Commensal Surveys
There are two programs (VLITE and realfast) that take data whenever the VLA is observing, including during VLASS observations. These will result in surveys of the sky visible to the VLA that are commensal to the main VLASS survey.
The VLASS Commensal Sky Survey (VCSS)
The VLITE system will be used to conduct a commensal sky survey at 320-384 MHz. During the first epoch of survey observations, VLITE operated with 15 to 16 antennas. Automated data processing is underway, and initial mosaics have noise levels at roughly 3mJy/beam and resolutions of ∼12–25 arcseconds. Observations from the VLITE for VLASS Commensal Sky Survey (VCSS), when combined with the VLASS data, offer instantaneous spectra for point sources across the sky and can serve as an independent verification of any transient events, both slow transients from the regular processing, and fast transients identified by a separate pipeline. VCSS will be of great value for detecting diffuse objects (with scale sizes ∼> 30 arcsec) that will be resolved out by VLASS. VCSS is also more sensitive to ultra-steep spectrum (α < −1.8) sources than VLASS.
The US Naval Research Laboratory (NRL) archives all raw and calibrated VLITE data and provides it to the community for scientific use. VCSS data products will eventually be served from the NRAO archive. The continued expansion of the VLITE system into a full 27 antenna wideband commensal system with better sensitivity and resolution, called the LOw Band Observatory (LOBO), may occur during the VLASS program.
Some links to VCSS products:
realfast
The realfast system will operate simultaneously with VLASS observations during VLASS Epochs 2 and 3. It is designed to detect short duration transients in real time at 5-20 ms sampling. If a transient is detected, the data around the burst (~ 1 second) is recorded in the NRAO archive and is immediately available for download with no proprietary period.
