XMM-牛顿EPIC相机通量交叉校准的统计评估
Statistical evaluation of the flux cross-calibration of the XMM-Newton EPIC cameras
摘要：
第二个XMM-牛顿偶然源目录，2XMM，为XMM-牛顿欧洲光子成像相机（EPIC）的通量交叉校准进行统计评估提供了理想的数据基础。我们的目标是评估的状态的EPIC相机上XMM牛顿（MOS 1，MOS 2，和pn）的相对通量校准，并调查的依赖性的能量，位置在视野中的X射线探测器，和任务的寿命校准。我们编制了至少两台EPIC相机检测到的“高质量”物体的大样本的通量百分比差异分布。然后通过高斯拟合找到通量的平均偏移和分布的色散。用固定的光谱模型进行计数率到通量的转换。研究了改变该模型对结果的影响。从0.2 keV到12.0 keV，两台EPIC MOS相机之间的一致性优于4%。MOS照相机在4.5 keV以下记录比pn高7-9%的通量，在4.5 keV以上记录10-13%的通量过剩。没有演变的通量比被视为随着时间的推移，除了在能量低于0.5千电子伏，在那里我们发现了强烈的MOS pn通量比随时间的下降。已知这种效应是由于逐渐退化的MOS再分布功能。的通量比显示出一定的依赖于距离光轴的MOS到pn通量过剩的意义上，离轴角增加。此外，在4.5-12.0 keV波段，MOS到pn过剩通量对方位角有很强的依赖性。这些结果强烈表明，反射光栅阵列（RGA）的阻塞因子的校准是不正确的高能量。最后，我们建议的方法，以改善计算通量在未来版本的XMM-牛顿源目录。
英文摘要：
The second XMM-Newton serendipitous source catalogue, 2XMM, provides the ideal data base for performing a statistical evaluation of the flux cross-calibration of the XMM-Newton European Photon Imaging Cameras (EPIC). We aim to evaluate the status of the relative flux calibration of the EPIC cameras on board XMM-Newton (MOS1, MOS2, and pn) and investigate the dependence of the calibration on energy, position in the field of view of the X-ray detectors, and lifetime of the mission. We compiled the distribution of flux percentage differences for large samples of 'good quality' objects detected with at least two of the EPIC cameras. The mean offset of the fluxes and dispersion of the distributions was then found by Gaussian fitting. Count rate to flux conversion was performed with a fixed spectral model. The impact on the results of varying this model was investigated. Excellent agreement was found between the two EPIC MOS cameras to better than 4% from 0.2 keV to 12.0 keV. MOS cameras register 7-9% higher flux than pn below 4.5 keV and 10-13% flux excess above 4.5 keV. No evolution of the flux ratios is seen with time, except at energies below 0.5 keV, where we found a strong decrease in the MOS to pn flux ratio with time. This effect is known to be due to a gradually degrading MOS redistribution function. The flux ratios show some dependence on distance from the optical axis in the sense that the MOS to pn flux excess increases with off-axis angle. Furthermore, in the 4.5-12.0 keV band there is a strong dependence of the MOS to pn excess flux on the azimuthal-angle. These results strongly suggest that the calibration of the Reflection Grating Array (RGA) blocking factors is incorrect at high energies. Finally, we recommend ways to improve the calculation of fluxes in future versions of XMM-Newton source catalogues.
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