Prsentation PowerPoint

Study performed by Donghua Zhao during her one year stay in France

Ms. Donghua is a IHEP PhD student. Her stay was founded by the CSC-FCPPL PhD grants programs.

She arrived in Saclay 2010, December the 1rst, and she leaved 2011, November the 31.

She plans to finish her PhD In 2012 June

Influence of the earth on the background of the SVOM instruments5th France China Particle Physics Laboratory (FCPPL) Workshop - 2012 March Orsay B. Cordier

The SVOM mission is devoted to the study of Gamma-ray burstIt is a french chinese collaboration. The main laboratories involved are:NAOC beijing, IHEP beijing, XIOPM Xian, CEA-Irfu, IRAP ToulouseLaunch date 2017

The scientific payload aboard SVOM

ECLAIRsMXT

GRM

VT

5th France China Particle Physics Laboratory (FCPPL) Workshop - 2012 March Orsay B. CordierSunSunSunNight sideNight sideNight sideSVOM Pointing StrategySVOM orbit (i ~ 30)A pointing close to the antisolar in the night part of the orbit is required in order to permit the fast follow-up of localized GRBs with large telescope on Earth

5th France China Particle Physics Laboratory (FCPPL) Workshop - 2012 March Orsay B. Cordier

SVOM Pointing StrategyAt each orbit (every 90 minutes) the Earth enters inside the instruments FOV5th France China Particle Physics Laboratory (FCPPL) Workshop - 2012 March Orsay B. CordierCosmic protonsCosmic X-ray backgroundX and gamma ray background issues in a low earth orbitThe presence of the Earth in the FOV introduces:An occultation of the diffused X-ray backgroundA reflection of the X-ray background on the EarthAn albedo component du to cosmic proton interactions in the earth atmosphere In this work we focus on the assessment of the albedo component

5th France China Particle Physics Laboratory (FCPPL) Workshop - 2012 March Orsay B. Cordier

Albedo gamma : computation of the emissivity 1/4Sazonov et al. 2007For 1 cm2 of earth atmosphere :For a given atmosphere cell of 1 cm2, the emissivity depends on:

1 the solar modulation at the epoch of observation

2 the zenithal angle of the cell viewed from the spacecraft

3 the rigidity cut off at the cell positionAlbedo gamma : computation of the emissivity 1/3

5th France China Particle Physics Laboratory (FCPPL) Workshop - 2012 March Orsay B. CordierThe spacecraft is moving, it intercepts different atmosphere spherical caps

At a given satellite position, one consider a spherical capWe divide the considered cap in elementary cellsFor each cell we compute RcutAt the end one integrate the emissivity over the spherical cap area.

Albedo gamma : computation of the emissivity 2/45th France China Particle Physics Laboratory (FCPPL) Workshop - 2012 March Orsay B. Cordier9

Albedo gamma : computation of the emissivity 4/4Taking into account the 2015 magnetic field model, the worse position on the SVOM orbit is: Alpha=287E delta=30N Emissivity computed along the SVOM orbit (Inclination 30)5th France China Particle Physics Laboratory (FCPPL) Workshop - 2012 March Orsay B. Cordier

Cosmic gammaReflected cosmic gammaAlbedo gammaX and gamma ray Background computation versus the position of the earth relative to the instrument field of view Using the previous results we performed Geant4 simulationsHypotheses position on the orbit Alpha=287E delta=30N (worse case) ConclusionsDonghua Zhao did a very serious work during her stay in SaclayThanks to her work, the collaboration is now in a position to compute the X and Gamma ray background and its variation at any time and at each point of the SVOM orbit.A paper summarizing this work has been submitted to NIM last month (Donghua Zhao et al.)

5th France China Particle Physics Laboratory (FCPPL) Workshop - 2012 March Orsay B. Cordier