Small-Scale Clustering in the Isotropic Arrival Distribution of Ultra-High-Energy Cosmic Rays and Implications for Their Source Candidates
Small-Scale Clustering in the Isotropic Arrival Distribution of Ultra-High-Energy Cosmic Rays and Implications for Their Source Candidates
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超高能宇宙线各向同性到达分布中的小尺度聚类及其对候选源的影响
DOI：
10.1086/367931
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发表时间：
2002
期刊：
影响因子：
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通讯作者：
Katsuhiko Sato
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文献类型：
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作者：
Hiroyuki Yoshiguchi;S. Nagataki;Sin;Katsuhiko Sato
我们提出了数值模拟的超高频质子的传播能量为1019.5-1022 eV的河外磁场超过1 Gpc。我们使用光学红移巡天（ORS）星系样本，这使我们能够准确地量化附近的源的能量谱和到达分布的贡献，作为源模型。对样本进行了修正，考虑到选择效应和回避区没有星系（|B| 20°）。我们从数值模拟的数据中计算了三个可观测量：宇宙线谱、谐波振幅和两点关联函数。利用这些量，我们将数值计算的结果与观测结果进行了比较。我们发现，超高能宇宙线（UHECRs）的到达分布变得最各向同性的源仅限于发光星系（Mlim = -20.5）。然而，即使Mlim =-20.5，它的各向同性也不足以与Akeno Giant Air Shower Array（AGASA）的观测一致。为了获得一个充分各向同性的到达分布，我们随机选择的光源比-20.5等的ORS样品，这有助于观察到的宇宙射线通量，并调查其数量的结果的依赖性。结果表明，当选择亮度大于-20.5等的ORS星系中的~10-1.7个作为UHECR源时，可以再现包括能谱的GZK截止值在内的三个观测量。就源数密度而言，该约束对应于~10-6 Mpc-3。然而，由于在这种情况下，GZK球体内的源的平均数量仅为~0.5，因此不能再现1020.0 eV以上的八个AGASA事件，它们不一起构成集群事件。另一方面，如果高分辨率复眼EHE宇宙线探测器（HiRes）测量的宇宙线通量与GZK截止一致，并且UHECR的到达分布的观测特征与AGASA相同，则我们的源模型可以同时解释到达分布和通量。因此，我们得出结论，1020 eV以上的八个AGASA事件中的很大一部分可能起源于自上而下的场景，或者HiRes实验测量的宇宙射线通量可能更好。我们还讨论了低于1020.0 eV的UHECR的起源，通过比较天体物理源候选者的数密度和我们的结果（~10-6 Mpc-3）。
We present numerical simulations on the propagation of ultra-high-frequency protons with energies of 1019.5-1022 eV in extragalactic magnetic fields over 1 Gpc. We use the Optical Redshift Survey (ORS) galaxy sample, which allows us to accurately quantify the contribution of nearby sources to the energy spectrum and the arrival distribution, as a source model. The sample is corrected, taking the selection effect and absence of galaxies in the zone of avoidance (|b| < 20°) into account. We calculate three observable quantities—cosmic-ray spectrum, harmonic amplitude, and two-point correlation function—from our data of numerical simulations. With these quantities, we compare the results of our numerical calculations with the observation. We find that the arrival distribution of ultra-high-energy cosmic rays (UHECRs) becomes most isotropic as sources are restricted to to luminous galaxies (Mlim = -20.5). However, it is not isotropic enough to be consistent with the Akeno Giant Air Shower Array (AGASA) observation, even for Mlim = -20.5. In order to obtain a sufficiently isotropic arrival distribution, we randomly select sources more luminous than -20.5 mag from the ORS sample, which contribute to the observed cosmic-ray flux, and investigate the dependence of the results on their number. We show that three observable quantities, including the Greisen-Zatsepin-Kuz'min (GZK) cutoff of the energy spectrum, can be reproduced in the case that the number fraction ~10-1.7 of the ORS galaxies more luminous than -20.5 mag is selected as UHECR sources. In terms of the source number density, this constraint corresponds to ~10-6 Mpc-3. However, since the mean number of sources within the GZK sphere is only ~0.5 in this case, the eight AGASA events above 1020.0 eV, which do not together constitute clustered events, cannot be reproduced. On the other hand, if the cosmic-ray flux measured by the High Resolution Fly's Eye EHE Cosmic-Ray Detector (HiRes), which is consistent with the GZK cutoff, is correct and observational features about the arrival distribution of UHECRs are same as the AGASA, our source model can explain both the arrival distribution and the flux at the same time. Thus, we conclude that a large fraction of the eight AGASA events above 1020 eV might originate in the top-down scenarios or that the cosmic-ray flux measured by the HiRes experiment might be better. We also discuss the origin of UHECRs below 1020.0 eV through comparisons between the number density of astrophysical source candidates and our result (~10-6 Mpc-3).