An Empirical Background Model for the NICER X-Ray Timing Instrument
An Empirical Background Model for the NICER X-Ray Timing Instrument
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DOI：
10.3847/1538-3881/ac4ae6
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发表时间：
2021-05
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通讯作者：
R. Remillard;M. Loewenstein;J. Steiner;G. Prigozhin;B. LaMarr;T. Enoto;K. Gendreau;Z. Arzoumanian;C. Markwardt;A. Basak;A. Stevens;P. Ray;D. Altamirano;D. Buisson
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文献类型：
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作者：
R. Remillard;M. Loewenstein;J. Steiner;G. Prigozhin;B. LaMarr;T. Enoto;K. Gendreau;Z. Arzoumanian;C. Markwardt;A. Basak;A. Stevens;P. Ray;D. Altamirano;D. Buisson
中子星星内部成分探测器的背景率相对较低，但它的变化很大，必须使用不受科学目标影响的测量来预测它的光谱。我们描述了一个经验，三参数模型的基础上观察的七个指向方向是无效的可检测的来源。两个模型参数跟踪不同类型的背景事件，而第三个参数用于预测与在阳光下进行的观测有关的低能量过剩。对3556个平均为570 s的良好时间间隔（GTI）进行检查，得出的中位速率（0.4-12 keV; 50个探测器）为0.87 c s−1，但在5%（1%）的情况下，速率超过10（300）c s−1。对于最亮的GTI，模型残差持续在初始速率的20%-30%，这意味着一个或多个模型参数缺失。给出过滤标准以标记可能具有不令人满意的背景预测的GTI。通过这种滤波，我们估计在0.4-12 keV下的检测限为1.20 c s−1（3σ，单个GTI），相当于Crab类光谱的3.6 × 10−12 erg cm−2 s−1。软X射线源在0.3-2.0 keV时的相应极限为0.51 c s−1，或100 eV黑体的4.3 × 10−13 erg cm−2 s−1。如果探测性GTI在对微弱源规定的水平进行过滤后积累了10 k的数据，则这些限制将降低四倍。这种过滤选择背景GTI的85%的时间。该模型的应用程序，以1秒的时间尺度，使人们有可能区分源耀斑可能在背景中的浪涌。
Neutron Star Interior Composition Explorer has a comparatively low background rate, but it is highly variable, and its spectrum must be predicted using measurements unaffected by the science target. We describe an empirical, three-parameter model based on observations of seven pointing directions that are void of detectable sources. Two model parameters track different types of background events, while the third is used to predict a low-energy excess tied to observations conducted in sunlight. An examination of 3556 good time intervals (GTIs), averaging 570 s, yields a median rate (0.4–12 keV; 50 detectors) of 0.87 c s−1, but in 5% (1%) of cases, the rate exceeds 10 (300) c s−1. Model residuals persist at 20%–30% of the initial rate for the brightest GTIs, implying one or more missing model parameters. Filtering criteria are given to flag GTIs likely to have unsatisfactory background predictions. With such filtering, we estimate a detection limit, 1.20 c s−1 (3σ, single GTI) at 0.4–12 keV, equivalent to 3.6 × 10−12 erg cm−2 s−1 for a Crab-like spectrum. The corresponding limit for soft X-ray sources is 0.51 c s−1 at 0.3–2.0 keV, or 4.3 × 10−13 erg cm−2 s−1 for a 100 eV blackbody. These limits would be four times lower if exploratory GTIs accumulate 10 ks of data after filtering at the level prescribed for faint sources. Such filtering selects background GTIs 85% of the time. An application of the model to a 1 s timescale makes it possible to distinguish source flares from possible surges in the background.