4C 21.35的γ射线光变特征及其与射电光变的相关性

γ-Ray Variability of 4C 21.35 and its Correlation with the Radio Variability

利用从2008年8月5日到2013年10月23日Fermi-LAT的观测数据,对4C 21.35的100 MeV到300 GeV的γ射线数据进行了分析,总结了1天bin情况下的光变特征,并在3小时bin的基础上详细研究了所选的11个大的爆发,得到了5.4 h的最短光变时标。先用对射电光变曲线减去一个线性增长,再通过相关分析得到100 MeV<E<300 GeV的γ射线光变领先于15 GHz射电光变351.2_(38.0)^(13.8)d,并用γ射线辐射区对于射电辐射是光学厚对其加以解释,从而在辐射区匀速运动的假设下得到,这样的时延对应着γ射线辐射区到射电光学薄区域的距离为△r≈44.4 pc。通过与VLBA观测得到的15 GHz射电核的半径相比较,得到辐射区向外运动过程中可能存在减速的结论。

Even though Blazars have been well studied at multiple wavelengths and much insight has been gained into the nature of these extreme objects, there are still numerous open issues remaining, such as the composition and formation of relativistic jets, the radia-tive mechanism of the high-energy part of the SED, the location of γ-ray emission region, etc. Variability studies, including the studies of variability time scale, light curve variation, spectral changes and multiwavelength correlation, could reveal the location of the emission region, the changes in the condition and structure in the emission region and the changes in the radiative processes and mechanisms. Therefore, it is essential to investigate the γ-ray variability. VLBI is the unique method to resolve Blazars on pc scale, thus the combination of γ-ray and radio studies would promote the localization of the γ-ray emission region and other research on jet properties. In particular, the connections between γ-ray flares and ejections of radio components have been found in a number of Blazars, for example, OJ 287, PKS 1510-089, Mrk 421, 3C 454.3, etc. However, there are also contradictions in previous studies, such as whetherγ-ray or radio leads, so further analyses and research are required. 〈br〉 In this paper, the Fermi-LAT data from 5 August 2008 to 23 October 2013 has been used to investigate theγ-ray properties of 4C 21.35 between 100 MeV and 300 GeV. Specifically, the variability properties with 1-day time bins have been summaried, and 11 chosen marked bursts have been analysed in detail with 3-hour time bins. The shortest variability time scale we have got is 5.4 hours. We also use the method of subtracting a linear increase from the original radio light curve, and then correlation analysis concludes that theγ-ray variations lead the 15 GHz radio variations by 351.2＋13.8？38.0 days. The radio opacity in theγ-ray emission region is used to interpret the delay, and the distance between theγ-ray emission region and the region becoming transparent in radio band, △r ≈ 44.4 pc has been obtained provided that the emission region is in uniform motion. Then by comparing it with the radio core radius obtained by VLBA, a decelarating inner jet is likely to exist.