天宫2号POLAR探测器的低能X射线在轨定标

伽马暴偏振探测仪(POLAR)是天宫2号实验室上搭载的一个γ射线偏振仪,于2016年9月15日搭载在天宫2号进入低轨运行,主要用于探测在50-500 keV能区的硬X射线辐射的线偏振.POLAR由25个模块组成,每个模块有64个塑料闪烁体棒,总计有1600个塑料闪烁体棒,具有较大的有效探测面积和视场.在轨运行期间探测到多个小耀斑,它们的硬X射线光子能量通常小于50 keV,无法直接使用在轨和地面的高能定标结果来进行能谱分析.结合拉马第太阳高能光谱成像探测器(RHESSI)对耀斑SOL2016112907能谱的观测和蒙特卡洛模拟,对耀斑期间被激活的闪烁体棒进行能量低于50 keV的低能相对定标.虽然定标得到的能量阈值(～10 keV)和转换因子相对稳定,但是和高能定标给出的结果相比有显著差异,并且不同闪烁体棒显示出的差异没有明显的规律性.

Solar Flares detected by POLAR on TG2

POLAR is a gamma-ray burst polarimeter on board TianGong2 space lab, which was launched into low earth orbit in 2016 September 15. It is designed to measure the linear polarization of hard X-ray in the 50--500keV energy range. The detector has 25 modules, and each module has 64 plastic scintillator bars. With a total number of 1600 plastic scintillator bars, POLAR has a very large effective detection area and field of view. During its in-orbit operation, POLAR detected multiple small flares. Those hard X-ray photons are usually less than 50keV and can not be analyzed directly by applying in-orbit and ground high energy calibration results. With simultaneous RHESSI (Reuven Ramaty High Energy Solar Spectroscopic Imager) observations of a flare SOL2016112907, this paper calibrates smaller than 50keV low-energy response of POLAR with Monte Carlo simulations. We find that energy threshold (sim 10keV) and conversion factor obtained via calibration are relatively stable, but they are different from values obtained via calibration in high-energy range, and there is no evident pattern in these differences.