明安图射电频谱日像仪图像的强度定标方法

Intensity Calibration for the Mingantu Spectral Radioheliograph Images

明安图射电频谱日像仪(Mingantu Spectral Radioheliograph,MUSER)能够在0.4–15 GHz超宽频带内实现高时间、高空间、高频率分辨率的太阳射电成像.而射电亮温度是描述太阳物理过程的一个重要的参数,在研究不同射电辐射机制、太阳磁场以及太阳爆发过程中非热粒子加速等问题上有着非常重要的作用,因此必须对MUSER观测的图像进行亮温度定标.将介绍一种适用于射电日像仪图像强度定标的方法.太阳射电图像中包含着太阳圆盘的结构信息,利用射电日像仪短基线的可视度函数拟合第一类贝塞尔函数,可以得到图像中宁静太阳圆盘的射电半径和强度,再利用瑞利-金斯定律和每天的太阳射电流量可以计算得到每天图像的定标因子Gc,从而实现对MUSER图像强度的定标.将该方法应用到MUSER的实际观测数据中,包括宁静太阳和有太阳射电爆发等不同的情况,Gc的误差基本不超过10%,得到的宁静太阳亮温度与其他宁静太阳的结果具有较高的相关性,表明了此方法的可行性和有效性.

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 magneticfield 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 byfitting thefirst kind of Bessel function with the visibilities of short baselines of the radioheliograph.Then,the Rayleigh-Jeans law and the daily solar radioflux can be used to calculate the calibration factor Gc 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 Gc 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.