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arXiv 0908.3301astro-ph.HE
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CANGAROO-III对来自两个星系团的TeV γ射线的搜寻

CANGAROO-III search for TeV Gamma-rays from two clusters of galaxies

R. Kiuchi, M. Mori, G. V. Bicknell, R. W. Clay, P. G. Edwards, R. Enomoto, S. Gunji, S. Hara, T. Hara, T. Hattori, S. Hayashi, Y. Higashi, Y. Hirai, K. Inoue, C… 展开作者

R. Kiuchi, M. Mori, G. V. Bicknell, R. W. Clay, P. G. Edwards, R. Enomoto, S. Gunji, S. Hara, T. Hara, T. Hattori, S. Hayashi, Y. Higashi, Y. Hirai, K. Inoue, C. Itoh, S. Kabuki, F. Kajino, H. Katagiri, A. Kawachi, T. Kifune, H. Kubo, J. Kushida, Y. Matsubara, T. Mizukami, Y. Mizumoto, R. Mizuniwa, H. Muraishi, Y. Muraki, T. Naito, T. Nakamori, S. Nakano, D. Nishida, K. Nishijima, M. Ohishi, Y. Sakamoto, A. Seki, V. Stamatescu, T. Suzuki, D. L. Swaby, T. Tanimori, G. Thornton, F. Tokanai, K. Tsuchiya, S. Watanabe, Y. Yamada, E. Yamazaki, S. Yanagita, T. Yoshida, T. Yoshikoshi, Y. Yukawa

摘要:

由于星系团中的吸积和合并冲击可以将粒子加速到高能,因此星系团是超高能宇宙线起源的候选地点。提出了一个预测,即用目前这一代成像大气切伦科夫望远镜可以探测到星系团的伽马射线发射。γ射线发射是由UHE宇宙射线碰撞产生的正负电子对宇宙微波背景(CMB)光子的逆康普顿上散射产生的。2006年,我们用CANGAROO-III大气切伦科夫望远镜系统观测了两个星系团,Abell 3667和Abell 4038,寻找甚高能量的伽马射线发射。分析显示,这些星团周围没有明显的过剩,从而产生了伽马射线发射的上限。通过比较Abell 3667西北射电遗迹区的上限值与模型预测值,我们得到了该区域磁场的下限值约为0.1微G。这显示了伽玛射线观测在星团环境研究中的潜力。我们还讨论了从集群中心区域使用的宇宙射线质子强子碰撞中产生的中性π介子的伽马射线发射的模型的流量上限与集群内介质(ICM)。在这个框架内,宇宙射线能量密度的上限比我们银河系的能量密度高一个数量级。

英文摘要:

Because accretion and merger shocks in clusters of galaxies may accelerate particles to high energies, clusters are candidate sites for the origin of ultra-high-energy (UHE) cosmic-rays. A prediction was presented for gamma-ray emission from a cluster of galaxies at a detectable level with the current generation of imaging atmospheric Cherenkov telescopes. The gamma-ray emission was produced via inverse Compton upscattering of cosmic microwave background (CMB) photons by electron-positron pairs generated by collisions of UHE cosmic rays in the cluster. We observed two clusters of galaxies, Abell 3667 and Abell 4038, searching for very-high-energy gamma-ray emission with the CANGAROO-III atmospheric Cherenkov telescope system in 2006. The analysis showed no significant excess around these clusters, yielding upper limits on the gamma-ray emission. From a comparison of the upper limit for the north-west radio relic region of Abell 3667 with a model prediction, we derive a lower limit for the magnetic field of the region of ~0.1 micro G. This shows the potential of gamma-ray observations in studies of the cluster environment. We also discuss the flux upper limit from cluster center regions using a model of gamma-ray emission from neutral pions produced in hadronic collisions of cosmic-ray protons with the intra-cluster medium (ICM). The derived upper limit of the cosmic-ray energy density within this framework is an order of magnitude higher than that of our Galaxy.

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