THE INFLUENCE OF THE INITIAL MASS FUNCTION ON POPULATIONS OF X-RAY BINARIES AFTER A BURST OF STAR-FORMATION

The evolution of populations of X-ray sources after a burst of star fo rmation is investigated using the ''Scenario Machine'' population synt hesis simulator. Four types of X-ray sources are considered: transient s associated with accreting neutron star-Be star binaries, accreting n eutron star-supergiant binaries, binaries with a superaccreting black hole, and black hole-supergiant binaries, such as Cyg X-1. The total m ass in binary stars after the starburst is 1.5 x 10(6) M., the initial mass function is taken to have either a Salpeter spectrum (index alph a = 2.35) or a flat spectrum (index alpha = 1.01), and the evolution i s followed up to 2 x 10(7) years after the starburst. For a flat initi al mass spectrum, the number of X-ray sources of all four types increa sed significantly. Calculations are presented for upper mass limits of 120 M. and 30 M.. Lowering the upper mass limit below the critical ma ss for the formation of black holes when the initial mass distribution is flat leads to a substantial increase in the number of X-ray system s with neutron stars (to approximate to 300). Approximate formulas for the number of sources as a function of time are presented.