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A database of phase calibration sources and their radio spectra for the Giant Metrewave Radio Telescope

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Abstract

We are pursuing a project to build a database of phase calibration sources suitable for Giant Metrewave Radio Telescope (GMRT). Here we present the first release of 45 low frequency calibration sources at 235 MHz and 610 MHz. These calibration sources are broadly divided into quasars, radio galaxies and unidentified sources. We provide their flux densities, models for calibration sources, (u,v) plots, final deconvolved restored maps and clean-component lists/files for use in the Astronomical Image Processing System (aips) and the Common Astronomy Software Applications (casa). We also assign a quality factor to each of the calibration sources. These data products are made available online through the GMRT observatory website. In addition we find that (i) these 45 low frequency calibration sources are uniformly distributed in the sky and future efforts to increase the size of the database should populate the sky further, (ii) spectra of these calibration sources are about equally divided between straight, curved and complex shapes, (iii) quasars tend to exhibit flatter radio spectra as compared to the radio galaxies or the unidentified sources, (iv) quasars are also known to be radio variable and hence possibly show complex spectra more frequently, and (v) radio galaxies tend to have steeper spectra, which are possibly due to the large redshifts of distant galaxies causing the shift of spectrum to lower frequencies.

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Notes

  1. GMRT upgrade: A major upgrade of several sub-systems of the GMRT has been initiated, which will result in significant changes in almost all aspects of the GMRT with the aim of significantly improving its capability and sensitivity. Key features of the upgrade are near seamless frequency coverage from 125 MHz to 1450 MHz and instantaneous bandwidth of 400 MHz along with several matching improvements in computing, receivers, servo and mechanical systems, electrical, and civil structures. The upgrade is nearing completion and the first phase of the upgraded system has already been released to the astronomical community.

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Acknowledgments

We would like to thank the anonymous referees for their useful suggestions and criticisms which helped improve the clarity of the paper. We thank M.J. Hardcastle for a careful reading of this manuscript. We thank the staff of the GMRT that made these observations possible. GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research. The VLA is operated by the US National Radio Astronomy Observatory which is operated by Associated Universities, Inc., under cooperative agreement with the National Science Foundation. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

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  1. National Centre for Radio Astrophysics (NCRA–TIFR), Post Box 3, Ganeshkhind P.O., Pune, 411007, India

    Dharam V. Lal, Shilpa S. Dubal & Sachin S. Sherkar

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  1. Dharam V. Lal
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  2. Shilpa S. Dubal
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  3. Sachin S. Sherkar
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Correspondence to Dharam V. Lal.

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Lal, D.V., Dubal, S.S. & Sherkar, S.S. A database of phase calibration sources and their radio spectra for the Giant Metrewave Radio Telescope. Exp Astron 42, 319–341 (2016). https://doi.org/10.1007/s10686-016-9512-3

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