Topology and geometry of 6-dimensional (1,0) supergravity black hole horizons

We show that the supersymmetric near horizon black hole geometries of 6-dimensional supergravity coupled to any number of scalar and tensor multiplets are either locally $Ad{S}_3\times {\mathrm{\Sigma }}^3$, where \Sigma^3 is a homology 3-sphere, or ${\text{bR}}^{1,1}\times {\mathcal{S}}^4$, where ${\mathcal{S}}^4$ is a 4-manifold whose geometry depends on the hypermultiplet scalars. In both cases, we find that the tensorini multiplet scalars are constant and the associated 3-form field strengths vanish. We also demonstrate that the $AdS_3\times \Sigma^3$ horizons preserve 2, 4 and 8 supersymmetries. For horizons with 4 supersymmetries, \Sigma^3 is in addition a non-trivial circle fibration over a topological 2-sphere. The near horizon geometries preserving 8 supersymmetries are locally isometric to either $Ad{S}_3\times S^3$ or ${\text{bR}}^{1,1}\times T^4$. Moreover, we show that the ${\text{bR}}^{1,1}\times \mathcal{S}$ horizons preserve 1, 2 and 4 supersymmetries and the geometry of $\mathcal{S}$ is Riemann, K"ahler and hyper-K"ahler, respectively.