SIMBAD references

C-band Mueller matrices for the Green Bank Telescope are presented here which enable on-sky Stokes parameters for point sources at the beam center to be determined. Standard calibrators, 3C 138 and 3C 286, were observed using the Spider program to steer the telescope across a broad range of R.A. on both sides of the zenith transit. For this analysis, only the observations at the peak of the Spider pattern were used rather than the full sweep of the runs. Therefore, the results presented here only apply to point sources at the beam center. The Mueller matrices are shown to vary with frequency and with use of the Hi-Cal or Lo-Cal noise diodes, due to the relative calibration gain between the X and Y components of the feed. However, the relative calibration gain can be determined from observations of a source with known polarization. Correcting the data for the relative calibration gain prior to data analysis allows for use of a frequency-independent Mueller matrix. This generic Mueller matrix is shown to provide reliable C-band polarization measurements.