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arXiv 0902.1118astro-ph.IM
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中法GRB任务SVOM上X射线和γ射线编码掩模照相机背景的蒙特卡罗模拟

Monte-Carlo simulations of the background of the coded-mask camera for X- and Gamma-rays on-board the Chinese-French GRB mission SVOM

O. Godet, P. Sizun, D. Barret, P. Mandrou, B. Cordier, S. Schanne, N. Remoue

摘要:

几十年来,宽视场编码掩模照相机已成功地用于定位伽马射线暴(GRB)。在这些仪器中,由于它们的大视场和大有效面积,事件计数率由光子背景决定。因此,必须在仪器设计的早期阶段估计预期在轨道上的仪器背景,以便优化飞行任务的科学性能。我们在这里提出了一个详细的研究仪器的背景和灵敏度的编码掩模相机的X-和伽马射线(CXG)用于高红移伽玛暴的探测和定位的国际伽玛暴任务SVOM。为了计算背景光谱,使用蒙特卡罗方法模拟SVOM将沿其低地球轨道(高度为600公里,倾角约为30度)遇到的空间环境主要组成部分的粒子与CXG主体之间的初级和次级相互作用。我们认为详细的质量模型的CXG在其最新的设计。根据我们的结果,i)相机的被动屏蔽的设计确保在4-50 keV成像频带中宇宙X-γ射线背景是主导的,而内部背景应该在70-90 keV以上开始变得主导; ii)目前的相机设计确保CXG相机将比Swift Burst Alert望远镜对高红移GRB更敏感,这要归功于低-能量阈值为4keV。

英文摘要:

For several decades now, wide-field coded mask cameras have been used with success to localise Gamma-ray bursts (GRBs). In these instruments, the event count rate is dominated by the photon background due to their large field of view and large effective area. It is therefore essential to estimate the instrument background expected in orbit during the early phases of the instrument design in order to optimise the scientific performances of the mission. We present here a detailed study of the instrument background and sensitivity of the coded-mask camera for X- and Gamma-rays (CXG) to be used in the detection and localisation of high-redshift GRBs on-board the international GRB mission SVOM. To compute the background spectrum, a Monte-Carlo approach was used to simulate the primary and secondary interactions between particles from the main components of the space environment that SVOM will encounter along its Low Earth Orbit (LEO) (with an altitude of 600 km and an inclination of ~ 30 deg) and the body of the CXG. We consider the detailed mass model of the CXG in its latest design. According to our results, i) the design of the passive shield of the camera ensures that in the 4-50 keV imaging band the cosmic X-Gamma-ray background is dominant whilst the internal background should start to become dominant above 70-90 keV; ii) the current camera design ensures that the CXG camera will be more sensitive to high-redshift GRBs than the Swift Burst Alert Telescope thanks to a low-energy threshold of 4 keV.

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