We consider the vectorial analogue of the thin free boundary problem introduced in cite{CRS} as a realization of a nonlocal version of the classical Bernoulli problem. We study optimal regularity, nondegeneracy, and density properties of local minimizers. Via a blow-up analysis based on a Weiss type monotonicity formula, we show that the free boundary is the union of a regular and a singular part. Finally we use a viscosity approach to prove $C^{1,alpha}$ regularity of the regular part of the free boundary.
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