标题： 伽马射线对撞级联在复合线辐射场中的特征 显示英文标题

标题： Gamma-ray signatures from pair cascades in recombination-line radiation fields

摘要： 在耀变体喷流中的超相对论性电子束与周围软光子相互作用，产生电子-正电子级联。 采用带有逃逸项的耦合动力学方程，我们模拟了未饱和的电子-正电子级联谱。 我们假设伽马射线主要散射来自被吸积盘和喷流辐射电离的云层的复合线光子。 级联谱对与耀变体短时变异性相关的硬电子谱注入不太敏感。 采用代表马克瑞安501和3C 279的物理参数，我们数值上获得了显示由复合线光子印记的显著特征的能谱分布。 在2014年7月马克瑞安501强X射线流量活动期间，MAGIC望远镜检测到约3 TeV处的特殊特征，这一现象在此情景中可以解释为束电子对线光子的上散射以及低电子-正电子产生光学深度的结果。 检查2018年1月3C 279的高保真费米-LAT谱显示，谱中存在与伽马射线与复合线光子碰撞产生电子-正电子对的阈值能量一致的凹陷，并且没有指数衰减。 我们的发现表明，3C 279中的伽马射线从宽发射线区的边缘逃逸。 显示英文摘要

摘要： Beams of ultra-relativistic electrons in blazar jets develop pair cascades interacting with ambient soft photons. Employing coupled kinetic equations with escape terms, we model the unsaturated pair cascade spectrum. We assume that the gamma rays predominantly scatter off recombination-line photons from clouds photoionised by the irradiation from the accretion disk and the jet. The cascade spectrum is rather insensitive to the injection of hard electron spectra associated with the short-time variability of blazars. Adopting physical parameters representative of Markarian 501 and 3C 279, respectively, we numerically obtain spectral energy distributions showing distinct features imprinted by the recombination-line photons. The hints for a peculiar feature at ~3 TeV in the spectrum of Markarian 501, detected with the MAGIC telescopes during a strong X-ray flux activity in 2014 July, can be explained in this scenario as a result of the up-scattering of line photons by beam electrons and the low pair-creation optical depth. Inspecting a high-fidelity Fermi-LAT spectrum of 3C 279 from January 2018 reveals troughs in the spectrum that coincide with the threshold energies for gamma rays producing pairs in collisions with recombination-line photons, and the absence of exponential attenuation. Our finding implies that the gamma rays in 3C 279 escape from the edge of the broad emission line region.