A Kiloparsec-Scale X-Ray Jet in the BL Lac Source S5 2007+777
A Kiloparsec-Scale X-Ray Jet in the BL Lac Source S5 2007+777
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DOI：
10.1086/589918
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发表时间：
2008-09
期刊：
影响因子：
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通讯作者：
R. Sambruna;D. Donato;C. Cheung;F. Tavecchio;L. Maraschi
中科院分区：
文献类型：
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作者：
R. Sambruna;D. Donato;C. Cheung;F. Tavecchio;L. Maraschi
活动星系核中的X射线喷流通常在FR II和FR I射电星系中观测到，但很少在BL Lac天体中观测到，这很可能是由于它们的方向接近视线和随之而来的透视缩短效应。到目前为止，已知只有三个BL Lac天体包含kpc尺度的X射线喷流。在本文中，我们提出了在经典射电选择源S5 2007+777中存在第四个扩展X射线喷流的证据，其混合FR I和FR II射电形态已被归类为HYMOR（混合形态射电源）。我们对这个源的钱德拉ACIS-S观测揭示了一个与19英寸长的射电喷流对应的X射线。有趣的是，S5 2007+777中kpc尺度喷流的X射线性质与FR II喷流中观察到的非常相似。首先，X射线形态与射电形态非常接近，X射线集中在离散的射电结中。第二，喷流/最亮结的X射线连续谱由非常硬的幂律描述，光子指数为ΓX <$1，尽管不确定性很大。第三，从档案HST数据的光学上限意味着一个凹的无线电到X射线SED。如果X射线辐射是由IC/CMB均分引起的，则需要强的聚束（δ = 13），这意味着一个非常大的尺度（Mpc）喷流。假设磁场低于均分，聚束的要求可以稍微放宽。或者，来自第二群非常高能量的电子的同步辐射是可行的。比较与钱德拉探测到的其他HYMOR喷流进行了讨论，以及一般意义上的起源FR I/FR II司。
X-ray jets in AGNs are commonly observed in FR II and FR I radio galaxies, but rarely in BL Lac objects, most probably due to their orientation close to the line of sight and the ensuing foreshortening effects. Only three BL Lac objects are known so far to contain a kpc-scale X-ray jet. In this paper we present the evidence for the existence of a fourth extended X-ray jet in the classical radio-selected source S5 2007+777, which for its hybrid FR I and FR II radio morphology has been classified as a HYMOR (HYbrid MOrphology Radio source). Our Chandra ACIS-S observations of this source revealed an X-ray counterpart to the 19″ long radio jet. Interestingly, the X-ray properties of the kpc-scale jet in S5 2007+777 are very similar to those observed in FR II jets. First, the X-ray morphology closely mirrors the radio one, with the X-rays being concentrated in the discrete radio knots. Second, the X-ray continuum of the jet/brightest knot is described by a very hard power law, with photon index ΓX ∼ 1, although the uncertainties are large. Third, the optical upper limit from archival HST data implies a concave radio-to-X-ray SED. If the X-ray emission is attributed to IC/CMB with equipartition, strong beaming (δ = 13) is required, implying a very large scale (Mpc) jet. The beaming requirement can be somewhat relaxed assuming a magnetic field lower than equipartition. Alternatively, synchrotron emission from a second population of very high-energy electrons is viable. Comparison to other HYMOR jets detected with Chandra is discussed, as well as general implications for the origin of the FR I/FR II division.