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Blazar射电与伽马射线辐射性质的统计研究
其他题名The Statistic Study between Radio and Gamma Ray Emission Properties in Blazars
范绪亮
学位类型硕士
导师白金明
2012-05
学位授予单位中国科学院研究生院(云南天文台)
学位授予地点北京
学位专业天体物理
关键词Blazar 喷流 伽马射线 辐射机制 光变
摘要Blazar(耀变体)是一类极端活动星系核(AGN),它的辐射几乎覆盖了整个电磁能谱。由于其剧烈的活动性,blazar受到很多天文学家的关注,很多空间和地面望远镜也把其作为很重要的观测目标。现有的AGN理论模型认为,blazar是一类喷流方向与视线方向夹角很小的活动星系核。喷流辐射受相对论聚束效应影响,表现出我们观测到的极端活动性。Blazar的研究,对于我们理解喷流、黑洞、活动星系核,以及高能天体物理现象,甚至星系和宇宙学演化都有非常重要的意义。 Fermi伽马射线望远镜上搭载的大天区望远镜(LAT)提供了更加丰富和准确的blazar数据和样本,为blazar研究带来了新的机遇和挑战。特别是对解决blazar伽马射线辐射理论存在的很多问题,包括辐射机制、辐射区尺度和位置、以及伽马射线短时标光变和光变起源等,Fermi/LAT绝对是目前最有利的工具之一。得益于射电观测的高空间分辨率和长周期监测,blazar的射电与伽马射线辐射相关可以用来限制伽马射线的辐射机制和辐射区。基于此,我们利用Fermi/LAT最新的伽马射线数据和射电监测项目的数据来从统计上限制射电和伽马射线的相关性。 我们选择了Fermi/LAT最新的两年AGN源表(2LAC)与MOJAVE项目的交叉样本,对之前存在争议的射电与伽马波段的相关性使用新的近同时数据进行验证。统计结果确定了两个波段的相关性,但是也发现了一些新的问题。首先射电和伽马射线的流量相关受各种选择效应的影响比较大,所以流量相关的使用必须很小心。其次,两个波段的相关性随着伽马射线能段的升高而变差,这也从侧面证明了blazar的轻子模型。除了两个波段的相关性,我们还对伽马射线的两个重要参量,光子谱指数和光变指数与其它量的相关性进行了检验。FSRQ和BL Lac天体在光变指数的统计结果上存在一些差异,表明在高能峰两侧的光变行为可能不同。FSRQ的伽马光变指数与伽马射电光度比正相关表明伽马光变更可能起源于辐射区内部,而不是起源于外部光子场的变化;伽马光变指数与光子谱指数的反相关表明光变幅度在离高能峰越近的地方越高。FSRQ的伽马光度与伽马光子谱指数的反相关促使我们强调,至少对FSRQ来说,Fermi/LAT能段的积分光度不能简单的代替峰值光度或总光度去检验blazar序列。当然我们的工作受限于当前的样本和数据,很多结果需要未来数据的进一步检验。 Blazar的伽马射线辐射还有许多没有解决的问题。本人硕士期间看过的文献和做的工作还很有限,希望可以在以后的学习和工作中进一步充实。
其他摘要Blazars, the most extreme subclass of Active Galactic Nuclei (AGNs), are observed at almost the full electromagnetic spectrum from radio to gamma-ray band. They get attentions by astronomers due to their violent activity. A number of telescopes also take them as important targets. The radiation from blazars is believed to be non-thermal emission of relativistic jets with small view angles to the line of sight. The emission from jets is Doppler boosted by beaming effect, and becomes extreme active. The research in blazars is very useful to jet physics, black hole, AGNs, and the high energy astrophysics, even the evolution of cosmology and galaxies. Thanks to the high sensitivity, broad energy range, and large view field of Large Area Telescope (LAT) on board the Fermi Gamma Ray Space Telescope, much larger sample and more accurate data can be achieved. It takes good chances, also challenges to blazar researches. For the theory research of blazar gamma-ray emission, as the radiation mechanism, the emission region size and location, the short timescale variability and variability origin, Fermi/LAT must be one of the most useful telescope at present. The radio observation has a very high spatial resolution and is easy to take long time monitors, so the connection between radio and gamma-ray emission can be used to constrain the radiation mechanism and the emission region of gamma-ray. Thus, we use the new data of Fermi/LAT and radio monitors to investigate the correlation of radio and gamma-ray band statistically. We use the cross sample of the second LAT AGN catalog (2LAC) and MOJAVE program. Then we collect the quasi-simultaneous data to investigate the correlation between radio and gamma-ray band, which is debatable before. Our results confirm the correlations of these two bands, but we find some new problems. The flux correlations of these two bands are affected strongly by selection effects. So the flux correlations should be used very carefully. Moreover, the correlations become worse when the gamma-ray energy bands get higher. This supports the leptonic model of gamma-ray emission. We also make the correlation tests of two important parameters in gamma-ray as photon spectral index and variability index with other parameters. We find some differences between FSRQs and BL Lacs in statistical results of variability index, which implies the variability behavior may differ below and above the high energy peak. The positive correlations of gamma-ray variability index and the gamma-radio luminosity ratio for FSRQs suggest that the variability should be from the gamma-ray emission region rather than the external radiation field. And the negative correlations of gamma-ray variability index and the gamma-ray photon spectrum index for FSRQs suggest the variability amplitude tends to be larger as the gamma-rays are closer to the high energy peak of SED. The negative correlations of the gamma-ray luminosity with gamma-ray photon spectral index suggest that the gamma-ray luminosity in Fermi/LAT range can not be used simply to investigate the blazar sequence instead of the the peak luminosity or the total luminosity, at least for FSRQs. However, our results are also limited by the source number of our sample. These results will be tested with larger samples. There are numbers of open questions in gamma-ray emission of blazars. The papers I read and the works I do are very limited during my master period. I hope I can do more in my following learning.
学科领域天文学
语种中文
文献类型学位论文
条目标识符http://ir.ynao.ac.cn/handle/114a53/5566
专题丽江天文观测站(南方基地)
推荐引用方式
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范绪亮. Blazar射电与伽马射线辐射性质的统计研究[D]. 北京. 中国科学院研究生院(云南天文台),2012.
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