Geant4-based simulations of the background for the erosita space observatory (with connections to IXO and Suzaku) Emanuele Perinati 1,2 1 IAAT - Institut fϋr Astronomie und Astrophysik, Universität Tϋbingen, Germany 2 INAF- Istituto di Astrofisica Spaziale e Fisica Cosmica di Palermo, Italy other members of the Geant4 group at IAAT : C. Tenzer A. Santangelo G. Warth 1st Australian Geant4 Workshop, Wollongong, 14-16.04.2011
OUTLINE IAAT Tϋbingen why we use Geant4 presenting erosita space mission Geant4-based study of erosita NXB similar work in progress for IXO validation of the Geant4 simulator by reproducing NXB data of Suzaku detectors conclusions
IAAT HEAD, Tϋbingen led by Prof. Dr. Andrea Santangelo currently involved in the technological and/or scientific activities for the following high energy astrophysics projects: erosita IXO LOFT SVOM JEM-EUSO CTA WSO HESS XMM INTEGRAL future of high energy astrophysics! past (but still active) projects
why Geant4 is helpful in space applications? The space environment in Solar System is filled with: radiation/particles from solar activity radiation/particles with cosmic (galactic and/or extragalactic) origin radiation/particles produced by atmospheric albedo (only for LEO orbits) radiation/particles produced by the interaction of solar,cosmic and albedo radiation/ particles with the spacecraft and onboard materials in a space-based mission such radiation and particles can pass across the spacecraft down to the the focal plane and hit the detectors with two main consequences: 1) producing X-ray-like signals = background has an impact on the S/N ratio of the detectors 2) producing interactions with the crystal structure of the materials the instruments are made of = possible technical damages Geant4 allows to simulate and quantify these effects: it is a support to the design and optimization of the configuration of space missions before launch, and to the interpretation of the background data and technical performances after launch
erosita = extended ROentgen Survey with an Imaging Telescope Array in simpler words: it will extend the ROSAT all-sky survey up to ~ 12 kev with a sensitivity similar to that of XMM (PI: P. Predhel,MPE)
erosita scientific goals 4 years all-sky and deep surveys to map new X-ray sources up to ~ 12 kev 3 years pointed observations Expected results ~ 100000 new clusters ~ 3000000 new AGNs
erosita specifications (MPE, Uni Tϋbingen, Uni Hamburg, Uni Erlangen-Nϋrnberg, AIP, MPA) 7 mirror modules * 54 Wolter-I shells (Ni/Au) FOV ~ 1 deg FL=1.6 m AE ~ 2400 cm 2 (max) AR ~15 arcsec (max) + 7 pn-ccd cameras ** 384x384 Si pixels TR ~ 50 msec ER ~ 80-150 ev sensitivity (all-sky) ~ 6 10-14 erg/cm 2 /sec * Kayser Threde (D)+Carl Zeiss (D) +Media Lario (I) ** PN-Sensor (D)
L2 orbit good sky visibility (almost) no torque stable thermal conditions no albedo radiation/particles no geomagnetic shielding ~ 1500000 Km L2 orbit
erosita: first (2013?) X-ray space mission to be flown in L2! No X-ray missions to date at L2 all background predictions based on theory, simulations and/or scaling of data measured by X-ray detectors in different orbits No geomagnetic shielding radiation environment more hostile than in LEO = background data and performances of erosita pn-ccds will be of great interest to the whole HEA community worldwide L2 radiation environment MC study of CXB and NXB background Ray-tracing (stray-light) Geant4
erosita Geant4 simulator pn-ccd with 450 µm Silicon depletion layer Predictions: instrumental NXB bkg level similar to that of XMM/pn-CCD Preliminary results (partial geometry model, only protons in input): ~ 3.5x10-6 cts/pix/sec Work in progress: Geant4 simulations on a full satellite geometry including mirrors and spacecraft structure,and all radiation components in L2 To otimize the trade-off between accuracy in secondary particles generation and cumputational time we set a graded cut PhysicsList derived by SLAC PrimaryGenerator with spherical simmetry L2 CGR
some results of new simulations total bkg ~ 10-5 cts/px/sec (NOTE: no pattern analysis is included)
Geant4-based study for the International X-ray Observatory (IXO) IXO will be equipped with a X-ray Microcalorimeter Spectrometer (XMS) to support the design and optimization of the XMS anticoincidence instrument, Geant4 PIXE package is mandatory! validated by reproducing the experimental fluorescence yields of several metals (Al,Cr,Cu,Ti)
the case of Suzaku (JAXA/NASA) in July 2005 Suzaku was placed in a ~ 600 Km LEO with ~ 30 deg inclination albedo neutrons
validation of Geant4 results with Suzaku data Geant4 was successful in reproducing the NXB background measured by the XIS and HXD detectors onboard of Suzaku thanks to the improvements of the latest version 9.4 of Geant4 we can now (almost) reproduce also the NXB background measured by the XRS microcalorimeter! XRS spectrum 50eV-binned ( by C. Kilbourne, NASA GSFC) only ~ 200 counts t ~ 37 ksec integral bkg ~ 0.04 cts/cm 2 /sec E<1keV: superposition of a continuum of (mostly) elastic scattering by albedo neutrons and some HgTe nuclear resonance lines??? Al-K Au-M Te-L something missing in the model? Au-L E >1 kev: superposition of a continuum of (mostly) secondary electrons and some characteristic fluorescence lines, such as Al K (1.48 kev) from XRS board, Au M (2.1 kev) and Au L (9.7 kev, 11.4 kev) lines from XRS detector box coating
CONCLUSIONS Geant4 is an essential tool in modern space research it is used to predict and/or understand the background of erosita,ixo, Suzaku and many others astrophysical projects it can be used also to verify the charged particles reflectivity of mirrors thanks to Geant4 developers for their efforts in making the toolkit more and more performing!