Equivariant and fractional index of projective elliptic operators
  In this note the fractional analytic index, for a projective elliptic operator associated to an Azumaya bundle, of DG/0402329 is related to the equivariant index of Atiyah and Singer for an associated transversally elliptic operator. 
V. Mathai, R.B. Melrose and I.M. Singer