Nondetection of FAST and Parkes Follow-up Observation for 27 Parkes-discovered Fast Radio Bursts

Abstract To investigate whether apparently nonrepeating fast radio bursts (FRBs) are truly one-off transients, we conducted systematic follow-up observations of 27 out of 81 nonrepeating FRBs identified in the Parkes Transient Database. Using 59.0 hr of data from the Parkes Ultra-Wideband Low receiver and 6.3 hr from the Five-hundred-meter Aperture Spherical Telescope 19-beam receiver, we searched for repeated bursts from these sources. No additional bursts were detected from any of the 27 FRBs. Combining these nondetections with prior archival observations, we derived stringent upper limits on their repetition rates above 1 Jy under two statistical models: Poisson process constraints range from ∼10 −3.5 to 10 −1.9 hr −1 , while Weibull process constraints range from ∼10 −3.4 to 10 −1.5 hr −1 . These limits are approximately an order of magnitude stricter than those reported in previous studies. By applying consistent observational setups and analytical methodologies across all sources, the derived rate limits converge to a narrow, well-defined range. This suggests that these FRBs form a relatively homogeneous population with extremely low intrinsic activity rates.