Abstract
We present the detection of rotationally modulated, circularly polarized radio emission from the T8 brown dwarf WISE J062309.94−045624.6 between 0.9 and 2.0 GHz. We detected this ...high-proper-motion ultracool dwarf with the Australian SKA Pathfinder in 1.36 GHz imaging data from the Rapid ASKAP Continuum Survey. We observed WISE J062309.94−045624.6 to have a time and frequency averaged Stokes
I
flux density of 4.17 ± 0.41 mJy beam
−1
, with an absolute circular polarization fraction of 66.3% ± 9.0%, and calculated a specific radio luminosity of
L
ν
∼ 10
14.8
erg s
−1
Hz
−1
. In follow-up observations with the Australian Telescope Compact Array and MeerKAT we identified a multipeaked pulse structure, used dynamic spectra to place a lower limit of
B
> 0.71 kG on the dwarf’s magnetic field, and measured a
P
= 1.912 ± 0.005 hr periodicity, which we concluded to be due to rotational modulation. The luminosity and period we measured are comparable to those of other ultracool dwarfs observed at radio wavelengths. This implies that future megahertz to gigahertz surveys, with increased cadence and improved sensitivity, are likely to detect similar or later-type dwarfs. Our detection of WISE J062309.94−045624.6 makes this dwarf the coolest and latest-type star observed to produce radio emission.
We present the detection of rotationally modulated, circularly polarized radio emission from the T8 brown dwarf WISE J062309.94-045624.6 between 0.9 and 2.0 GHz. We detected this high proper motion ...ultracool dwarf with the Australian SKA Pathfinder in \(1.36\) GHz imaging data from the Rapid ASKAP Continuum Survey. We observed WISE J062309.94-045624.6 to have a time and frequency averaged Stokes I flux density of \(4.17\pm0.41\) mJy beam\(^{-1}\), with an absolute circular polarization fraction of \(66.3\pm9.0\%\), and calculated a specific radio luminosity of \(L_{\nu}\sim10^{14.8}\) erg s\(^{-1}\) Hz\(^{-1}\). In follow-up observations with the Australian Telescope Compact Array and MeerKAT we identified a multi-peaked pulse structure, used dynamic spectra to place a lower limit of \(B>0.71\) kG on the dwarf's magnetic field, and measured a \(P=1.912\pm0.005\) h periodicity which we concluded to be due to rotational modulation. The luminosity and period we measured are comparable to those of other ultracool dwarfs observed at radio wavelengths. This implies that future megahertz to gigahertz surveys, with increased cadence and improved sensitivity, are likely to detect similar or later-type dwarfs. Our detection of WISE J062309.94-045624.6 makes this dwarf the coolest and latest-type star observed to produce radio emission.
We present the Sydney Radio Star Catalogue, a new catalogue of stars detected at megahertz to gigahertz radio frequencies. It consists of 839 unique stars with 3,405 radio detections, more than ...doubling the previously known number of radio stars. We have included stars from large area searches for radio stars found using circular polarisation searches, cross-matching, variability searches, and proper motion searches as well as presenting hundreds of newly detected stars from our search of Australian SKA Pathfinder observations. The focus of this first version of the catalogue is on objects detected in surveys using SKA precursor instruments; however we will expand this scope in future versions. The 839 objects in the Sydney Radio Star Catalogue are distributed across the whole sky and range from ultracool dwarfs to Wolf-Rayet stars. We find that the radio luminosities of cool dwarfs are lower than the radio luminosities of more evolved sub-giant and giant stars. We use X-ray detections of 530 radio stars by the eROSITA soft X-ray instrument onboard the SRG spacecraft to show that almost all of the radio stars in the catalogue are over-luminous in the radio, indicating that the majority of stars at these radio frequencies are coherent radio emitters. The Sydney Radio Star Catalogue can be found in Vizier or at https://radiostars.org.
