A perfect power-law spectrum even at highest frequencies: The Toothbrush relic
K. Rajpurohit, F. Vazza, M. Hoeft, F. Loi, R. Beck, V. Vacca, M. Kierdorf, R. J. van Weeren, D. Wittor, F. Govoni, M. Murgia, C. J. Riseley, N. Locatelli, A. Dr… 展开作者
K. Rajpurohit, F. Vazza, M. Hoeft, F. Loi, R. Beck, V. Vacca, M. Kierdorf, R. J. van Weeren, D. Wittor, F. Govoni, M. Murgia, C. J. Riseley, N. Locatelli, A. Drabent, E. Bonnassieux
Radio relics trace shock fronts generated in the intracluster medium (ICM) during cluster mergers. The particle acceleration mechanism at the shock fronts is not yet completely understood. We observed the Toothbrush relic with the Effelsberg and Sardinia Radio Telescope at 14.25 GHz and 18.6 GHz, respectively. Unlike previously claimed, the integrated spectrum of the relic closely follows a power law over almost three orders of magnitude in frequency, with a spectral index of $α_{\rm 58\,MHz}^{\rm 18.6\,GHz}=-1.16\pm0.03$. Our finding is consistent with a power-law injection spectrum, as predicted by diffusive shock acceleration theory. The result suggests that there is only little magnetic field strength evolution downstream to the shock. From the lack of spectral steepening, we find that either the Sunyaev-Zeldovich decrement produced by the pressure jump is less extended than $\sim$ 600\,kpc along the line of sight or, conversely, that the relic is located far behind in the cluster. For the first time, we detect linearly polarized emission from the "brush" at 18.6 GHz. Compared to 8.3 GHz, the degree of polarization across the brush increases at 18.6 GHz, suggesting a strong Faraday depolarization towards lower frequencies. The observed depolarization is consistent with an intervening magnetized screen that arise from the dense ICM containing turbulent magnetic fields. The depolarization, corresponding to a standard deviation of the Rotation Measures as high as $σ_{\rm RM}= 212\pm23\rm \,rad\,m^{-2}$, suggests that the brush is located in or behind the ICM. Our findings indicate that the Toothbrush can be consistently explained by the standard scenario for relic formation
MC^2: Mapping the Dark Matter Distribution of the "Toothbrush" Cluster RX J0603.3+4214 with Hubble Space Telescope and Subaru Weak-lensing
z=0.225的星系团RX J0603.3+4214是最罕见的星系团之一，拥有非常大的射电遗迹（~2 Mpc）。由于遗迹的显著形态，该集群被昵称为“牙刷集群”。虽然星团的基本质量分布是重建令人费解的射电遗迹形态的合并场景所需的关键信息之一，但它接近银河平面b~10度的位置给观测带来了重大挑战。我们提出了一个高分辨率的弱透镜研究与斯巴鲁/Suprime凸轮和哈勃太空望远镜的成像数据的集群。我们的质量重建显示，该集群是由复杂的暗物质子结构密切跟踪星系的分布，但在相对简单的二元X射线形态形成对比。然而，我们发现星团质量仍然由南北方向排列的两个质量最大的星团占主导地位，其质量比约为3：1（北部和南部星团的M_{200} =6.29_{-1.62}^{+2.24} x 10^{14} Msun和1.98_{-0.74}^{+1.24} x 10^{14} Msun）。南部的质量峰相对于相应的X射线峰向南偏移约2'，其具有指向南方的“子弹”状形态。目前的弱透镜结果与X射线，星系和射电遗迹的比较表明，也许负责观测遗迹的主要机制可能是两个最大质量的子星系团的高速碰撞，尽管形态的特殊性需要额外的子星系团的参与。随后应进行仔细的数值模拟，以便利用所有现有的观测资料更全面地了解合并的情况。
