高能Gamma-ray AGNs的射电观测和研究

【作者】 王伟华；

【导师】 洪晓瑜；

【作者基本信息】 中国科学院研究生院（上海天文台） ， 天体物理， 2003， 博士

【摘要】 在能谱大于100MeV的γ-ray波段上,空间的高能γ-ray实验望远镜(EGRET)和地面的Whippleγ-ray观测站已经检测到80多个活动星系核。它们都是射电噪源,属于blazar天体。在γ-ray爆发时,常在低频的射电波段上检测到爆发。该类源的射电喷流具有视超光速运动的比例甚高。由于所有的γ-rayAGNs都具有强的射电辐射,所以人们一直在努力研究γ-ray辐射和射电辐射之间的联系。VLBI技术是现代天文观测中能获得最高分辨本领的观测手段,利用VLBI技术对γ-rayAGNs的相对论射电喷流结构、视超光速运动和喷流的弯曲进行研究,将有助于我们探索该类源的γ-ray和射电辐射的关系。本文主要致力于进一步完备γ-rayAGNs的射电图像样本,利用VLBI技术对一些缺少射电图像的高能AGNs进行观测,获得它们的致密结构图像研究它们的形态结构和辐射特性。在第1章中,我们简单概述了AGNs的基本特性,并收集了87颗具有高能辐射的AGNs样本,以进行统计分析。在第2章,介绍了我们对一个γ-rayAGNs子样本的射电观测。并给出了利用欧洲VLBI网观测的13颗源的射电图像。其中1604+159和2022?077是首次获得VLBI图像。观测结果表明这些源在毫角秒尺度上大部分呈现核–喷流结构,只有两颗源较致密,尚未分解。通过比较两个历元的欧洲VLBI观测结果,我们检测到三颗AGNs(0827+243,0829+046,1604+159)的视超光速运动,它们的视横向速度分别为18.5c,6.9c,2.2–3.5c。其中1604+159是首次被证认为视超光速源。同时我们还研究了该子样本中,喷流从毫角秒到角秒尺度的弯曲情况。在第3章,我们介绍对γ-ray类星体0202+149进行多历元多波段的射电观测。给出了该源在5GHz的MERLIN图像和在1.67,5GHz和15GHz多历元的VLBI观测结果。在这些研究中,我们发现了该源在亚角秒尺度上有一强核和准对称双瓣结构。主瓣较强且离核较远。在毫角秒尺度上,我们发现该源的喷流有明显的弯曲,这可能意味着该源的喷流在一圆锥面上沿螺旋状运动。从0202+149的亚角秒形态分析,它极象致密对称源(CSO)。通过研究该源的射电流量变化,喷流的弯曲,以及其视超光速运动,我们判断该源并非致密对称第ix页<WP=13>摘要源。第4章给出类星体DA193四个历元的VLBI观测和模型拟合结果。我们检测出其喷流自行速度为0.105±0.02masyr?,相应的视横向速度为4.5±0.86c。计算出的多普勒因子和亮温度确认DA193的辐射靠近视线方向。我们测出的速度是以前观测给出速度的四倍,这可能有两种原因。其一,该喷流正在加速,可能是由于弯曲喷流靠近视线的投影效应引起的。其二,是两个不同分量,来自两次不同的射电爆发。在本章我们也给出了致密对称源(CSO)OQ208的5GHz和8.4GHz的VLBI观测结果。我们发现它的膨胀速度在减缓,原因可能是受到周围介质的冲击。同时发现在靠近核的热斑分量在低频波段上受到更多的自由–自由吸收,我们解释为是靠近核的地方的电子密度更高的缘故。在第5章研究了γ-rayAGNs的喷流方向从毫角秒尺度到角秒尺度的弯曲(?PA)。在洪晓瑜等人研究样本的基础上,我们利用本文的观测结果,扩大了?PA统计的样本源。我们的统计结果支持洪晓瑜等人的结论:γ-ray类星体具有较小的?PA。而γ-rayBLLac天体的?PA分布在较大的范围内。由于BLLac天体被认为其喷流很接近视线,大的?PA可能是投影效应造成的。因此说明较准直的AGNs有利于人们检测到它们的γ-ray辐射。我们同时分析了VLBI高频(22,43GHz)观测结果,发现γ-rayAGNs在亚毫角秒尺度上喷流弯曲是很普遍的。更多还原

