fast radio burst

A fast radio burst (FRB) is a high energy burst of radio a few milliseconds long. By 2022, thousands had been recorded, from thousands of sources, largely by radio telescopes adapted to detect them. The first burst (the Lorimer burst, FRB 010724) was unknowingly recorded in 2001, its recording noticed in 2007. For some years afterward, no more than a few were detected. Particular bursts were soon observed by multiple telescopes, establishing their identity as astronomical. The characteristics of the signals indicate they are from beyond the Milky Way: the dispersion measures (DM) indicate they passed through more electrons than can be accounted for by the Milky-Way interstellar medium. The origin of FRBs remains a topic of research, with numerous theories, including as neutron star quakes or superluminous supernovae, and there remains the possibility of more than one mechanism. Given current FRB observation-counts and the fields of view that yield these counts, their rate across the entire sky is thought to be on the order of a thousand per day.

Among the early recorded bursts were some termed perytons that were strongly suspected of being unreal, and indeed were shown to result from opening the door of a nearby microwave oven (a lesson about side lobes and the benefit of radio quiet zones). FRB121102 was the first FRB for which additional bursts were later detected from the same direction (non-periodically), allowing detailed study including identifying a source galaxy, and since 2018, more such repeaters have come to light, and the FRB sources are now classified as FRB repeaters or FRB non-repeaters. Additional efforts to record FRBs, using more-recently-completed radio telescopes (CHIME, FAST) have led to more information, such as the presence of shifts within a single burst to lower frequencies, even when discounting the obvious travel-induced dispersion. They show a pattern nicknamed sad trombone, incorporating several sub-bursts, each with a downward-sliding frequency and each starting at a lower frequency that the previous. Theories based upon repeating FRBs suggest there might exist fast optical bursts (FOBs) associated with them. Unfortunately, FOBs are presumed to be sufficiently dim that catching one could require continuous monitoring of an established source-location by a major research telescope and such an FOB would be much too short to be detected by Rubin Observatory's planned cadence.

FRBs have potential as probes of the intergalactic medium (IGM) and their host galaxy. An observed DM can be compared with models that calculate the expected contribution of the Milky Way, the IGM, and the FRB's host galaxy: if there are good independent estimates for two of those, the remainder is a possibly-useful estimate of the third. Another characteristic of interest is that some of the pulses are somewhat longer and tail off, presumed to have undergone a process termed scatter broadening, and a plausible explanation of the differing types is that it stems from characteristics of the host galaxy. The bursts are subject to gravitational lensing, and at least one recorded burst apparently traversed the halo of an intervening galaxy.

The term fast radio transient (FRT) means basically the same thing as FRB, but also includes any abrupt beginning or end of a lengthier signal. FRB astronomy is still relatively new but has potential as part of the future's multi-messenger astronomy. It also has the potential to be used as a probe, such as analysis of an FRB that passes through halo of an intervening galaxy, and also the possibility of gravitational microlensing.

The Transient Name Server (TNS) took over the tracking and cataloging FRBs in 2020, adopting the designator format "FRB YYYYMMDDabc", i.e., including a space character, an 8-digit date that begins with a 4-digit year, and alphabetic characters indicating the order of report-acceptance. This is analogous to the TNS's designation of other transients, including its supernova designators. FRBCAT (aka FRB Catalogue) is an older, no-longer-updated online catalog of FRBs and candidates.