Wide-field broad-band radio imaging with phased array feeds: a pilot multi-epoch continuum survey with ASKAP-BETA

Abstract

The Boolardy Engineering Test Array is a 6 x 12 m dish interferometer and the\nprototype of the Australian Square Kilometre Array Pathfinder (ASKAP), equipped\nwith the first generation of ASKAP's phased array feed (PAF) receivers. These\nfacilitate rapid wide-area imaging via the deployment of simultaneous multiple\nbeams within a 30 square degree field of view. By cycling the array through 12\ninterleaved pointing positions and using 9 digitally formed beams we\neffectively mimic a traditional 1 hour x 108 pointing survey, covering 150\nsquare degrees over 711 - 1015 MHz in 12 hours of observing time. Three such\nobservations were executed over the course of a week. We verify the full\nbandwidth continuum imaging performance and stability of the system via\nself-consistency checks and comparisons to existing radio data. The combined\nthree epoch image has arcminute resolution and a 1-sigma thermal noise level of\n375 micro-Jy per beam, although the effective noise is a factor 3 higher due to\nresidual sidelobe confusion. From this we derive a catalogue of 3,722 discrete\nradio components, using the 35 percent fractional bandwidth to measure in-band\nspectral indices for 1,037 of them. A search for transient events reveals one\nsignificantly variable source within the survey area. The survey covers\napproximately two-thirds of the Spitzer South Pole Telescope Deep Field. This\npilot project demonstrates the viability and potential of using PAFs to rapidly\nand accurately survey the sky at radio wavelengths.\n