Narrowband Radio Technosignature Search Toward 3I/ATLAS with FAST

Abstract 3I/ATLAS is the third confirmed interstellar object passing through the solar system. In this work, we conduct a narrowband radio technosignature search toward 3I/ATLAS using the Five-hundred-meter Aperture Spherical Telescope (FAST) L -band multibeam receiver from 2025 October to 2026 January on four separate dates (i.e., Mars closest, perihelion, Earth closest, and a post-Earth-closest epoch, respectively). We carry out frequency-drifting signal searching with signal-to-noise ratio (SNR) over 10 within 1.05–1.45 GHz via bliss pipeline. These signal hits are grouped into event by beam, frequency, and drift rate matching. The events are then filtered by cluster analysis and drift rate cutoff. We also characterized the events by their significance in SNR, structure tensor, and principal component analysis. No credible narrowband radio technosignatures are detected from 3I/ATLAS after visual inspections. The null results place constraints on the presence of transmitters above 2.862 × 10 −3 W. We further introduce a Bayesian inference framework to assess the occurrence probability of hypothetical transmitters while accounting for uncertainty in their characteristic transmitter power through physically motivated priors.