一种聚焦型X射线探测器在轨性能标定方法

A method of calibrating effective area of focusing X-ray detector by using normal spectrum of Crab pulsar

X射线探测器是X射线天文观测及脉冲星导航的核心器件,受发射振动、高能粒子辐射损伤及元器件老化等影响,X射线探测器空间观测性能会逐渐变化,X射线探测器在轨标定有利于观测天体X射线辐射信息的准确获取及精确建模.研究利用了脉冲星辐射能谱标定X射线探测器性能的方法,能较好地消除探测器本底及空间环境噪声的影响,通过处理脉冲星导航试验卫星(XPNAV-1卫星)的Crab脉冲星观测数据,评估了我国首款聚焦型X射线探测器的在轨性能.计算结果表明,XPNAV-1卫星上聚焦型X射线探测器的有效面积在0.6-1.9 keV能段内优于2 cm^2,其中在0.7 keV能量处取得最大值3.06 cm^2,探测效率约10%;有效面积随着探测能量增大而减小,在2—3.5 keV能段内有效面积约为1 cm^2,而大于5 keV能段的有效面积约为0.1 cm^2,且此能段估计精度明显受光子统计误差影响.同时研究了考虑能量响应矩阵的探测器有效面积标定新方法,利用地面性能测试中五个特征能谱处的能量分辨率重构其能量响应矩阵,重新标定了聚焦型X射线探测器有效面积,发现该能量响应矩阵对结果影响较小.最后建议观测某些超新星遗迹监测能量分辨率及能量线性等指标的变化.

X-ray detector is a core component for X-ray astronomical observation and pulsar navigation. The on-orbit observation performance of X-ray detector will change gradually, owing to the influences of emission vibration, radiation damage of high-energy particles, and the aging of the components. The on-orbit calibration of X-ray detector facilitates the accurate acquisition and the precise modeling of X-ray radiation of the observation celestial bodies. In this paper a new method of calibrating the performance of X-ray detector is studied by using the radiation spectrum of the pulsar,which can effectively eliminate the influences from detector background and space environment noise. The on-orbit performance of the first focusing X-ray detector in China has been evaluated by analyzing the observations of the X-ray pulsar-based navigation satellite-1（XPNAV-1） for the Crab pulsar. The XPNAV-1 was launched in November 2016,with the aim of conducting the test of the feasibility of applying the regular emission of X-ray signals from pulsars to spacecraft navigation. Now, the first batch of scientific data about the Crab pulsar observations gained by the focusing X-ray detector for almost one month has been released. The pulse profiles of 124 observations and the total observational spectrum of Crab pulsar are achieved from those data. According to the international accurate X-ray radiation parameters of Crab pulsar, which have been determined by other X-ray space satellites, together with the absorption effect of the neutral hydrogen gas in the universe, the effective area of the focusing X-ray detector is estimated. The result shows that the effective area of the focusing X-ray detector on XPNAV-1 in an energy range of 0.6-1.9 keV is better than 2 cm^2. The maximum effective area is 3.06 cm^2 at an energy of 0.7 keV, which means that its detection efficiency is about 10%. As the observed energy increases, the effective area decreases. The area of the focusing X-ray detector in an energy range of 2-3.5 keV is about 1 cm^2, and it is about 0.1 cm^2 at energies above 5 keV, and its estimation accuracy is affected seriously by the statistical errors of X-ray photons. At the same time, another method of calibrating the effective area is studied by considering the energy response matrix of detector. The energy response matrix of the focusing X-ray detector is estimated by using the five ground test values of energy resolution. The effective area of the focusing X-ray detector is re-calibrated. However, the result shows that the energy response matrix exerts little effect on the effective area of the focusing X-ray detector. Finally, we suggest that the XPNAV-1 should observe some supernova remnants to monitor the changes of energy resolution and energy linearity and so on.