A time-domain fourth-order-convergent numerical algorithm to integrate   black hole perturbations in the extreme-mass-ratio limit
  We obtain a fourth order accurate numerical algorithm to integrate the Zerilli and Regge-Wheeler wave equations, describing perturbations of nonrotating black holes, with source terms due to an orbiting particle. Those source terms contain the Dirac's delta and its first derivative. We also re-derive the source of the Zerilli and Regge-Wheeler equations for more convenient definitions of the waveforms, that allow direct metric reconstruction (in the Regge-Wheeler gauge). 
Carlos O. Lousto (UT Brownsville)