The effects of the GMF on the transition from Galactic to extragalactic cosmic rays

A. Kääpä, K. Kampert, E. Mayotte
{"title":"The effects of the GMF on the transition from Galactic to extragalactic cosmic rays","authors":"A. Kääpä, K. Kampert, E. Mayotte","doi":"10.22323/1.395.0004","DOIUrl":null,"url":null,"abstract":"Understanding the nature of the transition from Galactic to extragalactic cosmic rays (GCRs and EGCRs) has become especially challenging in light of recent spectral and composition data. Galactic contributions appear to be disfavoured at energies beyond the “second knee” where the composition becomes lighter. At the same time, a dominant EGCR contribution at the “2nd knee” appears unlikely. As a result, the measured flux in the transition region cannot easily be accounted for. With the model-dependence of proposed extensions to both the Galactic and extragalactic contributions, a deeper understanding of CR propagation, particularlywithin theGalacticmagnetic field (GMF), is in order. This is because propagation in this energy range shifts from diffusive to ballistic, which is expected to lead to a number of observable effects on CRs. Using CRPropa3, we study these effects for rigidities between 1016 and 1020 V. We identify various features at rigidities where the gyroradius is comparable to typical length scales of the Galaxy, suggesting causes related to changes in the propagation regime. We further quantify general modifications in the spectrum, composition and arrival direction of GCRs and EGCRs. We find that the GMF naturally induces a flux suppression of GCRs towards higher rigidities due to their increased leakage from the Galaxy. This, in consequence, would lead to an increase in the mean mass of GCR primaries up to energies around the “ankle” in the cosmic ray spectrum. It is also shown that the distribution of GCR arrival directions would be correlated with the Galactic plane for rigidities above 1017 V if sources are distributed evenly within the plane. EGCRs experience no flux modification in the GMF if injected isotropically. Injection of pure dipoles, as well as single source scenarios indicate that the GMF isotropises injected anisotropies below 1018 V, but can still cause flux modifications which depend on the direction of the anisotropy.","PeriodicalId":20473,"journal":{"name":"Proceedings of 37th International Cosmic Ray Conference — PoS(ICRC2021)","volume":null,"pages":null},"PeriodicalIF":0.0000,"publicationDate":"2021-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"2","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Proceedings of 37th International Cosmic Ray Conference — PoS(ICRC2021)","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.22323/1.395.0004","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 2

Abstract

Understanding the nature of the transition from Galactic to extragalactic cosmic rays (GCRs and EGCRs) has become especially challenging in light of recent spectral and composition data. Galactic contributions appear to be disfavoured at energies beyond the “second knee” where the composition becomes lighter. At the same time, a dominant EGCR contribution at the “2nd knee” appears unlikely. As a result, the measured flux in the transition region cannot easily be accounted for. With the model-dependence of proposed extensions to both the Galactic and extragalactic contributions, a deeper understanding of CR propagation, particularlywithin theGalacticmagnetic field (GMF), is in order. This is because propagation in this energy range shifts from diffusive to ballistic, which is expected to lead to a number of observable effects on CRs. Using CRPropa3, we study these effects for rigidities between 1016 and 1020 V. We identify various features at rigidities where the gyroradius is comparable to typical length scales of the Galaxy, suggesting causes related to changes in the propagation regime. We further quantify general modifications in the spectrum, composition and arrival direction of GCRs and EGCRs. We find that the GMF naturally induces a flux suppression of GCRs towards higher rigidities due to their increased leakage from the Galaxy. This, in consequence, would lead to an increase in the mean mass of GCR primaries up to energies around the “ankle” in the cosmic ray spectrum. It is also shown that the distribution of GCR arrival directions would be correlated with the Galactic plane for rigidities above 1017 V if sources are distributed evenly within the plane. EGCRs experience no flux modification in the GMF if injected isotropically. Injection of pure dipoles, as well as single source scenarios indicate that the GMF isotropises injected anisotropies below 1018 V, but can still cause flux modifications which depend on the direction of the anisotropy.
GMF对从银河系到河外宇宙射线的转变的影响
根据最近的光谱和成分数据,理解从银河系到河外宇宙射线(GCRs和EGCRs)转变的本质变得特别具有挑战性。星系的贡献在“第二膝盖”以外的能量上似乎不受欢迎,因为那里的成分变得更轻。与此同时,EGCR在“第二膝关节”的主要贡献似乎不太可能。因此,在过渡区测量的通量不容易解释。随着对银河系和星系外贡献的模型依赖性扩展,对CR传播的更深入理解,特别是在星系磁场(GMF)内,是有序的。这是因为在这个能量范围内的传播从扩散转变为弹道,这将导致对cr的许多可观察到的影响。使用CRPropa3,我们研究了在1016和1020 V之间的刚度的这些影响。我们确定了陀螺半径与银河系典型长度尺度相当的刚性的各种特征,表明与传播体制变化有关的原因。我们进一步量化了GCRs和EGCRs在光谱、组成和到达方向上的一般变化。我们发现,由于gcr从银河系中泄漏的增加,GMF自然地诱导了gcr向更高刚度方向的通量抑制。因此,这将导致GCR初级粒子的平均质量增加,直至宇宙射线光谱中“脚踝”附近的能量。在1017v以上的银河平面上,如果源均匀分布,GCR到达方向的分布将与银河平面相关。如果各向同性注射,egcr在GMF中没有通量改变。注入纯偶极子和单源情景表明,GMF各向同性注入了低于1018 V的各向异性,但仍会引起各向异性方向的通量修正。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
求助全文
约1分钟内获得全文 求助全文
来源期刊
自引率
0.00%
发文量
0
×
引用
GB/T 7714-2015
复制
MLA
复制
APA
复制
导出至
BibTeX EndNote RefMan NoteFirst NoteExpress
×
提示
您的信息不完整,为了账户安全,请先补充。
现在去补充
×
提示
您因"违规操作"
具体请查看互助需知
我知道了
×
提示
确定
请完成安全验证×
copy
已复制链接
快去分享给好友吧!
我知道了
右上角分享
点击右上角分享
0
联系我们:info@booksci.cn Book学术提供免费学术资源搜索服务,方便国内外学者检索中英文文献。致力于提供最便捷和优质的服务体验。 Copyright © 2023 布克学术 All rights reserved.
京ICP备2023020795号-1
ghs 京公网安备 11010802042870号
Book学术文献互助
Book学术文献互助群
群 号:481959085
Book学术官方微信