Fast radio burst - persistent radio source systems II. A faint PRS associated with the nearby FRB 20181030A?

D. Pelliciari; G. Bernardi; B. Margalit; B. D. Metzger; C. Nanci; L. Bruno; M. Pilia; L. Beduzzi; C. Spingola; C. Stanghellini; P. Esposito; A. Geminardi; M. Giroletti

arXiv · 2609.35730

Fast radio burst - persistent radio source systems II. A faint PRS associated with the nearby FRB 20181030A?

D. Pelliciari·G. Bernardi·B. Margalit·B. D. Metzger·C. Nanci·L. Bruno·M. Pilia·L. Beduzzi·C. Spingola·C. Stanghellini·P. Esposito·A. Geminardi·M. Giroletti

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Abstract

Persistent radio sources (PRSs) are the continuum counterparts of fast radio bursts (FRBs), the latter being extragalactic transients of millisecond duration and Jy-level flux density. An FRB-PRS system is thought to be a flaring magnetar surrounded by an highly magnetized, baryon-loaded nebula. We aim to constrain the size of 20181030A-S1, a new PRS candidate, potentially associated with the repeating FRB 20181030A. The latter is localized with $\sim 1'$ uncertainties in the outskirts of NGC 3252, which is a spiral galaxy at a luminosity distance of $20$ Mpc. We report very long baseline interferometric (VLBI) observations using the European VLBI Network at $1.7$ GHz of this PRS candidate at an angular resolution of $20$ milliarcseconds. Our observations reveal the presence of an unresolved radio source (20181030A-S1) at the position of the PRS candidate, confirming its compactness at milli-arcsecond angular scales. A fit to the position of the point-source yields a peak flux density of $280 \pm 30$ $μ$Jy and a transverse physical size constrained to be $R < 0.5$ pc at $68\%$ confidence level (CL). This flux density converts to a spectral luminosity of $(9 \pm 1) \times 10^{25}$ erg s$^{-1}$ Hz$^{-1}$, $\sim 3$ orders of magnitude lower than confirmed PRSs, making 20181030A-S1 the closest and faintest PRS candidate known. Its low luminosity and modest rotation measure are consistent with the $L_ν-$rotation measure (RM) relation followed by confirmed FRB--PRS systems, supporting a common physical origin in magnetar-powered nebulae. We show how a magnetized wind nebula powered by an initially weak ($B_\star \simeq 10^{15}$ G) and young ($t_{\rm age} \simeq 15 - 150$ yrs) magnetar can account for both the observed spectral luminosity and RM of the system. Other possible origin scenarios for 20181030A-S1, in the case in which it is unrelated to the FRB source, are also discussed.

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D. Pelliciari, G. Bernardi, B. Margalit, B. D. Metzger, C. Nanci, L. Bruno, M. Pilia, L. Beduzzi, C. Spingola, C. Stanghellini, P. Esposito, A. Geminardi, M. Giroletti. 2026-09-28. Fast radio burst - persistent radio source systems II. A faint PRS associated with the nearby FRB 20181030A?. https://arxiv.org/abs/2609.35730

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