North Celestial Region Observed with 21 CentiMeter Array

Abstract

Abstract The 21 CentiMeter Array (21CMA) is a radio interferometer in western China. The key science objective of 21CMA is statistically measuring the redshifted H i 21 cm signal of the Epoch of Reionization (EoR). In order to achieve this, a catalog of radio sources is necessary for both calibration and foreground removal. In this work, we present a catalog of 832 radio sources within a radius of 5° around the North Celestial Pole region observed with 21CMA. Three days of data taken in 2013 are used in the analysis, with a frequency coverage from 75 to 200 MHz and an angular resolution of about two arcminutes at 200 MHz. Flux densities and estimated spectral indices of the radio sources are provided in the source catalog. For simplicity, only the east–west baseline is used for the observations to avoid the so-called w − term in the data analysis. The longest baseline along the east–west direction is 2780 m. Comparing our source counts with other radio observations, we find a good agreement with the observations made with the Giant Metrewave Radio Telescope and Murchison Widefield Array. Our data reduction is still limited by grating lobes of very bright sources in the field due to the redundant configuration of 21CMA. We note that understanding the properties of radio sources, and modeling and removing the radio sources are challenges for the EoR experiments.