VLBI Observations
The VLA can participate in VLBI observations with the VLBA. This is possible by either using the VLA as a phased array (Y27) or using one of its dishes (single dish: Y1). We note that currently P-band cannot be phased. For more details see the VLBI at the VLA documentation. In phased array mode, the program TelCal derives the antenna-based delay and phase corrections needed for antenna phasing in real time. This correction is applied to the antenna signals before they are summed, requantized to 2-bits, and recorded in VDIF format on the Mark5C disk at the VLA site. The disk(s) are then transported to Socorro, NM and correlated on the DiFX correlator with other VLBI stations which participated in the observation.
Standard VLA data, i.e., correlations between VLA antennas, are also archived in the NRAO science data archive. By default, a maximum of 512 MHz dual polarization is phased/recorded and sent to the archive. This leaves a large portion of the possible VLA bandwidth unused (up to 2 or 8 GHz total depending on sampler choice). Increasing the bandwidth to the maximum that the VLA can provide has obvious benefits for most continuum observations. Pulsar gating can be performed commensally with the phased VLA, avoiding the need for extra single dish observations. Line VLBI observations that run through the WIDAR correlator currently produce each requested VLBI subband bandwidth divided into full polarization products with 64 frequency channels, regardless of the requested spectral resolution obtained in the VLBI correlation. By adding unused baseline boards to the VLBI-specified line subbands, a closer match in spectral resolution can be offered for the standalone VLA data. If you think your science could benefit from these capabilities, please review our documentation on VLBI at the VLA or contact the helpdesk for further guidance.
