Daily Image
26-08-2010
CALIM 2010 Image of Cygnus A from the EVLA
| Submitter: | Sarod Yatawatta (RuG/ASTRON), Tony Willis (DRAO) and Rick Perley (NRAO) |
| Description: | Cygnus A is the brightest extragalactic radio source in the sky. It exhibits the standard double lobe radio structure with a bright central nucleus. It is always a challenge to get a really high dynamic range image of Cygnus A with any telescope. This week the CALIM 2010 conference is being held in Dwingeloo. We were motivated to generate the best possible image of Cygnus A that we could obtain from some recent EVLA 8.5 GHz data kindly provided by Rick Perley. Since the conference is about new image processing techniques, we decided to do this without employing any 'Classical' CLEAN based algorithms. The dataset had 256 channels of 2 MHz bandwidth each. The baseline lengths varied from 34 m to about 1 km. At this resolution the hotspots are almost unresolved and shapelets provided an efficient way of processing the data. Moreover, high level of intrinsic polarization required usage of a measurement equation with full Jones matrices containing off axis terms. The first three frames in the above animation exhibit the fully calibrated Stokes I,Q and U images. The final image shows about twice the field of view of the previous three images and shows the residual errors. The large scale residuals we interpret as possible contamination by the galactic foreground, which we cannot properly model because of the lack of spacings less than 34 m (approximately 1000 wavelengths). The fine scale spokes emanating from the central area are probably due to tropospheric fluctuations at very small time scales (less than 5 seconds). The residual errors are at about the 2.5 mJy level and the peak flux is about 34 Jy, giving us a dynamic range over 13,000. |
| Copyright: | ASTRON/DRAO/NRAO |
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