A Radio Source Coincident with the Superluminous Supernova PTF10hgi: Evidence for a Central Engine and an Analog of the Repeating FRB 121102?

We present the detection of an unresolved radio source coincident with the position of the Type I superluminous supernova (SLSN) PTF10hgi (z = 0.098) about 7.5 yr post-explosion, with a flux density of F _ν(6 GHz) ≈ 47.3 μJy and a luminosity of L _ν(6 GHz) ≈ 1.1 × 10²⁸ erg s^-1 Hz^-1. This represents the first detection of radio emission coincident with an SLSN on any timescale. We investigate various scenarios for the origin of the radio emission: Star formation activity, an active galactic nucleus, and a non-relativistic supernova blastwave. While any of these would be quite novel if confirmed, none appear likely when considered within the context of the other properties of the host galaxy, previous radio observations of SLSNe, and the general population of hydrogen-poor supernovae (SNe). Instead, the radio emission is reminiscent of the quiescent radio source associated with the repeating FRB 121102, which has been argued to be powered by a magnetar born in a SLSN or long gamma-ray burst explosion several decades ago. We show that the properties of the radio source are consistent with a magnetar wind nebula or an off-axis jet, indicating the presence of a central engine. Our directed search for fast radio bursts from the location of PTF10hgi using 40 minutes of Very Large Array phased-array data reveals no detections to a limit of 22 mJy (10σ; 10 ms duration). We outline several follow-up observations that can conclusively establish the origin of the radio emission.