The Parkes UWL system contains a noise source that can be switched during the observations. The amplitude of that noise source is highly stable and therefore can be used to convert any spectra (or pulsar pulse profiles) from the arbitrary units that are recorded in the raw data files into units of janskys of Kelvins. To date we have only measured the noise source in units of Kelvins once (in December 2020). The text file given here (Parkes UWL TCal Absorber Measurements) provides the measurement frequency (MHz) and the polarisation channel A and B noise source signal strength in Kelvins. This was determined by placing absorber under the receiver system and knowing the temperature of the absorber. (This process was described in the Hobbs et al paper.)

The system equivalent flux density (SEFD) of the noise source is measured every few weeks typically by the Parkes Pulsar Timing Array project. An observation is made pointing directly towards a source with known flux density (either 1934-638 or 0407-638) with the noise source switching. Further observations are carried out to the North and to the South of the known flux density calibrator. The ON-source and OFF-source observations are averaged and compared using the PSRCHIVE package fluxcal. The electronic and telescope gain is not assumed to be the same between the observations. As the flux density of the calibrator source is known it is then possible to use these observations to determine the system equivalent flux density of the noise source for both channels: Scal_AA and Scal_BB and also the system temperature Ssys_AA and Ssys_BB. The output files are in FITS format and we have also produced a text file. The FITS format file can be used by pulsar, spectral line and continuum astronomers in the PSRCHIVE (pulsars) and SDHDFproc (spectral line and continuum) packages. The text files have the following columns:

Column 1: channel number (the 0th channel is 704 MHz and the channel bandwidth is 1MHz)
Column 2: Ssys_AA (mJy)
Column 3: The uncertainty on the Ssys_AA (mJy) measurement
Column 4: Scal_AA (mJy)
Column 5: The uncertainty on the Scal_AA (mJy) measurement
Column 6: Ssys_BB (mJy)
Column 7: The uncertainty on the Ssys_BB (mJy) measurement
Column 8: Scal_BB (mJy)
Column 9: The uncertainty on the Scal_BB (mJy) measurement

In some cases the values cannot be determined because of strong RFI. In these cases the values are set to 0 (or left out)

Note that the total signal strength will be Scal_AA + Scal_BB (note no divide by 2 here).

The Ssys and Scal values are expected to be very stable. Pulsar astronomers typically use psrchive routines to average multiple flux calibration files together. This is currently not possible within sdhdfProc.