米波频谱急剧倒转的河外射电源
Extragalactic radio sources with sharply inverted spectrum at metre wavelengths
摘要：
我们提出的第一个结果，系统搜索罕见的河外射电源显示倒置（集成）的频谱，频谱指数$α\ge +2.0$，以前未开发的频谱域。搜索预计将产生强有力的候选人$α\ge +2.5$，其中标准的同步自吸收（其特征在于相对论电子布居的单一幂律能量分布）将不是一个合理的解释，即使在一个理想的情况下，一个完美的均匀的非相干同步辐射源。这种急剧反转的光谱，如果发现，将需要替代的解释，例如，自由-自由吸收，或不同于幂律的相对论电子的非标准能量分布（例如，Maxwellian）。搜寻工作是通过比较两个分辨率为亚弧分的灵敏低频无线电勘测，即352兆赫的WISH勘测和150兆赫的TGSS/DR 5勘测进行的。这两个调查之间的重叠区域包含7056个WISH源，这些源被归类为“单一”源，在352 MHz时亮度超过100 mJy。我们在这里集中在七个这些来源，我们发现$α> +2.0$。其中两个在150 MHz时未检测到，是$α> +2.5$的特别好的候选者。七个源中有五个显示出“千兆赫兹峰值频谱”。
英文摘要：
We present the first results of a systematic search for the rare extragalactic radio sources showing an inverted (integrated) spectrum, with spectral index $α\ge +2.0$, a previously unexplored spectral domain. The search is expected to yield strong candidates for $α\ge +2.5$, for which the standard synchrotron self-absorption (characterized by a single power-law energy distribution of relativistic electron population) would not be a plausible explanation, even in an ideal case of a perfectly homogeneous source of incoherent synchrotron radiation. Such sharply inverted spectra, if found, would require alternative explanations, e.g., free-free absorption, or non-standard energy distribution of relativistic electrons which differs from a power-law (e.g., Maxwellian). The search was carried out by comparing two sensitive low-frequency radio surveys made with sub-arcminute resolution, namely, the WISH survey at 352 MHz and TGSS/DR5 at 150 MHz. The overlap region between these two surveys contains 7056 WISH sources classified as `single' and brighter than 100 mJy at 352 MHz. We focus here on the seven of these sources for which we find $α> +2.0$. Two of these are undetected at 150 MHz and are particularly good candidates for $α> +2.5$. Five of the seven sources exhibit a `Gigahertz-Peaked-Spectrum' (GPS).
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