Rotating Radio Transients

Gamma-ray and X-ray telescopes have long been sensitive to transient phenomena, with rich scientific returns resulting from the discovery of sources such as gamma-ray bursts, soft gamma-ray repeaters and anomalous X-ray pulsars. The situation at radio wavelengths, however, is dramatically different. While radio telescopes typically have sensitivity to events with short timescales, they have much narrower fields of view than their high-energy counterparts. Consequently, most transient radio studies have been follow-up observations of events first detected at higher energies. Radio transient studies are important, however, as they can probe explosive and dynamic events which do not necessarily have counterparts at other wavelengths.

Figure 3.1 illustrates the types of objects that we might expect to discover with surveys for short timescale (i.e. durations ≲ 1 day) radio transients. The brightest such sources are radio pulsars, with the “nano-giant” pulses from the Crab pulsar having brightness temperatures up to 10³⁸ K [23] and the single pulses of “normal” pulsars having brightness temperatures of 10²⁸ K. Well-known weaker sources include planetary radio flares [6], Type I and Type II flares from the Sun and other stars [41], bursts from active stars such as UV Ceti and AD Leo [42], OH maser emission [10], radio flares from brown dwarfs such as BD LP944—20 [3], AGN radio outbursts [1] and intraday variability of GRB afterglows [19] and other extra-galactic radio sources due to interstellar scintillation [32].