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

Alexandra M. Moroianu; Shivani Bhandari; Maria R. Drout; Jason W. T. Hessels; Danté M. Hewitt; Franz Kirsten; Benito Marcote; Ziggy Pleunis; Mark P. Snelders; Navin Sridhar; Uwe Bach; Emmanuel K. Bempong-Manful; Vladislavs Bezrukovs; Richard Blaauw; Justin D. Bray; Salvatore Buttaccio; Shami Chatterjee; Alessandro Corongiu; Roman Feiler; B. M. Gaensler; Marcin P. Gawroński; Marcello Giroletti; Adaeze L. Ibik; Ramesh Karuppusamy; Mattias Lazda; Calvin Leung; Michael Lindqvist; Kiyoshi W. Masui; Daniele Michilli; Kenzie Nimmo; Omar S. Ould-Boukattine; Ayush Pandhi; Zsolt Paragi; Aaron B. Pearlman; Weronika Puchalska; Paul Scholz; Kaitlyn Shin; Jurjen J. Sluman; Matteo Trudu; David Williams-Baldwin; Jun Yang

arXiv · 2509.05174

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

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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.

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Alexandra M. Moroianu, Shivani Bhandari, Maria R. Drout, Jason W. T. Hessels, Danté M. Hewitt, Franz Kirsten, Benito Marcote, Ziggy Pleunis, Mark P. Snelders, Navin Sridhar, Uwe Bach, Emmanuel K. Bempong-Manful, Vladislavs Bezrukovs, Richard Blaauw, Justin D. Bray, Salvatore Buttaccio, Shami Chatterjee, Alessandro Corongiu, Roman Feiler, B. M. Gaensler, Marcin P. Gawroński, Marcello Giroletti, Adaeze L. Ibik, Ramesh Karuppusamy, Mattias Lazda, Calvin Leung, Michael Lindqvist, Kiyoshi W. Masui, Daniele Michilli, Kenzie Nimmo, Omar S. Ould-Boukattine, Ayush Pandhi, Zsolt Paragi, Aaron B. Pearlman, Weronika Puchalska, Paul Scholz, Kaitlyn Shin, Jurjen J. Sluman, Matteo Trudu, David Williams-Baldwin, Jun Yang. 2025-12-11. A milliarcsecond localization associates FRB 20190417A with a compact persistent radio source and an extreme magneto-ionic environment. https://arxiv.org/abs/2509.05174

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