文章基本信息

标题：rPICARD: A CASA-based calibration pipeline for VLBI data
其他标题：Calibration and imaging of 7 mm VLBA observations of the AGN jet in M 87
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作者：M. Janssen ; C. Goddi ; I. M. van Bemmel 等
期刊名称：Astronomy & Astrophysics
印刷版ISSN：0004-6361
电子版ISSN：1432-0746
出版年度：2019
卷号：626
DOI：10.1051/0004-6361/201935181
语种：English
出版社：EDP Sciences
摘要：Context.The Common Astronomy Software Application (CASA) software suite, which is a state-of-the-art package for radio astronomy, can now reduce very long baseline interferometry (VLBI) data with the recent addition of a fringe fitter.Aims.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.Methods.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 allowrPICARDto 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.Results.In this work we demonstrate the capabilities ofrPICARDby calibrating and imaging 7 mm Very Long Baseline Array (VLBA) data of the central radio source in the M 87 galaxy. The reconstructed jet image reveals a complex collimation profile and edge-brightened structure, in accordance with previous results. 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.
关键词：enatmospheric effectstechniques: high angular resolutioninstrumentation: interferometersmethods: data analysis