Present Epoch Plus - An X-ray Survey for Cosmology

This paper summarizes some cosmologically interesting measurements which are uniquely possible in the hard X-ray band and presents a mission concept capable of achieving them. The Present Epoch Plus mission will achieve a surface brightness sensitivity of better than 1% per square degree in the 2-10 keV band, and create a catalog of about 10^6 sources. About 160,000 extragalactic sources are expected to be detected in the 2-10 keV band, providing an all sky survey with nearly uniform selection effects 10 times deeper than exisiting or planned surveys. The PEP concept can be achieved within the size and budgetary constraints of a NASA Medium Explorer (MIDEX) mission.