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MeerKAT currently uses J1331+3030 (3C 286) as the preferred fundamental polarisation reference calibrator. However, due to its high northern declination, it is only visible to the telescope for ~5 hours above 20° elevation. The other commonly used calibrator is 3C 138. The properties of these calibrators are summarised in Table 1 below. However, we have been finding anomalous results for 3C 138, and there are some indications that the model for 3C 286 may not be accurate in the UHF band. 3C 286 is seen to rapidly depolarise below 1 GHz, with an intrinsic rotation measure that gradually increases to about 0.12 rad/m² (Hugo & Perley, 2024). Work is underway to make new measurements. In the meantime, users are requested to contact the helpdesk if they are concerned about their results. Note that despite uncertainties in calibrating the polarisation angle, it is still possible to obtain significant scientific results, e.g. Cotton et al. (2020).

Table 1: Properties of suggested polarisation calibrators at the MeerKAT L-band.

While we have identified 10 new polarised sources with low (< 10 rad/m²) rotation measure, we have only recently started a monitoring programme to determine their long-term stability. Users interested in using one of these potential calibrators should contact the helpdesk when setting up their observation for scheduling.

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