S5 2007+777的射电性质研究

S5 2007+777是一个典型的低峰值频率的蝎虎天体,该天体具有kpc尺度的X射线喷流,文献中利用模型估算的方法,得出X射线波段的多普勒因子达到13.0,从而喷流尺度可以达到Mpc量级.在此,搜集了有关S5 2007+777的欧洲甚长基线射电干涉网(European VLBI Network, EVN)高分辨率档案数据、美国甚长基线射电干涉网(Very Long Baseline Array, VLBA) 15 GHz观测数据等,研究了喷流的射电结构、亮温度、自行等方面的性质,发现该源的甚长基线干涉测量(Very Long Baseline Interferometry,VLBI)不同波段的喷流方向一致,但与文献中给出的kpc尺度的X射线喷流和甚大阵(Very Large Array, VLA)射电喷流方向存在一定的差异,说明该源的喷流辐射存在多普勒增亮效应.由VLBI观测得到的亮温度,估算了该源的射电多普勒因子的平均值及中值均为5.0,此值小于文献中X射线波段的多普勒因子,但与文献中利用其他方法得到的射电波段多普勒因子是一致的;另外,对多历元观测数据的拟合发现此源相同波段的各个成分在长历元上没有明显的自行,短历元上的自行甚至是视超光速运动.这可能是由低表面亮度成分中心位置的转移造成的.这同时也验证了之前估算的射电多普勒因子不是很大,小于X射线波段多普勒因子的结论.利用所得到的射电多普勒因子,发现该源具有较大尺度的本征射电喷流,可达到0.5 Mpc,由于这里使用的是均值,因此说明该源也有可能具有接近巨射电星系尺度的喷流.

The Radio Properties for BL Lac Object S5 2007+777

The object S5 2007+777 is a classic radio-selected BL Lac object with a kpc-scale extended X-ray jet. The Doppler factor derived from the X-ray emission in literatures is around 13.0, then the intrinsic jet scale will be around 1 Mpc. In this work, we present the jet structure, brightness temperature, proper motion, and other radio properties of this source by collecting the EVN (European VLBI Network) data and VLBA (Very Long Baseline Array) 15 GHz survey archival data. We found that all the EVN and VLBA images show a core-jet structure, and the jet direction is similar in all the VLBI (Very Long Baseline Interferometry) images, but slightly different from the kpc-scale jet. The Doppler factor constrained from the brightness temperature of radio core is around 5.0, smaller than the value estimated from X-ray emission, however consistent with those derived with other methods at radio band. After considering all the VLBI data, we found that there is no a significant proper motion in the source. These results indicate that the Doppler factor of this source may not be very high. However, even with the estimated Doppler factor of 5.0, the jet linear size may still be large, around 0.5 Mpc. This implies that this source probably possesses a very large intrinsic jet, similar to the giant radio galaxies.