| Description: | These plots show the pulse profile of pulsar B1133+16 obtained from three consecutive 20-minute LBA observations done on November 5th, 2010 by Jason Hessels and Arno Schoenmakers during the recent Pulsar Busy Week. During these measurements, the station calibration table was alternatingly used and ignored. This result shows that the station calibration tables made by Stefan Wijnholds provide, on average, more than a factor two sensitivity improvement per station. In fact the observed, cumulative signal-to-noise ratio of the pulsar is roughly 3 times better when calibration is used. This also shows that the new Beam Server, developed by Ruud Overeem, correctly applies the calibration factors in the beamforming process.
The station calibration tables for the LBA station array are extracted from a 24-hour calibration run to reduce the impact of ionospheric turbulence and RFI present in individual observations. The calibration results as well as 48-hour stability measurements indicate that the LOFAR hardware is sufficiently stable to allow a fixed calibration table to reduce the signal losses in the station beamformer from up to 40% to order 0.1%. Further improvement will require an even better understanding of the minutiae of the LOFAR system as well as further improvement of the data model used for calibration. |
