蝎虎天体能谱曲率与其伽马射线辐射亮度的关系  

The Curvature of Spectral Energy Distribution and γ-ray Dominance of Fermi BL Lac Objects

作　　者：Muhammad Shahzad Anjum 陈亮[1] 顾敏峰[1] ANJUM Muhammad Shahzad;CHEN Liang;GU Min-feng(Key Laboratory for Research in Galaxies and Cosmology,Shanghai Astronomical Observatory,Chinese Academy of Sciences,Shanghai 200030,China;University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院上海天文台星系和宇宙学重点实验室,上海200030 [2]中国科学院大学,北京100049

出　　处：《天文学进展》2021年第1期82-93,共12页Progress In Astronomy

基　　金：国家自然科学基金(U1831138,11873073)。

摘　　要：银河系外的伽马射线辐射源主要是耀变体,对其研究有助于揭示活动星系核喷流物理、高能宇宙线起源甚至宇宙演化等。研究了为什么有些蝎虎天体有强的伽马射线辐射,而有些却没有。选了170个有多普勒因子和能谱曲率测量的蝎虎天体,并把它们分成被费米LAT探测到的和未被费米LAT探测到的两类。研究发现这两类源的多波段能谱曲率有显著区别,即费米LAT探测到的源的曲率明显小于未被费米LAT探测到的源;即使扣除了多普勒因子的影响,结果也相近。蝎虎天体PKS 0048-09和S50716+714有着相似的同步辐射光度但却不同的伽马射线光度。基于同步自康普顿模型,再结合二次曲线电子谱可以很好地拟合它们的多波段能谱,并发现拟合的曲率和辐射区尺度不同但却成正比。PKS 0048-09可能有一个更致密的喷流,从而产生了更大康普顿因子。结果表明,给定同步辐射光度,能谱曲率和康普顿因子对于能否被Fermi伽马射线卫星探测到非常重要;讨论了这一结果对粒子统计加速和辐射机制的限制。The extragalacticγ-ray sky is dominated by blazars and their study plays an important role in understanding jet physics,cosmic evolution history and origin of ultra high energy cosmic rays.In this work,we study a large sample of BL Lac objects to investigate why some sources are detected inγ-rays,while others not.We selected 170 BL Lac objects,with measured synchrotron spectral curvature and Doppler factor,and divided them into Fermi-LAT detected(FBLs)and non-detected(NFBLs)sources.We show that FBLs have smaller curvature than NFBLs,even after getting rid of Doppler beaming effect.The BL Lac objects PKS 0048-09 and S50716+714 have similar synchrotron peak frequency and luminosity but differentγ-ray dominance and their quasi-simultaneous broadband spectral energy distributions(SEDs)can be well fitted by a log-parabolic synchrotron self-Compton(SSC)model with same jet parameters except for the curvature and source size,assuming curvature being proportional to the size of emission region.Our results imply that for a given synchrotron luminosity,the different SED curvature and Compton dominance may account for the discrepancy between FBLs and NFBLs.We discuss these results in context of stochastic particle acceleration and radiation mechanisms.

关 键 词：活动星系核 BL Lac天体 辐射机制 非热辐射 

分 类 号：P157.7[天文地球—天文学]