FRB repetition and non-Poissonian statistics

TL;DR

This paper examines the statistical properties of fast radio bursts (FRBs), suggesting non-Poissonian repetition could influence detection strategies and interpretations of their spatial distribution, with implications for understanding their origins.

Contribution

It introduces a Bayesian framework for analyzing FRB statistics, explores the impact of non-Poissonian repetition on observed distributions, and reevaluates the significance of latitudinal dependence.

Findings

Non-Poissonian repetition can weaken current limits on FRB repeat rates.

The significance of the latitudinal gradient in FRB distribution is less than previously thought.

Survey strategy should favor shallow, wide-field observations due to non-repeating scenarios.

Abstract

We discuss some of the claims that have been made regarding the statistics of fast radio bursts (FRBs). In an earlier paper \citep{2015arXiv150505535C} we conjectured that flicker noise associated with FRB repetition could show up in non-cataclysmic neutron star emission models, like supergiant pulses. We show how the current limits of repetition would be significantly weakened if their repeat rate really were non-Poissonian and had a pink or red spectrum. Repetition and its statistics have implications for observing strategy, generally favouring shallow wide-field surveys, since in the non-repeating scenario survey depth is unimportant. We also discuss the statistics of the apparent latitudinal dependence of FRBs, and offer a simple method for calculating the significance of this effect. We provide a generalized Bayesian framework for addressing this problem, which allows for direct model comparison. It is shown how the evidence for a steep latitudinal gradient of the FRB rate is less strong than initially suggested and simple explanations like increased scattering and sky temperature in the plane are sufficient to decrease the low-latitude burst rate, given current data. The reported dearth of bursts near the plane is further complicated if FRBs have non-Poissonian repetition, since in that case the event rate inferred from observation depends on observing strategy.