Aleksey Kostenko and Gerald Teschl On the Singular Weyl-Titchmarsh Function of Perturbed Spherical Schroedinger Operators (97K, LaTeX2e) ABSTRACT. We investigate the singular Weyl--Titchmarsh $m$-function of perturbed spherical Schr\"odinger operators (also known as Bessel operators) under the assumption that the perturbation $q(x)$ satisfies $x q(x) \in L^1(0,1)$. We show existence plus detailed properties of a fundamental system of solutions which are entire with respect to the energy parameter. Based on this we show that the singular $m$-function belongs to the generalized Nevanlinna class and connect our results with the theory of super singular perturbations.