The Australian SKA Pathfinder (ASKAP) has surveyed the sky at multiple frequencies as part of the Rapid ASKAP Continuum Survey (RACS). The first two RACS observing epochs, at 887.5 (RACS-low) and 1 ...367.5 (RACS-mid) MHz, have been released (McConnell, et al. 2020, PASA, 37, e048; Duchesne, et al. 2023, PASA, 40, e034). A catalogue of radio sources from RACS-low has also been released, covering the sky south of declination
$+30^{\circ}$
(Hale, et al., 2021, PASA, 38, e058). With this paper, we describe and release the first set of catalogues from RACS-mid, covering the sky below declination
$+49^{\circ}$
. The catalogues are created in a similar manner to the RACS-low catalogue, and we discuss this process and highlight additional changes. The general purpose primary catalogue covering 36 200 deg
$^2$
features a variable angular resolution to maximise sensitivity and sky coverage across the catalogued area, with a median angular resolution of
$11.2^{\prime\prime} \times 9.3^{\prime\prime}$
. The primary catalogue comprises 3 105 668 radio sources, including those in the Galactic Plane (2 861 923 excluding Galactic latitudes of
$|b|<5^{\circ}$
), and we estimate the catalogue to be 95% complete for sources above 2 mJy. With the primary catalogue, we also provide two auxiliary catalogues. The first is a fixed-resolution, 25-arcsec catalogue approximately matching the sky coverage of the RACS-low catalogue. This 25-arcsec catalogue is constructed identically to the primary catalogue, except images are convolved to a less-sensitive 25-arcsec angular resolution. The second auxiliary catalogue is designed for time-domain science and is the concatenation of source lists from the original RACS-mid images with no additional convolution, mosaicking, or de-duplication of source entries to avoid losing time-variable signals. All three RACS-mid catalogues, and all RACS data products, are available through the CSIRO ASKAP Science Data Archive (https://research.csiro.au/casda/).
The Australian SKA Pathfinder (ASKAP) has surveyed the sky at multiple frequencies as part of the Rapid ASKAP Continuum Survey (RACS). The first two RACS observing epochs, at 887.5 (RACS-low) and ...1367.5 (RACS-mid) MHz, have been released (McConnell et al., 2020; Duchesne et al., 2023). A catalogue of radio sources from RACS-low has also been released, covering the sky south of declination +30\(^\circ\) (Hale et al., 2021). With this paper, we describe and release the first set of catalogues from RACS-mid, covering the sky below declination +49\(^\circ\). The catalogues are created in a similar manner to the RACS-low catalogue, and we discuss this process and highlight additional changes. The general purpose primary catalogue covering 36 200 deg\(^2\) features a variable angular resolution to maximise sensitivity and sky coverage across the catalogued area, with a median angular resolution of 11.2" times 9.3". The primary catalogue comprises 3 105 668 radio sources, including those in the Galactic Plane (2 861 923 excluding Galactic latitudes of \(|b|<5^\circ\)) and we estimate the catalogue to be 95% complete for sources above 1.6 mJy. With the primary catalogue, we also provide two auxiliary catalogues. The first is a fixed-resolution, 25-arcsec catalogue approximately matching the sky coverage of the RACS-low catalogue. This 25-arcsec catalogue is constructed identically to the primary catalogue, except images are convolved to a less-sensitive 25-arcsec angular resolution. The second auxiliary catalogue is designed for time-domain science, and is the concatenation of source-lists from the original RACS-mid images with no additional convolution, mosaicking, or de-duplication of source entries to avoid losing time-variable signals. All three RACS-mid catalogues, and all RACS data products, are available through the CSIRO ASKAP Science Data Archive (CASDA).
Neutron stars and stellar-mass black holes are the remnants of massive star explosions. Most massive stars reside in close binary systems, and the interplay between the companion star and the newly ...formed compact object has been theoretically explored, but signatures for binarity or evidence for the formation of a compact object during a supernova explosion are still lacking. Here we report a stripped-envelope supernova, SN 2022jli, which shows 12.4-day periodic undulations during the declining light curve. Narrow H\(\alpha\) emission is detected in late-time spectra with concordant periodic velocity shifts, likely arising from hydrogen gas stripped from a companion and accreted onto the compact remnant. A new Fermi/LAT \(\gamma\)-ray source is temporally and positionally consistent with SN 2022jli. The observed properties of SN 2022jli, including periodic undulations in the optical light curve, coherent H\(\alpha\) emission shifting, and evidence for association with a \(\gamma\)-ray source, point to the explosion of a massive star in a binary system leaving behind a bound compact remnant. Mass accretion from the companion star onto the compact object powers the light curve of the supernova and generates the \(\gamma\)-ray emission.
