[论文解读] Prospects for a survey of the Galactic plane with the Cherenkov Telescope Array

CTA Consortium, Acero, Fabio+3 more|arXiv (Cornell University)|Oct 3, 2023

Astrophysics and Cosmic Phenomena被引用 3

一句话总结

本文评估了利用切伦科夫望远镜阵列（CTA）在银河系平面探测伽马射线源的前景，通过模拟具有不同光谱和测时模型的脉冲星与伽马射线双星的观测。结果表明，CTA能够分辨类蟹状星云（幂律谱）和类船帆座（截断幂律谱 + TeV成分）的脉冲星，其灵敏度取决于源的流量、光谱指数和测时精度，从而可实现对银河系内高能暂现源和持久源的全面调查。

ABSTRACT

Approximately one hundred sources of very-high-energy (VHE) gamma rays are known in the Milky Way. A survey of the entire Galactic Plane in the energy range from a few tens of GeV to a few hundred TeV has been proposed as a Key Science Project for the upcoming Cherenkov Telescope Array Observatory (CTAO). This article presents the status of the studies towards the Galactic Plane Survey (GPS). We build and make publicly available a sky model that combines data from observations of known gamma-ray emitters with state-of-the-art physically-driven models of synthetic populations of the main classes of established Galactic VHE sources, as well as of interstellar emission from cosmic-ray interactions in the Milky Way. We also perform an optimisation of the observation strategy. We use the improved sky model and observation strategy to simulate GPS data that are analysed using the methods and software tools under development for real data. We show that the GPS has the potential to increase the number of known Galactic VHE emitters by almost a factor of five. This corresponds to the detection of more than two hundred pulsar wind nebulae and a few tens of supernova remnants at average integral fluxes one order of magnitude lower than in the existing sample above 1 TeV, therefore opening the possibility to perform unprecedented population studies. The GPS also has the potential to provide new VHE detections of binary systems and pulsars, and to detect bright PeVatrons. Furthermore, the GPS will constitute a pathfinder for deeper follow-up observations of these source classes. Finally, we show that we can extract from GPS data an estimate of the contribution to diffuse emission from unresolved sources, and that there are good prospects of detecting interstellar emission and statistically distinguishing different scenarios. (Abridged)

研究动机与目标

• 评估切伦科夫望远镜阵列（CTA）对银河系平面中暂现源与持久源的灵敏度。
• 对已知与候选伽马射线脉冲星的光谱与时间行为进行建模，区分类蟹状星云与类船帆座两类群体。
• 模拟CTA对银河系平面内伽马射线双星与年轻脉冲星的探测性能。
• 为未来CTA银河系平面巡天建立观测策略与灵敏度阈值。

提出的方法

• 使用GeV能段的幂律谱（PWL）对25个类蟹状星云脉冲星进行模拟观测，并将谱外推至VHE能段而不引入截断。
• 对13个类船帆座脉冲星建模，结合Fermi-LAT类幂律谱加指数截断（PLEC）在GeV能段，外加一个额外的TeV能段调制成分。
• 采用Fermi-2PC与3FHL星表中的相位平均光谱参数，对TeV成分通量（ηTeV/GeV：5×10⁻⁵ 至 10⁻²）与截断能量（7 TeV ± 3 TeV）进行随机化处理。
• 在10 GeV以上应用Fermi-LAT相位模板，假设脉冲轮廓无能量演化。
• 使用三阶多项式频率演化模型进行脉冲星测时，缺失源的测时参数参考[114]与[27]。
• 在模拟中包含8个已知与候选伽马射线双星（如PSR B1259−63、LSI +61◦303），其轨道周期从数天至数年不等。

实验结果

研究问题

• RQ1 在不同光谱类型下，CTA在银河系平面探测VHE脉冲星的预期探测数量是多少？
• RQ2 包含TeV能段调制成分如何影响类船帆座脉冲星在CTA巡天中的可探测性？
• RQ3 CTA在100 GeV至10 TeV能量范围内，对具有轨道调制特性的伽马射线双星的灵敏度阈值是多少？
• RQ4 在大规模巡天中，测时与光谱建模的不确定性如何影响源的识别与通量测量？
• RQ5 为最大化CTA在银河系平面的源探测效率，最优的观测策略是什么？

主要发现

• 在假设光谱指数约为2.0且GeV通量高于10⁻¹² ph cm⁻² s⁻¹的条件下，CTA预计可探测到全部25个类蟹状星云脉冲星。
• 类船帆座脉冲星（如Vela与Geminga）仅在TeV成分通量超过GeV通量约5×10⁻⁵时才可探测，且随着该比值降低，探测概率随之下降。
• 当TeV成分通量比达到10⁻²时，CTA在每源10小时的观测下可实现信噪比 >5，从而实现可靠探测。
• 模拟结果表明，采用三阶频率演化模型对分辨长自转周期脉冲星（如PSR J2032+4127，周期50年）至关重要。
• 如LSI +61◦303与LS 5039等伽马射线双星可在其轨道周期内被CTA探测到，且在VHE能段的调制深度超过10%。
• 当源通量低于约10⁻¹³ ph cm⁻² s⁻¹（100 GeV至1 TeV能量范围）时，巡天灵敏度受限于混淆效应，尤其在银河系平面密集区域更为显著。