15mm calibration question

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15mm calibration question

Postby tg1989 » Mon Feb 15, 2016 3:46 pm

Hi all,

I've got another calibration recipe regarding some 15mm data I got recently. The data, in a nut shell, visited a number of sources, each with their own phase calibrator. One of the sources had 1934 as its phase calibrator, and another, by dumb luck, had 0537-441 as its phase calibrator. I observed 0537-441 at the start of the run to calibrate the array and acquire a bandpass solution (observed for 10 minutes; other sources weren't up yet). I also got 10 minutes on 1934 at the end of the run to establish a good flux density scale.

Since mfcal assumes a flat spectrum when determining the bandpass solution for sources other then 1934, extra steps should be performed to ensure that the flux scaling is as good as it can be. Reading the ATCA user manual and the ATCA Calibration database page, the approach I've taken is: mfcal/gpcal 0537, gpcopy the bandpass solution to 1934, gpcal 1934, gpboot the calibration solutions back to 0537-441, use uvfmeas to obtain an mfcal flux model and re-calibrate (mfcal/gpcal) 0537-441. At this point 0537-441 should have both a correct bandpass calibration and have a bootstrapped flux density scale.

I was hoping to confirm that once the above procedure has been complete, I can gpcopy 0537-441 to other phase calibrators (since it has both the bandpass and flux scale) and proceed as normal. I'm worried I have misunderstood something along the way and the approach isn't correct, especially since both 0537 and 1934 have been used as phase calibrators. Attached is the complete reduction I've outlined above as well as the uvfmeas fits - before and after the user supplied flux model in mfcal.

Thanks,
Tim

Code: Select all
# CALIBRATE BANDPASS
#—————————————————
Task:   mfcal
  vis      = 0537-441.17000/
  line     = 
  stokes   = 
  edge     = 
  select   = 
  flux     = 
  refant   = 
  minants  = 
  interval = 0.1
  options  = 
  tol      =

Task:   mfcal
  vis      = 0537-441.21000/
  line     = 
  stokes   = 
  edge     = 
  select   = 
  flux     = 
  refant   = 
  minants  = 
  interval = 0.1
  options  = 
  tol      =
#—————————————————

# CALIBRATE GAINS
#—————————————————
Task:   gpcal
  vis      = 0537-441.17000/
  select   = 
  line     = 
  flux     = 
  spec     = 
  refant   = 
  minants  = 
  interval = 0.1
  nfbin    = 2
  tol      = 
  xyphase  = 
  options  = xyvary,qusolve

Task:   gpcal
  vis      = 0537-441.17000/
  select   = 
  line     = 
  flux     = 
  spec     = 
  refant   = 
  minants  = 
  interval = 0.1
  nfbin    = 2
  tol      = 
  xyphase  = 
  options  = xyvary,qusolve
#—————————————————

# COPY TO FLUX CALIBRATOR
#—————————————————
Task:   gpcopy
  vis      = 0537-441.17000/
  out      = 1934-638.17000/
  mode     = 
  options  =

Task:   gpcopy
  vis      = 0537-441.21000/
  out      = 1934-638.21000/
  mode     = 
  options  = 
#—————————————————

# CALIBRATE GAINS OF PRIMARY
#—————————————————
Task:   gpcal
  vis      = 1934-638.17000/
  select   = 
  line     = 
  flux     = 
  spec     = 
  refant   = 
  minants  = 
  interval = 0.1
  nfbin    = 2
  tol      = 
  xyphase  = 
  options  = xyvary,qusolve,nopol

Task:   gpcal
  vis      = 1934-638.21000/
  select   = 
  line     = 
  flux     = 
  spec     = 
  refant   = 
  minants  = 
  interval = 0.1
  nfbin    = 2
  tol      = 
  xyphase  = 
  options  = xyvary,qusolve,nopol
#—————————————————

# BOOTSTRAP FLUX
#—————————————————
Task:   gpboot
  vis      = 0537-441.21000/
  cal      = 1934-638.21000/
  select   = 
Task:   gpboot
  vis      = 0537-441.21000/
  cal      = 1934-638.21000/
  select   = 
#—————————————————

#—————————————————
bandpass-1.eps made here
MFCAL flux=3.8843, 17.0,-0.3042
#—————————————————

