Extremely band-limited repetition from a fast radio burst source

TL;DR

This paper reports the detection of a highly band-limited repeating fast radio burst from FRB 20190711A, providing new insights into the emission mechanism and emphasizing the importance of sub-banded search techniques.

Contribution

It presents the first detection of a narrowband repeating FRB burst at 0.7-4.0 GHz, constraining emission models and demonstrating the need for sub-banded searches.

Findings

Detected a 1 ms burst with 65 MHz bandwidth from FRB 20190711A.

Observed spectral scaling consistent with propagation effects, not diffractive scintillation.

Rules out models predicting broad-band emission for this FRB source.

Abstract

The fast radio burst (FRB) population is observationally divided into sources that have been observed to repeat and those that have not. There is tentative evidence that the bursts from repeating sources have different properties than the non-repeating ones. In order to determine the occurrence rate of repeating sources and characterize the nature of repeat emission, we have been conducting sensitive searches for repetitions from bursts detected with the Australian Square Kilometre Array Pathfinder (ASKAP) with the 64-m Parkes radio telescope, using the recently commissioned Ultra-wideband Low (UWL) receiver system, over a band spanning 0.7$-$4.0 GHz. We report the detection of a repeat burst from the source of FRB 20190711A. The detected burst is 1 ms wide and has a bandwidth of just 65 MHz. We find no evidence of any emission in the remaining part of the 3.3 GHz UWL band. While the emission bandwidths of the ASKAP and UWL bursts show $\nu^{-4}$ scaling consistent with a propagation effect, the spectral occupancy is inconsistent with diffractive scintillation. This detection rules out models predicting broad-band emission from the FRB 20190711A source and puts stringent constraints on the emission mechanism. The low spectral occupancy highlights the importance of sub-banded search methods in detecting FRBs.