Radio emission in the form of giant radio relics is observed at the periphery of galaxy clusters. This non-thermal emission is an important tracer for cosmic-ray electrons and intracluster magnetic fields. One striking observational feature of these objects is their high degree of polarisation which provides information on the magnetic fields at the relics' positions. In this contribution, we test if state-of-the-art high resolution cosmological simulations are able to reproduce the polarisation features of radio relics. Therefore, we present a new analysis of high-resolution cosmological simu…
Zooming in on radio relics -- II. How relic morphology probes density fluctuations at the edge of galaxy clusters
Leibniz-Institut für Astrophysik Potsdam (AIP)（波茨坦莱布尼茨天体物理研究所）；Max-Planck-Institut für Astrophysik（马克斯·普朗克天体物理研究所）；Universität Potsdam（波茨坦大学）；Universität Heidelberg（海德堡大学）
A Brush with Turbulence: Probing the ICM Dynamics in the Merging Toothbrush Cluster using XRISM
Leiden University（莱顿大学）；SRON, Space Research Organisation Netherlands（荷兰空间研究组织）；Leiden Observatory, Leiden University（莱顿天文台，莱顿大学）；Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo（东京大学宇宙物理与数学 Kavli 研究所（WPI））；Waterloo Centre for Astrophysics, Department of Physics and Astronomy, University of Waterloo（滑铁卢大学天体物理中心，物理与天文学系，滑铁卢大学）；Department of Physics, Nagoya University（名古屋大学物理学系）；KMI, Nagoya University（名古屋大学 KMI）；Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA)（日本宇宙航空研究开发机构 JAXA 宇宙科学研究所 (ISAS)）；INAF - Istituto di Radioastronomia（意大利国家天体物理研究所射电天文研究所）
Another shock for the Bullet cluster, and the source of seed electrons for radio relics
与澳大利亚望远镜紧凑阵列的观测，我们发现一个高度细长的Mpc尺度的扩散射电源的子弹集群1 E0657 -55.8，我们认为具有的位置，光谱和偏振特性的射电遗迹的东部外围。这个强大的遗迹（2.3+/-0.1 x 10^25 W Hz^-1）由一个明亮的北方灯泡和一个微弱的线性尾巴组成。该灯泡发射出观测到的无线电通量的94%，并具有任何已知遗迹中最高的表面亮度。与线性尾部完全一致，我们在星团的钱德拉深像中发现了一个尖锐的X射线表面亮度边缘-这是热星团内介质（ICM）中激波前沿的特征，位于星团的另一侧，与著名的弓形激波相反。这个X射线冲击波与遗迹重合的新例子进一步支持了这样一个假设，即星团外部区域的冲击波可以通过扩散冲击波（再）加速形成遗迹。有趣的是，我们的新遗物表明，再加速的种子电子来自射电星系的局部残余，我们很幸运在它完全分裂之前抓住了它。如果这种情况下，当冲击穿过被老化的相对论等离子体污染的ICM的明确区域时，遗迹形成-与通常的假设相反，种子均匀地混合在ICM中-也是其他遗迹的情况，这可能解释外围遗迹的一些特殊性质。
Provided the consistency relations are not violated, the recent Bicep2 observations pin down the absolute normalization, the spectral slope and the maximal frequency of the cosmic graviton background produced during inflation. The properly normalized spectra are hereby computed from the lowest frequencies (of the order of the present Hubble rate) up to the highest frequency range in the GHz region. Deviations from the conventional paradigm cannot be excluded and are examined by allowing for different physical possibilities including, in particular, a running of the tensor spectral index, an ex…
We present new low-frequency ($ν= 88$-216 MHz) observations of the complex merging galaxy cluster Abell 3266. These new observations are taken with the Murchison Widefield Array (MWA) in its Phase II 'extended', long-baseline configuration, offering the highest-resolution low-frequency view of the cluster to date. We report on the detection of four steep spectrum ($α\lesssim -1$ for $S_ν\propto ν^α$) extended radio sources within the cluster. We confirm the detection of a $\sim 570$ kpc radio relic to the south of the cluster, and a possible bridge of emission connecting the relic to the clust…
