Rossi X-Ray Timing Explorer Observations of the Coma Cluster
Rossi X-Ray Timing Explorer Observations of the Coma Cluster
复制标题
罗西 X 射线计时探测器对后发星团的观测
DOI：
10.1086/311828
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发表时间：
1999
期刊：
影响因子：
--
通讯作者：
Philip Blanco
中科院分区：
文献类型：
--
作者：
Y. Rephaeli;D. Gruber;Philip Blanco
后发座星系团于1996年由Rossi X射线定时探测器（RXTE）卫星上的PCA和HEXTE仪器观测到1090 kS，这是第一次在2-250 keV的宽能带上同时对后发座进行定点测量。在长时间的观测过程中获得的高灵敏度允许精确测定光谱。我们对测量结果的分析清楚地表明，除了来自kT ~ 7.5 keV的热团内气体的主要热发射外，还需要第二个光谱分量来最好地拟合数据。如果是热的，这个组件的温度为4.7 keV，它贡献了总通量的20%。或者，第二个分量可以是幂律，可能是由于宇宙微波背景对相对论电子的康普顿散射。这种解释是基于对漫射射电发射的测量以及射电和X射线光谱指数的类似值。非热分量的康普顿起源意味着后发座中心区域的体积平均磁场为B = 0.2 μG，这个值与通常的能量均分假设无关。那么发射电子的能量密度将为~8 × 10-14 ergs cm-3。除非存在未知的系统误差的RXTE源或背景测量，我们的光谱分析产生了相当多的证据，康普顿X射线发射后发座星系团。
The Coma Cluster was observed in 1996 for ≃90 ks by the PCA and HEXTE instruments aboard the Rossi X-ray Timing Explorer (RXTE) satellite—the first simultaneous, pointing measurement of Coma in the broad, 2-250 keV energy band. The high sensitivity achieved during this long observation allows precise determination of the spectrum. Our analysis of the measurements clearly indicates that in addition to the main thermal emission from hot intracluster gas at kT ≃ 7.5 keV, a second spectral component is required to best fit the data. If thermal, this component has a temperature ≃4.7 keV, and it contributes ≃20% of the total flux. Alternatively, the second component can be a power law, likely due to Compton scattering of relativistic electrons by the cosmic microwave background. This interpretation is based on the measurements of diffuse radio emission and the similar values of the radio and X-ray spectral indices. A Compton origin of the nonthermal component would imply that the volume-averaged magnetic field in the central region of Coma is B ≃ 0.2 μG, a value that is free of the usual assumption of energy equipartition. The energy density of the emitting electrons would then be ~8 × 10-14 ergs cm-3. Barring the presence of unknown systematic errors in the RXTE source or background measurements, our spectral analysis yields considerable evidence for Compton X-ray emission in the Coma Cluster.