The FAST-SETI Milky Way Globular Cluster Survey I: A Pilot Multibeam On-the-Fly Search of Five Globular Clusters at L-Band

TL;DR

This study conducted a sensitive search for technosignatures in five Milky Way globular clusters using FAST's multibeam capabilities, but found no evidence of extraterrestrial signals, setting new sensitivity limits and methodological benchmarks.

Contribution

It introduces a novel multibeam on-the-fly search strategy with geometry-aware gating for globular clusters, pioneering the use of FAST for such technosignature surveys.

Findings

No technosignatures detected above the sensitivity threshold.

Established flux density and power limits for potential extraterrestrial beacons.

Demonstrated the effectiveness of geometry-aware gating and multibeam strategies.

Abstract

We report a narrowband technosignature search toward five Milky Way globular clusters (NGC 6171, NGC 6218, NGC 6254, NGC 6838, and IC 1276) using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) 19-beam L-band receiver (1.05-1.45 GHz). We adapt the MultiBeam Point-source Scanning (MBPS) strategy to extended targets by gating detections to generalized on-target windows (gOTWs), i.e. the time intervals when a beam main lobe intersects a buffered cluster mask, and by enforcing the deterministic multibeam illumination sequence as a geometry test. Dynamic spectra with frequency resolution about 7.5 Hz and time resolution about 10 s are searched with turboSETI over drift rates |nu_dot| <= 4 Hz s^-1 at signal-to-noise ratio S/N >= 10. From about 2.75e5 raw hits across both linear polarizations, none survive the gOTW gating, array-wide simultaneity veto, in-stripe ordering, and single-drift coherence checks, yielding a robust null result. With system equivalent flux density SEFD about 1.5 Jy and an effective 60 s per illuminated crossing, our per-crossing flux density threshold is S_min about 0.50 Jy, corresponding to minimum isotropic-equivalent radiated power EIRP_min in the range (0.72-1.8)e16 W for cluster distances 4-6.5 kpc; when multiple illuminated crossings occur, non-coherent stacking improves sensitivity by up to sqrt(N). To our knowledge this is the first FAST technosignature survey dedicated to globular clusters and the first to use MBPS as the primary observing strategy. These limits disfavor bright, persistent, isotropic L-band beacons above the stated thresholds during our epochs and establish a scalable blueprint, based on geometry-aware gating and verification, for multi-epoch MBPS campaigns that expand signal morphologies and combine passes to deepen constraints on transmitters in dense stellar systems.