Simulations for WXT aboard Einstein Probe mission with Geant4 2017 G4SUW, 10-12 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)

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

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:

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

Main Characteristics A focusing telescope with largest FOV : 60o X 60o Energy Range: 0.5-4 keV most sensitive all-sky monitor 60o X 60o, it will be a Focusing telescope with the largest FoV.

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

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.

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

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

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

Background Simulations

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. 2012 and Miyaji T. et al. 1998

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

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

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

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

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

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