Title:	SARAS measurement of the radio background at long wavelengths
Authors:	Patra, Nipanjana Subrahmanyan, Ravi Sethi, S.K. Udaya Shankar, N. Raghunathan, A.
Issue Date:	10-Mar-2015
Publisher:	IOP Sciences for The American Astronomical Society
Citation:	Astrophysical Journal, 2015, Vol. 801, p 138
Abstract:	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.
Description:	Restricted Access. An open-access version is available at arXiv.org (one of the alternative locations)
URI:	http://hdl.handle.net/2289/6254
ISSN:	0004-637X 1538-4357-(Online)
Alternative Location:	http://adsabs.harvard.edu/abs/2015ApJ...801..138P http://arxiv.org/abs/1412.7762 http://dx.doi.org/10.1088/0004-637X/801/2/138
Copyright:	2015, The American Astronomical Society.
Appears in Collections:	Research Papers (A&A)

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