FRB microstructure revealed by the real-time detection of FRB170827

TL;DR

This paper reports the real-time detection and detailed analysis of a new FRB with fine temporal and spectral structures, revealing insights into its origin and properties using advanced low-latency machine learning methods.

Contribution

First real-time detection of an FRB with a machine-learning system enabling high-resolution analysis of its microstructure.

Findings

FRB170827 has the lowest dispersion measure in the population.

The burst exhibits three temporal components with sub-30 microsecond widths.

Spectral modulations suggest origin in the host galaxy or nearby environment.

Abstract

We report a new Fast Radio Burst (FRB) discovered in real-time as part of the UTMOST project at the Molonglo Observatory Synthesis Radio Telescope (MOST). FRB170827 is the first detected with our low-latency ($< 24$ s), machine-learning-based FRB detection system. The FRB discovery was accompanied by the capture of voltage data at the native time and frequency resolution of the observing system, enabling coherent dedispersion and detailed off-line analysis, which have unveiled fine temporal and frequency structure. The dispersion measure (DM) of 176.80 $\pm$ 0.04 pc cm$^{-3}$, is the lowest of the FRB population. The Milky Way contribution along the line of sight is $\sim$ 40 pc cm$^{-3}$, leaving an excess DM of $\sim$ 145 pc cm$^{-3}$. The FRB has a fluence $>$ 20 $\pm$ 7 Jy ms, and is narrow, with a width of $\sim$ 400 $\mu$s at 10$\%$ of its maximum amplitude. However, the burst shows three temporal components, the narrowest of which is $\sim$ 30 $\mu$s, and a scattering timescale of $4.1 \pm 2.7$ $\mu$s. The FRB shows spectral modulations on frequency scales of 1.5 MHz and 0.1 MHz. Both are prominent in the dynamic spectrum, which shows a very bright region of emission between 841 and 843 MHz, and weaker, patchy emission across the entire band. We show the fine spectral structure could arise in the FRB host galaxy, or its immediate vicinity.