The Square Kilometre Array (SKA)

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Anomaly Detection and Radio-frequency Interference Classification with Unsupervised Learning in Narrowband Radio Technosignature Searches

The Astronomical Journal American Astronomical Society 169:4 (2025) 206-206

Authors:

Ben Jacobson-Bell, Steve Croft, Carmen Choza, Alex Andersson, Daniel Bautista, Vishal Gajjar, Matthew Lebofsky, David HE MacMahon, Caleb Painter, Andrew PV Siemion

Abstract:

Abstract The search for radio technosignatures is an anomaly detection problem: Candidate signals represent needles of interest in the proverbial haystack of radio-frequency interference (RFI). Current search frameworks find an enormity of false-positive signals, especially in large surveys, requiring manual follow-up to a sometimes prohibitive degree. Unsupervised learning provides an algorithmic way to winnow the most anomalous signals from the chaff, as well as group together RFI signals that bear morphological similarities. We present Grouping Low-frequency Observations By Unsupervised Learning After Reduction (GLOBULAR) clustering, a signal processing method that uses hierarchical density-based spatial clustering of applications with noise (or HDBSCAN) to reduce the false-positive rate and isolate outlier signals for further analysis. When combined with a standard narrowband signal detection and spatial filtering pipeline, such as turboSETI, GLOBULAR clustering offers significant improvements in the false-positive rate over the standard pipeline alone, suggesting dramatic potential for the amelioration of manual follow-up requirements for future large surveys. By removing RFI signals in regions of high spectral occupancy, GLOBULAR clustering may also enable the detection of signals missed by the standard pipeline. We benchmark our method against the C. Choza et al. turboSETI-only search of 97 nearby galaxies at the L band, demonstrating a false-positive hit reduction rate of 93.1% and a false-positive event reduction rate of 99.3%.
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Contemporaneous optical-radio observations of a fast radio burst in a close galaxy pair

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 538:3 (2025) 1800-1815

Authors:

KY Hanmer, I Pastor-Marazuela, J Brink, D Malesani, BW Stappers, PJ Groot, AJ Cooper, N Tejos, DAH Buckley, ED Barr, MC Bezuidenhout, S Bloemen, M Caleb, LN Driessen, R Fender, F Jankowski, M Kramer, DLA Pieterse, KM Rajwade, J Tian, PM Vreeswijk, R Wijnands, PA Woudt
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Looking at the Distant Universe with the MeerKAT Array: The H i Mass Function in the Local Universe

The Astrophysical Journal American Astronomical Society 981:2 (2025) 208

Authors:

Amir Kazemi-Moridani, Andrew J Baker, Marc Verheijen, Eric Gawiser, Sarah-Louise Blyth, Danail Obreschkow, Laurent Chemin, Jordan D Collier, Kyle W Cook, Jacinta Delhaize, Ed Elson, Bradley S Frank, Marcin Glowacki, Kelley M Hess, Benne W Holwerda, Zackary L Hutchens, Matt J Jarvis, Melanie Kaasinen, Sphesihle Makhathini, Abhisek Mohapatra, Hengxing Pan, Anja C Schröder, Leyya Stockenstroom, Mattia Vaccari, Tobias Westmeier, John F Wu, Martin Zwaan
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The Ejection of Transient Jets in Swift J1727.8-1613 Revealed by Time-Dependent Visibility Modelling

(2025)

Authors:

Callan M Wood, James CA Miller-Jones, Arash Bahramian, Steven J Tingay, He-Xin Liu, Diego Altamirano, Rob Fender, Elmar Körding, Dipankar Maitra, Sera Markoff, David M Russell, Thomas D Russell, Craig L Sarazin, Gregory R Sivakoff, Roberto Soria, Alexandra J Tetarenko, Valeriu Tudose

The Radio Counterpart to the Fast X-Ray Transient EP240414a

The Astrophysical Journal American Astronomical Society 981:1 (2025) 48-48

Authors:

Joe S Bright, Francesco Carotenuto, Rob Fender, Carmen Choza, Andrew Mummery, Peter G Jonker, Stephen J Smartt, David R DeBoer, Wael Farah, James Matthews, Alexander W Pollak, Lauren Rhodes, Andrew Siemion

Abstract:

Abstract Despite being operational for only a short time, the Einstein Probe mission, with its large field of view and rapid localization capabilities, has already significantly advanced the study of rapid variability in the soft X-ray sky. We report the discovery of luminous and variable radio emission from the Einstein Probe fast X-ray transient EP240414a, the second such source with a radio counterpart. The radio emission at 3 GHz peaks at ∼30 days postexplosion and with a spectral luminosity ∼2 × 1030 erg s−1 Hz−1, similar to what is seen from long gamma-ray bursts, and distinct from other extragalactic transients including supernovae and tidal disruption events, although we cannot completely rule out emission from engine driven stellar explosions, e.g., the fast blue optical transients. An equipartition analysis of our radio data reveals that an outflow with at least a moderate bulk Lorentz factor (Γ ≳ 1.6) with a minimum energy of ∼1048 erg is required to explain our observations. The apparent lack of a reported gamma-ray counterpart to EP240414a could suggest that an off-axis or choked jet could be responsible for the radio emission, although a low-luminosity gamma-ray burst may have gone undetected. Our observations are consistent with the hypothesis that a significant fraction of extragalactic fast X-ray transients are associated with the deaths of massive stars.
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