rPICARD：一种基于CASA的VLBI数据校准管道。M87中AGN喷流的7 mm VLBA观测的校准和成像
rPICARD: A CASA-based Calibration Pipeline for VLBI Data. Calibration and imaging of 7 mm VLBA observations of the AGN jet in M87
摘要：
（节略）CASA软件套件，现在可以减少非常长的基线干涉测量（VLBI）数据与最近增加的条纹拟合。在这里，我们提出了Radboud PIpeline高角分辨率数据的校准（rPICARD），这是一个开源的VLBI校准和成像管道建立在CASA框架之上。该流水线能够减少来自不同VLBI阵列的数据。只需设置几个非默认输入参数，就可以非交互式运行，并提供高质量的校准数据。基于消息传递接口（MPI）实现的CPU可伸缩性确保了可以在合理的计算时间内处理来自未来阵列的大带宽数据。相位校准用Schwab-Cotton条纹拟合算法完成。对于残余大气影响的校准，基于每次扫描的数据的信噪比（S/N）来确定最佳解区间。在相同的扫描中，可以为不同的天线设置不同的解决方案间隔，以增加低S/N状态下的检测次数。这些新技术允许rPICARD校准来自不同阵列的数据，包括高频和低灵敏度阵列。振幅校准是基于标准的望远镜元数据，和一个强大的算法可以解决在高频区的大气不透明度衰减。标准CASA任务用于CLEAN成像和自校准。在这项工作中，我们证明了rPICARD的能力，通过校准和成像7毫米VLBA数据的中央无线电源在M87星系。重建的射流图像显示出复杂的准直轮廓和边缘增亮结构。探测到潜在的反向喷流，其亮度为接近喷流的10%。这就限制了射电核心附近的喷流速度，使其在小倾角时只有光速的一半。
英文摘要：
(Abridged) The CASA software suite, can now reduce very long baseline interferometry (VLBI) data with the recent addition of a fringe fitter. Here, we present the Radboud PIpeline for the Calibration of high Angular Resolution Data (rPICARD), which is an open-source VLBI calibration and imaging pipeline built on top of the CASA framework. The pipeline is capable of reducing data from different VLBI arrays. It can be run non-interactively after only a few non-default input parameters are set and delivers high-quality calibrated data. CPU scalability based on a message-passing interface (MPI) implementation ensures that large bandwidth data from future arrays can be processed within reasonable computing times. Phase calibration is done with a Schwab-Cotton fringe fit algorithm. For the calibration of residual atmospheric effects, optimal solution intervals are determined based on the signal-to-noise ratio (S/N) of the data for each scan. Different solution intervals can be set for different antennas in the same scan to increase the number of detections in the low S/N regime. These novel techniques allow rPICARD to calibrate data from different arrays, including high-frequency and low-sensitivity arrays. The amplitude calibration is based on standard telescope metadata, and a robust algorithm can solve for atmospheric opacity attenuation in the high-frequency regime. Standard CASA tasks are used for CLEAN imaging and self-calibration. In this work we demonstrate the capabilities of rPICARD by calibrating and imaging 7 mm VLBA data of the central radio source in the M87 galaxy. The reconstructed jet image reveals a complex collimation profile and edge-brightened structure. A potential counter-jet is detected that has 10 % of the brightness of the approaching jet. This constrains jet speeds close to the radio core to about half the speed of light for small inclination angles.
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