arXiv 1210.76172012-10-29astro-ph.CO

GMRT射电晕团调查中射电晕和遗迹的低频跟踪

Low frequency follow up of radio halos and relics in the GMRT Radio Halo Cluster Survey

Tiziana Venturi, Simona Giacintucci, Daniele Dallacasa, Rossella Cassano, Gianfranco Brunetti, Giulia Macario, Ramana Athreya

备注：: 19 pages, 10 figures, 5 tables, accepted for publication on A&A
DOI：: 10.1051/0004-6361/201219872

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摘要：

我们进行了GMRT低频观测的射电晕，文物和新的候选人属于GMRT射电晕集群样本首次观察到610兆赫。使用GMRT在325 MHz和240 MHz下进行高灵敏度成像。在每个集群中的扩散发射的属性进行了比较，我们的610 MHz的图像和/或文献信息，在其他频率，以获得综合频谱在很宽的频率范围。除了经典的无线电晕，其光谱指数$α$的范围内$\sim1.2\div1.3$（S $\proptoν^{-α}$），我们发现源与$α\sim1.6\div1.9$。这一结果支持了这样一种观点，即射电晕中辐射粒子的光谱并不普遍，粒子加速的低效机制是其起源的原因。我们还发现了各种亮度分布，即中央峰值以及clujiang晕。尽管热等离子体和相对论等离子体倾向于占据相同的团簇体积，但在某些情况下，射电和X射线发射峰之间的位置偏移是明显的。我们的观测还揭示了存在的扩散集群源，不能很容易地归类为晕或遗物。在A1300和A1682发现了新的候选遗迹，在一些星团中发现了无线电发射的“桥梁”，连接遗迹和无线电晕发射。结合我们的新数据和文献资料，我们导出了射电晕的$_{\rm X}$ $_{\rm 325 MHz}$关联式，并研究了射电晕光谱指数随团内介质温度变化的可能趋势。

英文摘要：

We performed GMRT low frequency observations of the radio halos, relics and new candidates belonging to the GMRT Radio Halo Cluster Sample first observed at 610 MHz. High sensitivity imaging was performed using the GMRT at 325 MHz and 240 MHz. The properties of the diffuse emission in each cluster were compared to our 610 MHz images and/or literature information available at other frequencies, in order to derive the integrated spectra over a wide frequency range.Beyond the classical radio halos, whose spectral index $α$ is in the range $\sim1.2\div1.3$ (S$\proptoν^{-α}$), we found sources with $α\sim1.6\div1.9$. This result supports the idea that the spectra of the radiating particles in radio halos is not universal, and that inefficient mechanisms of particle acceleration are responsible for their origin. We also found a variety of brightness distributions, i.e. centrally peaked as well as clumpy halos. Even though the thermal and relativistic plasma tend to occupy the same cluster volume, in some cases a positional shift between the radio and X-ray peaks of emission is evident. Our observations also revealed the existence of diffuse cluster sources which cannot be easily classified either as halos or relics. New candidate relics were found in A1300 and in A1682, and in some clusters "bridges" of radio emission have been detected, connecting the relic and radio halo emission. Combining our new data with literature information, we derived the LogL$_{\rm X}$-LogP$_{\rm 325 MHz}$ correlation for radio halos, and investigated the possible trend of the spectral index of radio halos with the temperature of the intracluster medium.

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