The point source parameter estimation via Maximum Likelihood Estimation in
ROSAT data is documented. The infall of X-ray photons is treated as a Poiss
on process. Based on she Poisson model, the log-likelihood function for unb
inned data is derived. The adopted source and background models are explain
ed. In the chosen parameterization, the Maximum Likelihood equations and th
eir numerical solution are expounded. The performance of the method is illu
strated by an example and tests on simulated observations.