Cosmic rays in the immediate local interstellar medium

对宇宙射线(CRS)的精确观测只能从我们在银河系中的位置进行，并且受到我们当地环境结构的影响：地球位于日光层，这抑制了能量小于几GeV的通量。日光层本身嵌在一个低密度的超级气泡中，称为局部气泡(LB)。附近震源的确切历史和空间分布也是未知的，这导致了高能和极低能量下光谱的相当大的不确定性。最近，由于两个进入星际空间的旅行者号探测器，首次在日光层外进行的直接观测可以在GeV以下的能量下进行。我们注意到，与LB的维度相比，这些测量仍然只探测直接的星际局部介质(ISM)。扩散发射，最突出的来自产生伽马射线的CR核，以及扩散分子云(MC)中的电离率，远程探测银河系其他地方的CRS。这种方法提供了互补的约束，但受到涉及的天体物理和星际化学的不确定性的影响。虽然伽马射线测量的推断显示了一些有趣的反常现象，但电离率显示出更大的偏差，从银河系其他地方的MC推断的电离率比从当地测量的通量推断的电离率大一到两个数量级。对于银河系中心附近的电离率测量来说，这种差异甚至更大，因为它几乎比本地速率大四个数量级！为了解决这个经常被忽视的异常，我们主要考虑了两种情况：第一，能量低于GeV的CRS通量在银河系内的空间波动。这是由于源的离散性质和低能量下的电离和库仑损耗造成的有限范围的综合影响。如果局部观测到的通量处于通量分布的低端，或者观测到的电离率偏向分布的高端，这可以解释这种差异。我们将预测通量的分布，并统计地评估局部光谱和电离测量之间的兼容性。第二，局部CRS的通量可能会因为LB的存在而受到抑制。在小尺度上，由于规则磁场的存在，CR的输运是各向异性的。在观测条件限制较少的情况下，我们将考虑各种解析和数值模式，研究初级和次级CRS的扩散。最终，我们将在一个一致的全球图景中将这两种情况结合在一起。巴黎合作伙伴、弥散排放和电离率专家、亚琛合作伙伴、CR运输专家，以及柏林合作伙伴--ISM流体动力学模拟专家--的协同作用，将确保解决CRS中最令人困惑的异常之一。

Precise observations of cosmic rays (CRs) are only available from our position in the Galaxy and are affected by the structure of our local environment: The Earth is situated in the heliosphere, which suppresses fluxes at energies smaller than a few GeV. The heliosphere itself is embedded in a low-density superbubble, called the Local Bubble (LB). The exact history and spatial distribution of nearby sources are also unknown, leading to sizeable uncertainties of the spectra at high and very low energies. Recently, the first direct observations outside the heliosphere have become available at energies below a GeV thanks to the two Voyager probes which have crossed into interstellar space. We note that compared to the dimensions of the LB, these measurements are still only probing the immediate local interstellar medium (ISM).Diffuse emission, most prominently from CR nuclei producing gamma-rays, and ionisation rates in diffuse molecular clouds (MCs) remotely probe CRs elsewhere in the Galaxy. This approach gives complementary constraints, but is affected by uncertainties in the astrophysics and interstellar chemistry involved. While the inferences from the gamma-ray measurements have displayed some interesting anomalies, the ionisation rates show an even stronger deviation, with the ones inferred from MCs elsewhere in the Galaxy one to two orders of magnitude large than what is inferred from the locally measured fluxes. The discrepancy is even stronger for measurements of ionisation rates close to the galactic centre which are almost four orders of magnitude larger than the local rate!For the resolution of this oftentimes ignored anomaly, we consider mainly two scenarios: First, the fluxes of CRs at energies below a GeV fluctuate spatially within the Galaxy. This is due to the combined effect of the discrete nature of sources and the limited range due to ionisation and Coulomb losses at low energies. If the locally observed flux were at the low end of the distribution of fluxes or the observed ionisation rates were biased towards the high end of the distribution, this could explain the discrepancy. We will predict the distribution of fluxes and statistically evaluate the compatibility between local spectra and ionisation measurements.Second, the flux of local CRs could be suppressed due to the presence of the LB. On small scales, CR transport is anisotropic due to the presence of the regular magnetic field. With little observational constraints on the regular component of the LB, we will instead consider a variety of analytical and numerical models, and study the diffusion of primary and secondary CRs. Eventually, we will combine both scenarios in a consistent global picture.The synergy between the Paris partners, experts on diffuse emission and ionisation rates, the Aachen ones, experts on CR transport, and the Berlin ones, experts on hydrodynamical simulations of the ISM, will guarantee resolving one of the most puzzling anomalies in CRs.