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arXiv 1207.0506astro-ph.COastro-ph.HE
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HIFLUGCS星系团非热辐射的Swift BAT观点

The Swift BAT Perspective on Non-thermal Emission in HIFLUGCS Galaxy Clusters

Daniel R. Wik, Craig L. Sarazin, Yu-Ying Zhang, Wayne H. Baumgartner, Richard F. Mushotzky, Jack Tueller, Takashi Okajima, Tracy E. Clarke

摘要:

对星系团在硬X射线能量下的弥散非热逆康普顿(IC)发射的研究已经进行了很多年,大多数探测要么意义不大,要么有争议。在这项工作中,我们调查14-195千电子伏的光谱从雨燕突发警报望远镜(BAT)的全天空调查的证据,非热过量发射以上的指数下降的尾巴的热发射的通量限制HIFLUGCS样品。为了解释BAT能量下的热贡献,从重合的空间区域提取XMM-牛顿EPIC光谱,以便可以同时确定热和非热光谱分量。我们发现轻微显着的IC组件在六个集群,虽然经过仔细检查和考虑的系统误差,我们无法声称在其中任何一个明确的检测。所有簇的光谱也被求和以增强在单个簇中不太可检测的累积非热信号。在构建了一个模型的基础上,单温度适合XMM-牛顿数据单独,我们没有看到显着的过量排放以上的热模型在软能量确定的预测。这一结果也适用于各种子群的总谱,除了具有弥散射电发射的星团子样本。对于具有弥散射电晕、遗迹或迷你晕的星团,最初在\sim 5 σ置信水平下检测到非热发射-由迷你晕星团驱动-但建模和系统不确定性最终降低了这一意义。在个别的星系团中,相对论电子的非热压力被限制在热电子压力的\sim 10%,对于质量更大的星系团有更严格的限制,这表明这些电子在星系团的中心区域可能不是动态重要的。

英文摘要:

The search for diffuse non-thermal, inverse Compton (IC) emission from galaxy clusters at hard X-ray energies has been underway for many years, with most detections being either of low significance or controversial. In this work, we investigate 14-195 keV spectra from the Swift Burst Alert Telescope (BAT) all-sky survey for evidence of non-thermal excess emission above the exponentially decreasing tail of thermal emission in the flux-limited HIFLUGCS sample. To account for the thermal contribution at BAT energies, XMM-Newton EPIC spectra are extracted from coincident spatial regions so that both thermal and non-thermal spectral components can be determined simultaneously. We find marginally significant IC components in six clusters, though after closer inspection and consideration of systematic errors we are unable to claim a clear detection in any of them. The spectra of all clusters are also summed to enhance a cumulative non-thermal signal not quite detectable in individual clusters. After constructing a model based on single-temperature fits to the XMM-Newton data alone, we see no significant excess emission above that predicted by the thermal model determined at soft energies. This result also holds for the summed spectra of various subgroups, except for the subsample of clusters with diffuse radio emission. For clusters hosting a diffuse radio halo, a relic, or a mini-halo, non-thermal emission is initially detected at the \sim5-sigma confidence level - driven by clusters with mini-halos - but modeling and systematic uncertainties ultimately degrade this significance. In individual clusters, the non-thermal pressure of relativistic electrons is limited to \sim10% of the thermal electron pressure, with stricter limits for the more massive clusters, indicating that these electrons are likely not dynamically important in the central regions of clusters.

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