arXiv 1703.068022017-03-20astro-ph.COastro-ph.GA

Abell 2142星系团中的双分量巨射电晕

The two-component giant radio halo in the galaxy cluster Abell 2142

T. Venturi, M. Rossetti, G. Brunetti, D. Farnsworth, F. Gastaldello, S. Giacintucci, D. V. Lal, L. Rudnick, T. W. Shimwell, D. Eckert, S. Molendi, M. Owers

备注：: 18 pages, 10 figures, 4 tables - A&A, accepted
发表信息：: A&A 603, A125 (2017)
DOI：: 10.1051/0004-6361/201630014

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摘要：

我们报告的频谱研究在射频的巨型射电晕在A2142（z=0.0909），我们进行了探索其性质和起源。A2142并不是一个大的合并，一个巨大的射电晕的存在有点令人惊讶。我们在608 MHz，322 MHz和234 MHz的GMRT和1-2 GHz频段的VLA进行了深射电观测。我们在各种分辨率下获得了所有频率的高质量图像。射电晕在所有频率上都能被很好地探测到，并延伸到A2142中最远的冷锋。我们研究了两个区域的光谱指数：晕的中心部分和最远的东南冷锋方向的第二个区域，选择跟随晕和X射线发射的明亮部分。我们补充了我们的观察与初步LOFAR图像在118 MHz和档案VLA数据在1.4 GHz的重新分析。射电晕的两个分量表现出不同的观测性质。中心最亮的部分具有较高的表面亮度和光谱，其陡度类似于已知的射电晕，即$α^{\rm 1.78~GHz}_{\rm 118~MHz}=1.33\pm 0.08$。逐渐消失为较大尺度辐射的脊的尺寸较宽，表面亮度低得多，光谱略陡，即$α^{\rm 1.78~GHz}_{\rm 118~MHz}\sim 1.5$。我们认为射电晕最亮的部分是由A2142中的中心晃动提供能量的，类似于对迷你晕的建议，或者是由ICM中强子碰撞产生的次级电子提供能量的。另一方面，较陡的脊可能探测到粒子再加速的湍流产生的气体和磁场在更大的规模或较低的能量机制，如星系群的连续下降或离轴合并。

英文摘要：

We report on a spectral study at radio frequencies of the giant radio halo in A2142 (z=0.0909), which we performed to explore its nature and origin. A2142 is not a major merger and the presence of a giant radio halo is somewhat surprising. We performed deep radio observations with the GMRT at 608 MHz, 322 MHz, and 234 MHz and with the VLA in the 1-2 GHz band. We obtained high-quality images at all frequencies in a wide range of resolutions. The radio halo is well detected at all frequencies and extends out to the most distant cold front in A2142. We studied the spectral index in two regions: the central part of the halo and a second region in the direction of the most distant south-eastern cold front, selected to follow the bright part of the halo and X-ray emission. We complemented our observations with a preliminary LOFAR image at 118 MHz and with the re-analysis of archival VLA data at 1.4 GHz. The two components of the radio halo show different observational properties. The central brightest part has higher surface brightess and a spectrum whose steepness is similar to those of the known radio halos, i.e. $α^{\rm 1.78~GHz}_{\rm 118~MHz}=1.33\pm 0.08$. The ridge, which fades into the larger scale emission, is broader in size and has considerably lower surface brightess and a moderately steeper spectrum, i.e. $α^{\rm 1.78~GHz}_{\rm 118~MHz}\sim 1.5$. We propose that the brightest part of the radio halo is powered by the central sloshing in A2142, similar to what has been suggested for mini-halos, or by secondary electrons generated by hadronic collisions in the ICM. On the other hand, the steeper ridge may probe particle re-acceleration by turbulence generated either by stirring the gas and magnetic fields on a larger scale or by less energetic mechanisms, such as continuous infall of galaxy groups or an off-axis merger.

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