INAF-Osservatorio Astrofisico di Arcetri, Firenze, Italy.
Phys Rev Lett. 2012 Aug 10;109(6):061101. doi: 10.1103/PhysRevLett.109.061101. Epub 2012 Aug 9.
We show that the complex shape of the cosmic ray (CR) spectrum, as recently measured by PAMELA and inferred from Fermi-LAT γ-ray observations of molecular clouds in the Gould belt, can be naturally understood in terms of basic plasma astrophysics phenomena. A break from a harder to a softer spectrum at rigidity R is approximately equal to 10 GV follows from a transition from transport dominated by advection of particles with Alfvén waves to a regime where diffusion in the turbulence generated by the same CRs is dominant. A second break at R is approximately equal to 200 GV happens when the diffusive propagation is no longer determined by the self-generated turbulence, but rather by the cascading of externally generated turbulence (for instance due to supernova bubbles) from large spatial scales to smaller scales where CRs can resonate. Implications of this scenario for the cosmic ray spectrum, grammage, and anisotropy are discussed.
我们表明，宇宙射线（CR）谱的复杂形状，如最近由 PAMELA 测量并从 Gould 带中分子云的费米-LATγ射线观测推断得出，可以用基本的等离子体天体物理现象来自然地理解。从更硬到更软的谱的转变在刚性 R 处的大约为 10GV，这是由于从由阿尔文波主导的粒子输运的过渡到由相同的 CRs 产生的湍流中的扩散主导的区域。当扩散传播不再由自产生的湍流决定，而是由外部产生的湍流（例如由于超新星气泡）从大的空间尺度到较小的尺度（在较小的尺度上 CR 可以共振）时，R 处的第二个转变大约为 200GV。讨论了这种情况对宇宙射线谱、质量和各向异性的影响。
