标题： 陡谱源与射电发射的 Duty Cycle 显示英文标题

标题： Steep-spectrum sources and the duty cycle of the radio emission

摘要： 目前普遍接受的观点是，具有凸谱且峰值频率范围从100 MHz到几GHz的固有紧凑明亮的射电源被认为是年轻的天体。根据演化模型，这些天体会演化为经典的射电星系群体。然而，在流量密度受限样本中的年轻射电源比例远大于大型射电源数目计数所预期的比例。这可能表明，由于某种原因，相当一部分年轻天体永远不会演化为尺度达几兆秒差距的大尺度射电星系。发现的具有非同寻常陡峭谱的年轻射电源PKS 1518+047证实了射电源发射在开始后不久可能会关闭。随后，源谱变陡并由于能量损失而演化。如果中断不是暂时性的，那么消退源的命运是在低于当前射电望远镜探测频率的范围内消失。最近在新诞生的射电源的秒差距距离处发现了过去活动的遗迹，表明存在具有间歇性射电辐射的短寿命天体。 显示英文摘要

摘要： It is currently accepted that intrinsically compact and bright radio sources characterized by a convex spectrum peaking at frequencies ranging from 100 MHz to a few GHz are young objects. Following the evolutionary models, these objects would evolve into the population of classical radio galaxies. However, the fraction of young radio sources in flux density-limited samples is much larger than what expected from the number counts of large radio sources. This may suggest that for some reason a significant fraction of young objects would never become large radio galaxies with sizes up to a few Mpc. The discovery of the young radio source PKS 1518+047 characterized by an uncommonly steep spectrum confirms that the radio emission may switch off shortly after its onset. Then the source spectrum steepens and evolves due to energy losses. If the interruption is not temporary, the fate of the fading sources is to disappear at frequencies lower than those explored by current radio telescopes. Fossils of past activities have been recently found at pc-scale distances from newly born radio sources, suggesting the presence of short-lived objects with an intermittent radio emission.