Observations of Fast Radio Bursts at Frequencies down to 400 Megahertz

TL;DR

This study reports the first detections of fast radio bursts at frequencies as low as 400 MHz, revealing diverse scattering behaviors and suggesting potential for future low-frequency FRB observations.

Contribution

First detection of FRBs at frequencies down to 400 MHz, expanding the observable frequency range and providing insights into their scattering environments.

Findings

Detected 13 FRBs at 400 MHz during early CHIME observations

Observed a variety of scattering behaviors among the FRBs

Identified an FRB with the lowest dispersion measure to date

Abstract

Fast radio bursts (FRBs) are highly dispersed millisecond-duration radio flashes likely arriving from far outside the Milky Way galaxy. This phenomenon was discovered at radio frequencies near 1.4 GHz and to date has been observed in one case at as high as 8 GHz, but not below 700 MHz in spite of significant searches at low frequencies. Here we report detections of FRBs at radio frequencies as low as 400 MHz, on the Canadian Hydrogen Intensity Mapping Experiment (CHIME) using the CHIME/FRB instrument. We present 13 FRBs detected during a telescope pre-commissioning phase, when our sensitivity and field-of-view were not yet at design specifications. Emission in multiple events is seen down to 400 MHz, the lowest radio frequency to which we are sensitive. The FRBs show a variety of temporal scattering behaviours, with the majority significantly scattered, and some apparently unscattered to within measurement uncertainty even at our lowest frequencies. Of the 13 reported here, one event has the lowest dispersion measure yet reported, implying it is among the closest yet known, and another has shown multiple repeat bursts, as described in a companion paper. Our low-scattering events suggest that efforts to detect FRBs at radio frequencies below 400 MHz will eventually be successful. The overall scattering properties of our sample suggest that FRBs as a class are preferentially located in environments that scatter radio waves more strongly than the diffuse interstellar medium (ISM) in the Milky Way.