V. Mitov, K. et M. Yanev, N., Bellman-Harris branching processes with a special type of state-dependent immigration, Advances in applied probability , 21(2), 1989, pp. 270-283
We investigate critical Bellman-Harris processes which allow immigration of new particles whenever the population size is 0. Under some special conditions on the immigration component the asymptotic behaviour of the probability of extinction is obtained and limit theorems are also proved.