Apertif drift scan based compound beam maps (1220-1520 MHz)
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Apertif (APERture Tile In Focus) is a Phased Array Feed (PAF) system on the Westerbork Synthesis Radio Telescope (WSRT) that conducted the Apertif legacy surveys between the 1st of July 2019 and the 28th of February 2022. Apertif carried out a two tiered imaging survey, with a shallow, wide-area and a medium-deep, small-area component, and a time domain survey. In the standard observing mode for imaging 40 partially overlapping compound beams (CBs) are formed simultaneously in a rectangular configuration. Each of these 40 CBs have a unique shape that differs substantially from the "old" WSRT beam shape. This data set contains Apertif drift scan based CB maps measured at the second Apertif imaging survey frequency setting (1220-1520 MHz). Apertif imaging observations were take at these frequencies between January 2021 and February 2022. The CB maps are generated from drift scan observations using the AperPB scrips (DOI: https://doi.org/10.5281/zenodo.6544109). These CB maps can be used to primary beam correct or mosaic images or data cubes from the Apertif imaging surveys. The dataset contains two types of fits files: 1) Reconstructed CB maps from the drift scans. These maps are within directories called "drift_maps" and have the following naming scheme: <source>_<CB map ID>_<CB number>_<polarisation>.fits. The source refers to the continuum source used for the drift scan observations, this can be either CygA or CasA. The CB map ID is the identification of a set of CB maps based on the observing date in the format of yymmdd e.g. 190628. The CB number refers to which of the 40 Apertif CBs the map presents (numbering from 00 to 39). Polarisation denotes which polarisation the map shows, these can be xx, yy, I and diff, where diff refers to xx-yy. These maps are 3.36 × 2.3 deg in size and are oriented upside down compared to the sky. 2) Spline fitted CB maps. These are within directories called "beam_models" and have the following naming: <CB map ID>_<CB number>_<polarisation>_model.fits. The CB map ID is the identification of a set of CB maps based on the observing date e.g. 190628. The CB number refers to which of the 40 Apertif CBs the map presents. Polarisation denotes which polarisation the map shows, these can be xx, yy, I. These maps are 1.1 × 1.1 deg in size and are subdivided into 18 frequency bins in directories called "channel_<num>". These maps are suitable for primary beam correcting or mosaicing Apertif images and data cubes. Since the CB shapes of Apertif change over time, we recommend to use the closest CB data set in time to the observation that the primary beam correction or mosaicing is going to be applied to. All CB data sets also contain per antenna CB maps and spline fitted CB maps within the directory "per_antenna_maps". The naming and organisation of the per antenna maps is the same as described