of astrophysical studies, which we showcase with the presentation of a few findings. Within the LMC we identify a new supernova remnant candidate; present planetary nebulae and Wolf-Rayet stars without previous radio detections; and show the MeerKAT view of the well-known star-forming region 30 Doradus. We also present some examples of interesting foreground and background sources in the field, including the AB~Dor multiple-star system, a radio ring galaxy, a possible Odd Radio Circle, and a remarkable bent-tail radio galaxy.

astro-ph.GA↗

arXiv2026

ASKAP EMU detection of an Odd Radio Circle (ORC) candidate: J094412-751016 (Anglerfish)

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 emission's non-thermal nature and 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 (SNR); 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 spectral index. 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.

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arXiv2026

The MeerKAT 1.3 GHz survey of the Large Magellanic Cloud: Point Source Catalogue

We present a point source catalogue of the Large Magellanic Cloud (LMC) using observations from the MeerKAT radio telescope across a broad frequency band centred at 1295 MHz (L-band) with 12 sub-bands and an angular resolution of 8 arcsec x 8 arcsec. We investigate the source flux density distribution and spectral indices and compare these results with previous radio catalogues, such as surveys conducted with the Australian Square Kilometre Array Pathfinder (ASKAP) at 888 MHz. This new MeerKAT survey reaches a lower average noise level of 11 microJy beam^-1, compared with the previous ASKAP level of 58 microJy beam^-1. The higher sensitivity and resolution enable the detection of a significantly larger number of faint sources. The catalogue contains 339,128 point sources, representing a substantial increase compared with the 54,612 sources detected in the ASKAP survey. This catalogue provides improved insight into the source population distribution, spectral properties, positional accuracy, and the overall improvement in source recovery and survey depth in the LMC region.

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arXiv2025

Evolutionary Map of the Universe: Detection of the Wolf-Rayet Star WR40

We present a radio-continuum detection of the well-known Wolf-Rayet star WR40 at 943.5 MHz using observations from the EMU survey. We find that the shell surrounding WR40, known as RCW 58, has a flux density of 158.9+/-15.8 mJy and the star itself is 0.41+/-0.04 mJy. The shell size is found to be 9' x 6', which matches well with the shell in Halpha and is similarly matched to the shell at 22 um in infrared. Using Gaia data, we derive a linear size of 7.32(+/-0.34) x 4.89(+/-0.23) pc at a distance of 2.79+/-0.13 kpc. We use previous ATCA observations at 8.64, 4.80, and 2.4 GHz to determine a spectral index of WR40, which is estimated to be alpha = 0.80+/-0.11, indicating that the emission from the star is thermal.

astro-ph.SR↗

arXiv2025

Evolutionary Map of the Universe: Detection and Analysis of the Shell Surrounding the Runaway Wolf-Rayet Star WR16

We present the first radio--continuum detection of the circumstellar shell around the well-known WN8 type Wolf-Rayet star WR16 at 943.5\,MHz using the \ac{ASKAP} \ac{EMU} survey. At this frequency, the shell has a measured flux density of 72.2$\pm$7.2\,mJy. Using previous \ac{ATCA} measurements at 2.4, 4.8, and 8.64~GHz, as well as the \ac{EMU} observations of the star itself, we determine a spectral index of $α\,=\,+0.74\pm0.02$, indicating thermal emission. We propose that the shell and star both exhibit thermal emission, supported by the its appearance in near-infrared and H$α$ observations. The latest \textit{Gaia} parallax is used to determine a distance of 2.28$\pm$0.09\,kpc. This star is well-known for its surrounding circular nebulosity, and using the distance and an angular diameter of 8\farcm42, we determine the shell size to be 5.57$\pm$0.22~pc. We use the \textit{Gaia} \acp{PM} of WR16 to determine peculiar velocities of the star as $V_α(pec) =$ --45.3$\pm$5.4\,\kms\ and $V_δ(pec) =$ 22.8$\pm$4.7\,\kms, which indicates that the star is moving in a north-west direction, and translates to a peculiar tangential velocity to be 50.7$\pm$6.9\,\kms. We also use these \acp{PM} to determine the shell's origin, estimate an age of $\sim 9500\pm 1300$\,yr, and determine its average expansion velocity to be $280\pm40$\,\kms. This average expansion velocity suggests that the previous transitional phase is a \ac{LBV} phase, rather than a \ac{RSG} phase. We also use the measured flux at 943.5~MHz to determine a mass-loss rate of $1.753\times 10^{-5}~M_\odot~$yr$^{-1}$, and use this to determine a lower-limit on ionising photons of $N_{UV} > 1.406\times 10^{47}~$s$^{-1}$.

