March 13, 2021 Dataset Open Access

Cassiopeia A and Cygnus A interferometric observation with Allen Telescope Array

Boven, Paul; Estévez, Daniel; Farah, Wael

This dataset corresponds to an interferometric observation that was done by the GNU Radio community at Allen Telescope Array. The observation was mainly intended as a test/proof of concept of the feasibility of using GNU Radio and two USRP N32x SDR transceivers for interferometric imaging at ATA.

Cassiopeia A, Cygnus A and some compact sources (3C84, 3C286, 3C147, 3C345, J2202+422) were observed over a period of 18 hours on 2021-02-21 using 11 antennas from the array. The observation frequency was 4.9 GHz. Two USRP N32x were connected to the 512 MHz IF output of the RFCB LO d. Each USRP digitized the two polarizations of one antenna. This setup requires baselines to be iterated one at a time for interferometric observing. The observing bandwidth was 40.96 MHz.

An FX correlator with 2048 channels and an integration time of 0.1 seconds was implemented in GNU Radio. The drifting correlations were then phased to each source in post processing. CASA was used for calibration and imaging.

This post contains the following files:

• ATA-20210221-uvfits.tar contains the phased correlator output in UVFITS format, reduced to a rate of 1 second and 64 channels
• CASA-flags-masks.tar contains flags and CLEAN masks to be used with CASA and this script to reproduce the whole CASA pipeline starting from the UVFITS files
• CASA-caltables.tar contains the calibration tables obtained in CASA
• ATA-20210221-CasA.tar and ATA-20210221-CygA.tar contain the calibrated and reduced visibility data for Cassiopeia A and Cygnus A respectively, as well as the multi-scale CLEAN images obtained with CASA.

The raw FX correlator output is not included in this dataset because of size constraints.

More information about this observation and the processing pipeline can be found in the post "Interferometric Imaging with Allen Telescope Array" by the second author.