To cite gets in publications use:

  Cebrian A, Abaurrea J, Asin J (2015). “NHPoisson: An R Package for
  Fitting and Validating Nonhomogeneous Poisson Processes.” _Journal of
  Statistical Software_, *64*(6), 1-25. doi:10.18637/jss.v064.i06
  <https://doi.org/10.18637/jss.v064.i06>.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {{NHPoisson}: An R Package for Fitting and Validating Nonhomogeneous Poisson Processes},
    author = {Ana C. Cebrian and Jesus Abaurrea and Jesus Asin},
    journal = {Journal of Statistical Software},
    year = {2015},
    volume = {64},
    number = {6},
    pages = {1--25},
    doi = {10.18637/jss.v064.i06},
  }