Systematic KMTNet Planetary Anomaly Search. XIII. Complete Sample of 2021 Prime Field Planets

The Systematic KMTNet Planetary Anomaly Search series was conducted using the KMTNet data archived from 2016 to 2019. From this first phase of the series, we reported a total of 50 planetary systems hidden in the data archive, which represent about 35% of the total microlensing planets discovered from 2016 to 2019, demonstrating that this semi-machine-based search is a crucial channel for building a complete microlensing planet sample. We continue this series for 2021 and beyond to expand the microlensing planet sample. In this work for the 2021 KMTNet high-cadence fields (Prime fields), we find seven hidden planetary systems and three planet candidates. These new planets represent about 33% of the total microlensing planets discovered within the Prime fields observed during the 2021 bulge season. While the by-eye search is the primary channel for detecting microlensing planets (i.e., two-thirds of microlensing planet discoveries), this work clearly shows that a systematic search series is still necessary for constructing a complete microlensing planet sample. Such a sample is essential for conducting unbiased statistical studies of planet demographics in our Galaxy. Datasets for all the events used for analyses in this work are publicly available: doi:10.5281/zenodo.21472225.