Singularities in the Kerr-Newman and charged $\delta=2$ Tomimatsu-Sato   spacetimes endowed with negative mass
  The Kerr-Newman solution with negative mass is shown to develop a massless ring singularity off the symmetry axis. The singularity is located inside the region with closed timelike curves which has topology of a torus and lies outside the ergoregion. These characteristics are also shared by the charged Tomimatsu-Sato delta=2 solution with negative total mass to which in particular a simple form in terms of four polynomials is provided. 
V. S. Manko and E. Ruiz
gr-qc hep-th