Dual-Backend Multibeam Position Switching Targeted SETI Observations toward Nearby Active Planet-Hosting Systems with FAST

Abstract: The Five-hundred-meter Aperture Spherical Telescope (FAST), the world's largest single-dish radio telescope, lists the search for extraterrestrial intelligence (SETI) as one of its key scientific objectives. In this work, we present a targeted SETI observation for 7 nearby active stars utilizing the FAST L-band multibeam receiver, employing a observational strategy that combines position switching with multibeam tracking to balance on-source integration time with the accuracy of the beam response. Using both pulsar and SETI backends, we perform a comprehensive search for narrowband drifting signals with Doppler drift rates within $\pm 4 \ \mathrm{Hz\ s^{-1}}$ and channel-width periodic signal with periods between 0.12 and 100 s and duty cycles between 10\% and 50\%. No credible radio technosignatures were detected from any of the target systems. Based on this null result, we place constraints on the presence of transmitters at a 95\% confidence level, ruling out narrowband transmitters with with EIRP above $3.98\times10^8 \,\mathrm{W}$ and periodic transmitter with EIRP above $1.80\times10^{10} \,\mathrm{W}$,respectively, within the observation band.