When a strong calibrator is available it can be used using mfcal to correct the passband of your other sources (not just the target source, but also for example the phase and amplitude calibrator). Choose a small interval to construct the antenna based passband, and inspect the solutions with gpplt:
% mfcal vis=pbcal.mir interval=0.5 refant=9 % gpplt vis=pbcal.mir device=/xs options=bandpass yaxis=amp nxy=5,3 % gpplt vis=pbcal.mir device=/xs options=bandpass yaxis=phase nxy=5,3 % gpplt vis=pbcal.mir device=/xs options=gains
The passband gains can then be copied to your other sources, for subsequent calibration and/or mapping:
% gpcopy vis=pbcal.mir out=phasecal.mir options=nocal % uvcat vis=phasecal.mir out=phasecal_pb.mir
and then you can proceed calibrating the now passband corrected data for the phase calibrator. The same applies to any other (e.g. your science source) sources that need to be further calibrated.