2025ApJ...991L..27L

The nature of dark matter remains unknown, motivating the study of fuzzy/wave dark matter (FDM/ψDM) and self-interacting dark matter (SIDM) as alternative frameworks to address small-scale discrepancies in halo profiles inferred from observations. This study presents a nonparametric reconstruction of the mass distribution of the previously found dark subhalo in the strong lensing system JVAS B1938+666. Compared with the standard Navarro-Frenk-White profile, both SIDM and ψDM (${m}_{\psi }=1.3{2}_{-0.31}^{+0.22}\times 1{0}^{-22}\,{\rm{eV}}$) provide significantly better fits to the resulting density profile. Moreover, the SIDM model is favored over ψDM with a Bayes factor of 14.44. The reconstructed density profile features a characteristic kiloparsec-scale core (r_c ≈ 0.5 kpc) with central density ${\rho }_{c}\approx 2.5\times 1{0}^{7}\,{{M}_{\odot }\,\mathrm{kpc}}^{-3}$, exhibiting remarkable consistency with the core-halo mass scaling relations observed in Local Group dwarf spheroidals. These findings offer insights that may help address the core-cusp discrepancy in ΛCDM substructure predictions.