Sensitive Multibeam Targeted SETI Observations toward 33 Exoplanet Systems with FAST

As a major approach to looking for life beyond the Earth, the search for extraterrestrial intelligence (SETI) is committed to searching for technosignatures such as engineered radio signals that are indicative of technologically capable life. In this paper, we report a targeted SETI campaign employing an observation strategy named multibeam coincidence matching at the Five-hundred-meter Aperture Spherical radio Telescope toward 33 known exoplanet systems, searching for ETI narrowband drifting signals across 1.05-1.45 GHz in two orthogonal linear polarization directions separately. A signal at 1140.604 MHz detected from the observation toward Kepler-438 originally piqued our interest because its features are roughly consistent with assumed ETI technosignatures. However, evidences such as its polarization characteristics are able to eliminate the possibility of an extraterrestrial origin. Our observations achieve an unprecedented sensitivity because the minimum equivalent isotropic radiated power we are able to detect reaches 1.48 x 10(9) W.