Very high energy gamma-ray observations of the galaxy clusters Abell 496 and Abell 85 with HESS
Very high energy gamma-ray observations of the galaxy clusters Abell 496 and Abell 85 with HESS
复制标题
使用 HESS 对星系团 Abell 496 和 Abell 85 进行甚高能伽马射线观测
DOI：
10.1051/0004-6361:200811372
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发表时间：
2008
影响因子：
6.5
通讯作者：
E. al.
中科院分区：
文献类型：
--
作者：
H. C. Aharonian;E. al.
目标：在极高能量（VHE，E > 100 GeV）波段研究附近的星系团 Abell 496 和 Abell 85，以研究这类天体中的 VHE 宇宙射线（CR），这些天体是宇宙中最大的引力束缚系统。方法：H.E.S.S.是由四个成像大气切伦科夫望远镜（IACT）组成的阵列，用于观察VHE伽马射线范围内的目标。结果：在两个簇的各自位置没有发现明显的伽马射线信号，每个目标有几个不同的源尺寸假设。特别是，研究了与高密度核心相对应的发射区域、这些星团中整个 X 射线发射的延伸以及与预期吸积激波的非常延伸的区域相对应的发射区域。推导了阿贝尔 496 能量 E>570 GeV 和阿贝尔 85 E>460 GeV 的伽马射线通量上限。结论：根据 VHE 伽马射线的未探测到，计算了星团中强子 CR 总能量的上限。如果宇宙射线能量密度遵循大尺度气体密度分布，则这些非热粒子的能量相对于星团内介质（ICM）总热能的比例限制，对于Abell 496来说是51%，而对于Abell 85来说，由于其较大的质量和较高的气体密度，只有8%。将这些上限与理论估计值进行比较。他们预测大约 10% 的 ICM 热能存在于非热粒子中。这里提出的观察结果可以限制这些预测，特别是对于 Abell 85 星团的情况。
Aims: The nearby galaxy clusters Abell 496 and Abell 85 are studied in the very high energy (VHE, E > 100 GeV) band to investigate VHE cosmic rays (CRs) in this class of objects which are the largest gravitationally bound systems in the Universe. Methods: H.E.S.S., an array of four Imaging Atmospheric Cherenkov Telescopes (IACT), is used to observe the targets in the range of VHE gamma rays. Results: No significant gamma-ray signal is found at the respective position of the two clusters with several different source size assumptions for each target. In particular, emission regions corresponding to the high density core, to the extension of the entire X-ray emission in these clusters, and to the very extended region where the accretion shock is expected, are investigated. Upper limits are derived for the gamma-ray flux at energies E>570 GeV for Abell 496 and E>460 GeV for Abell 85. Conclusions: From the non-detection in VHE gamma rays, upper limits on the total energy of hadronic CRs in the clusters are calculated. If the cosmic-ray energy density follows the large scale gas density profile, the limit on the fraction of energy in these non-thermal particles with respect to the total thermal energy of the intra-cluster medium (ICM) is 51% for Abell 496 and only 8% for Abell 85 due to its larger mass and higher gas density. These upper limits are compared with theoretical estimates. They predict about ~10% of the thermal energy of the ICM in non-thermal particles. The observations presented here can constrain these predictions especially for the case of the Abell 85 cluster.