Intro

      Crosses were done in jun22 after the s,x receiver was remounted on the telescope (following the  QRFH testing). This was to check the pointing and the telescope gain. CasA (3C461) and CygnusA( 3C405) were the main sources tracked.

     To check the telescope gain we needed the flux of these two sources. Perley & butler and Baars et al were used to compute the flux. We also needed  the source size to correct for an extended source.

    Chris salter's catalog has casA fwhm =5' while cygA was 96"/60" = 1.6 '.

When i used the correction: fwhmBm^2/(fwhmBm^2 + fwhmSrc^2)   the sefd for casA came out a lot lower than cygA (sefd page inp preparation).
To see what was going on:

• I used the 2d gauss fits to all of the crosses for cygA, casA and found the measured bmWidthRatios between the two sources.
  
• I then convolved 1 to 5 amin gaussians with a 10' beam and measured their fwhm.
• dividing these widths by the fwhm of casA (1.6amin  source convolved with 10' beam) i compared these ratios with the measured ratios.

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Setup

The setup was:

• xband was used.
  
• 7 freq bands of 172.032 MHz each was used.
• cfr of bands:
• 8223. 8363. 8505. 8647. 8789. 8931. 9073.
• 142 MHz between band centers
• total span 1022 MHz
  
• A  10sec cal on,off was fired at the start of each cross.
• 2 sources:
• 3C405 (cygA)  (crab)
  
• 3C461 (CasA) 5
  
• pointing:
• az, el strips.
• 1.2 deg each. 120 secs/strip,10 hz sampling. bm fwhm=10amin
  
• mock setup:
• 172.032 bw, 1024 channels , 166Khz/channel, 10Hz sampling
  
• pola,b recorded separately

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Processing the data

• idl was used for the processing.
• mascrossfind, mascrossinp, mascrossfit2d
• polA,B was added before fitting.
  
• The resulting 2d gaussfit  parameters were used to give
• Tsrc/Tsys, Tsys (degK)
  
• az,el pointing error
• sefd
• fwhm of beam
• Data was selected by:
• only using fits with  9' < bmwd<11'
• do a robust linear fit of bmWidth vs elevation for all freq bands, and sources.
• only use points with elevation > 20 deg.
  
• average the fits between elevation  40<= el <= 45 deg
• find the ratio of fwhm bm on casA and cygA
• convolve various source gaussians  with the 10 amin fwhm of the beam and then  fit gaussians to get the convolved widths.
  
• divide these widths by a 10amin beam convolved with a 1.6amin gaussian (sized of cygA)
• Find which of these approximates the measured beamwidth ratio of CasA/cygA.
  

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Plotting the results:

    The plots show the  measured, computed beamwidths (.ps) (.pdf)

• Page 1: measured beam widths for 3C405 (CygnusA).
  
• Page 2: measured beam widths for 3C461 (CasA).
• Top Frame: azimuth fwhm
• bottom frame: elevation fwhm
• Each color is the fit from a separate 172 Mhz band.
• The solid lines are the linear fits ( el >=20deg)
• the purple lines  (40-45 deg el) showed the part of the fits used to get the measured avg fwhm.
• Page 3:  averaged beam widths
• top: plot average beam widths vs  cfr of band
• black: azimuth width
• red: elevation width
• green: fwhm for a 10meter telescope using lambda/D =10. ..( i left out the 1.2 factor.)
• + are 3C405 fits
• * are 3C461 fits
• The azimuth is a bit larger than the el at all freq for  CasA. It may be a bit elliptical.
  
• Bottom: fwhm3C461/fwhm3C405
• Black is the average for the azimuth width ratio:  about 1.04
• red is the average of the elevation width ratio: about 1.02
• Averaging the 2, the fwhm bm on casA is about 3% larger than the fwhm bm on cygnusA
  
• page 4: bmWidth ratios assuming casA is 5Amin and cygA is 1.6 Amin
• top: gaussians for beam and sources:
• black: fwhm=10'  12meter beam
• red  :  fwhm for cygA: 1.6 amin
• green: fwhm for casA: 5Amin (from chris salters catalog).
• Bottom: the 12m beam after convolving with the source widths:
• black: 12m no convolution
• red: convolve with 1.6 amin: cygA
• green: convolve with 5amin : casA
• doing a gauss fit to the red and green lines, the fwhm ratios casA/cygA should be about 1.10
• Page 5: convolve   gaussians 1' to 5' to a 10' beam.
• top: gaussians of 1 to 5' in 1' steps were convolved with a 10' gaussian
• a 2d gaussfit was then done to get the convolved fwhm
• a 1.6 amin (red) was also convolved with a 10' gaussian (cygA width)
• bottom:Ratio of convolved gaussians with cyga results
• the x axis is the width of the guassian used for the convolution
• the y axis is the convolved gaussian divided by the cygA width (10amin beam with 1.6' source width)
• The red line is the measured ratio of casA/cygA beamwidths. (1.03)
• A width of 3Amin for casA matches the measured ratio of casA/cygA fwhm.

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SUMMARY:

• The ratio of the fwhm measured beams on CasA/Cyga = 1.03
• chris salters catatlog had 1.6' for cygA and 5' for Casa
• Assuming cygA was 1.6':
• casa fwhm of 3' matched the ratio of CasA/cygA measured beamwidths.
• using the extended source correction:   fwhmBm^/(fwhmBm^2 + fwhmSrc^)
• fwhmBm=10'
  
• flux correction of 5' source : .8
  
• flux correction of 3' source : .92
  
• the 5' correction was causing the gain for casA to be too large (or sefd too small).