A hybrid approach to event reconstruction for atmospheric Cherenkov Telescopes combining machine learning and likelihood fitting

IF 4.2 3区 物理与天体物理 Q1 ASTRONOMY & ASTROPHYSICS
Georg Schwefer , Robert Parsons , Jim Hinton
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引用次数: 0

Abstract

The imaging atmospheric Cherenkov technique provides potentially the highest angular resolution achievable in astronomy at energies above the X-ray waveband. High-resolution measurements provide the key to progress on many of the major questions in high energy astrophysics, including the sites and mechanisms of particle acceleration to PeV energies. The huge potential of the next-generation CTA observatory in this regard can be realised with the help of improved algorithms for the reconstruction of the air-shower direction and energy.

Hybrid methods combining maximum-likelihood-fitting techniques with neural networks represent a particularly promising approach and have recently been successfully applied for the reconstruction of astrophysical neutrinos. Here, we present the FreePACT algorithm, a hybrid reconstruction method for IACTs. In this, making use of the neural ratio estimation technique from the field of likelihood-free inference, the analytical likelihood used in traditional image likelihood fitting is replaced by a neural network that approximates the charge probability density function for each pixel in the camera.

The performance of this improved algorithm is demonstrated using simulations of the planned CTA southern array. For this setupFreePACT provides significant performance improvements over analytical likelihood techniques, with improvements in angular and energy resolution of 25% or more over a wide energy range and an angular resolution as low as 40 at energies above 50TeV for observations at 20° zenith angle. It also yields more accurate estimations of the uncertainties on the reconstructed parameters and significantly speeds up the reconstruction compared to analytical likelihood techniques while showing the same stability with respect to changes in the observation conditions. Therefore, the FreePACT method is a promising upgrade over the current state-of-the-art likelihood event reconstruction techniques.

结合机器学习和似然拟合的大气切伦科夫望远镜事件重建混合方法
大气切伦科夫成像技术为天文学提供了在 X 射线波段以上能量所能达到的最高角度分辨率。高分辨率测量是在高能天体物理学的许多重大问题上取得进展的关键,包括粒子加速到 PeV 能量的场所和机制。将最大似然拟合技术与神经网络相结合的混合方法是一种特别有前途的方法,最近已成功应用于天体物理中微子的重建。在这里,我们介绍一种针对中微子的混合重建方法--FreePACT 算法。在该算法中,利用无似然推理领域的神经比值估计技术,传统图像似然拟合中使用的分析似然被神经网络所取代,该神经网络可逼近相机中每个像素的电荷概率密度函数。在这种设置下,FreePACT的性能比分析似然技术有了显著提高,在很宽的能量范围内,其角度和能量分辨率提高了25%或更多,在天顶角为20°的观测中,当能量超过50TeV时,其角度分辨率低至40′′。它还能对重建参数的不确定性进行更精确的估计,与分析似然法相比,能显著加快重建速度,同时在观测条件变化时也表现出同样的稳定性。因此,与目前最先进的似然事件重建技术相比,FreePACT 方法是一种很有前途的升级方法。
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来源期刊
Astroparticle Physics
Astroparticle Physics 地学天文-天文与天体物理
CiteScore
8.00
自引率
2.90%
发文量
41
审稿时长
79 days
期刊介绍: Astroparticle Physics publishes experimental and theoretical research papers in the interacting fields of Cosmic Ray Physics, Astronomy and Astrophysics, Cosmology and Particle Physics focusing on new developments in the following areas: High-energy cosmic-ray physics and astrophysics; Particle cosmology; Particle astrophysics; Related astrophysics: supernova, AGN, cosmic abundances, dark matter etc.; Gravitational waves; High-energy, VHE and UHE gamma-ray astronomy; High- and low-energy neutrino astronomy; Instrumentation and detector developments related to the above-mentioned fields.
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