To cite NHPoisson in publications use:

Ana C. Cebrian, Jesus Abaurrea, Jesus Asin (2015). NHPoisson: An R Package for Fitting and Validating Nonhomogeneous Poisson Processes. Journal of Statistical Software, 64(6), 1-24. URL http://www.jstatsoft.org/v64/i06/.

Corresponding BibTeX entry:

  @Article{,
    title = {{NHPoisson}: An {R} Package for Fitting and Validating
      Nonhomogeneous Poisson Processes},
    author = {Ana C. Cebri{\'a}n and Jes{\'u}s Abaurrea and Jes{\'u}s
      As{\'\i}n},
    journal = {Journal of Statistical Software},
    year = {2015},
    volume = {64},
    number = {6},
    pages = {1--25},
    url = {http://www.jstatsoft.org/v64/i06/},
  }