Nondetection of CHIME/Fast Radio Burst Sources with the Arecibo Observatory

In this work, we present follow-up observations of two known repeating fast radio bursts (FRBs) and seven nonrepeating FRBs with complex morphology discovered with the CHIME/FRB project. These observations were conducted with the Arecibo Observatory 327 MHz receiver. We detected no additional bursts from these sources, nor did CHIME/FRB detect any additional bursts from these sources during our follow-up program. Based on these nondetections, we provide constraints on the repetition rate for all nine sources. We calculate repetition rates above 1 Jy using both a Poisson distribution of repetition and the Weibull distribution of repetition presented by Oppermann et al. For both distributions we find repetition upper limits of the order λ = 10⁻²-10⁻¹ hr⁻¹ for all sources. These rates are much lower than those published for notable repeating FRBs like FRB 20121102A and FRB 20201124A, suggesting the possibility of a low-repetition subpopulation.