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Initiator: ASTRON Netherlands Institute for Radio Astronomy

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This project was co-financed by the EU, the European Fund for Regional Development and the Northern Netherlands Provinces (SNN), and EZ/KOMPAS.

Cygnus A at 240 MHz with LOFAR

Copyright: John McKean (LOFAR/ASTRON)

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 science observations, each member of the A-team must be imaged over the LOFAR observing band and be removed them from the uv-data of the 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. 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). The complex structure within the lobes and in the space between them can also be seen. The next step is to make an image with the full bandwidth and investigate the broad-band spectral properties of the features observed.

ASTRON initiated LOFAR as a new and innovative effort to force a breakthrough in sensitivity for astronomical observations at radio-frequencies below 250 MHz. 
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