A depolarization census of ASKAP fast radio bursts

ABSTRACT Fast radio bursts (FRBs) are luminous, dispersed pulses of extragalactic origin. The physics of the emission mechanism, the progenitor environment, and their origin are unclear. Some repeating FRBs exhibit a frequency-dependent decrease in linear polarization fraction. This has been attributed to multipath propagation in a surrounding complex magneto-ionic environment. In this framework, the depolarization magnitude can be quantified using the parameter $\sigma ^{\prime }_{\rm RM}$, which can be used to model the magneto-ionic complexity of the medium. In addition to depolarization, some repeating sources (specifically, those with complex magneto-ionic environments) have been identified to have co-located persistent radio sources (PRS). Searches for depolarization of non-repeating sources are challenging due to the limited bandwidth of most FRB detection systems. However, even with a limited bandwidth, such depolarization can be identified if it lies within the $\sigma ^{\prime }_{\rm RM}$ sensitivity window of the telescope. In this paper, we present a search for depolarization in 12 one-off FRBs detected by the Australian SKA Pathfinder. We report on a strongly depolarized (apparently) non-repeating FRB detected by ASKAP (FRB 20230526A). The source shows a decrease in linear polarization fraction from $\sim$60 per cent at 1440 MHz to $\sim$20 per cent at 1110 MHz. We also report constraints on the presence of a PRS coincident with FRB 20230526A using observations obtained with the Australia Telescope Compact Array. We use this to study the relationship between $\sigma ^{\prime }_{\rm RM}$ and PRS luminosity. Our 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 FRB sources.