The Apertif imaging surveys will use the large field of view provided by the forty compound beams of Apertif to make radio continuum maps and neutral hydrogen data cubes over large regions of the sky. The imaging survey will observe in two tiers: a single shallow pointing over a larger region (called the “shallow northern sky survey”) and multiple pointings
Figure 2: Single pulse of PSR B1933+16 after dedispersion; (top) Timeseries of the pulse (bottom); Pulse intensity over the 300 MHz wide frequency band. Credits: L. Oostrum, L. Connor.
to build up sensitivity over a smaller area (called the “medium deep survey”). Gearing up for operations and survey observing early next year, we used the shakedown period to observe several pointings from the planned survey footprint for both survey tiers. These observations served multiple purposes: evaluating the observing and calibration strategy, stress-testing the current state of the reduction pipelines, and assessing the data quality. We learned a lot about our readiness for the surveys and had fun looking at lots of data, including producing the first full-field image with compound beams (Figure 3, produced entirely in the Apercal pipeline, developed for the purpose of automating Apertif imaging). The action points that came out of this shakedown period have been identified and added to the work list of the ARTS and Apertif development team. We plan to have tackled many of these by the time that we will have the next shakedown period, from 7 to 12 of December. This period will be the final rehearsal before Apertif goes operational.
Figure 3: A full-field continuum image produced automatically by the Apercal pipeline. This image is comprised of 37 of the final 40 compound beams. The full moon is shown for scale, representing the field of view of a single WSRT beam. Image credit: H. Dénes.
ASTRON News / Winter 2018