A fast radio burst (FRB) is a high energy burst of radio a few milliseconds long. Only a small number have been recorded, i.e., on the order of 35 through 2018, the first one having been recorded in 2001. The origin is unknown: only one has been found that repeats (irregularly), and for the others, no corresponding signals have been caught that would help indicate possible sources. However, characteristics of the signals suggest they are from beyond the Milky Way. A number of theories have been put forward, such as neutron star quakes or superluminous supernovae. The antennas that have caught them have isolated them to arcminutes, but their direction needs to be identified to arcseconds to identify a galaxy or other source. Given observation counts and the fields of view that yielded the observations, it has been estimated that their rate across the sky is on the order of 6000 per day.
The characteristic that indicates they are extra-galactic is their high pulse velocity dispersion and its form: the frequency drops roughly linearly with time, as it would if the burst traveled through the intergalactic medium. This is evidence against theories that suggest they originate at nearby stars.
Among the early bursts were some that are now discounted. They had been labeled perytons and strongly suspected of being unreal, and later where shown to be from opening the door of a nearby microwave oven. An early claim was that one (non-peryton) burst came from M87, but this has been discounted. Some bursts have been observed by multiple telescopes, establishing their identity as astronomical. One burst, FRB 121102 has since repeated (non-periodically), yielding a means of studying at least this series in detail and a galaxy has been identified as its source.