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.

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The National Radio Astronomy Observatory and Green Bank Observatory are facilities of the U.S. National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Founded in 1956, the NRAO provides state-of-the-art radio telescope facilities for use by the international scientific community. NRAO telescopes are open to all astronomers regardless of institutional or national affiliation. Observing time on NRAO telescopes is available on a competitive basis to qualified scientists after evaluation of research proposals on the basis of scientific merit, the capability of the instruments to do the work, and the availability of the telescope during the requested time. NRAO also provides both formal and informal programs in education and public outreach for teachers, students, the general public, and the media.

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