A milliarcsecond localization associates FRB 20190417A with a compact persistent radio source and an extreme magneto-ionic environment

TL;DR

This paper precisely localizes FRB 20190417A, links it to a compact persistent radio source in a dwarf galaxy, and reveals an extreme, variable magneto-ionic environment, advancing understanding of FRB origins.

Contribution

It provides the first milliarcsecond localization of FRB 20190417A and characterizes its environment and persistent radio source in detail, highlighting a rare subclass of FRBs.

Findings

FRB 20190417A is associated with a compact radio source less than 23 pc in size.

The host galaxy is a low-metallicity, star-forming dwarf at z=0.12817.

The FRB exhibits a highly variable rotation measure over three years.

Abstract

We report the milliarcsecond localization of a high (1379 pc/cc) dispersion measure (DM) repeating fast radio burst, 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 FRBs 20121102A, 20190520B and 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 < 23 pc and yields an integrated flux density of 191(39) microJy 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) and +5061(24) rad/m2 over three years. 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/cc (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.