一种重建甚高能gamma-ray谱的新方法：模板背景谱
A new method of reconstructing very-high-energy gamma-ray spectra: the Template Background Spectrum
摘要：
极高能（VHE，E>0.1 TeV）伽马射线发射区的角度范围与当前成像空气切伦科夫望远镜（IACT）的视场相当，需要对无源区域进行额外的观测，以估计对能谱的背景贡献。这减少了有效的观察时间并降低了灵敏度。本文提出了一种不需要对无源区进行额外观测就能从IACT数据重建光谱的新方法。其应用不限于任何特定的IACT或数据格式。在模板背景法的基础上，提出了一种新的基于IACT数据的光谱重建方法--模板背景谱（TBS），并在已发表的H.E.S.S.数据和H.E.S.S.结果在H.E.S.S.报告的VHE γ射线谱之间发现了很好的一致性。与TBS重新分析的数据。这包括分析点状源，在拥挤的地区，非常广泛的来源，直到源的流量的百分之几的蟹状星云流量和过剩的背景比约0.1。然而，TBS背景归一化引入了新的统计和系统误差，这些误差被考虑在内，但可能构成非常微弱的扩展源的限制情况。TBS方法使得能够在其他方法受到阻碍甚至失败时进行数据的光谱重建。它不需要专门观察VHE伽马射线自由区域（例如，如开/关背景所做的那样），并且规避了用于重建VHE伽马射线发射区域的谱信息的其他方法（例如，反射区域背景）易于遇到的已知几何限制;在特定情况下，TBS将是重建能谱的唯一可行方式。
英文摘要：
Very-high-energy (VHE, E>0.1 TeV) gamma-ray emission regions with angular extents comparable to the field-of-view of current imaging air-Cherenkov telescopes (IACT) require additional observations of source-free regions to estimate the background contribution to the energy spectrum. This reduces the effective observation time and deteriorates the sensitivity. A new method of reconstructing spectra from IACT data without the need of additional observations of source-free regions is developed. Its application is not restricted to any specific IACT or data format. On the basis of the template background method, which defines the background in air-shower parameter space, a new spectral reconstruction method from IACT data is developed and studied, the Template Background Spectrum (TBS); TBS is tested on published H.E.S.S. data and H.E.S.S. results. Good agreement is found between VHE gamma-ray spectra reported by the H.E.S.S. collaboration and those re-analysed with TBS. This includes analyses of point-like sources, sources in crowded regions, and of very extended sources down to sources with fluxes of a few percent of the Crab Nebula flux and excess-to-background ratios around 0.1. However, the TBS background normalisation introduces new statistical and systematic errors which are accounted for, but may constitute a limiting case for very faint extended sources. The TBS method enables the spectral reconstruction of data when other methods are hampered or even fail. It does not need dedicated observations of VHE gamma-ray-free regions (e.g. as the On/Off background does) and circumvents known geometrical limitations to which other methods (e.g. the reflected-region background) for reconstructing spectral information of VHE gamma-ray emission regions are prone to; TBS would be, in specific cases, the only feasible way to reconstruct energy spectra.
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