活动星系核射电延展区观测和理论研究

Observational and Theoretical Progress for Radio Extended Regions in AGNs

随着探测设备角分辨率和灵敏度的提高,喷流、喷流节点和热斑等活动星系核延展结构在射电、红外、光学、X射线等越来越多的波段被探测到,分辨出其更细致的结构,促进了理论研究热潮的兴起,使该领域成为当今天体物理研究的活跃领域之一。喷流是由活动星系核中心产生的准直等离子体外流,由中心黑洞驱动。至今,对喷流的成分、产生、准直原理和加速机制等基本问题并不清楚。另一方面,对于喷流、喷流节点和热斑等活动星系核延展区的辐射机制,一般认为其射电和光学辐射由相对论电子的同步辐射产生,但X射线的起源就存在着一定的争议。简单概述该领域近年来观测和理论研究进展。

We present a brief review on both observational and theoretical progress of the extended structures of AGNs（active galactic nuclei） in the recent years.With great improvements on both the space resolution and detection sensitivity of current instruments,these sub-structures, including knots and hot spots were observed in the radio,infrared,optical and X-ray bands. Hot spots are often found near the outmost boundaries of radio lobes,being regarded as jet termination.Knots are usually thought to be a part of a well-collimated jet.The two kinds of extended regions show different observational properties in the radio,optical,and X-ray bands. It is believed that the synchrotron radiation of relativistic electrons is responsible for the radio emission of these extended regions.The detection of polarization in the optical band indicates that the optical emission is also from synchrotron radiation.The X-ray radiation mechanisms of the extended regions are highly debated.For a few sources,the observed X-ray spectra smoothly connect to the radio-optical band,and can be fitted by the synchrotron radiation model,indicating that the X-rays of these sources are the high energy tail of the synchrotron radiation by the same electron population for the radio and optical emission.However,an inverse Compton（IC） scattering component,the synchrotron self-Compton（SSC） scattering and/or the IC/CMB（the relativistic electrons IC scattering the cosmic microwave background photons）,is necessary to model the X-ray spectra for most of the sources.It is found that the X-ray emission for hot spots with high radio luminosity could be roughly explained with the SSC model under equipartition condition.But the same model cannot explain the X-ray emission for hot spots with low radio luminosity and the most knots.Considering the beaming effect,the IC/CMB model can reproduce the X-ray emission for most of the hot spots and knots under the equipartition condition.The deriving bulk Lorentz factors of the knots generally are larger than that of the hot spots.Both the SSC and IC/CMB models predict a prominent GeV-TeV emission for some sources,which could be detectable with H.E.S.S.and Fermi/LAT.The detections of these high energy emission would place much stronger constraints on the radiation mechanisms and on the physical parameters of these sources.