First science image from the CASA VLBI tools

Image may be NSFW.
Clik here to view.© Cristiana Spingola

On November 22-23 JIVE hosted a scaled down version of the first successful CASA VLBI workshop held in October. This smaller version catered to Dutch and local astronomers, taught them the ropes of processing VLBI data in CASA, and served to identify problems and missing functionality. A major milestone was reached: Cristiana Spingola (Kapteyn Institute, University of Groningen) produced the first image of a VLBI science target which was fully processed with the new CASA tools.

The image is of a gravitational lens with emission from four images of the lensed source (A through D) and from the lensing galaxy. The data were obtained with the VLBA at L-band, in a 12 hour run. The data was amplitude calibrated, phase calibrated with the new fringe fitter, imaged and cleaned fully in CASA.

The new CASA VLBI tools consist of a newly implemented fringe fitting task, upgrades of existing tasks to handle VLBI data, and a collection of scripts to ensure proper handling and import of the meta-data. The new fringefit task is based on the AIPS FRING task. The development of the CASA VLBI tools was started for the ERC BlackHoleCam project, with financial support from SKA-NL. It currently continues under the RadioNet RINGS JRA, with help from the CASA developers at NRAO, Socorro.

Further testing and development is still ongoing, e.g. prototyping a dispersive delay fit has started, and a next step will be the handling of discontinuous frequency bands. The current plan is to provide a beta-version of the VLBI tools in CASA 5.3.