We seek to understand the propagation mechanisms of positrons in the interstellar medium (ISM). This understanding is a key to determine whether the spatial distribution of the annihilation emission observed in our Galaxy reflects the spatial distribution of positron sources and, therefore, makes it possible to place constraints on the origin of positrons. We review the different processes that are likely to affect the transport of positrons in the ISM. These processes fall into three broad categories: scattering off magnetohydrodynamic waves, collisions with particles of the interstellar gas and advection with large-scale fluid motions. We assess the efficiency of each process and describe its impact on the propagation of positrons. We also develop a model of positron propagation, based on Monte-Carlo simulations, which enable us to estimate the distances traveled by positrons in the different phases of the ISM. We find that low-energy (< 10 MeV) positrons generally have negligible interactions with magnetohydrodynamic waves, insofar as these waves are heavily damped. Positron propagation is mainly controlled by collisions with gas particles. Under these circumstances, positrons can travel huge distances (up to 30 kpc/n_H for 1 MeV positrons) along magnetic field lines before annihilating.
Low energy cosmic rays are modulated by the solar activity when they propagation in the heliosphere, leading to ambiguities in understanding their acceleration at sources and propagation in the Milky Way. By means of the precise measurements of the $e^-$, $e^+$, $e^-+e^+$, and $e^+/(e^-+e^+)$ spectra by AMS-02 near the Earth, as well as the very low energy measurements of the $e^-+e^+$ fluxes by Voyager-1 far away from the Sun, we derive the local interstellar spectra (LIS) of $e^-$ and $e^+$ components individually. Our method is based on a non-parametric description of the LIS of $e^-$ and $…
GX 301-2 is a high-mass X-ray binary (HMXB) with strong stellar outflows. The evolution of these binaries can be closely related with the interstellar environment due to strong wind interactions. We try to constrain the energy injected in the interstellar medium by GX 301-2 through stellar wind using HAWK-I and Herschel data. We analysed HAWK-I images in four different filters (Br$γ$, H$_2$, J, and Ks) and tried to retrieve signatures of the impact of GX 301-2 on its environment. We used Herschel data to outline the interstellar medium and the Gaia DR3 catalogue to infer the proper motion of G…
Diverse Properties of Interstellar Medium Embedding Gamma-Ray Bursts at the Epoch of Reionization
分析超高分辨率大尺度宇宙辐射流体动力学模拟，首次量化的物理环境的长持续时间伽马射线暴（GRB）在再电离的时代。我们发现，在秒差距尺度上，13%的伽玛暴保持在高密度（$\ge 10^4$ cm $^{-3}$）的低温恒星形成区域，而87%的伽玛暴发生在低密度（$\sim 10^{-2.5}$ cm $^{-3}$）的高温区域超新星加热。更重要的是，伽玛射线暴余辉的光谱特性，如中性氢柱密度，总氢柱密度，尘埃柱密度，气体温度和金属含量的干预吸收剂，从视线到视线变化很大。虽然我们的模型解释了现存的有限的观测推断值环暴密度，金属丰度，柱密度和灰尘的属性，一个大得多的样本高Z伽玛暴余辉将需要促进模型的统计坚实的测试。我们的研究结果表明，任何试图推断的物理性质（如金属丰度）的星际介质的主机星系的基础上非常少量的（通常是一个）视线将是不稳定的。利用高Z伽玛暴探测星际介质和星系际介质时，应考虑到星际介质的物理性质。
Probing X-ray Absorption and Optical Extinction in the Interstellar Medium Using Chandra Observations of Supernova Remnants
我们提出了一个全面的研究星际X射线消光使用广泛的钱德拉超新星遗迹档案，并使用我们的结果来完善氢柱密度和光学消光之间的经验关系。在我们的分析中，我们利用大的，统一的数据样本，以评估各种系统的不确定性测量的星际X射线吸收。具体来说，我们解决系统的不确定性，源于（一）用于拟合超新星遗迹光谱的发射模型，（二）在个别遗迹的空间变化，（三）的物理条件的遗迹，如成分，温度和非平衡区，和（四）用于X射线的吸收模型在星际介质。使用贝叶斯框架来量化这些系统的不确定性，并将由此产生的氢柱密度测量结果与相同残留物的光学消光测量结果相结合，我们发现经验关系NH =（2.87+/-0.12）x 10^21 AV cm^（-2），这明显高于以前的测量结果。
Propagation of Galactic cosmic rays (CR) in the interstellar medium (ISM) is among the unsolved problems in particle astrophysics. Interpretation of CR spectrum and composition measurements and their possible link to dark matter crucially relies on our understanding of CR propagation in the Galaxy. Several air shower experiments have measured a significant anisotropy of CRs in the TeV to PeV energy range. These observations hint to a complicated overlap of more than one cause: from the distribution of the CR sources in the Milky Way to the nature of such sources, from the turbulence properties…
Radioactive components of the interstellar medium provide an entirely-different and new aspect to the studies of the interstellar medium. Injected from sources of nucleosynthesis, unstable nuclei decay along their trajectories. Measurements can occur through characteristic gamma rays that are emitted with the decay, or in cosmic material samples through abundances of parent and daughter isotopes as they change with decay. The dynamics and material flows within interstellar medium are thus accessible to measurement, making use of the intrinsic clock that radioactive decay provides. We describe …
The TeV $γ$-ray halo around the Geminga pulsar is an important indicator of cosmic-ray (CR) propagation in the local zone of the Galaxy as it reveals the spatial distribution of the electrons and positrons escaping from the pulsar. Considering the intricate magnetic field in the interstellar medium (ISM), it is proposed that superdiffusion model could be more realistic to describe the CR propagation than the commonly used normal diffusion model. In this work, we test the superdiffusion model in the ISM around the Geminga pulsar by fitting to the surface brightness profile of the Geminga halo m…
Massive stars drive strong winds that impact the surrounding interstellar medium, producing parsec-scale bubbles for isolated stars and superbubbles around young clusters. These bubbles can be observed across the electromagnetic spectrum, both the wind itself and the swept up interstellar gas. Runaway massive stars produce bow shocks that strongly compresses interstellar gas, producing bright infrared, optical and radio nebulae. With the detection of non-thermal radio emission from bow shocks, particle acceleration can now also be investigated. I review research on wind bubbles and bow shocks …
The Analytical Solution to the Temporal Broadening of a Gaussian-Shaped Radio Pulse by Multipath Scattering from a Thin Screen in the Interstellar Medium
A relativistic spacecraft of the type envisioned by the Breakthrough Starshot initiative will inevitably get charged through collisions with interstellar particles and UV photons. Interstellar magnetic fields would, therefore, deflect the trajectory of the spacecraft. We calculate the expected deflection for typical interstellar conditions. We also find that the charge distribution of the spacecraft is asymmetric, producing an electric dipole moment. The interaction between the moving electric dipole and the interstellar magnetic field is found to produce a large torque, which can result in fa…
