Daily Image

30-11-2007
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LOFAR Snapshot Movie

Submitter: Sarod Yatawatta
Description: This is an animation of how a LOFAR low band (LBA) dipole sees the sky during a 24 hour period. The left panel shows the average beam gain for a one hour time interval. The right panel shows the image made during the same time interval using 16 LBA dipoles. Both images are centred at the north celestial pole (NCP). However, the dipoles have maximum gain towards the zenith, which moves relative to the NCP as seen on the left panel. The purple area on the left panel is below the horizon and thus have zero beam gain.

The two strongest sources (Cas A, Cyg A) have been removed from the image on the right panel. The subtraction of Cyg A is least accurate when it 'kisses' the horizon.

The remaining sources are stationary in the sky, of course, but their Point-Spread Function (PSF) changes. The clearest example is Tycho, above the image centre. We also see several sources (Taurus A, Virgo A, Sun) disappear (and reapper) as they go below (and above) the horizon.

Note the moving feature in the fourth ring. This is an RFI source, which is stationary w.r.t. the station beam, but moves across the sky. It is probably on the horizon, but it appears to have an elevation of 50-60 degrees.


Copyright: ASTRON
 
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