Fast Radio Bursts (FRBs) are extra-galactic millisecond bursts of radio emission. FRBs are extremely bright, with spectral luminosities up to ten orders of magnitude greater than radio emission from Galactic pulsars, and are visible to high redshift. In the last decade they have proven great potential in probing free-electrons in the intergalactic medium (IGM), which help us in understanding the evolution of baryons and large-scale structure formation. However, because their observables provide information of integrated line-of-sight quantities, unlocking their potential to probe large scale structure is dependent on modelling their progenitors and surrounding environments.  Polarisation provides perhaps the most direct probe of the FRB emission mechanism, and hence the FRB progenitor population.  FRBs typically have high levels of linear polarisation and modest circular polarisation.

Dial et al. present high-time resolution (HTR) spectro-polarimetric data for 34 new fast radio bursts (FRBs) discovered by the Commensal Real-time Fast Transients (CRAFT) survey on ASKAP during the period May 2024 to June 2026. Most of these were detected by the higher-sensitivity CRAFT COherent (CRACO) detection system that was commissioned on the telescope during this period. This new sample doubles the size of the CRAFT HTR catalogue and probes a fainter population of FRBs thanks to the improved sensitivity of CRACO. The team compare the distribution of extragalactic rotation measure (RM) and polarisation fraction to FRBs detected by the CHIME and DSA telescopes. While no significant differences were seen between CRAFT and DSA, the extragalactic RM distribution seen in CHIME FRBs (which are detected at lower frequency) was substantially lower. Surprisingly, no significant differences were found in the linear polarisation fraction distribution between the three FRB catalogues, suggesting an indifference to the different telescope observing frequencies.

The image above shows a mosaic of CRAFT FRBs, dedispersed to the structure-maximising DM and averaged in time and frequency for visual clarity. Top panel: Polarisation angle profile.  Middle panel: Stokes I (total intensity), L (linear polarisation) and V (circular polarisation) time series.  The time and frequency resolution are labeled in the upper right corner of the panel. Bottom panel: Dynamic spectra.  Flagged channels are denoted by orange markings. A green star next to FRB name indicates the burst has been properly polarisation calibrated.

As Monday October 5th is a public holiday in NSW, the next ADAP will be Tuesday October 6th.