Intensity Calibration for the Mingantu Spectral Radioheliograph Images

The Mingantu Spectral Radioheliograph (MUSER), a new generation of solar dedicated radio imaging spectroscopic telescope, has realized high-time, high-angular, and high-frequency resolution imaging of the Sun in the 0.4--15 GHz ultra-broadband frequency range. The radio brightness temperature is an important parameter to describe the solar physical process. It plays a very important role in the study of different radio radiation mechanisms, solar magnetic field and the acceleration of non-thermal particles in the solar burst process. Therefore, the image of radioheliograph must be calibrated for brightness temperature. This paper introduces a method suitable for radioheliograph image intensity calibration. The solar radio image contains the structural information of the solar disk. The radio radius and intensity of the quiet solar disk in the image can be obtained by fitting the first kind of Bessel function with the visibilities of short baselines of the radioheliograph. Then, the Rayleigh-Jeans law and the daily solar radio flux can be used to calculate the calibration factor G_c of the daily image, so as to realize the calibration of the MUSER image intensity. Applying this method to the actual observation data of MUSER, including different situations such as the quiet sun and solar radio bursts, the error of the daily calibration factor G_c is within 10% of its value, and the obtained bright temperature of the quiet sun has a high correlation with the result obtained by other people. These indicate the feasibility and effectiveness of this method.