L2TS sky image of Cas A

© ASTRON

To test the entire LOFAR 2.0 station signal chain from celestial source to station beam, a sky image of Cassiopeia A was made using the LOFAR 2.0 Test Station (L2TS). The L2TS is a limited LOFAR2 setup at LOFAR station CS001, working with a small number of receivers and processing hardware (Uniboards) only. Eight low-band antennes (LBAs) were chosen, laying approximately on a 75m diameter circle, to give an angular resolution of about 4 degrees at zenith at 62 MHz. The station was configured to have 484 station beams at 62 MHz in a fine grid in the direction of Cassiopeia A, to give the two images as shown above (one for each polarisation). Each pixel in the image shows the power in one station beam integrated for 1s. The stations beams tracked Cassiopeia A for 24 hours (see the rightmost picture), producing the movie. Notice how the beam shape elongates as the beam approaches the horizon towards the North.   Due to the sparse antenna configuration, the station beams has as a lot of sidelobes which pick up signal in other directions and distorts the image of Cassiopeia A (especially in the north to east directions). The test also demonstrate that LOFAR 2.0 stations can re-use the LOFAR1 coax cable delays and subband gain and phase calibration tables.