FRB 20250607A: Weirder Than Fiction
Abstract
We present a detailed analysis of FRB 20250607A, a two-component FRB detected by the CRAFT survey which exhibits several unusual component-dependent properties, including apparent differential DM, circular polarisation, and time-resolved RM, together with a polarisation-angle (PA) swing that persists through the scattering tail. The scattering timescale and scintillation bandwidth are inconsistent with a single thin-screen origin, placing the dominant scattering screen within ≲61 kpc of the FRB source. The lack of PA flattening in the scattering tail is a behaviour not previously reported in an FRB or pulsar and difficult to reconcile with a simple propagation origin. We find no statistically significant differential DM between the two components despite an apparent, and visually obvious, difference in their dispersion, indicating that current uncertainties may be overly conservative. If this apparent differential DM is true, it implies a substantial difference in electron column density between the component sightlines. Two further CRAFT FRBs, FRB 20190611B and FRB 20210407E, show similarly large component-dependent electron-column differences, corresponding to electron-density contrasts consistent with plasma local to a neutron-star magnetosphere. We find no evidence for generalised Faraday rotation, and FRB 20210407E shows component-dependent PA structure. Taken together, these results suggest that the observed DM, circular polarisation, and PA behaviour may arise from differing sightlines through an inhomogeneous or evolving magnetosphere rather than from independent phenomena. Multi-component FRBs therefore provide a sensitive probe of plasma structure local to their progenitors.
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BibTeX
@misc{balzan202620250607a,
title = {{FRB 20250607A: Weirder Than Fiction}},
author = {J. C. F. Balzan and A. Bera and C. W. James and B. W. Meyers and A. T. Deller and R. M. Shannon and Z. Wang},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.18086},
eprint = {2609.18086},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.18086},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - FRB 20250607A: Weirder Than Fiction
AU - J. C. F. Balzan
AU - A. Bera
AU - C. W. James
AU - B. W. Meyers
AU - A. T. Deller
AU - R. M. Shannon
AU - Z. Wang
PY - 2026
DA - 2026/09/16
PB - arXiv
DO - 10.48550/arxiv.2609.18086
UR - https://arxiv.org/abs/2609.18086
AB - We present a detailed analysis of FRB 20250607A, a two-component FRB detected by the CRAFT survey which exhibits several unusual component-dependent properties, including apparent differential DM, circular polarisation, and time-resolved RM, together with a polarisation-angle (PA) swing that persists through the scattering tail. The scattering timescale and scintillation bandwidth are inconsistent with a single thin-screen origin, placing the dominant scattering screen within ≲61 kpc of the FRB source. The lack of PA flattening in the scattering tail is a behaviour not previously reported in an FRB or pulsar and difficult to reconcile with a simple propagation origin. We find no statistically significant differential DM between the two components despite an apparent, and visually obvious, difference in their dispersion, indicating that current uncertainties may be overly conservative. If this apparent differential DM is true, it implies a substantial difference in electron column density between the component sightlines. Two further CRAFT FRBs, FRB 20190611B and FRB 20210407E, show similarly large component-dependent electron-column differences, corresponding to electron-density contrasts consistent with plasma local to a neutron-star magnetosphere. We find no evidence for generalised Faraday rotation, and FRB 20210407E shows component-dependent PA structure. Taken together, these results suggest that the observed DM, circular polarisation, and PA behaviour may arise from differing sightlines through an inhomogeneous or evolving magnetosphere rather than from independent phenomena. Multi-component FRBs therefore provide a sensitive probe of plasma structure local to their progenitors.
ER -