Computing the L-narrow Gain


g(az,za) fit:

The fit is for 1415 MHz, and is in K/Jy. The zenith angle (za) and azimuth (az) are in degrees and the (za-15) terms are only used for za > 15 degrees.

Average Gain [(polA+polB)/2]:

gainavg(az,za,f=1415MHz) = 9.0855699 -0.13198736*za + 0.020340197*(za-15)2 -0.012610386*(za-15)3 +0.39268538*cos(az) -0.027570212*sin(az) -0.48670176*cos(2*az) -0.064635743*sin(2*az) +0.076154653*cos(3*az) + 0.090970115*sin(3*az)

gainavg(az,za,f=all) = 8.8121317 -0.12526847*za +0.034930436*(za-15)2 - 0.017510095*(za-15)3 +0.46118491*cos(az) -0.04814893*sin(az) -0.4657348*cos(2*az) -0.060191821*sin(2*az) +0.10344289*cos(3*az) +0.079684658*sin(3*az)

How good is the fit for calibrating data:

Errors in the gain measurement come from the measurement technique, the source fluxes, and the cal values used. The r.m.s. of the fit was 0.56 K/Jy (.56/9.3= 6%). This probably includes the errors in the source fluxes, but is also do to the undersampling of the dish. The data was taken with the lband narrow receiver. Be aware that if your data lies in an undersampled region of the dish this curve should be treated with suspicion!! This is particularly true if your obervations were taken at high zenith angle (za > 17)

A plot of the residuals (really |data-fit|) is below:

Fit for f=1415MHz:

Fit for all frequencies:

Converting the cals to Janskies:

A large uncertainty in the above measurement is the value of the cal in Kelvins. If the cals are stable over long periods of time, which it is supposed to be, then we can use the size of the cal itself as the temperature unit and bypass the uncertainty in the kelvins/cal.  The conversion is:  (K/Cal)/(gainK/Jy) = Jy/Cal. So take the measured calVal and divide it by the gain in K/Jy to get  Jy per cal.

Frequencies other than 1415 Mhz:

Although the `new' cal values were applied to the data, it still appears that there is an offset between the predicted and observed values, particularly at 1300MHz and 1500MHz. This can be seen in the plot below, where data for all four boards (1300MHz, 1375MHz, 1415MHz, and 1500MHz) is shown and an offest is visible for the same source at a given zenith angle. This offset, though, appears to be in the 5\% error range. Hopefully new cals values will be obtained soon which will eliminate these offsets.

The old (pre June 26, 2001) fit (the precursor to this one), which you SHOULD NOT USE can be obtained here

Last updated: Monday, 03-Dec-2001 14:50:04 AST