A new class of nonthermal radio sources
A new class of nonthermal radio sources
复制标题
新型非热射电源
作者：
R. Becker;D. Helfand
目前的射电星表1，2列出了大约145个银河系超新星残留物，主要是根据它们表现出的非热射电谱、扩展发射的证据以及位于银河系平面几度内的证据而列入的。已经获得了包括空间分辨光谱信息和偏振数据在内的详细地图，其中包括大约一半编目的天体，主要是那些位于太阳∼5kpc内的天体，并揭示了三类残留物：贝壳状来源、蟹状同步加速器星云和复合残骸3，4其中一个中心类蟹成分被贝壳包围。虽然绘制了许多迄今为止没有很好研究的残骸，但我们已经发现了至少两个非热扩展天体，它们不能归类到这些类别中的任何一个。这两个源表现出明显的轴对称，在轴的一端有致密成分的证据。它们的扩散发射包括叠加在较低表面亮度分量上的明亮的丝状结构，该亮度分量逐渐褪色，在与紧凑源相对的轴端变得不可检测。这些源的平均光谱指数介于贝壳残留物和蟹状残留物之间。我们在这里提出，这些天体代表了一类新的非热射电源；在本期5的其他地方，我们认为这种源是通过高速吸积双星系统产生的相对论粒子的发射而形成的。
Current radio catalogues1,2 list some 145 sources as galactic supernova remnants which are included primarily on the basis of their exhibiting a nonthermal radio spectrum, evidence for extended emission and being located within a few degrees of the galactic plane. Detailed maps including spatially-resolved spectral information and polarimetric data have been obtained for about half of the catalogued objects, primarily those lying within ∼5 kpc of the Sun, and have revealed three classes of remnants: shell-like sources, Crab-like synchrotron nebulae and composite remnants3,4 containing a central Crab-like component surrounded by a shell. While mapping many of the remnants not well studied to date, we have discovered at least two nonthermal extended objects which defy classification in any of these categories. The two sources exhibit a marked axial symmetry with evidence for a compact component at one extreme of the axis. Their diffuse emission includes bright filamentary structures superimposed on a lower surface brightness component which gradually fades, becoming undetectable at the end of the axis opposite the compact source. The mean spectral indices of these sources are intermediate between the shell- and Crab-like remnants. We propose here that these objects are representative of a new class of nonthermal radio sources; elsewhere in this issue5, we suggest that such sources are formed through the emission of relativistic particles produced by high-velocity accreting binary systems.