LOFAR LBA巡天一号。调查说明及初步数据公布
The LOFAR LBA Sky Survey I. survey description and preliminary data release
摘要：
LOFAR是目前唯一能够在超低频（<100 MHz）进行高灵敏度、高分辨率（<1 mJy/b和<15”）观测的射电望远镜。为了利用这些能力，LOFAR调查关键科学项目正在进行一项大型调查，以覆盖整个北部天空的低波段天线（LBA）观测。LOFAR LBA巡天（LoLSS）的目标是在42-66 MHz的频率范围内覆盖整个北方天空的3170个点，分辨率为15角秒，灵敏度为1 mJy/b。在这里，我们概述了调查策略，观测状况，目前的校准技术，并简要描述了几个科学动机。我们还描述了初步的公共数据发布。初步图像是使用全自动流水线生成的，旨在纠正数据中所有与方向无关的影响。虽然方向相关的影响，如电离层的影响，尚未得到纠正，但这项工作中呈现的图像仍然比以前在这些低频下进行的调查灵敏10倍。初步数据发布覆盖了HETDEX泉场区域周围的740平方度，分辨率为47”，噪声水平中值为5 mJy/b。公开发布的图像和目录有25，247个来源。我们证明，该系统是能够达到1 mJy/b的均方根噪声和15”的分辨率，一旦方向相关的影响进行校正。LoLSS将为数十万个射电源提供超低频信息，提供关键的光谱信息，并产生一个独特的数据集，可用于广泛的科学主题，如：寻找高红移星系和类星体，研究系外行星的磁层，探测星系中最古老的宇宙射线群，星系团和AGN活动。
英文摘要：
LOFAR is the only radio telescope that is presently capable of high-sensitivity, high-resolution (<1 mJy/b and <15") observations at ultra-low frequencies (<100 MHz). To utilise these capabilities, the LOFAR Surveys Key Science Project is undertaking a large survey to cover the entire northern sky with Low Band Antenna (LBA) observations. The LOFAR LBA Sky Survey (LoLSS) aims to cover the entire northern sky with 3170 pointings in the frequency range 42-66 MHz, at a resolution of 15 arcsec and at a sensitivity of 1 mJy/b. Here we outline the survey strategy, the observational status, the current calibration techniques, and briefly describe several scientific motivations. We also describe the preliminary public data release. The preliminary images were produced using a fully automated pipeline that aims to correct all direction-independent effects in the data. Whilst the direction-dependent effects, such as those from the ionosphere, are not yet corrected, the images presented in this work are still 10 times more sensitive than previous surveys available at these low frequencies. The preliminary data release covers 740 sqdeg around the HETDEX spring field region at a resolution of 47" with a median noise level of 5 mJy/b. The images and the catalogue with 25,247 sources are publicly released. We demonstrate that the system is capable of reaching an rms noise of 1 mJy/b and the resolution of 15" once direction-dependent effects are corrected for. LoLSS will provide the ultra-low-frequency information for hundreds of thousands of radio sources, providing critical spectral information and producing a unique dataset that can be used for a wide range of science topics such as: the search for high redshift galaxies and quasars, the study of the magnetosphere of exoplanets, and the detection of the oldest populations of cosmic-rays in galaxies, clusters of galaxies, and from AGN activity.
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