Calibrating VLBI Polarization Data Using GPCAL. II. Time-dependent Calibration

IF 4.8 2区 物理与天体物理 Q1 ASTRONOMY & ASTROPHYSICS
Jongho Park, Keiichi Asada, Do-Young Byun
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引用次数: 1

Abstract

Abstract We present a new method of time-dependent instrumental polarization calibration for very long baseline interferometry (VLBI). This method has been implemented in the recently developed polarization calibration pipeline GPCAL. Instrumental polarization, also known as polarimetric leakage, is a direction-dependent effect, and it is not constant across the beam of a telescope. Antenna pointing model accuracy is usually dependent on time, resulting in off-axis polarimetric leakages that can vary with time. The method is designed to correct for the off-axis leakages with large amplitudes that can severely degrade linear polarization images. Using synthetic data generated based on real Very Long Baseline Array (VLBA) data observed at 43 GHz, we evaluate the performance of the method. It was able to reproduce the off-axis leakages assumed in the synthetic data, particularly those with large amplitudes. The method has been applied to two sets of real VLBA data, and the derived off-axis leakages show very similar trends over time for pairs of nearby sources. Furthermore, the amplitudes of the off-axis leakages are strongly correlated with the antenna gain correction factors. The results demonstrate that the method is capable of correcting for the off-axis leakages present in VLBI data. By calibrating time-dependent instrumental polarization, the rms noise levels of the updated linear polarization images have been significantly reduced. The method is expected to substantially enhance the quality of linear polarization images obtained from existing and future VLBI observations.
用GPCAL标定VLBI偏振数据。2时间校准
摘要:提出了一种用于甚长基线干涉测量(VLBI)的时变仪器偏振校准新方法。该方法已在新近研制的偏振校准管道GPCAL中实现。仪器偏振,也被称为偏振泄漏,是一种方向依赖效应,它在望远镜光束上不是恒定的。天线指向模型的精度通常依赖于时间,导致离轴极化泄漏可能随时间变化。该方法用于校正大振幅离轴泄漏,这种泄漏会严重降低线偏振图像的质量。利用基于43 GHz甚长基线阵列(VLBA)实际观测数据生成的合成数据,对该方法的性能进行了评估。它能够再现合成数据中假设的离轴泄漏,特别是那些振幅较大的泄漏。该方法已应用于两组真实的VLBA数据,得出的离轴泄漏随时间的变化趋势与附近源对非常相似。此外,离轴泄漏的幅度与天线增益校正系数密切相关。结果表明,该方法能够校正VLBI数据中存在的离轴泄漏。通过校准随时间变化的仪器偏振,更新后的线性偏振图像的均方根噪声水平显著降低。该方法有望大大提高从现有和未来的VLBI观测中获得的线偏振图像的质量。
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来源期刊
Astrophysical Journal
Astrophysical Journal 地学天文-天文与天体物理
CiteScore
8.40
自引率
30.60%
发文量
2854
审稿时长
1 months
期刊介绍: The Astrophysical Journal is the foremost research journal in the world devoted to recent developments, discoveries, and theories in astronomy and astrophysics.
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