Unveiling the Local Environment of FRB 20220912A Subarcsecond 4–26 GHz Radio Continuum Mapping

The local environments of repeating fast radio bursts (FRBs) provide critical clues to their progenitors. While some active repeaters (e.g., FRB 20121102A and FRB 20190520B) are embedded in compact persistent radio sources (PRS), others appear to reside in cleaner environments. We present a high-resolution, multifrequency (4−26 GHz) continuum study of the hyperactive repeater FRB 20220912A using the Karl G. Jansky Very Large Array (VLA). We report the discovery of a previously unknown radio source distinct from the compact PRSs seen in other FRBs, spatially coincident with the FRB position and offset by ≈300 mas (≈450 pc) from the host galaxy’s center. The absence of continuum emission in archival milliarcsecond-resolution VLBI observations indicates that the source is resolved out, ruling out a hypercompact (<1 pc) central-engine-powered origin. We constrain the physical diameter of the emitting region between 75 pc and 190 pc. We further demonstrate that the source is characterized by a steep nonthermal spectral index (α ≈ −0.73) and a remarkably high star formation rate surface density Σ_SFR ≳ 13 M_⊙ yr⁻¹ kpc⁻². We argue that this emission is best explained as a compact star-forming region within the host galaxy. This association with a site of ongoing star formation provides strong observational support for a core-collapse supernova origin for the progenitor of FRB 20220912A, highlighting that at least a subpopulation of active, repeating FRBs originates from young magnetars embedded in intense star-forming knots.