First fast radio burst search campaign at the Argentine Institute of Radio Astronomy

Abstract

Fast radio bursts (FRBs) are intense millisecond-duration radio transients of extragalactic origin whose physical nature remains under active investigation, and which also serve as probes of the intergalactic medium. We report on the first FRB search campaign carried out at the Argentine Institute of Radio Astronomy (IAR) between December 2024 and March 2026, targeting nearby galaxy superclusters in the southern sky. We observed fields in the Ophiuchus, Shapley, and Sculptor/Phoenix supercluster regions with one of the two 30~m antennas of the IAR, using a ROACH-based backend with 400~MHz of bandwidth centred at 1400~MHz and a time resolution of 41--82~$\mu$s, for a total net observing time of 212~h. The data were searched for dispersed single pulses with \texttt{PRESTO} in the dispersion measure range $100 \leq \mathrm{DM} \leq 500$, and candidates were classified with the FETCH machine learning classifier. The pipeline was validated on archival Parkes data containing known FRBs and on synthetic bursts injected into IAR observations. One FRB candidate, FRB~20251018, was identified on 18 October 2025 in an observation pointed towards the galaxy cluster A2870, in the Phoenix supercluster, with a dispersion measure of $243$, a signal-to-noise ratio of 8.2, and a FETCH probability of $p=0.99$. To the best of our knowledge, this would be the first FRB detected from South America. A set of more marginal candidates is also presented. These results demonstrate the capability of the IAR antennas to detect FRBs and support the continuation and extension of the monitoring campaign, including coincident dual-antenna observations and cross-matches with gravitational-wave events and electromagnetic transients.