The Galactic Position Dependence of Fast Radio Bursts and the Discovery of FRB 011025

TL;DR

This paper reports the discovery of an archival fast radio burst (FRB) and analyzes its Galactic position dependence, providing evidence supporting an extragalactic origin for FRBs through statistical modeling and comparison of detection rates.

Contribution

It presents the first detection of an FRB in archival data and develops a model to test the Galactic versus extragalactic origin hypothesis based on detection rates.

Findings

Detection of an FRB in archival data from 10 years earlier.

Statistical analysis strongly favors an extragalactic origin for FRBs.

Discrepancies between predicted and observed detection rates are discussed.

Abstract

We report the detection of a dispersed Fast Radio Burst (FRB) in archival intermediate-latitude Parkes Radio Telescope data. The burst appears to be of the same physical origin as the four purported extragalactic FRBs reported by Thornton et al. (2013). This burst's arrival time precedes the Thornton et al.~bursts by ten years. We consider that this survey, and many other archival low-latitude (|gb|<30deg) pulsar surveys, have been searched for FRBs but produced fewer detections than the comparatively brief Thornton et al.~search. Such a rate dependence on Galactic position could provide critical supporting evidence for an extragalactic origin for FRBs. To test this, we form an analytic expression to account for Galactic position and survey setup in FRB rate predictions. Employing a sky temperature, scattering, and dispersion model of the Milky Way, we compute the expected number of FRBs if they are isotropically distributed on the sky w.r.t. Galactic position (i.e. local), and if they are of extragalactic origin. We demonstrate that the relative detection rates reject a local origin with a confidence of 99.96% (~3.6 sigma). The extragalactic predictions provide a better agreement, however are still strong discrepancies with the low-latitude detection rate at a confidence of 99.69% (~2.9 sigma). However, for the extragalactic population, the differences in predicted vs.~detected population may be accounted for by a number of factors, which we discuss.