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Determining Gains and Bandpass Functions - MFCAL

As noted above, mfcal solves for antenna gains and bandpass function. It can also solve for the delay terms, but this is rarely useful. However it does assume an unpolarised calibrator and that the polarisation leakage terms are zero. If you have measured only the XX and YY correlations, you have to make these assumptions. However if you have measured all four polarisation products, then you can correct for these assumptions by running gpcal after mfcal.

We will now discuss some of the inputs to mfcal.

• vis: The input dataset - the dataset containing the primary calibrator in this case.
• line: The standard linetype parameter, used to select and average channels. See the discussion of this in Section 5.4. Assuming the old-correlator's 128 MHz / 33 channel continuum system, you will want to discard the first and last few channels, calibrating only the central 25 channels of so. Otherwise you will not normally want to perform any averaging.
• edge: This is an alternative way of indicating the channels to discard. When working with single IF datasets, it is probably easier to use the line parameter.
• interval: This gives one or two numbers, in minutes, being the maximum solution interval length, and maximum solution gap, in minutes. The latter can usually be allowed to default. The default maximum interval length is 5 minutes. During stable observing conditions (good phase stability) you should set the maximum solution length to no more than the calibrator scan time. Set it to a small value if phase stability is poor (e.g. 1 to 0.1 minutes). If you set it to a smaller value, however, the solution process becomes more sensitive to bad data - make sure you flag it well. Additionally you might run into program memory limitations, where it aborts due to ``buffer overflows'' or the like. However, it is generally advisable to set this as small as possible.
• select: Normal data-selection.
• refant: The reference antenna. Set this to the antenna which had the cleanest XY phase. The default is 3 (which may not be very appropriate). It should be noted also that the default antenna will not change from 3, even if antenna 3 is not present in the dataset.
• flux: This gives the flux density and spectral index of the calibrator.
• options: There are a few extra options, which are not of great use or interest.

  delay

  Note that old versions of mfcal attempted to solve for a delay by default. This is no longer the case. To solve for delays (which is strongly discouraged when calibrating a single IF band), you now have to explicitly use the delay option.

  interpolate

  The interpolate option may be useful if you cannot determine the bandpass for some completely flagged channels but still need an estimate of the bandpass function. With this option, the bandpass is spline fit (in real and imaginary) and evaluated for the flagged channels. Be careful if a substantial fraction of channels are bad - the algorithm is only implemented if less than 50% of the channels are flagged bad.

  oldflux

  If you are calibrated data that are to be combined or compared with ATCA data reduced before August 1994, you will generally want to use the `oldflux' option to select the pre-August 1994 ATCA flux scale. See Section 12.6 for more information.