On the origin of a highly-dispersed coherent radio burst

TL;DR

This paper explores potential origins of a highly-dispersed radio burst, considering magnetar emissions, black hole annihilation, and other models, and constrains their likelihood based on observational data and theoretical limits.

Contribution

It introduces a comprehensive analysis of the burst's properties, evaluates multiple origin hypotheses, and sets new constraints on the density of black holes based on the detection rate.

Findings

The burst's flat spectrum suggests a magnetar origin.

Non-detection of subsequent bursts constrains pulsar periods to over 1 second.

Limits on black hole density are established based on detection rates.

Abstract

We discuss the possible source of a highly-dispersed radio transient discovered in the Parkes Multi-beam Pulsar Survey (PMPS). The pulse has a dispersion measure of $746\mathrm{cm}^{-3}\mathrm{pc}$, a peak flux density of 400 mJy for the observed pulse width of 7.8 ms, and a flat spectrum across a 288-MHz band centred on 1374 MHz. The flat spectrum suggests that the pulse did not originate from a pulsar, but is consistent with radio-emitting magnetar spectra. The non-detection of subsequent bursts constrains any possible pulsar period to $\gtrsim1$ s, and the pulse energy distribution to being much flatter than typical giant pulse emitting pulsars. The burst is also consistent with the radio signal theorised from an annihilating mini black hole. Extrapolating the PMPS detection rate, provides a limit of $\Omega_{BH}\lesssim5\times10^{-14}$ on the density of these objects. We investigate the consistency of these two scenarios, plus several other possible solutions, as potential explanations to the origin of the pulse, as well as for another transient with similar properties: the Lorimer Burst.