  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.
