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Description
The Boolardy Engineering Test Array (BETA) is a 6 x 12m-dish interferometer and the prototype of the Australian Square Kilometre Array Pathfinder (ASKAP), equipped with the first generation of ASKAP's phased array feed (PAF) receivers. These facilitate rapid wide-area imaging via the deployment of simultaneous multiple beams within an ~30 deg<sup>2</sup> field of view. By cycling the array through 12 interleaved pointing positions and using nine digitally formed beams, the authors have effectively mimicked a traditional 1 hours x 108 pointing survey, covering ~150 deg<sup>2</sup> over 711-1015 MHz in just 12 hours of observing time. Three such observations were executed over the course of a week. The authors verified the full bandwidth continuum imaging performance and stability of the system via self-consistency checks and comparisons to existing radio data. The combined three epoch image has arcminute resolution and a 1-sigma thermal noise level of 375 µJy/beam, although the effective noise is a factor of ~3 higher due to residual sidelobe confusion. From this, the authors have derived a catalog of 3,722 discrete radio components, using the 35% fractional bandwidth to measure in-band spectral indices for 1037 of them. A search for transient events reveals one significantly variable source within the survey area. The survey covers approximately two-thirds of the Spitzer South Pole Telescope (SPT) Deep Field. This pilot project demonstrates the viability and potential of using PAFs to rapidly and accurately survey the sky at radio wavelengths. The target field was observed with BETA on three separate occasions as part of the commissioning and verification of the instrument. The telescope delivers 304 MHz of instantaneous bandwidth and for these observations the sky frequency range was 711-1015 MHz, corresponding to a fractional bandwidth of 35%. The data were captured with a frequency resolution of 18.5 kHz, using 16,416 frequency channels across the band. The PYBDSM source finder was used to extract a component catalog from the deep mosaic image formed from a combination of all epochs and sub-bands. Components were fit to islands of emission that had a peak brightness of >5 sigma and an island boundary threshold of >3 sigma, where sigma is the local estimate of the background noise level. Component spectral indices were assigned by matching positions at which spectral indices were successfully fit (Section 4.5 of the reference paper). Following the excision of some spurious detections at the noisy edge of the mosaic, the final catalog contains 3,722 components, 1,037 of which have in-band spectral index measurements. This table was created by the HEASARC in March 2017 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/MNRAS/457/4160">CDS Catalog J/MNRAS/457/4160</a> file table3.dat, the list of source components found in the ASKAP-BETA Survey covering two-thirds of the Spitzer SPT Deep Field. This is a service provided by NASA HEASARC .
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