Porter T A, Rowell G P, Jóhannesson G, Moskalenko I V
W. W. Hansen Experimental Physics Laboratory and Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Stanford, California 94305, USA.
School of Physical Sciences, University of Adelaide, Adelaide, South Australia 5000, Australia.
Phys Rev D. 2018 Aug 15;98(4). doi: 10.1103/physrevd.98.041302. Epub 2018 Aug 21.
Identification of the cosmic-ray (CR) "PeVatrons," which are sources capable of accelerating particles to ~10 eV energies and higher, may lead to resolving the long-standing question of the origin of the spectral feature in the all-particle CR spectrum known as the "knee." Because CRs with these energies are deflected by interstellar magnetic fields identification of individual sources and determination of their spectral characteristics is more likely via very high energy -ray emissions, which provide the necessary directional information. However, pair production on the interstellar radiation field (ISRF) and cosmic microwave background (CMB) leads to steepening of the high energy tails of -ray spectra, and should be corrected for to enable true properties of the spectrum at the source to be recovered. Employing recently developed three-dimensional ISRF models this paper quantifies the pair-absorption effect on spectra for sources in the Galactic center (GC) direction at 8.5 and 23.5 kpc distances, with the latter corresponding to the far side of the Galactic stellar disc where it is expected that discrimination of spectral features >10 TeV is possible by the forthcoming Cherenkov Telescope Array (CTA). The estimates made suggest spectral cutoffs could be underestimated by factors of a few in the energy range so far sampled by TeV -ray telescopes. As an example to illustrate this, the recent HESS measurements of diffuse -ray emissions possibly associated with injection of CRs nearby Sgr A* are ISRF corrected, and estimates of the spectral cutoff are reevaluated. It is found that it could be higher by up to a factor of ~2, indicating that these emissions may be consistent with a CR accelerator with a spectral cutoff of at least 1 PeV at the 95% confidence level.
识别宇宙射线（CR）“PeVatrons”（即能够将粒子加速到10 eV及更高能量的源），可能有助于解决全粒子CR谱中被称为“膝部”的光谱特征起源这一长期存在的问题。由于具有这些能量的CR会被星际磁场偏转，因此通过非常高能量的γ射线发射来识别单个源并确定其光谱特征更有可能，因为γ射线发射提供了必要的方向信息。然而，星际辐射场（ISRF）和宇宙微波背景（CMB）上的对产生会导致γ射线谱的高能尾部变陡，应该对此进行校正，以便能够恢复源处光谱的真实特性。本文采用最近开发的三维ISRF模型，对距离为8.5和23.5 kpc的银心（GC）方向的源光谱的对吸收效应进行了量化，后者对应于银河系恒星盘的远侧，预计即将到来的切伦科夫望远镜阵列（CTA）能够分辨>10 TeV的光谱特征。所作的估计表明，在TeV射线望远镜迄今采样的能量范围内，光谱截止可能被低估了几个因子。作为说明这一点的一个例子，对最近HESS测量的可能与Sgr A*附近CR注入相关的弥漫γ射线发射进行了ISRF校正，并重新评估了光谱截止的估计值。发现它可能高出多达2倍，这表明这些发射可能与一个在95%置信水平下光谱截止至少为1 PeV的CR加速器一致。
