Abstract

We report the discovery of a highly dispersed fast radio burst (FRB), FRB 181123, from an analysis of similar to 1500 hr of drift scan survey data taken using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The pulse has three distinct emission components, which vary with frequency across our 1.0-1.5 GHz observing band. We measure the peak flux density to be >0.065 Jy and the corresponding fluence >0.2 Jy ms. Based on the observed dispersion measure of 1812 cm(-3) pc, we infer a redshift of similar to 1.9. From this, we estimate the peak luminosity and isotropic energy to be less than or similar to 2 x 10(43) erg s(-1) and less than or similar to 2 x 10(40) erg, respectively. With only one FRB from the survey detected so far, our constraints on the event rate are limited. We derive a 95% confidence lower limit for the event rate of 900 FRBs per day for FRBs with fluences >0.025 Jy ms. We performed follow-up observations of the source with FAST for four hours and have not found a repeated burst. We discuss the implications of this discovery for our understanding of the physical mechanisms of FRBs.