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arXiv 1108.4602astro-ph.CO
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根据逆康普顿散射观测的巨型射电星系叶的能量学

The energetics of giant radio galaxy lobes from inverse Compton scattering observations

S. Colafrancesco, P. Marchegiani

摘要:

巨射电星系(GRG)叶是研究粒子演化和B场能量学的极好实验室。然而,这些结果是基于假设的形状和扩展的GRG波瓣电子光谱。我们重新检查GRG瓣的能量学,通过RG瓣中的相对论电子对CMB光子的逆康普顿散射(ICS-CMB)来评估RG瓣的物理条件,它们的能量学和它们的辐射制度。我们认为GRG DA 240最近观察到的朱雀作为一个参考案例,我们也讨论了其他RG叶观察钱德拉和XMM。利用从射电到伽玛射线的多频信息,对DA 240东瓣的能量分布进行了建模,得到了对电子能谱形状和扩展的约束。我们使用无线电和X射线数据来约束电子光谱的形状和归一化,然后计算对总电子能量密度敏感的GRG瓣中预期的SZ效应。我们表明,由X射线观测得到的电子能量密度U_e仅比实际值有一个粗略的下限,而且考虑到较低的电子动量p_1的实际估计,大多数基于X射线测量的U_e估计值都必须增加一个很大的因子。这使得RG波瓣远离均分条件,朝向粒子主导和康普顿功率主导的状态。我们使用RG波瓣在U_e/U_B与U_e/U_CMB平面上的分布作为RG波瓣中粒子和场主导以及辐射机制主导的不同物理状态之间的进一步划分。我们的结论是,在RG叶中观察到的ICS-CMB机制产生的SZ效应提供了可靠的p_1和U_e的估计,是确定RG叶的总能量密度和评估其物理状态的最佳工具。

英文摘要:

Giant radio galaxy (GRG) lobes are excellent laboratories to study the evolution of the particle and B-field energetics. However, these results are based on assumptions of the shape and extension of the GRG lobe electron spectrum. We re-examine the energetics of GRG lobes as derived by inverse Compton scattering of CMB photons (ICS-CMB) by relativistic electrons in RG lobes to assess the physical conditions of RG lobes, their energetics and their radiation regime. We consider the GRG DA 240 recently observed by Suzaku as a reference case and we also discuss other RG lobes observed with Chandra and XMM. We model the spectral energy distribution of the DA 240 East lobe to get constraint on the shape and the extension of the electron spectrum in the lobe by using multi-frequency information from radio to gamma-rays. We use radio and X-ray data to constrain the shape and normalization of the electron spectrum and we then calculate the SZ effect expected in GRG lobes that is sensitive to the total electron energy density. We show that the electron energy density U_e derived form X-ray observations yields only a rough lower limit to its actual value and that most of the estimates of U_e based on X-ray measurements have to be increased even by a large factor by considering realistic estimates of the lower electron momentum p_1. This brings RG lobes away from the equipartition condition towards a particle-dominated and Compton power dominance regime. We use the distribution of RG lobes in the U_e/U_B vs. U_e/U_CMB plane as a further divide between different physical regimes of particle and field dominance, and radiation mechanism dominance in RG lobes. We conclude that the SZ effect produced by ICS-CMB mechanism observable in RG lobes provides reliable estimate of p_1 and U_e and is the best tool to determine the total energy density of RG lobes and to assess their physical regime.

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