Persistence Confirmation and Observational Follow-up Strategy for Unidentified Circularly Polarized V-LoTSS Radio Sources

The V-LoTSS survey (Callingham et al. 2023) detected 68 circularly polarized radio sources at 144 MHz, of which five to six remain unidentified in any multiwavelength catalog. Two sources — ILTJ100804. 68+594731. 5 (|V/I| = 61. 5%, SI = 0. 87 mJy) and ILTJ104408. 20+341243. 6 (|V/I| = 48. 5%, SI = 0. 90 mJy) — were previously identified as priority follow-up targets (Leonforte 2026, VFD Technical Note LXXII) on account of their anomalously high circular polarization fraction and absence of known counterparts. We report here the results of a comprehensive archival catalog search conducted on 2026-03-19, and develop the observational follow-up strategy. Key findings: (1) Both sources are independently confirmed in LoTSS DR3 (Shimwell et al. 2026), establishing source persistence over a baseline of 3-8 years and definitively ruling out single flare events. (2) ILTJ104408 has a candidate K5-M0 main-sequence stellar counterpart at 3. 7 arcsec separation (Pan-STARRS r = 15. 37, Gaia G = 15. 42, BP-RP = 1. 097, WISE W1 = 13. 36, W1-W2 = -0. 06), whose physical association is ambiguous given a 3. 7-sigma positional offset; this source is reclassified as Tier 2. (3) ILTJ100804 remains completely unidentified at all wavelengths across Pan-STARRS, Gaia EDR3, AllWISE, FIRST, SDSS, LAMOST, and SIMBAD, and is elevated to primary Tier 1 status. We propose a five-epoch LOFAR monitoring campaign totaling 20 hours, with international-baseline imaging in epoch 1 for precision astrometry, and sub-band imaging at 10 MHz channel resolution to characterize spectral morphology. We also discuss the theoretical context and the physically attainable spectral discrimination tests.