EP is an astronomic science mission aimed to discover new objects, new phenomena and inherent mechanisms in the dynamic universe.

With its outstanding capability of large-scale survey and follow-up observing with high sensitivity in the X-ray band, the EP project focuses on the following scientific objectives:

(1) To discover and characterize a number of cosmic X-ray transients, some of which are faint, distant in the universal.

(2) To discover and characterize X-ray outbursts of quiescent black holes, obtain the distribution of black holes in the universal, understand the origin, evolution and accretion of black holes.

(3) To localize gravitation-wave events by capturing X-ray signals from the GW sources, which will significantly trigger the follow-up multi-messenger system to carry out multi-wavelength observing of the GW events.

Research Content

(1)Discovery and study of quiescent black holes

EP is able to detect explosive events in the soft X-ray band, through which we can discover and identify quiescent black holes in the universe.

Anticipated important results:

• To discover hundreds of quiescent black holes in the center ofgalaxies, and carry out detailed observing during explosive events.
• Based on independent accessment to the event ratio, information of the proportion of massive black holes in the center of galaxies will be given to answer the basic question of "Is there a massive black hole in every galaxy center?" which helps to understand formation and evolution of black holes, galaxies and the structure of the Universe.
• To provide observational evidence for intermediate-massive black holes and large-massive black hole, obtain their ratio information, which helps to understand origin and distribution of black holes, as well as formation and evolution of large-massive black-hole binary.
• To discover various phenomena related to tidal disruption events (TDEs), testing the theoretical models, including relative jet TDEs, uncovering condition and mechanism.
• To examine the general relativity effects close to black hole, to trace and study how materials fall into black hole.
• By detecting eruptional events, to discover new stellar-like black holes and intermediate-massive black holes in the Milky Way galaxy and the nearby galaxies, and black holes in the center of globular clusters.

(2)All-sky survey of transients and explosive objects

With high sensitivity in X-ray observing, the EP is able to detect more distant, fainter and rarer transients. It will provide historical chances to discover new types of transients previously unknown, send alerts for transients that leads to joint observations for transients by astronomic instruments allover the world.

Anticipated important results:

• Detecting the X-ray emission from supernovae at the moment of explosion.
• Discovering a number of high-redshift (redshift > 6) eruptive events in the early Universe.
• Providing crucial data for resolving the puzzle of X-ray flash.
• Discovering a number of new neutron stars and magnetars.
• Obtaining the observational characteristics of various transients systematically, and providing valuable data for studying the origin of various transients and the physical mechanism of their explosions.
• Discovering transients of previously unknown types.

(3)Detecting the electro-magnetic counterparts of gravitational-wave events.

EP will cooperate with the second-generation gravitational-wave detectors (A-LIGO, A-VIRGO) in the world to carry out searches for the electro-magnetic counterparts of gravitational-wave events. If an electro-magnetic counterpart is detected, the statistical confidence in the detection of gravitational-wave source will be improved, and the position of the gravitational-wave event can be located (with an accuracy from 20 arcsec to 2 arcmin, or higher). X-ray spectrum and variability data can be obtained by EP at the same time. These results will guide international large-scale multi-wavelength instruments to carry out follow-up observations of electro-magnetic counterparts and verify the corresponding objects.