above, with the exception that the spline fitted CB maps are not subdivided by frequency bins into separate directories, but are contained within a single fits file. The Apertif system uses 12 of the 14 WSRT antennas. In some cases one or two antennas were malfunctioning during the observations and there are only 10 or 11 per antenna CB map sets. Notes on the individual CB data sets CB map ID continuum source notes 210205 Cyg A RFI in channels 13-15 (1.46-1.48 GHz) 210402 Cas A RFI in channels 13-15 (1.46-1.48 GHz), no RTC and RTD, spline fit for CB01 failed for the per antenna maps 211103 Cas A RFI in channels 13-15 (1.46-1.48 GHz), spline fit for CB01 failed for the per antenna maps 211118 Cyg A RFI in channels 13-15 (1.46-1.48 GHz), spline fit for CB01 failed for the per antenna maps For a detailed description of the characteristics of the Apertif CBs and how the CB maps are produced see the upcoming publication Dénes et al. 2022 submitted to A&A (ArXiv: https://arxiv.org/abs/2205.09662).<br> <br> For more information on the Apertif system see: van Cappellen et al. 2022, A&A, 658, 146 DOI: https://doi.org/10.1051/0004-6361/202141739
Apertif（APERture Tile In Focus）是安装于韦斯特博克综合孔径射电望远镜（Westerbork Synthesis Radio Telescope，WSRT）的相控阵馈源（Phased Array Feed，PAF）系统，于2019年7月1日至2022年2月28日期间开展了阿佩蒂夫遗产巡天项目。阿佩蒂夫实施了两级成像巡天与一个时域巡天：其中一级为浅覆盖宽视场巡天，另一级为中等深度小视场巡天。在标准成像观测模式下，系统可同时在矩形排布中生成40个部分重叠的复合波束（Compound Beam，CB）。每个复合波束均具备独特的波束形状，与传统WSRT波束形状差异显著。 本数据集包含基于漂移扫描的阿佩蒂夫复合波束映射数据，测量于第二次阿佩蒂夫成像巡天的频率设置区间（1220–1520 MHz）。阿佩蒂夫成像观测于2021年1月至2022年2月期间在该频率区间内开展。复合波束映射数据由漂移扫描观测数据通过AperPB脚本（DOI: https://doi.org/10.5281/zenodo.6544109）生成。此类复合波束映射可用于对阿佩蒂夫成像巡天得到的图像或数据立方体进行主束校正或拼接成像。 数据集包含两类FITS文件： 1. 漂移扫描重建复合波束映射文件：存储于名为`drift_maps`的目录中，命名规则为：`<源名称>_<复合波束映射ID>_<复合波束编号>_<极化方式>.fits`。其中，源名称指代漂移扫描观测所用的连续谱源，可选值为CygA或CasA；复合波束映射ID为基于观测日期的映射集标识，格式为`yymmdd`，例如`190628`；复合波束编号指代该映射对应的40个阿佩蒂夫复合波束之一（编号范围为00至39）；极化方式标识映射所展示的极化分量，可选值包括xx、yy、I与diff，其中diff指代xx与yy的差值。此类映射的视场尺寸为3.36°×2.3°，且相对于天空朝向呈上下翻转状态。 2. 样条拟合复合波束映射文件：存储于名为`beam_models`的目录中，命名规则为：`<复合波束映射ID>_<复合波束编号>_<极化方式>_model.fits`。其中，复合波束映射ID、复合波束编号与极化方式的定义与前述一致，极化方式可选值为xx、yy、I。此类映射的视场尺寸为1.1°×1.1°，并被划分为18个频率子带，存储于名为`channel_<num>`的子目录中。此类映射适用于阿佩蒂夫图像与数据立方体的主束校正及拼接。 由于阿佩蒂夫的复合波束形状随时间变化，我们建议使用与待校正或拼接观测时刻时间最接近的复合波束数据集，以开展主束校正或拼接成像。 所有复合波束数据集均在`per_antenna_maps`目录中包含单天线复合波束映射文件与样条拟合复合波束映射文件。单天线映射文件的命名与组织形式与前述一致，唯一区别在于样条拟合复合波束映射文件未按频率子带划分至不同子目录，而是存储于单个FITS文件中。 阿佩蒂夫系统使用14台WSRT天线中的12台。部分观测期间存在1台或2台天线故障的情况，因此仅存在10或11组单天线复合波束映射数据集。 单复合波束数据集备注： - 210205 Cyg A：13-15号通道（1.46–1.48 GHz）存在射频干扰（Radio Frequency Interference，RFI） - 210402 Cas A：13-15号通道（1.46–1.48 GHz）存在射频干扰，无RTC与RTD功能，单天线映射的CB01样条拟合失败 - 211103 Cas A：13-15号通道（1.46–1.48 GHz）存在射频干扰，单天线映射的CB01样条拟合失败 - 211118 Cyg A：13-15号通道（1.46–1.48 GHz）存在射频干扰，单天线映射的CB01样条拟合失败 关于阿佩蒂夫复合波束特性及复合波束映射生成方式的详细说明，请参阅即将提交至《A&A》（《天文学与天体物理学》）的Dénes等人2022年稿件，其预印本链接为：https://arxiv.org/abs/2205.09662。 有关阿佩蒂夫系统的更多信息，请参阅：van Cappellen等人2022年发表于《A&A》第658卷第146页的论文，DOI: https://doi.org/10.1051/0004-6361/202141739
