Archival Very Large Array Non-Detection of a Persistent Radio Source associated with FRB 20250316A

ATel #17111; Walter W. Golay (Harvard), Edo Berger (Harvard), Harsh Kumar (Harvard), and Daichi Hiramatsu (Harvard)
on 25 Mar 2025; 21:45 UT
Credential Certification: Walter Golay (wgolay@cfa.harvard.edu)

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We analyzed archival NRAO Very Large Array (VLA) observations of the field of FRB 20250316A (VOEvent #439373176, ATel #17081) to search for an associated persistent radio source (PRS). The VLA observed the field most recently on 2012 November 30 from 18:00-18:30 UTC under program VLA/12A-059 to target SN 2008X in NGC 4141. The total on-source time was 13m21s, the array was in A-configuration, and observed the field with the lower subband of the EVLA X-band (8-10 GHz) for an approximate synthesized beam size of 0.2 arcseconds. We calibrated the data using NRAO CASA (v6.6.1) with the most recent VLA Pipeline (v2024.1.0.8) and imaged the field using standard wideband parameters. The image phase center was set to the originally-reported coordinates of 12h09m54.24s +58d50m57.84s (J2000) from CHIME (ATel #17081) which revealed a single source in the field consistent with the reported errors of the original position. The source is located at 12h09m56.18s +58d51m05.00s (J2000) and has a flux density of 30 +/- 5 micro-Jy, and is coincident with the nucleus of the galaxy WISEA J120956.19+585105.1 (z=0.245+/-0.03 from the Legacy Survey DR9 Photo-z Survey). We estimate a luminosity nu L_nu = 3E38 erg/s, typical for radio-quiet active galactic nuclei (AGN) and attribute the radio source to a low-level AGN in this background galaxy.

The updated CHIME-KKO position (ATel #17086) is approximately 2 arcminutes westward from the original position and no PRS is detected with a 3-sigma upper limit of 15 micro-Jy. At the distance of 40 Mpc for NGC 4141 the luminosity upper limit on a PRS is L_nu = 3E25 erg/s/Hz. This limit is ~1E3.5 lower than previously-detected PRSs associated with some repeating FRBs, and the best limit to date other than FRB 20200120E in M81.

We note that this limit also applies at the position of the weak and apparently steady X-ray source identified in Einstein Probe Wide-field X-ray Telescope (ATel #17083), Einstein Probe Follow-up X-ray Telescope (ATel #17100), and Swift/XRT observations (ATel #17101, ATel #17109).

The Photometric Redshifts for the Legacy Surveys (PRLS) catalog used in this work was produced thanks to funding from the U.S. Department of Energy Office of Science, Office of High Energy Physics via grant DE-SC0007914.

VLA Image