Radio Properties of BL Lac Object S5 2007+777 |
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| Institution: | 1. College of Physics, Guizhou University, Guiyang 550025;2. Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030;3. School of Physics and Electronics, Qiannan Normal University for Nationalities, Duyun 558000;1. School of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024;2. School of Astronomy and Space Science, Nanjing University, Nanjing 210034;1. Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101;2. School of Astronomy and Space Sciences, University of Chinese Academy of Sciences, Beijing 100049;3. Shandong Zhengyuan Construction Engineering Co. Lit., Jinan 250100;1. Department of Astronomy, University of Science and Technology of China, Hefei 230026;2. Polar Research Institute of China, Shanghai 200136;3. Center for Astrophysics, Guangzhou University, Guangzhou 510006;4. Yunnan Observatories, Chinese Academy of Sciences, Kunming 650216;1. Istituto Nazionale di Fisica Nucleare – Sezione di Napoli, Complesso di Monte S. Angelo Edificio 6, via Cintia 80126 Napoli, Italy;2. Università degli Studi di Napoli “Federico II”, Dipartimento di Fisica, via Cintia 80126 Napoli, Italy |
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| Abstract: | S5 2007+777 is a typical BL Lac object with a low peak frequency, and a kpc-scale extended X-ray jet. In the literature, the Doppler factor derived at the X-ray waveband by means of model estimation is about 13.0, then the intrinsic jet scale can reach the order of magnitude of 1 Mpc. In this work, we have studied the radio structure of the jet, the brightness temperature, proper motion and other properties of this source with the collected EVN (European VLBI Network) high-resolution archive data, and the American VLBA (Very Long Baseline Array) 15 GHz observed data, etc. It is found that the jet directions measured at the different wavebands of the VLBI (Very Long Baseline Interferometry) are consistent, but slightly different from the direction of the kpc-scale X-ray jet given by the literature and the direction of the VLA (Very Large Array) radio jet, which means that the Doppler brightening effect exists in the jet emission of the source. Both the mean value and median value of the radio Doppler factor of this source estimated from the brightness temperature that measured by the VLBI are 5.0, which is smaller than the Doppler factor at the X-ray waveband given by the literature, but consistent with the Doppler factor at the radio waveband obtained by using the other methods in the literature. Furthermore, by fitting the data observed in multiple epochs, it is found that the various components of the source at the same waveband do not have an evident proper motion in a long epoch, but the proper motion in short epochs exhibits even a super-luminal motion. This may be caused by the transfer of the central position of the component with a low surface brightness. Meanwhile, this also verifies the conclusion that the radio Doppler factor estimated previously is not very large, and smaller than the Doppler factor in the X-ray waveband. By using the obtained radio Doppler factor, it is found that the source has an intrinsic radio jet of rather large scale, which may reach 0.5 Mpc, because the mean value is adopted in this case, thus it indicates that the source also possibly possesses a jet close to the scale of a giant radio galaxy. |
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| Keywords: | BL Lacertae objects individual S5 2007+777—galaxies jets—X-rays galaxies |
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