用CRbeam代码模拟甚高能伽马射线传播：与CRPropa和ELMAG代码的比较
Modelling the propagation of very-high-energy gamma rays with the CRbeam code: Comparison with CRPropa and ELMAG codes
AI总结：
本文比较CRbeam、CRPropa和ELMAG三种代码对甚高能伽马射线次级辐射的建模精度，发现并修正差异来源后，CRbeam能为CTA研究星系际磁场提供可靠预测。
摘要：
甚高能伽马射线在穿过星系际介质传播过程中，会与河外背景光的低能光子发生相互作用，产生电子-正电子对。这些电子-正电子对会产生可被伽马射线望远镜探测到的次级伽马射线。这种次级辐射可用于探测大尺度结构空洞中的星系际磁场（IGMF）。新一代伽马射线观测站，即切伦科夫望远镜阵列（CTA），将提高对这些次级伽马射线辐射的探测灵敏度，并使得对宇宙学距离处源的辐射特性测量成为可能。对CTA数据的解释，包括探测IGMF以及研究其性质和起源，将需要对初级和次级伽马射线通量进行精确建模。我们利用公开可用的蒙特卡洛代码CRPropa和ELMAG进行模型计算，评估次级伽马射线辐射建模的精度，并将其预测结果与理论预期以及新开发的CRbeam代码的模型计算结果进行比较。我们发现，对于低红移源，不同代码的模型预测结果差异最高可达50%，且随着源红移的增加，差异会增大到量级水平。我们确定了这些差异的来源，并证明在消除所发现的不准确性之后，对于红移z~0.1的邻近源进行建模时，三个代码之间的差异可降低到10%。我们认为，新的CRbeam代码能够为邻近源和红移z~1的遥远源的次级伽马射线信号的光谱、时间以及成像特性提供可靠的预测。因此，它可以用于研究伽马射线源和IGMF，其精度水平适合未来CTA对伽马射线穿过星系际介质传播效应的研究。
英文摘要：
Very-high-energy gamma rays produce electron positron pairs in interactions with low-energy photons of extragalactic background light during propagation through the intergalactic medium. The electron-positron pairs generate secondary gamma rays detectable by gamma-ray telescopes. This secondary emission can be used to detect intergalactic magnetic fields (IGMF) in the voids of large-scale structure. A new gamma-ray observatory, namely, Cherenkov Telescope Array (CTA), will provide an increase in sensitivity for detections of these secondary gamma-ray emission and enable the measurement of its properties for sources at cosmological distances. The interpretation of the CTA data, including detection of IGMF and study of its properties and origins, will require precision modeling of the primary and secondary gamma-ray fluxes. We asses the precision of the modeling of the secondary gamma-ray emission using model calculations with publicly available Monte-Carlo codes CRPropa and ELMAG and compare their predictions with theoretical expectations and with model calculations of a newly developed CRbeam code. We find that model predictions of different codes differ by up to 50% for low-redshift sources, with discrepancies increasing up to order-of-magnitude level with the increasing source redshifts. We identify the origin of these discrepancies and demonstrate that after eliminating the inaccuracies found, the discrepancies between the three codes are reduced to 10% when modeling nearby sources with z~0.1. We argue that the new CRbeam code provides reliable predictions for spectral, timing and imaging properties of the secondary gamma-ray signal for both nearby and distant sources with z~1. Thus, it can be used to study gamma-ray sources and IGMF with a level of precision that is appropriate for the prospective CTA study of the effects of gamma-ray propagation through the intergalactic medium.
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