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First astronomical image with an FPA

Submitter: Tom Oosterloo (for the APERTIF team)
Description: When, in 2020, you marvel at the spectacular images SKA produces of all the HI over all the sky, remember that it all started with the image shown above, because what is shown here is the first image of an astronomical object at decimeter wavelengths made using dish equipped with a Focal Plane Array feed.

Last week (see the ASTRON JIVE Daily Image 28-02-2008), you will have seen that, using DIGESTIF on one of the WSRT dishes, overlapping compound beams using a dense Focal Plane Array (FPA) feed in a deep reflector have been constructed. The importance of this is that such a set a beams can be used to instantaneously image much larger regions of the sky than what is possible with current systems. It is the technology that will enable SKA to make the huge images at decimeter wavelengths that we hope to make.

What is shown here is the first image ever made using this technology and is a major milestone on the path of developing APERTIF. It is the result of a 6.7 sec DIGESTIF observation, using one WSRT dish, of the radio galaxy Cygnus A. Using the signals of 36 active elements, 121 optimised beams were constructed that allowed to instantaneously image an area of 2.5x2.5 degrees. This is 25 times larger than what is normally imaged by a WSRT dish (the circle in the figure).

PS: Cygnus A is much smaller than the WSRT beam, so here it appears as a point source. For comparsion, a VLA image of this source is shown. The two black dots in the centre of the DIGESTIF image indicate the size of Cygnus A
Copyright: ASTRON
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