On the Fast Radio Burst and Persistent Radio Source Populations

TL;DR

This paper analyzes the properties and population of Fast Radio Bursts (FRBs) and their associated persistent radio sources (PRS), providing new definitions, statistical bounds, and insights into their nature and relation to other cosmic sources.

Contribution

It introduces a practical definition for PRS, models the FRB/PRS association probability, and bounds the FRB source density and PRS prevalence in the universe.

Findings

No evidence that repeaters are more associated with PRS.

Bounds on FRB per-source repetition rate: 25-440 yr$^{-1}$.

PRs may constitute up to 1% of local luminous radio sources.

Abstract

The first Fast Radio Burst (FRB) to be precisely localized was associated with a luminous persistent radio source (PRS). Recently, a second FRB/PRS association was discovered for another repeating source of FRBs. However, it is not clear what makes FRBs or PRS or how they are related. We compile FRB and PRS properties to consider the population of FRB/PRS sources. We suggest a practical definition for PRS as FRB associations with luminosity greater than $10^{29}$ erg s$^{-1}$ Hz$^{-1}$ that is not attributed to star-formation activity in the host galaxy. We model the probability distribution of the fraction of FRBs with PRS for repeaters and non-repeaters, showing there is not yet evidence for repeaters to be preferentially associated with PRS. We discuss how FRB/PRS sources may be distinguished by the combination of active repetition and an excess dispersion measure local to the FRB environment. We use CHIME/FRB event statistics to bound the mean per-source repetition rate of FRBs to be between 25 and 440 yr$^{-1}$. We use this to provide a bound on the density of FRB-emitting sources in the local universe of between $2.2\times10^2$ and $5.2\times10^4$ Gpc$^{-3}$ assuming a pulsar-like beam width for FRB emission. This density implies that PRS may comprise as much as 1\% of compact, luminous radio sources detected in the local universe. The cosmic density and phenomenology of PRS are similar to that of the newly-discovered, off-nuclear "wandering" AGN. We argue that it is likely that some PRS have already been detected and misidentified as AGN.