SARAS MEASUREMENT OF THE RADIO BACKGROUND AT LONG WAVELENGTHS
SARAS MEASUREMENT OF THE RADIO BACKGROUND AT LONG WAVELENGTHS
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长波长无线电背景的 SARAS 测量
DOI：
10.1088/0004-637x/801/2/138
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
A. Raghunathan
中科院分区：
文献类型：
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作者：
Nipanjana Patra;Nipanjana Patra;R. Subrahmanyan;S. Sethi;N. Shankar;A. Raghunathan
SARAS是一种与频率无关的天线相连的相关光谱仪，用于精确测量长波长的无线电背景。设计、校准和观察策略允许解决内部添加剂对辐射计响应的贡献，从而将这些污染物从天线温度中分离出来。我们在这里展示了SARAS对无线电天空频谱的宽带测量，它提供了110和175 MHz之间绝对亮度和光谱指数的精确测量。测量绝对天空亮度的精度受到1.2%等系统误差的限制；校正误差和天空和系统模型参数联合估计误差相对较小。我们使用精密宽带偶极子天线对天空亮度进行广角测量，为Landecker和Wielebinski的150 MHz全天图提供改进的绝对校准：减去21.4 K的偏移量并按1.05因子缩放，将总偏移误差从50 K减小到8 K，缩放误差从5%减小到0.8%。在110 ~ 175 MHz波段，SARAS测量的温度光谱指数在−2.3 ~−2.45之间，表明朝向银河系凸起的区域具有相对平坦的指数。
SARAS is a correlation spectrometer connected to a frequency independent antenna that is purpose-designed for precision measurements of the radio background at long wavelengths. The design, calibration, and observing strategies admit solutions for the internal additive contributions to the radiometer response, and hence a separation of these contaminants from the antenna temperature. We present here a wideband measurement of the radio sky spectrum by SARAS that provides an accurate measurement of the absolute brightness and spectral index between 110 and 175 MHz. Accuracy in the measurement of absolute sky brightness is limited by systematic errors of magnitude 1.2%; errors in calibration and in the joint estimation of sky and system model parameters are relatively smaller. We use this wide-angle measurement of the sky brightness using the precision wide-band dipole antenna to provide an improved absolute calibration for the 150 MHz all-sky map of Landecker and Wielebinski: subtracting an offset of 21.4 K and scaling by a factor of 1.05 will reduce the overall offset error to 8 K (from 50 K) and scale error to 0.8% (from 5%). The SARAS measurement of the temperature spectral index is in the range −2.3 to −2.45 in the 110–175 MHz band and indicates that the region toward the Galactic bulge has a relatively flatter index.