| Description: | The enigmatic radio galaxy Cygnus A is one of the brightest sources in the LOFAR sky. It is one of the objects that makes up the `A-team'; a small number of very strong radio sources that can potentially contaminate every LOFAR observation. To reduce the effect of these sources on our science observations, we must image each member of the A-team over the LOFAR observing band and remove them from the uv-data of our target fields. The large luminosity and small distance to Cygnus A also makes this source interesting for studying the properties of AGN, for example, to investigate feedback processes. Its complex double structure also makes for an excellent commissioning target to test the LOFAR system.
Cygnus A was observed for 6 hours in the LOFAR high band (210--240 MHz) on 2010 May 30. The array consisted of 12 core stations, 4 remote stations and 1 international station. However, after data editing and calibration (within CASA), only 8 core stations and 4 remote stations were used for imaging. A single sub-band (0.2 MHz bandwidth) image of Cygnus A at ~239 MHz is shown. This image is uniformly weighted and has an elliptical restoring beam with a FWHM of 9 x 5 arcsec at a position angle of 79 degrees. The rms noise in the image is 0.3 Jy / beam, giving a dynamic range of about 1000. The limiting factor in the dynamic range is the cleaning. The image shows the expected double lobe structure that has been observed from Cygnus A at other frequencies (for example, note the similarity to the 330 MHz image shown by Kassim et al 1993). We also see complex structure within the lobes and in the space between them. The next step is to make an image with the full bandwidth and investigate the broad-band spectral properties of the features we observe. |
