Circular geodesics and accretion disks in Janis-Newman-Winicour and   Gamma metric
  We study here circular timelike geodesics in the Janis-Newman-Winicour and Gamma metric spacetimes which contain a strong curvature naked singularity and reduce to the Schwarzschild metric for a specific value of one of the parameters. We show that for both the metrics the range of allowed parameters can be divided into three regimes where structure of the circular geodesics is qualitatively different. It follows that the properties of the accretion disks around such naked singularities can be significantly different from those of disks around black holes. This adds to previous studies showing that if naked singularities exist in nature, their observational signature would be significantly different from that of the black hole. 
Anirban N. Chowdhury, Mandar Patil, Daniele Malafarina and Pankaj S.   Joshi
gr-qc astro-ph.HE