SETI Observations of k-Hz Periodic Radio Signals from Five Nearby Stars with FAST at L Band

TL;DR

This study adapts a per-channel Fast Folding Algorithm (FFA)–based technosignature search to FAST’s 19-beam L-band data to look for periodic, kHz-wide radio beacons from five nearby stars. The authors implement a multi-layer RFI mitigation and clustering pipeline, validate it on PSR B0329+54, and apply it to Groombridge 34 A/B, Ross 248, 61 Cyg B, and Ross 128, finding no convincing detections. They derive stringent EIRP limits of roughly $7$–$9 \times 10^{9}$ W for 1.05–1.45 GHz kHz-wide periodic signals, representing among the strongest constraints to date on such technosignatures from nearby stellar systems. The work demonstrates FAST’s capability for periodic beacons, provides a template for linking technosignature limits to stellar/planetary demographics, and outlines clear paths for future multi-epoch, multi-band surveys to tighten population-level constraints.

Abstract

We report a radio SETI search for periodic, kHz-wide signals from five of the nearest stars observable with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Using the 19-beam L-band receiver (1.05-1.45 GHz), we obtained 1200 s tracking observations of Groombridge 34 A/B, Ross 248, 61 Cygni B, and Ross 128. Dynamic spectra from all beams and both linear polarisations were searched channel by channel with a fast-folding algorithm sensitive to periods between 1.1 and 300 s. A multi-layer RFI-mitigation pipeline exploits multi-beam occupancy, cross-target bad-channel statistics, XX/YY polarisation coincidence, broad frequency masks, and narrow site-specific RFI exclusion zones, followed by clustering in period-frequency space. The pipeline is validated on FAST observations of PSR B0329+54, where we recover the known 0.714 s spin period and harmonic structure in the expected beam. For the stellar sample, successive cuts reduce the raw FFA hit lists (> 10^6 hits per target) to a small number of cluster-level candidates, all of which exhibit clear radio-frequency interference signatures in phase-time and phase-frequency diagnostics. We therefore report no convincing detections of periodic transmitters in our searched parameter space. Using the radiometer equation with our adopted detection threshold (S/N = 25) and assuming a duty cycle delta = 0.1, we obtain upper limits of approximately (7-9) x 10^9 W on the isotropic-equivalent EIRP of kHz-wide periodic beacons at these stars, among the most stringent constraints to date on periodic radio emission from nearby stellar systems.

Figures (6)

• Figure 1: The positions of the five target stars on the FAST sky coverage map
• Figure 2: Schematic workflow of the data analysis and RFI mitigation pipeline. The sequence progresses from the initial search (Stage A0) through multi-beam (A1), cross-target (A2), polarization (A3), and frequency-domain (A4) masking, followed by the working-band excision (A5). The "A6 Local RFI Zones Excision" step is an additional refinement applied exclusively to the 61 Cyg B dataset to remove persistent target-specific interference (see Section \ref{['sec:rfizones']}). The hit count reductions resulting from each filtering stage (A0--A5) are detailed in Table \ref{['tab:rfi_flagging_aastex']}.
• Figure 3: Detection of test pulsar B0329+54 and its harmonics as the two distinct peaks at $\approx 0.71s$ and $1.42 s$.
• Figure 4: The phase-resolved spectrum of the pulsar B0329+54 based on the period obtained by BLIPSS.The top panel shows the average flux density ($\overline{S}$) in arbitrary units as a function of the phase relative to MJD 60219.7792 UTC. The bottom panel is a grayscale plot showing the radio frequency (MHz) on the vertical axis and the phase on the horizontal axis.The right panel plots the average flux density ($\overline{S}$) in arbitrary units as a function of radio frequency.
• Figure 5: Examples of phase--time diagnostic plots for representative high-S/N hits in the final stages of the pipeline. Left: A5 hits for Groombridge 34 A, illustrating typical residual RFI morphology in the phase--time domain where a consistent vertical line is absent (short-lived, band-limited bursts or obvious instrumental artefacts). Right: A6 hits for 61 Cyg B after application of the RMS-based RFI exclusion zones (Table \ref{['tab:rfizones']}); all exhibit clear RFI-like behaviour rather than stable, strictly periodic technosignatures.