A Deep SETI Search for Technosignatures in the TRAPPIST-1 System with FAST

The Five-hundred-meter Aperture Spherical Telescope (FAST) is the world’s largest single-dish radio telescope, and the search for extraterrestrial intelligence (SETI) is one of its five key science objectives. We conducted a targeted search for unresolved narrowband radio technosignatures toward the TRAPPIST-1 system using FAST. The observations consisted of five independent L -band pointings, each with a 20 minute integration, for a total on-source time of 1.67 hr. The frequency coverage spanned 1.05–1.45 GHz with a spectral resolution of ∼7.5 Hz. We searched Stokes I (total intensity) data for drifting signals with Doppler drift rates within ±20 Hz s ^−1 and a signal-to-noise ratio threshold of S/N = 10. For unresolved, minimally drifting narrowband signals, the nominal minimum detectable equivalent isotropic radiated power is ${{\rm{EIRP}}}_{\min }\approx 1.44\times 1{0}^{10}\,{\rm{W}}$ . We explicitly quantify how this limit degrades at high drift rates because of tree de-Doppler power smearing, reaching ≈3.84 × 10 ^11 W at $| \dot{\nu }| =20\,{\rm{Hz}}\,{{\rm{s}}}^{-1}$ under a conservative peak-channel sensitivity correction. No credible technosignature candidates attributable to the TRAPPIST-1 system were identified within the searched parameter space. Nevertheless, TRAPPIST-1 remains a compelling target for future SETI efforts. We plan to extend our search to other signal types, such as periodic, transient, broadband, and propagation-broadened transmitters, and to carry out broader surveys of nearby exoplanetary systems with FAST.