Probing the sea of galactic cosmic rays with Fermi-LAT
Probing the sea of galactic cosmic rays with Fermi-LAT
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DOI：
10.1103/physrevd.101.083018
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发表时间：
2020-04-15
影响因子：
5
通讯作者：
Zanin, Roberta
中科院分区：
文献类型：
--
作者：
Aharonian, Felix;Peron, Giada;Zanin, Roberta
来自巨分子云（GMCs）的高能伽马射线携带着银河宇宙射线（CRs）空间和能量分布的直接信息。最近发布的gmc目录包含足够大的云，可以用作气压计，通过它们的伽马射线发射来探测整个星系盘的cr密度。基于Fermi-LAT的数据，我们报告了在距离12.5 kpc的地方发现了19个gmc的伽马射线信号。从这些天体的伽马射线和CO观测得来的CR密度的星系中心径向分布，以及从属于古尔德带复合体的一些附近的云中得出的CR密度，揭示了一个均匀的CR“海洋”，其密度恒定，光谱形状接近直接（局部）测量到的CR通量。这涉及到星系中心距离超过8kpc，以及银河系中心区域的人马座B复合体。另一方面，在4 ~ 8 kpc之间的星系中心距离，我们发现与CR海平面有明显的偏差；在某些地区，gmc的特征是CR密度增加。这可能是由于向银河系中心方向的CR海洋的海平面可能在全球范围内升高，或者是由于最近靠近某些特定云层的CR加速器的存在。
High energy gamma-rays from giant molecular clouds (GMCs) carry direct information about the spatial and energy distributions of galactic cosmic rays (CRs). The recently released catalogs of GMCs contain sufficiently massive clouds to be used as barometers for probing, through their gamma-ray emission, the density of CRs throughout the galactic disk. Based on the data of Fermi-LAT, we report the discovery of gamma-ray signals from nineteen GMCs located at distances up to 12.5 kpc. The galactocentric radial distribution of the CR density derived from the gamma-ray and CO observations of these objects, as well as from some nearby clouds that belong to the Gould Belt complex, unveil a homogeneous "sea" of CRs with a constant density and spectral shape close to the flux of directly (locally) measured CRs. This concerns the galactocentric distances exceeding 8 kpc, as well as the Sagittarius B complex, in the region of the Galactic Center. On the other hand, for the galactocentric distances between 4 and 8 kpc, we found noticeable deviations from the CR sea level; in some locations, GMCs are characterized by enhanced CR density. This could be the result of a possible global increase of the level of the CR sea towards the Galactic Center and/or by the presence of recent CR accelerators close to some specific clouds.