Fast radio burst morphology in the first CHIME/FRB catalog

Fast radio bursts (FRBs) exhibit a variety of time-frequency structures, shaped by an unknown emission mechanism and transformed by propagation through an ionized and inhomogeneous medium. FRBs comprised of downward-drifting sub-bursts seem ubiquitous among repeating sources of FRBs but have so far not been seen in one-off FRBs. The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a 4-cylinder 80m x 100m transit radio interferometer, located at the Dominion Radio Astrophysical Observatory near Penticton, B.C. The CHIME/FRB experiment is set to release a first catalog of 517 FRBs, 60 of which are bursts from 18 different repeater sources, detected in the 400-800 MHz octave, all detected with the same instrument and a similar selection function. With this first catalog, we confirm that repeater bursts, on average, have larger widths and we show, for the first time, that repeater bursts, on average, are narrower in bandwidth. This difference could be due to a beaming or propagation effect, or it can be intrinsic to the populations.