Daily Image
29-08-2007
Darts anyone?
| Submitter: | Sarod Yatawatta |
| Description: | This is (again) an improved version of the LOFAR/CS1/LBA image presented as daily image on 10-08-2007. Firstly, more data have been added from two new observations (now totalling 36 subbands of 156 kHz each, and about 96 hours of observation time). Secondly, the image has been corrected for the average attenuation due to the dipole beam over 24 hours. The correction is different for each point of the sky, since each point plies a different path through the dipole beam(s). The latter are pointed towards the zenith, and are assumed to be identical for all 16 dipoles. After correction, the relative fluxes of the 3C and 4C sources (which are well known) have the expected values, to within a few percent. This suggests that the calculated beamshape is correct to that accuracy, even at low elevations. The left panel shows the full hemisphere centred at the north celestical pole (NCP). On the right side is a zoomed-in view of the area around the NCP. The sources at the perimeter of the image are attenuated more by the beam, as compared to sources at the centre. Hence, after correction, the perimeter of the image appears more noisy. The correction does not change the local signal-to-noise ratio, of course. As usual, the two brightest sources (Cas A and Cygnus A) have been subtracted. The brightest remaining sources are Tycho (top centre), Taurus A (right) and Virgo A (bottom). |
| Copyright: | ASTRON/LOFAR |
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