EP is a CAS-led mission with potential international participation from the pre-launch phase. Several lines of possible collaboration via the provision of in-kind contribution have been promoted and under discussion currently, on the basis of no exchange of fund. Promising collaborations will involve the following partners: the European Space Agency (ESA) (via the provision of the FXT mirror assembly and possibly other contributions), the Max-Planck-Institute for Extraterrestrial Physics (MPE) in Germany (via the provision of pn-CCDs and support to the delivery of the mirror assembly for the FXT instrument), the French space agency (CNES) (via the provision of the VHF network for quick telemetry of alert data), and possibly the University of Leicester in the UK (via design advice, testing and possibly parts for WXT).

Regarding the potential collaboration with ESA, in the general principal all the EP mission elements (except for those from MPE and CNES) are open to ESA's participation. We envisage the sharing of responsibilities and scientific return for the EP mission, all the way from the development of the science case and the payloads, to the ground segment and post launch science operations and exploitation, in the spirit of a true joint adventure, shared tasks and exchange of expertise between European and Chinese scientists and engineers. The EP mission concept, of exploring consequential steps for its scientific objectives, demands expertise in a range of research fields that are brought together for the first time. Necessarily this requires a joint implementation throughout the mission life cycle. Precise share of responsibilities is still under discussion.