astro-ph.SR↗

arXiv2025

The Evolutionary Map of the Universe: A new radio atlas for the southern hemisphere sky

We present the Evolutionary Map of the Universe (EMU) survey conducted with the Australian Square Kilometre Array Pathfinder (ASKAP). EMU aims to deliver the touchstone radio atlas of the southern hemisphere. We introduce EMU and review its science drivers and key science goals, updated and tailored to the current ASKAP five-year survey plan. The development of the survey strategy and planned sky coverage is presented, along with the operational aspects of the survey and associated data analysis, together with a selection of diagnostics demonstrating the imaging quality and data characteristics. We give a general description of the value-added data pipeline and data products before concluding with a discussion of links to other surveys and projects and an outline of EMU's legacy value.

astro-ph.GA↗

arXiv2025

ASKAP and VLASS search for a radio-continuum counterpart of ultra-high-energy neutrino event KM3-230213A

We present the results of an Australian Square Kilometre Array Pathfinder (ASKAP) 944 MHz and Very Large Array Sky Survey (VLASS) 3~GHz search for a radio-continuum counterpart of the recent ultra-high-energy (UHE) neutrino event, KM3-230213A. Using (ASKAP), we catalog 1052 radio sources within the 1.5$^\circ$ radius search area (68% certainty region) around the particle's calculated origin, 10 of which we classify as blazar candidates based on their radio spectra. The most prominent radio source in the search area is the nearby spiral galaxy UGCA 127 (nicknamed Phaedra, From Greek: $ϕαiδρα$, a Cretan princess of Greek Mythology, derived from Phaidros, Greek: $ϕαιδρoς$, meaning 'bright'.). Its non-thermal radio spectrum classifies it as a non-blazar active galactic nucleus (AGN). We also present an extended radio source, WISEA J061715.89-075455.4 (nicknamed Hebe, From Greek: $Hβη$, the Greek goddess of youth.), located only ~7' from the geometric center of the search area, with a very unusual highly polarized compact component. Finally, we present a strong radio source, EMU J062248-072246 (nicknamed Narcissus, From Greek $Nαρκισσoζ$ was a self-absorbed hunter from Thespiae in Boeotia.), which has a maximum self-absorption spectral slope of +2.5 at low frequencies, and exhibits ~25% flux density variability over the ~5-year VLASS 3~GHz survey.

astro-ph.HE↗

arXiv2025

ASKAP EMU Radio Detection of the Reflection Nebula VdB-80 in the Monoceros Crossbones Filamentary Structure

We present a new radio detection from the Australian Square Kilometre Array Pathfinder (ASKAP) Evolutionary Map of the Universe (EMU) survey associated with the reflection nebula (RN) VdB-80. The radio detection is determined to be a previously unidentified HII region, now named Lagotis. The RN is located towards Monoceros, centred in the molecular cloud feature known as the `Crossbones'. The 944 MHz EMU image shows a roughly semicircular HII region with an integrated flux density of 30.2$\pm$0.3 mJy. The HII region is also seen at 1.4 GHz by NVSS, yielding an estimated spectral index of 0.65$\pm$0.51, consistent with thermal radio emission. Gaia DR3 and 2MASS data give a distance to the stars associated with the HII region of $\sim$960 pc. This implies a size of 0.76$\times$0.68($\pm$0.09) pc for the HII region. We derive an HII region electron density of the bright radio feature to be 26 cm$^{-3}$, requiring a Lyman-alpha photon flux of $10^{45.6}$ s$^{-1}$, which is consistent with the expected Lyman flux of HD 46060, the B2II type star which is the likely ionising star of the region. The derived distance to this region implies that the Crossbones feature is a superposition of two filamentary clouds, with Lagotis embedded in the far cloud.

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