1. Simulations for WXT aboard Einstein Probe mission with Geant4
2017 G4SUW, April, University of Surrey, Guildford, UK
Simulations for WXT aboard Einstein Probe mission with Geant4
Donghua Zhao, Chen Zhang, Weimin Yuan
National Astronomical Observatories,
Chinese Academy of Sciences (NAOC)

2. Einstein Probe (EP) An X-ray focusing telescope with very wide FOV
Proposed by NAOC, IHEP (Chinese Academy of Sciences (CAS) institutes)
Currently under final review for formal approval, engineering expected to start this year
Launch Time: 2021/22

3. Scientific Objectives of EP
Systematic surveys of X-ray transients at unprecedented sensitivity, detect faint X-ray transients and find new types of transients.
Reveal quiescent black holes by catching their X-ray flares
Detect electromagnetic wave counterparts of gravitational wave events and precisely locate them.
Predictions of General Relativity:

4. Instruments on EP and MPO
WXT
FXT
Wide-field X-ray telescope
Follow-up X-ray telescope
60o X 60o, it will be a Focusing telescope with the largest FoV.
very light , make large FOV possible

5. Main Characteristics
A focusing telescope with largest FOV : 60o X 60o
Energy Range: keV
most sensitive all-sky monitor
60o X 60o, it will be a Focusing telescope with the largest FoV.

6. Simulations for WXT with Geant4
Geant4.9.6p02
Build Monte Carlo model
Simulations on the performance of the optical system
Instrumental background simulations

7. WXT model with Geant4 WXT and Platform Physics processes Frame MPO
Detector shell
Bottom Shield
surrounding Shield
surrounding Shield
Frame
MPO
Building the optics is the key. Millions of micro pores are built.

8. X-ray reflection at grazing angles
Use XRTG4 developed by Buis and Vacanti in the program based on Geant4.
Q: an independent software developed by professor Willingale at LE University
Results from Geant4 and Q agree well with each other with an averaged deviation < 3%.
Donghua Zhao, et al., 2017

9. PSF and effective area of WXT
Surface plot and contour plot，1.0 keV parallel X-rays , on axis

10. Simulated sky observations
Donghua Zhao, et al., 2017
point sources from RASS Bright Source Catalogue

11. Background Simulations

12. Background sources Cosmic Particles X rays NH=3E20 cm^2
total Soft X-rays
NH=3E20 cm^2
Campana, R. et al. 2013
Zhao D. et al and Miyaji T. et al. 1998

13. Background due to different source
BKG when FOV points the Galaxy or other directions.

14. Impact of Grazing Reflection on BKG
Without grazing reflection
With grazing reflection
Physics process
Energy range
Total
(cts/s/cm^2)
X rays
Particles
Without
grazing scattering
0.5-4keV
0.043
0.027
0.016
With
0.187
0.173
0.014

15. CMOS detector of WXT Al Film Sensitive Si Substrate Si Frame MPO
Detector shell
Bottom Shield
surrounding Shield
surrounding Shield
Frame
MPO
Al Film
Sensitive Si
Substrate Si

16. Impact of detector thickness on background
10 um
30 um
Thickness
X rays
Particles
Total(cts/s/cm^2)
10 um
0.180
0.108 (37 %)
0.288
30 um
0.156
0.001 (0.4%)
0.157

17. Summary
EP will be an X-ray focusing telescope with largest FOV, and a most sensitive all-sky monitor.
Built a Monte Carlo model for WXT
Studied WXT’s performance including the PSF, effective area, background, etc.
Thank you

19. Shield of WXT Outside -> Inside Pb Cu C Al Frame MPO
Detector shell
Bottom Shield
surrounding Shield
surrounding Shield
Frame
MPO
Outside -> Inside Pb Cu C Al