The XXL Survey: XXIX. GMRT 610 MHz continuum observations
  We present the 25 square-degree GMRT-XXL-N 610 MHz radio continuum survey,
conducted at 50~cm wavelength with the Giant Metrewave Radio Telescope (GMRT)
towards the XXL Northern field (XXL-N). We combined previously published
observations of the XMM-Large Scale Structure (XMM-LSS) field, located in the
central part of XXL-N, with newly conducted observations towards the remaining
XXL-N area, and imaged the combined data-set using the Source Peeling and
Atmospheric Modeling ({\sc SPAM}) pipeline. The final mosaic encompasses a
total area of $30.4$ square degrees, with ${\rm rms}<150~\mu$Jy/beam over 60\%
of the area. The ${\rm rms}$ achieved in the inner 9.6 square degree area,
enclosing the XMM-LSS field, is about $200~\mu$Jy/beam, while that over the
outer 12.66 square degree area (which excludes the noisy edges) is about
$45~\mu$Jy/beam. The resolution of the final mosaic is 6.5 arcsec. We present a
catalogue of 5\,434 sources detected at $\geq7\times {\rm rms}$. We verify, and
correct the reliability of, the catalog in terms of astrometry, flux, and false
detection rate. Making use of the (to date) deepest radio continuum survey over
a relatively large (2 square degree) field, complete at the flux levels probed
by the GMRT-XXL-N survey, we also assess the survey's incompleteness as a
function of flux density. The radio continuum sensitivity reached over a large
field with a wealth of multi-wavelength data available makes the GMRT-XXL-N 610
MHz survey an important asset for studying the physical properties,
environments and cosmic evolution of radio sources, in particular
radio-selected active galactic nuclei (AGN).
