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Characterizing the radio emission from the binary galaxy cluster merger Abell 2146

机译：表征二元星系团合并Abell 2146的无线电发射

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Context. Collisions of galaxy clusters generate shocks and turbulence in the intra-cluster medium (ICM). The presence of relativistic particles and magnetic fields is inferred through the detection of extended synchrotron radio sources such as haloes and relics and implies that merger shocks and turbulence are capable of (re-)accelerating particles to relativistic energies. However, the precise relationship between merger shocks, turbulence, and extended radio emission is still unclear. Studies of the most simple binary cluster mergers are important to help understand the particle acceleration in the ICM. Aims. Our main aim is to study the properties of the extended radio emission and particle acceleration mechanism(s) associated with the generation of relativistic particles in the ICM. Methods. We measure the low-frequency radio emission from the merging galaxy cluster Abell 2146 with LOFAR at 144 MHz. We characterize the spectral properties of the radio emission by combining these data with data from archival Giant Metrewave Radio Telescope (GMRT) at 238 MHz and 612 MHz and Very Large Array (VLA) at 1.5 GHz. Results. We observe extended radio emission at 144 MHz behind the NW and SE shocks. Across the NW extended source, the spectral index steepens from ?1.06?±?0.06 to ?1.29?±?0.09 in the direction of the cluster centre. This spectral behaviour suggests that a relic is associated with the NW upstream shock. The precise nature of the SE extended emission is unclear. It may be a radio halo bounded by a shock or a superposition of a relic and halo. At 144 MHz, we detect a faint emission that was not seen with high-frequency observations, implying a steep ( α ?< ??1.3) spectrum nature of the bridge emission. Conclusions. Our results imply that the extended radio emission in Abell 2146 is probably associated with shocks and turbulence during cluster merger. The relativistic electrons in the NW and SE may originate from fossil plasma and thermal electrons, respectively.
机译：上下文。星系团的碰撞会在团簇内介质（ICM）中产生震动和湍流。相对论粒子和磁场的存在是通过检测扩展的同步加速器无线电源（例如晕轮和遗物）来推断的，这意味着合并冲击和湍流能够（重新）加速粒子产生相对论能量。但是，并购冲击，湍流和扩大的无线电发射之间的确切关系仍然不清楚。对最简单的二元集群合并的研究对于帮助理解ICM中的粒子加速非常重要。目的我们的主要目的是研究与ICM中相对论粒子的产生有关的扩展无线电发射和粒子加速机制的性质。方法。我们测量了合并的银河星团Abell 2146与LOFAR在144 MHz处的低频无线电发射。通过将这些数据与来自238 MHz和612 MHz的档案巨型大波无线电望远镜（GMRT）以及1.5 GHz的超大型阵列（VLA）的数据进行组合，我们可以表征无线电发射的频谱特性。结果。我们观察到在NW和SE冲击之后144 MHz处无线电发射的扩展。在整个NW扩展源中，光谱指数在聚类中心方向上从1.06±0.06陡峭到1.29±0.09。这种频谱行为表明，文物与西北西北上游的冲击有关。 SE扩展发射的确切性质尚不清楚。它可能是受到撞击或遗物与光环重叠限制的无线电光环。在144 MHz处，我们检测到微弱的发射，这在高频观察中是看不到的，这意味着电桥发射具有陡峭的（α≤<≤1.3）频谱特性。结论。我们的结果表明，Abell 2146中扩展的无线电发射可能与集群合并期间的冲击和湍流有关。 NW和SE中的相对论电子可能分别来自化石等离子体和热电子。

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