Phenomenology and Observational Signatures of the S-RUF Model

We investigate the effective phenomenology of compact objects within the Shielded Regular Unified Framework (S-RUF). Based on Simpson–Visser black-bounce geometries supported by magnetic
Nonlinear Electrodynamics (NLED) sources, we analyze the near-extremal regime (ℓ ≈ 2M) and its
impact on internal stability. In this configuration, the surface gravity of the inner horizon is strongly
suppressed, mitigating the classical mass inflation mechanism and allowing for a geodesically complete interior description.
From an astrophysical perspective, the model admits stationary solutions in the compact-object
mass gap (M ∼ 2.6 M⊙), offering a geometric alternative to the secondary component of the
GW190814 event. We further examine how modifications of the innermost stable circular orbit
(ISCO) in the S-RUF geometry are compatible with rapid early black hole growth scenarios inferred
from JWST observations of compact high-redshift galaxies, while maintaining a radiative efficiency
comparable to the Schwarzschild case. Finally, we discuss optical and transient signatures, including
echoes and shadow substructures, that provide falsifiable observational tests for future facilities