Bogoliubov-Cerenkov radiation in a Bose-Einstein condensate flowing   against an obstacle
  We study the density modulation that appears in a Bose-Einstein condensate flowing with supersonic velocity against an obstacle. The experimental density profiles observed at JILA are reproduced by a numerical integration of the Gross-Pitaevskii equation and then interpreted in terms of Cerenkov emission of Bogoliubov excitations by the defect. The phonon and the single-particle regions of the Bogoliubov spectrum are respectively responsible for a conical wavefront and a fan-shaped series of precursors. 
I. Carusotto, S. X. Hu, L. A. Collins, A. Smerzi