Orbifolds of M-strings

We consider M theory in the presence of M parallel M5-branes probing a transverse A(N-1) singularity. This leads to a superconformal theory with (1,0) supersymmetry in six dimensions. We compute the supersymmetric partition function of this theory on a two-torus, with arbitrary supersymmetry preserving twists, using the topological vertex formalism. Alternatively, we show that this can also be obtained by computing the elliptic genus of an orbifold of recently studied M-strings. The resulting two-dimensional theory is a (4,0) supersymmetric quiver gauge theory whose Higgs branch corresponds to strings propagating on the moduli space of SU(N)(M-1) instantons on R-4, where the right-moving fermions are coupled to a particular bundle.