Einstein Probe (EP) mission(Wide-field X-ray Telescope, WXT)
http://ep.bao.ac.cn/

Sugizaki, Mutsumi (杉崎 睦)
National Astronomical Observatories of China (NAOC)(中国科学院国家天文台)
Einstein Probe (爱因斯坦探针卫星) mission team1

Einstein Probe mission overview• Satellite profile• Weight: ~1400 kg, Power ~1100 W• Orbit: 600 km, inclination ~ 29 deg. (Xichang, 西昌, 四川)• Science instruments• WXT (Wide-field X-ray Telescope) 12 units. 0.5-4 keV (soft X-ray)• Lobster-eye X-ray mirrors + BI CMOS - products of ChineseCompanies• One-unit FOV = 9x9 deg^2 x4. Total 3600 deg^2 = 1.1 sr• FXT (Follow-up X-ray Telescope) 2 units. 0.3-10 keV• Walter-I mirror + PN CCD• FOV: phi=30 arcmin.

• Schedule• 2019/12 Qualification modeling(Phase C)• 2021/03 Flight production (Phase D)• 2022/12 launch2Collaboration Team• China• National Astronomical Observatories, CAS (NAOC)• Institute of High Energy Physics, CAS (IHEP)• Shanghai Institute of Technical Physics, CAS (SITP)• National Space Science Center, CAS (NSSC)• Shanghai Micro-Satellite (Microsat)• Chinese Academy of Launch Vehicle Technology• Outside of China• European Space Agency (ESA)• MPE, Germany• CNES, France3

Zoom collaboration meeting in 2020 Nov.

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NAOC team members

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Operation plan
• Operation modes• Survey: 3 pointing per orbit, each
~20 min exposure to cover wholenight sky in 3 orbits (~4.5 hour).
• On-board WXT data reduction andtriggering FXT follow-up of newtransients.
Maneuver time: 60 deg / 3 min.

• ToO observations.

Sun• Alert downlink• Baseline: Beidou system (30 sat.)• Backup: VHF network (French)• Quick ToO command• Baidou system: latency < 10 min• Mission life

• Nominal 3 +2 years

Beidou Navigation system
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Main scientific objectives• Monitoring soft X-ray transients andvariable sources with unprecedented
sensitivity and high cadence• Discovering normally quiescent black
holes at all astrophysical mass scales by
capturing the transient flares, particularly
TDE from SMBHs• Soft X-ray counterpart search forgravitational-wave events, fast radio
bursts (FRBs), ….
• Finding new types of soft X-ray events
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EP WXT Sensitivity

Scan period gap

Coverage duty cycle

EP sensitivity (Yuan 2018)MAXI sensitivity (Negoro 2016)8

Target space in soft X-ray time domain
astronomy

EP sensitivity (Yuan 2018)9

Wide-field X-ray Telescope (WXT)• Lobster-eye X-ray mirrors (NNVT, China) + BI CMOS (Gpixel, China)• Total FOV = 1.1 sr with 12 WXT units• Spatial resolution~ 5’ (FWHM)• Position accuracy< 1’• Effective area

~ 3 cm2 at 1keV

• Energy resolution: 170 eV at 1 keV• Readout rate:

50 ms per frame10

Lobster-eye optics
Simulation
Schematic

Measured PSF (NAOC)(Yuan et al. 2017)(Zhao et al. 2014)11

Follow-up X-ray Telescope (FXT)• 2 Walter-I mirror (1 MadiaLario + 1 eROSITA spare or Chinese product)+ PN CCD (MPE) = nearly eROSITA module on SRG• FOV phi38’• Spatial resolution

0.5’ (HPD)• Position accuracy~ 5”.

• Effective are

300 cm2 @ 1keV

• Energy resolution:

170 eV @ 1 keV• Readout rate:

1 s per frame

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WXT feasibility prospects fromdata simulation and analysis

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WXT survey monitoring footprints (1 daysimulations)

WXT FoV (1.1sr)
Galactic coor. sys.

• In 3 orbits (~ 5hr) WXT covers most of the night sky (can be disrupted)• Cover the whole sky in half year
• Synergy with other M-W & M-M facilities (LSST/SKA/Swift/SVOM/LIGO/...)
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GW-counterpart search
LIGO/Virgo O3 run (2019/3 -2020/4)
GW source alerts
https://gracedb.ligo.org/superevents/public/O3/

Confidence contours ofGW source location
S200316bj

Typical error area
S200311bg

Very good case15

Example in GW counterpart search with MAXI
S200316bj
March 16, 2020
21:57:56 UTC (= T)

MAXI event image on
GW contours

T-5 min to T+5 min

Uncovered area for high radiation
zone, sun angle, and scan pole.

T-5 min to T+30 min

Covered area

MAXI covers 85% sky by~90 minutes.

T-5 min to T=90 min
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Tests with EP observation simulator(Preliminary)
Assume the event time
March 16, 2020 -> 2023
21:57:56 UTC (= T)

WXT event image
on GW contours
T to T+45 min

T to T+ 4 hr

2023-03-16 WXT exposure map
T to T+ 8 hr
17Search for X-rays from gravitational waveevents
Quick ToO observationcommands uplink within
10minuts after GW alert(1) pointed obs. withWXT for 1-2 orbits(2) a sequence ofsnapshots with FXTof 5 min each(3) deep follow-upobs with FXT forpromising candidates

WXT FoV (1.1sr)18

Synergy with MAXI, XRISM• MAXI• Sensitivity is better in EP• Sky coverage is better in MAXI
• Complementary energy band: MAXI 2-30 keV vs. EP 0.5-4 keV• Monitoring soft-to-hard X-ray behaviors of• Galactic X-ray objects• Top-bright extragalactic sources• XRISM• Spectroscopic observations of EP transients• XRISM ToO time scale ~ 1 day• Tidal disruption events• Ultraluminous X-ray sources19Summary• Einstein Probe (EP) is the Chinese X-ray satellite
mission for soft X-ray survey, launched in 2022
• International collaboration mission with ESA, MPE,(CNES)• EP WXT will achieve the 10 times better sensitivity thanthe past surveys, using Lobster-eye optics and CMOS
image sensors.
• Key devices: Lobster-eye mirrors and CMOS sensors
are manufactured in Chinese companies• Think good science collaborations, MAXI, XRISM

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