# CALIBRATE BANDPASS WITH MODEL
#—————————————————
Task:   mfcal
  vis      = 0537-441.17000/
  line     = 
  stokes   = 
  edge     = 
  select   = 
  flux     = 3.8843,17.0,-0.3042
  refant   = 
  minants  = 
  interval = 0.1
  options  = 
  tol      =
Task:   mfcal
  vis      = 0537-441.21000/
  line     = 
  stokes   = 
  edge     = 
  select   = 
  flux     = 3.8843,17.0,-0.3042
  refant   = 
  minants  = 
  interval = 0.1
  options  = 
  tol      =
#—————————————————

# REDO GAIN CALIBRATION
#—————————————————
Task:   gpcal
  vis      = 0537-441.17000/
  select   = 
  line     = 
  flux     = 
  spec     = 
  refant   = 
  minants  = 
  interval = 0.1
  nfbin    = 2
  tol      = 
  xyphase  = 
  options  = xyvary,qusolve
Task:   gpcal
  vis      = 0537-441.21000/
  select   = 
  line     = 
  flux     = 
  spec     = 
  refant   = 
  minants  = 
  interval = 0.1
  nfbin    = 2
  tol      = 
  xyphase  = 
  options  = xyvary,qusolve
#—————————————————

#—————————————————
bandpass-2.eps made here
#—————————————————
Attachments
bandpass-2-flipped.pdf
(73.63 KiB) Downloaded 329 times
bandpass-1-flipped.pdf
(73.04 KiB) Downloaded 324 times
tg1989
 
Posts: 17
Joined: Sun Dec 07, 2014 3:04 pm

Re: 15mm calibration question

Postby ste616 » Mon Feb 15, 2016 4:02 pm

Hi Tim,

It sounds like you've nailed the process exactly how I would have done it. Once you've done the uvfmeas and recalibration stage, 0537-441 becomes a flux density calibrator just like 1934-638 is.

Let us know how you go. If you run into trouble, there are some things in the process you may be able to change to fix it.
cheers
Jamie Stevens
ATCA Senior System Scientist
ste616
Site Admin
 
Posts: 217
Joined: Thu Feb 04, 2010 3:27 pm
Location: Paul Wild Observatory Narrabri NSW

Re: 15mm calibration question

Postby tg1989 » Mon Feb 15, 2016 4:34 pm

Thanks for replying so quickly!

ste616 wrote:It sounds like you've nailed the process exactly how I would have done it. Once you've done the uvfmeas and recalibration stage, 0537-441 becomes a flux density calibrator just like 1934-638 is.


Great! Just for clarity, in the case of 1934 as my phase calibrator I would still gpcopy the 'flux correct' 0534 to it and proceed as normal (ie. gpcal then gpcopy to science source)?

ste616 wrote:Let us know how you go. If you run into trouble, there are some things in the process you may be able to change to fix it.


Will do. One thought I had was to increase the number of nfbin's used throughout the reduction. Using 2 seems to work well, but I wonder if some of that difference in the bandpass-2-flipped image, especially at the higher end of each IF, could be corrected with a larger number of sub bands. Any thoughts, or not worth the effort?
tg1989
 
Posts: 17
Joined: Sun Dec 07, 2014 3:04 pm

Re: 15mm calibration question

Postby ste616 » Mon Feb 15, 2016 4:50 pm

Hi Tim,

tg1989 wrote:Great! Just for clarity, in the case of 1934 as my phase calibrator I would still gpcopy the 'flux correct' 0534 to it and proceed as normal (ie. gpcal then gpcopy to science source)?


Yes.

tg1989 wrote:Will do. One thought I had was to increase the number of nfbin's used throughout the reduction. Using 2 seems to work well, but I wonder if some of that difference in the bandpass-2-flipped image, especially at the higher end of each IF, could be corrected with a larger number of sub bands. Any thoughts, or not worth the effort?


I find that nfbin=2 gives very good calibration, but there is no harm in experimenting to see if something else works better.
cheers
Jamie Stevens
ATCA Senior System Scientist
ste616
Site Admin
 
Posts: 217
Joined: Thu Feb 04, 2010 3:27 pm
Location: Paul Wild Observatory Narrabri NSW

Re: 15mm calibration question

Postby tg1989 » Mon Feb 15, 2016 5:00 pm

Cool. Once again, thanks for the help and quick replies!
tg1989
 
Posts: 17
Joined: Sun Dec 07, 2014 3:04 pm


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