Polarization Properties of 128 Nonrepeating Fast Radio Bursts from the First CHIME/FRB Baseband Catalog

Abstract

We present a 400–800 MHz polarimetric analysis of 128 nonrepeating fast radio bursts (FRBs) from the first CHIME/FRB baseband catalog, increasing the total number of FRB sources with polarization properties by a factor of ∼3. A total of 89 FRBs have >6σ linearly polarized detections, 29 FRBs fall below this significance threshold and are deemed linearly unpolarized, and for 10 FRBs, the polarization data are contaminated by instrumental polarization. For the 89 polarized FRBs, we find Faraday rotation measure (RM) amplitudes, after subtracting approximate Milky Way contributions, in the range 0.5–1160 rad m−2 with a median of 53.8 rad m−2. Most nonrepeating FRBs in our sample have RMs consistent with Milky Way–like host galaxies, and their linear polarization fractions range from ≤10% to 100% with a median of 63%. We see marginal evidence that nonrepeating FRBs have more constraining lower limits than repeating FRBs for the host electron-density-weighted line of sight magnetic field strength. We classify the nonrepeating FRB polarization position angle (PA) profiles into four archetypes: (i) single component with constant PA (57% of the sample), (ii) single component with variable PA (10%), (iii) multiple components with a single-constant PA (22%), and (iv) multiple components with different or variable PAs (11%). We see no evidence for population-wide frequency-dependent depolarization, and, therefore, the spread in the distribution of fractional linear polarization is likely intrinsic to the FRB emission mechanism. Finally, we present a novel method to derive redshift lower limits for polarized FRBs without host galaxy identification and test this method on 20 FRBs with independently measured redshifts.

The Curious Case of Twin Fast Radio Bursts: Evidence for Neutron Star Origin?

“…Pulsar-like PA evolution has been observed for other FRBs (e.g., Mckinven et al 2024;Pandhi et al 2024). The PA "swing" in pulsars (albeit typically for average profiles) is generally described by the "rotating vector model" (RVM; Radhakrishnan & Cooke 1969;Johnston & Kramer 2019), where the PA traces the projection of the magnetic field at the emission site onto the sky plane as the neutron star rotates.…”

“…Time-resolved analysis of the bursts, with full polarization information, provides key insights into the nature of the FRB progenitors, since changes on submillisecond timescales can only be attributed to the progenitor itself, or the magneto-ionic environment in the immediate vicinity of the progenitor (e.g., Luo et al 2020). Such studies require very high signal-to-noise ratio (S/N) polarization profiles of FRBs at microsecond time resolution, which are relatively rare for nonrepeating FRBs (see also Pandhi et al 2024).…”

Updating the First CHIME/FRB Catalog of Fast Radio Bursts with Baseband Data

“…Host galaxies of four FRBs in the sample have been presented by Bhardwaj et al (2023); analysis is in progress to extend the number of host associations in the local Universe. Finally, the polarization properties of the FRB sample have been recently presented by Pandhi et al (2024), and they will be compared with the polarization properties of a large sample of repeating FRBs.…”