@conference{4622,
  author = {Mitchell Begelman and M. de Kool},
  title = {Constraints on central engine models from rapid X-ray variability},
  year = {1991},
  journal = {unknown},
  publisher = {Cambridge University Press, Cambridge, England},
  isbn = {0 521 41295 1},
  note = {JILA Pub. 4367},
}