Fast radio transients are pulses of dispersed radio emission lasting less than 1 second. Slower radio transients originate predominantly in synchrotron emission, while faster transients are caused by coherent processes. Furthermore, at timescales faster than 1 second, propagation through the Galactic plasma induces dispersion, the frequency-dependent arrival time quantified by dispersion measure (DM), that begins to be detectable at MHz through GHz radio frequencies.
Fast transients surveys at the Parkes Observatory has revealed a new population of radio transients: the FRB \cite{2007Sci...318..777L,2013Sci...341...53T}. Their DMs range up to 1100 pc cm\(^{-3}\), an order of magnitude larger than expected from the Galaxy and consistent with propagation through the IGM from distances up to z\(\sim\)1.
Basic questions about FRBs remain open: What are they? and How can we use them? If they do in fact lie at cosmological distances, their dispersion can measure the baryonic mass of the IGM, much as Galactic pulsars of known distance have mapped the electron content of the Milky Way \cite{2002astro.ph..7156C}. Beyond using FRBs as probes, understanding the origin of FRBs may have relevance to gamma-ray bursts and sources of gravitational waves \cite{2013arXiv1307.1409F,2013ApJ...776L..39K}.
Similar pulsar surveys have discovered a new class of Galactic radio transient: the rotating radio transient \cite{2006Natur.439..817M}. It is unclear whether extreme objects like magnetars or ordinary pulsars can generate pulses detected as RRATs \cite{2006ApJ...645L.149W}.
Moving slightly beyond our Galaxy, the most distant radio transients associated with a host galaxy are in M31 \cite{2013MNRAS.428.2857R}. The dispersion measure of any pulses known to be in M31 would make the first constraint on the Milky Way and M31 halo baryon content, which would help address the “missing baryon problem” \cite{2007ARA&A..45..221B}.
Jupiter emits intense radio bursts that make it the brightest astronomical object in the solar system below 100 MHz. Coronal mass ejections (much as seen in the Sun), also drive radio fast, coherent radio flares. These processes could be used to measure magnetism and plasma properties of other stars \cite{2007ApJ...663L..25H} and should profoundly affect the habitability of orbiting exoplanets \cite{2007AsBio...7...30T}. transients.