A Milliarcsecond Localization Associates FRB 20190417A with a Compact Persistent Radio Source and an Extreme Magnetoionic Environment

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Abstract
We report the milliarcsecond localization of a high (∼1379 pc cm −3 ) dispersion measure (DM) repeating fast radio burst (FRB), FRB 20190417A. Combining European VLBI Network detections of five repeat bursts, we confirm the FRB’s host to be a low-metallicity, star-forming dwarf galaxy at z = 0.12817, similar to the hosts of FRB 20121102A, FRB 20190520B, and FRB 20240114A. We also confirm that it is associated with a previously reported persistent radio source (PRS), which is compact on milliarcsecond scales. Visibility-domain model fitting constrains the transverse physical size of the PRS to μ Jy at 1.4 GHz. Though we do not find significant evidence for DM evolution, FRB 20190417A exhibits a time-variable rotation measure (RM) ranging between +3958 ± 11 rad m −2 and +5061 ± 24 rad m −2 over a 50-day period. We find no evidence for intervening galaxy clusters in the FRB’s line of sight and place a conservative lower limit on the rest-frame host DM contribution of 1228 pc cm −3 (90% confidence)—the largest known for any FRB so far. This system strengthens the emerging picture of a rare subclass of repeating FRBs with large and variable RMs, above-average host DMs, and luminous PRS counterparts in metal-poor dwarf galaxies. Our results suggest that these systems are the result of environmental selection, or a distinct engine for FRB emission.
Funding Information
  • Simons Foundation (MP-SCMPS-00001470)
  • Nederlandse Organisatie voor Wetenschappelijk Onderzoek (VI.Veni.212.058)
  • EC ∣ European Research Council (101098079)
  • Canada Excellence Research Chairs, Government of Canada (CERC-2022-00009)
  • Nederlandse Organisatie voor Wetenschappelijk Onderzoek (VI.C.192.045)
  • National Science Foundation (2018490)
  • Natural Sciences and Engineering Research Council of Canada (RGPIN-2019-06186)
  • Natural Sciences and Engineering Research Council of Canada (RGPIN-2024-06266)

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