@article{dexter:2009:fnp,
    author = {Dexter, Jason and Agol, Eric},
     title = {A fast new public code for computing photon orbits in a {K}err spacetime},
   journal = {The Astrophysical Journal},
      year = {2009},
    volume = {696},
     pages = {1616–1629},
       doi = {10.1088/0004-637X/696/2/1616}}