Orange webs

© Ger de Bruyn

The WSRT, an East-West array, requires 12 hours to fill the uv-plane, using Earth rotation Synthesis, and make high qulity images. That is of course great if you want sensitivity as well. However, if you want to image a large field of view you have to resort to a technique called mozaicing, where the telescope scans a large number of positions in a short time. This produces nice (raw) images as shown above, where 2 out of 32 pointings are shown. The bright source is 3C295, about 65 Jy. The frequency is 324 MHz (but all frequencies from 310-381 MHz are recorded).

Each of the 32 grid positions, 1.3 degrees apart in RA and Dec, was visited for only 70 seconds with 10s to move on. The total area thus imaged is about 8 x 8 degrees. By combining up to 6 12 hour observations, where the starttimes are appropriately phased to yield a slghtly rotated 'spiderweb' this will produce a full uv-coverage.

The data will be used by the LOFAR EoR group to study diffuse Galactic foreground polarization towards 'EoR windows'. Similar data have been acquired on the fields surrounding 3C196, Elais-N1 and the NCP. Especially the latter mozaic required some creative scheduling by Hans van Someren Greve, due to limitations in the hour angle coverage of the WSRT. The data were taken on 27/28 April 2013 and will be reduced in NEWSTAR.