A kpc-scale X-ray jet in the BL Lac source S5 2007+777
A kpc-scale X-ray jet in the BL Lac source S5 2007+777
复制标题
BL Lac 源 S5 中的 kpc 级 X 射线喷射 2007 777
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
L. Maraschi
中科院分区：
文献类型：
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作者：
R. Sambruna;D. Donato;C.C.Cheung;F. Tavecchio;L. Maraschi
AGN中的x射线喷流通常在FRII和FRI射电星系中观察到，但在BL星系中很少观察到，这很可能是由于它们的方向接近视线和随后的缩短效应。到目前为止，已知只有三个BL lac包含kpc规模的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中存在第四扩展x射线射流的证据，该射电选择源S5 2007+777由于其混合FRI/II射电形态被归类为HYMOR（混合形态射电源）。钱德拉ACISS对这个源的观测揭示了一个x射线对应的19英寸长的射电喷流。有趣的是，S5 2007+777中kpc级喷流的x射线特性与FRII喷流中观测到的非常相似。首先，x射线的形态与射电的形态非常接近，x射线集中在离散的射电节中。其次，射流/最亮结的x射线连续体由一个非常硬的幂律描述，光子指数伽马（下标x）约为1。第三，档案HST数据的光学上限意味着一个凹的射电- x射线SED。如果x射线发射归因于IC/CMB的均分，则需要强光束（δ = 13），这意味着非常大规模（Mpc）射流。假设磁场低于均分，可以稍微放宽对光束的要求。另一种选择是，第二种高能电子的同步加速器发射是可行的。讨论了与钱德拉探测到的其他HYMOR射流的比较，以及FRI/II分裂起源的一般含义。
X-ray jets in AGN are commonly observed in FRII and FRI radiogalaxies, but rarely in BL Lacs, most probably due to their orientation close to the line of sight and the ensuing foreshortening effects. Only three BL Lacs 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 FRI/II radio morphology has been classified as a HYMOR (HYbrid MOrphology Radio source). Our Chandra ACISS 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 FRII 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 gamma(sub x) approximately 1. 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 (delta= 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 FRI/II division.