后发座星系团中缺乏弥散的非热硬X射线发射：Swift BAT的观测
The Lack of Diffuse, Nonthermal Hard X-ray Emission in the Coma Cluster: The Swift BAT's Eye View
摘要：
后发座星系团拥有已知的最亮的射电晕，因此一直是众多搜索相关逆康普顿（IC）发射的目标，特别是在硬X射线能量下，IC信号最终必须占主导地位。最近使用朱雀硬X射线探测器（HXD）进行的搜索未能确认先前使用RXTE和BeppoSAX进行的IC探测，而是将上限设置为非热通量的2.5倍。然而，如果IC辐射非常扩展，超出星团射电晕的尺度，这种差异就可以解决。使用重建的天空图像从58个月的雨燕BAT全天调查，这样的解决方案的可行性进行了研究。在Renaud等人的基础上，我们测试并实现了一种用于提取扩展源的通量的方法，假设指定的空间分布。BAT光谱与来自镶嵌观测的XMM-牛顿EPIC-pn光谱联合拟合。我们发现没有证据表明大规模IC排放的水平预期从以前检测到的非热通量。对于所考虑的所有非热空间分布，它们跨越了物理上合理的IC模型的范围，我们确定了上限，其最大（最保守）极限为<4.2 × 10 ^{-12} erg/s/cm ^2（20-80 keV），这对应于磁场B> 0.2 μ G的下限。根据射电晕的大小和可能的磁场径向分布，导出了最可能的IC分布的标称通量上限为<2.7 × 10 ^{-12} erg/s/cm ^2，相应的B> 0.25 μ G。
英文摘要：
The Coma cluster of galaxies hosts the brightest radio halo known and has therefore been the target of numerous searches for associated inverse Compton (IC) emission, particularly at hard X-ray energies where the IC signal must eventually dominate over thermal emission. The most recent search with the Suzaku Hard X-ray Detector (HXD) failed to confirm previous IC detections with RXTE and BeppoSAX, instead setting an upper limit 2.5 times below their nonthermal flux. However, this discrepancy can be resolved if the IC emission is very extended, beyond the scale of the cluster radio halo. Using reconstructed sky images from the 58-month Swift BAT all sky survey, the feasibility of such a solution is investigated. Building on Renaud et al., we test and implement a method for extracting the fluxes of extended sources, assuming specified spatial distributions. BAT spectra are jointly fit with an XMM-Newton EPIC-pn spectrum derived from mosaic observations. We find no evidence for large-scale IC emission at the level expected from the previously detected nonthermal fluxes. For all nonthermal spatial distributions considered, which span the gamut of physically reasonable IC models, we determine upper limits for which the largest (most conservative) limit is <4.2x10^{-12} erg/s/cm^2 (20-80 keV), which corresponds to a lower limit on the magnetic field B>0.2uG. A nominal flux upper limit of <2.7x10^{-12} erg/s/cm^2, with corresponding B>0.25uG, is derived for the most probable IC distribution given the size of the radio halo and likely magnetic field radial profile.
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