文章基本信息

标题：Steep spectrum sources and the duty cycle of the radio emission
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作者：M. Orienti
期刊名称：PoS - Proceedings of Science
印刷版ISSN：1824-8039
出版年度：2010
卷号：2010
出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
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 expected from the number counts of large radio sources. This may suggest that for some reason a significant fraction of young objects 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 has been recently found at pc-scale distances from newly born radio sources, suggesting the presence of short-lived objects with an intermittent radio emission.