Fast radio bursts at the dawn of the 2020s
  Since the discovery of the first fast radio burst (FRB) in 2007, and their
confirmation as an abundant extragalactic population in 2013, the study of
these sources has expanded at an incredible rate. In our 2019 review on the
subject we presented a growing, but still mysterious, population of FRBs -- 60
unique sources, 2 repeating FRBs, and only 1 identified host galaxy. However,
in only a few short years new observations and discoveries have given us a
wealth of information about these sources. The total FRB population now stands
at over 600 published sources, 24 repeaters, and 19 host galaxies. Higher time
resolution data, sustained monitoring, and precision localisations have given
us insight into repeaters, host galaxies, burst morphology, source activity,
progenitor models, and the use of FRBs as cosmological probes. The recent
detection of a bright FRB-like burst from the Galactic magnetar SGR~1935+2154
provides an important link between FRBs and magnetars. There also continue to
be surprising discoveries, like periodic modulation of activity from repeaters
and the localisation of one FRB source to a relatively nearby globular cluster
associated with the M81 galaxy. In this review, we summarise the exciting
observational results from the past few years. We also highlight their impact
on our understanding of the FRB population and proposed progenitor models. We
build on the introduction to FRBs in our earlier review, update our readers on
recent results, and discuss interesting avenues for exploration as the field
enters a new regime where hundreds to thousands of new FRBs will be discovered
and reported each year.
