First LOFAR observations at very low frequencies of cluster-scale non-thermal emission: the case of Abell 2256
First LOFAR observations at very low frequencies of cluster-scale non-thermal emission: the case of Abell 2256
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首次 LOFAR 星团规模非热发射频率极低的观测：Abell 2256 的案例
DOI：
10.1051/0004-6361/201219154
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发表时间：
2012
影响因子：
6.5
通讯作者：
Van Weeren R
中科院分区：
文献类型：
--
作者：
Van Weeren R
阿贝尔2256是最著名的星系团之一，它拥有与单个星系无关的大规模漫射射电辐射。它包含一个巨大的射电晕和一个遗迹，以及一些头尾源和较小的弥散陡谱射电源。射电晕和遗迹的起源仍在争论中，但在过去的几年里，这些射电源的存在与星系团合并事件密切相关。在这里，我们提出的结果，从第一LOFAR低波段天线（LBA）的观测阿贝尔2256之间的18和67兆赫。据我们所知，本文在63 MHz下呈现的图像是在低于100 MHz的频率下获得的最深的图像。射电晕和巨型遗迹都在63 MHz的图像中被检测到，而散射的射电辐射在低至20 MHz的频率下仍然可见。观测结果证实了在星团中心以西存在一个先前声称的超陡光谱源，其光谱指数为−2.3 ± 0.4，介于63和153 MHz之间。陡峭的频谱表明，这个源是星团中头-尾射电源的旧部分。对于射电遗迹，我们发现在去除其他源的通量贡献后，积分谱指数为−0.81 ± 0.03。这是相对平坦的，这可能表明，由于激波马赫数的增加，在最后~0.1 Gyr，激波处的粒子加速效率发生了实质性变化。在另一种情况下，粒子在激波下游区域被某种机制重新加速，导致相对平坦的综合无线电频谱。在无线电晕区域，我们发现的迹象表明，低频频谱陡峭，这可能表明，相对论粒子加速在一个相当不均匀的湍流区域。
Abell 2256 is one of the best known examples of a galaxy cluster hosting large-scale diffuse radio emission that is unrelated to individual galaxies. It contains both a giant radio halo and a relic, as well as a number of head-tail sources and smaller diffuse steep-spectrum radio sources. The origin of radio halos and relics is still being debated, but over the last years it has become clear that the presence of these radio sources is closely related to galaxy cluster merger events. Here we present the results from the first LOFAR low band antenna (LBA) observations of Abell 2256 between 18 and 67 MHz. To our knowledge, the image presented in this paper at 63 MHz is the deepest ever obtained at frequencies below 100 MHz in general. Both the radio halo and the giant relic are detected in the image at 63 MHz, and the diffuse radio emission remains visible at frequencies as low as 20 MHz. The observations confirm the presence of a previously claimed ultra-steep spectrum source to the west of the cluster center with a spectral index of −2.3 ± 0.4 between 63 and 153 MHz. The steep spectrum suggests that this source is an old part of a head-tail radio source in the cluster. For the radio relic we find an integrated spectral index of −0.81 ± 0.03, after removing the flux contribution from the other sources. This is relatively flat which could indicate that the efficiency of particle acceleration at the shock substantially changed in the last ~0.1 Gyr due to an increase of the shock Mach number. In an alternative scenario, particles are re-accelerated by some mechanism in the downstream region of the shock, resulting in the relatively flat integrated radio spectrum. In the radio halo region we find indications of low-frequency spectral steepening which may suggest that relativistic particles are accelerated in a rather inhomogeneous turbulent region.
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对阿贝尔 2256 中陡频谱射电源的观测
DOI：
--
发表时间：
1978
期刊：
影响因子：
--
作者：
C. Masson;C. J. Mayer
通讯作者：
C. J. Mayer
翁萨拉太空天文台
DOI：
10.1888/0333750888/4290
发表时间：
2000
期刊：
Krankenpflege
影响因子：
--
作者：
P. Murdin
通讯作者：
P. Murdin
影响因子：
1
作者：
G. Brunetti
通讯作者：
G. Brunetti
DOI：
10.1086/504076
发表时间：
2006-03
期刊：
The Astronomical Journal
影响因子：
--
作者：
T. Clarke;Torsten A. Ensslin Naval Research Laboratory;Interferometrics Inc.;M. F. Astrophysik
通讯作者：
T. Clarke;Torsten A. Ensslin Naval Research Laboratory;Interferometrics Inc.;M. F. Astrophysik
星系团 Abell 3376 周围的巨型环形射电结构
影响因子：
56.9
作者：
J. Bagchi;F. Durret;G. L. Neto;S. Paul
通讯作者：
S. Paul