Einstein Probe（EP）

The EP satellite will provide a powerful tool to discover the merger of black holes with other objects, to servey the black holes to find out their distribution, formation and evolution in the Universe, to capture the electromagnetic counterparts of gravitational waves, provide unique new evidence for studying the early Universe, supernovae, and the activities of compact objects. EP will produce larges mounts of observational data such as X-ray all-sky dynamic images and X-ray spectral timing data for various X-ray sources, which will provide valuable data accumulation for the development of time-domain astronomy. It is also the first time that quiescent (inactive) black holes are treated as the main observational targets of an X-ray satellite, which gives the EP the capability to greatly promote the research field in the event of black holes swallowing stars.

To take all-sky survey in X-ray band, the EP carries a set of widefield-of-view X-ray imagers and two Wolter-I type X-ray telescopes with high sensitivity to discover rare X-ray transients and to detect unknown type X-ray transient objects. The mission is expected to make important scientific discoveries in time-domain astronomy and its multiple intersections with astrophysics and cosmology.

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.

(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.

1.The platform and its specification

The Structure Model of EP

EP mission will develop a astronomic satellite which has wide field-of-view and high sensitivity to carry out all-sky survey in soft X-ray band for discovery of transient sources and variable sources. The EP satellite equips advanced Lobster-eye-type MPO X-ray imagers with much better capability to GRASP X-ray transients in the universe than all the other instruments flight before.。

The EP is able to downlink alarm information quickly after detecting transients and guide the other astronomic instruments for the follow up observations. And also has the ability of receiving upload alarming information from the ground station and guide EP to carry out follow-up observation for transients.

satellite:lifetime of satellite not less than 3 years and the design of life time is not less than five years

orbital altitude : > 650 km

orbital inclination: < 30°

scientific data reception: Sanya scientific data receiving station, HBK and Maspaloms scientific data receiving station(coordinate with ESA), the X-band data rate not less than 80 Mbps

2.Scientific Instruments

The scientific instruments of EP satellite is composed of Wide-field X-ray Telescope (WXT, for X-ray all-sky monitoring) and Follow-up X-ray Telescope (FXT, for transient sources and variable sources observations)

(1) Wide field-of-view X-ray Telescope (WXT)

WXT

the total field of view: ≥3600 square degrees

Detection energy range: 0.5～4.0 keV;

Energy resolution: ≤170 eV@ 1.25 keV(FWHM);

Effective area( parallel x-rays incidence) ≥2cm2@1 keV;

space resolution: ≤5′(FWHM);

Precision of source location: 1′(confidence>90%, number of photo larger than 200 in the center of focal spot)

Triger threshold: ≥10mCrab transient(the integration time is 10 minutes)

(2) Follow-up X-ray Telescope (FXT)

FXT

field of view: diameter≥38′;

Detection energy range: 0.5～8.0 keV (the X-ray effective area in the detection energy range is greater than 10cm2)

Energy resolution: ≤170 eV@ 1.25 keV;

Effective area(arallel x-rays direction), ≥100 cm2@1.25 keV，on axis;

spatial resolution: ≤2′(FWHM);

Object localization: Better than 20 arcsec