【Abstract】 Energetic Gamma Ray Experiment Telescope (EGRET) in space and Whip-ple γ-ray telescope on the ground have detected more than 80 AGNs on γ-rayband at energies above 100 MeV. They are all radio-loud sources, and classi?edas blazars. The γ-ray ?are is usually accompanied by the radio ?are. The frac-tion with superluminal motion of radio jet is rather high. Since all γ-ray AGNshave strong radio emission, the relationship between γ-ray and radio emission isworthy to study. As the modern astronomical observational technique with the highest resolu-tion, VLBI can provide key contribution to the study of relativistic jets structure,superluminal motion and bending jet of γ-ray AGNs. It is helpful to discover therelationship between γ-ray and radio emission of them. The purpose of this thesis is to complete the sample of radio images of γ-rayAGNs. We use VLBI to observe some γ-ray AGNs without radio images, get theircompact structure, and study their morphology structure and emission property. In Chapter 1, the basic properties of AGNs are introduced. 87 AGNs withhigh-energy emission were collected for research. In Chapter 2, we present the radio observations of a sub-sample of γ-rayAGNs. Radio images of 13 γ-ray AGNs observed by European VLBI Network(EVN) are given. The VLBI structures of 1604+159 and 2022?077 are reportedfor the ?rst time. The observed results show that most of these sources are re-solved with core-jet structure on the mas scale, except two are too compact to beresolved. Compared with the previous EVN VLBI images, we detect the super-luminal motion in 0827+243, 0829+046 and 1604+159. Their apparent velocitiesare 18.5, 6.9, 2.2–3.5 c, respectively. 1604+159 is identi?ed as superluminal sourcefor the ?rst time. Meanwhile, we investigate the bending jet of the sample frommas scale to arcsec scale. In Chapter 3, we present the results of the VLBI observations at 1.67, 5 and15 GHz and MERLIN observations at 5 GHz for γ-ray quasar 0202+149. Theresults ?rst reveal that the source contains two mini-lobes located on both sides 第xi页<WP=15>Abstractof a bright radio core on subarcsecond scales. The main mini-lobe is brighter andfarer from the core than the other one. We found that the jet is strong bent onmas scale. This means the jet in 0202+149 maybe follows a helical path on acone. According to the subarcsecond structures, 0202+149 is easily to be thoughtas a compact symmetric object (CSO). But based on the facts of the superluminalmotion, the variability of ?ux density and bending jet, we don’t think that thesource 0202+149 is a CSO. In Chapter 4, four epoch VLBI observations and the model-?tting results ofDA193 are presented. We detect a proper motion of 0.105 ± 0.02 masyr? of 1the jet component, which corresponds to an apparent velocity of 4.5 ± 0.86 c.According to the Doppler factor and of the brightness temperature, this sourceis considerably boosted towards the line of sight. The velocity is about 4 timeslarger than previous estimation, which may indicate (1) that the jet componentis being accelerated, possibly due to a bending jet aligned close to the line ofsight; or (2) that there are two di?erent components ejected in two ?ares. In thisChapter, we also present the results of the VLBI observations at 5 and 8.4 GHz ofthe compact symmetric object (CSO) OQ208. We ?nd that the expansion speedbecome slow, which maybe due to the shocked ambient medium on the front. Atthe same time, we ?nd that the hot-spots component near core is more free-freeabsorbed at low frequency. The reason is that the electron density is larger nearlyin the nuclear region than in outer region. In Chapter 5, we analysis the position angle (?PA) between mas scale andarcsecond scale. On the basis of the sample given by Hong, we expand the samplewith our observational results. Our statistical results support those of Hong, i.e.γ-ray quasars have small ?更多还原