Software

Successful low frequency observations largely depend on the availability of new digital backends with numerous narrow-frequency channels to cope with man-made interference signals and to avoid depolarisation by Faraday rotation across the observing band. Multi-channel polarisation data (spectro-polarimetry) are used for the technique of Rotation Measure (RM) Synthesis. This method has first been successfully applied on data taken with the Westerbork Synthesis Radio Telescope (WSRT) and is presently further developed by the project Team. The multi-channel polarisation data are Fourier-transformed into a data cube With Faraday depth as the third coordinate. The Faraday depth (FD) is the integral of the plasma density times the regular field strength along the line of sight.

RM Synthesis with LOFAR takes advantage of the broad frequency coverage achievable with this new-technology telescope. LOFAR observations with large signal-to-noise in the higher band (120-240 MHz) will allow the detection of FD values with precisions below 1 rad/m².  This is sufficient to detect magnetic fields below 1 μG (0.1 nT), which was never possible before. In the LOFAR lowband range (30-80 MHz), the FD accuracy is formally even better, but the calibration is more difficult and the sensitivity of the antennae is lower than in the highband range.