The VLITE Commensal Sky Survey (VCSS): A 340 MHz Companion to the VLA Sky Survey (VLASS)

The VLA Low Band Ionosphere and Transient Experiment (VLITE) is a commensal observing system on the Karl G. Jansky Very Large Array (VLA). A 64 MHz sub-band centered at 340 MHz is recorded and correlated for up to 18 antennas during nearly all regular VLA operations. Pipeline software calibrates and images the data within a few days after observation. Here we give a brief overview of the instrument and present the first epoch of the VLITE Commensal Sky Survey (VCSS). These data were taken simultaneously with the ongoing VLA Sky Survey (VLASS; url: https://science.nrao.edu/vlass/). VLITE breaks the continuous “on-the-fly” (OTF) VLASS scans into 2-second integrations and correlates these at a central “pointing” position every 1.5 degrees in right ascension. VLITE’s field of view is 2 degrees across, while the declination rows are spaced by only 7.25’, so there is a large overlap between each row and a high tolerance for failure. The data for each correlator position is imaged separately, corrected and weighted by an appropriately elongated primary beam model, and then combined in the image plane to create a mosaic of the sky. Catalogs of the sources in both the individual pointing images and the final mosaics are extracted using PyBDSF. In addition to providing a sky model at 340 MHz, VCSS complements VLASS by providing source spectral indices and intermediate resolution images for extended sources. The observations also provide a rich database for transient searches.