Check the fluxes of the calibration sources
Last updated: sep17
The plots below show the gain
all calibration sources plotted versus frequency. There are
per page. Each plot holds 5 sources. Sources are distinguished by
and symbol. The large variation for some sources (especially
frequencies) is caused by collimation errors (and the
fits inability to fit it).
How the fluxes were checked:
The telescope gain curves are made using a set of
sources selected by chris salter. The fluxes of these sources are
in different catalogs at discrete frequencies. Chris has fit
fluxes to the functional form:
y= a0 + a1*x + a2*exp(-x)
To compute a gain curve for a receiver we do a
of calibration scans using some of the calibration sources and then
the gain as a function of azimuth and zenith angle.
To check that the source fluxes used are ok we
We do this for each calibration scan taken for all receivers.
Some things to keep in mind are:
- When taking the ratio we always use the gain curve that was
that epoch . The gain curves have changed over time do to
- A gain curve is made and then not changed until
a new gain curve (new receiver, telescope alignment, etc.). We
doing calibration scans to check things out. So there are many
scans that were not used in creating a gain curve.
- A point whose ratio is an outlier could be caused by:
- The source flux at that frequency is inaccurate
- The measurement may have had some problems (e.g.. we were
and it was cloudy or raining).
- The gain curve fit is not doing a good job of fitting the az