Diffuse radio sources in galaxy clusters: multi-wavelength observations

射电遗迹是漫射的、低表面亮度的、陡峭的光谱源，通常位于星系团的外围。虽然已知非热电子是观测到的同步辐射的原因，但粒子加速的机制以及这些尺度上磁场的起源却知之甚少。低频阵列（LOFAR）是寻找和研究无线电遗迹的理想仪器，因为它在低频时非常敏感，并且具有广阔的视野。随着最近的发展，我们现在能够产生几乎达到热噪声的精美校准图像。作为一个案例，我们已经用LOFAR发现了低质量星系团Abell 1931中的漫射，现在希望在x射线和其他射电波段（JVLA， GMRT）研究星系团中漫射的起源。钱德拉对这个目标的观测已经得到批准。由于我们对低质量星系团中的漫射射电辐射了解不多，这强调了这个目标的发现潜力。到目前为止，射电晕和遗迹主要是在大质量星系团中发现的。在该项目的第二部分，我们将使用方向相关校准和成像技术，在LOFAR Tier-1调查中寻找更陡谱的漫射发射。通过将LOFAR Tier-1调查的区域与Planck Sunyaev-Zeldovich集群数据库交叉关联，编制了初步目标列表，共产生31个集群。新的漫射、陡峭光谱源的发现将揭示旧的（化石）相对论性电子在产生无线电遗迹中的作用。

Radio relics are diffuse, low surface brightness, steep-spectrum sources that are typically located in the periphery of galaxy clusters. While it is known that non-thermal electrons are responsible for the observed synchrotron radiation, the mechanism of particle acceleration as well as the origins of the magnetic fields on these scales are poorly understood.The Low-Frequency Array (LOFAR) is the ideal instrument to find and study radio relics because it is very sensitive at low-frequencies and has a wide field of-view. With recent developments we are now capable of producing exquisite calibrated images that almost reach the thermal noise. As a point in case we have discovered with LOFAR diffuse emission in the low-mass galaxy cluster Abell 1931 which now wish to study in the X-rays and other radio bands (JVLA, GMRT) to investigate the origin of diffuse emission in galaxy clusters. Chandra observations for this target have already been approved. Since we do not know much about diffuse radio emission in lower mass clusters, this underlines the discovery potential of this target. So far, radio halos and relics have been found pre-dominantly in massive galaxy clusters.In a second part of this project, we will search for more steep-spectrum, diffuse emission in LOFAR Tier-1 surveys using direction-dependent calibration and imaging. A preliminary list of targets has been compiled from cross-correlating the area that has been surveyed by LOFAR Tier-1 survey with the Planck Sunyaev-Zeldovich cluster database yielding a total of 31 clusters. The discovery of new diffuse, steep spectrum sources will shed light on the role of old (fossil) relativistic electrons in producing radio relics.