Upper limits for the radio pulse emission rate from exploding black holes

Abstract

IT has been suggested¹ that the explosion of a primordial black hole (pbh) might produce a coherent radio pulse detectable at a distance of ∼ 10⁴ pc with a simple antenna. Several searches^2–5 for radio pulses arriving from random directions in space, such as might be produced by supernovae^5–7, have already been carried out using wide beam (all-sky) antennas, and the negative results obtained are used here to place limits on the pbh radio pulse emission rate per unit volume. An indication has already been given⁸ of the limits which some previous radio searches impose, and of the influence of antenna aperture and beamwidth on achievable limits. This paper presents a more general analysis of limit criteria, including consideration of the effects on the pulse timescale of the interstellar medium, and examines the factors which determine the optimum search strategy for pbh radio pulses. It is reported that the best radio limit⁴ known to the author, could be improved by at least times 10⁶ using existing techniques. In addition, examination of this existing limit⁴ shows that it is already ∼ 80 times better (99.5% confidence level) than a limit which it has been suggested⁸ might be attainable in the optical region, and is ∼ 10⁶ times better than pbh explosion rate limits obtained from γ-ray observations^9,10, although the γ-ray limits do not involve the generation of a coherent electromagnetic pulse.