Fast radio bursts (FRBs) are luminous, dispersed pulses of extra-galactic origin. The physics of the emission mechanism, the progenitor environment, and their origin are unclear. Some repeating FRBs are observed to have frequency-dependent exponential suppression in linear polarisation fraction. This has been attributed to multipath propagation in a surrounding complex magneto-ionic environment. The magnitude of depolarisation can be quantified using the parameter σ′RM, which can be used to model the magneto-ionic complexity of the medium. In addition to depolarisation, some repeating sources (in particular those with active magneto-ionic environments) have been identified to have co-located persistent radio sources (PRS). Searches for depolarisation of non-repeating sources are challenging due to the limited bandwidth of most FRB detection systems used to detect one-off bursts. However, even with a limited bandwidth, such depolarisation can be identified if it lies within the σ′RM sensitivity window of the telescope. In this paper, Uttarkar et al. present a search for depolarisation in 12 one-off FRBs detected by the Australian SKA Pathfinder. They report on the first strongly depolarised FRB detected by ASKAP (FRB 20230526A) and a marginal detection of depolarisation in a second. They also report constraints on the presence of a PRS coincident with FRB 20230526A using observations obtained with the Australia Telescope Compact Array. They use this to study the relationship between σ′RM and PRS luminosity. Their investigation supports a scenario in which repeaters and non-repeaters share a common origin and where non-repeaters represent an older population relative to repeating FRBs.

The above image shows the spectral depolarisation of FRBs 20210320C and 20230526A. The most favoured model is plotted for each burst by the dashed line. FRBs 20210320C and 20230526A show evidence for exponential suppression of the linear polarisation fraction over the ASKAP observing band.