2014/12/31 by Nipanjana Patra, Ravi Subrahmanyan, Shiv Sethi +2 · 57 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Brightness #Brightness temperature #Calibration #Galaxies: Formation, Evolution, Phenomena #Offset (computer science) #Radio Astronomy Observations and Technology #Sky #Sky brightness #Spectral index #Spectrometer #Wavelength #astro-ph.CO #astro-ph.IM
paper · pdf · doi:10.1088/0004-637x/801/2/138
published in The Astrophysical Journal 801(2), 138 (IOP Publishing) · 19 pages, 11 Figures, Accepted by ApJ
arxiv created 2015/01/15 · openalex publication_date 2015/03/12 · arxiv updated 2015/06/23 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
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.