Restrictions on the short time constant astrophysics

The comparatively new field of short time-constant astrophysics is investigated with the aim of checking the statement that there is a maximum amount of electromagnetic energy which can be radiated at a frequencev _m by an object whose size isL and during a time Δτ. Such limits are found under the assumptions that the emission is isotropic, thatL?cΔτ, and for the following four radiation mechanisms: incoherent synchrotron radiation, synchrotron maser, antenna radiation and for one simple case of radiation by a turbulent plasma. These limits are compared and found to be consistent with experimental data referring to the Sun, the pulsar NP 0532, the Quasar 3C 273 and the Seyfert galaxy NGC 4151. The main conclusion is that extragalactic radio astronomy at the present sensitivity level of observations is not likely to allow for the detection of pulses lasting less than 0.1 s.