标题： 磁拱在解释太阳盘面上伽马射线发射之谜中的作用 显示英文标题

标题： Role of magnetic arcades in explaining the puzzle of the gamma-ray emission from the solar disk

摘要： 太阳盘面发出的伽马射线（角大小为$0.5^\circ$）被解释为银河宇宙射线（GCRs）与太阳大气相互作用的结果，这一直是太阳物理学中的一个核心挑战。在 Seckel、Stanev 和 Gaisser（SSG91）基于 GCRs 磁镜效应的经典工作之后，模型和观测之间的差异仍然存在，表明需要一种新的方法。本研究的重点是探索低光球层中闭合磁场几何结构对观测到的伽马射线通量的影响。我们使用 PLUTO 代码数值追踪了静止磁场高度为$\sim 20$兆米的磁拱内测试质子的轨迹，这些磁拱位于喷流附近。通过利用数值垂直密度剖面，我们在不同的色球/光球高度注入粒子，模拟邻近磁管中的 GCRs 进入闭合磁拱的过程。值得注意的是，我们的模型重现了低于$\sim 33$吉电子伏特的平坦伽马射线能谱、接近$\sim 10$吉电子伏特的近乎各向同性的发射，两者均与费米-拉特观测一致，并且在$\sim 1$太电子伏特处的近地平线发射。我们的模型还可以重现 HAWC 检测到的通量下降（$\sim 1$太电子伏特）。最后，我们认为在$\sim$40 吉电子伏特处观察到的光谱凹陷可能是由于低能范围内的交叉场扩散导致的通量抑制，从而产生截止效应。这些发现强调了闭合磁场结构在塑造太阳盘面伽马射线发射中的关键作用。 显示英文摘要

摘要： The interpretation of gamma-ray emission originating from the solar disk ($0.5^\circ$ in angular size) as due to the interaction of Galactic Cosmic Rays (GCRs) with the solar atmosphere has remained a central challenge in solar physics. After the seminal work by Seckel, Stanev, and Gaisser (SSG91) based on GCRs magnetic mirroring, discrepancies between models and observations persist, indicating the need for a novel approach. The present work focuses on exploring the impact of a closed magnetic field geometry in the low photosphere on the observed gamma-ray flux. We track numerically with the PLUTO code the trajectories of test-particle protons within a static $\sim 20$ Mm scale height magnetic arcade adjacent to jets. By making use of numerical vertical density profiles we inject particles at distinct chromospheric/photospheric altitudes, mimicking the migration of GCRs from neighboring flux tubes into closed arcades. Remarkably, our model reproduces a flat gamma-ray spectrum below $\sim 33$ GeV, a nearly-isotropic emission at $\sim 10$ GeV, both consistent with Fermi-LAT observations, and a near-limb emission at $\sim 1$ TeV. Our model can also reproduce the flux-drop detected by HAWC ($\sim 1$ TeV). Finally, we argue that the spectral dip observed at $\sim$ 40 GeV may result from the flux suppression at low energy due to the cross-field diffusion, which would produce a cutoff. These findings underscore the pivotal role of closed magnetic field structures in shaping the solar disk gamma-ray emission.