7mm Bandpass Spectrum - IFs not aligning
Posted: Fri Nov 03, 2017 1:19 pm
I am reducing some recent data at 33 and 35GHz I observed in a H168 array.
As 1934-638 is not bright enough at these frequencies, I used a different source to perform the bandpass calibration step with. On this particular day this source was 0420-014.
As 0420-014 does not have a spectral model built into miriad, mfcal assumes a flat spectral shape when solving for the bandpass solution - see the '0420-014_mfcalgpcal.png' file. Following the process outlined on the ATCA User Guide, the true intrinsic shape of 0420-014 can be estimated and used as part of the bandpass calibration by:
(1) - Copying the initial bandpass/gain solutions across both IFs from 0420-014 to 1934-638
(2) - gpcal 1934-638 across both IFs
(3) - gpboot 0420-014 with 1934-638
(4) - use uvfmeas on 0420-014 to constrain a spectral index compatible with mfcal flux keyword
In the past this has worked well for me, where after step (3) I get the two IFs following a consistent slope. With these data though I am getting something that I am having trouble making much sense of. If you refer to the '0420_mismatch.png' file I attach, you can see that the two IFs are not exactly being consistent with one another.
An oversight when observing, I had the pointing mode set to 'point' and not 'dwell' in the schedule file for both 0420-014 and 1934-638. Hence, when tracking these sources all data were being flagged. I can get around this in miriad by using atlod with the caldata keyword, and subsequently manually flagging the pointing update data. I don't think is related to what I am seeing in the attached plot, but thought I'd share just to be sure.
I am wondering if anyone has any suggestions on what to do? Is this is as good as it is going to get, or is there something else that I should be doing?
As 1934-638 is not bright enough at these frequencies, I used a different source to perform the bandpass calibration step with. On this particular day this source was 0420-014.
As 0420-014 does not have a spectral model built into miriad, mfcal assumes a flat spectral shape when solving for the bandpass solution - see the '0420-014_mfcalgpcal.png' file. Following the process outlined on the ATCA User Guide, the true intrinsic shape of 0420-014 can be estimated and used as part of the bandpass calibration by:
(1) - Copying the initial bandpass/gain solutions across both IFs from 0420-014 to 1934-638
(2) - gpcal 1934-638 across both IFs
(3) - gpboot 0420-014 with 1934-638
(4) - use uvfmeas on 0420-014 to constrain a spectral index compatible with mfcal flux keyword
In the past this has worked well for me, where after step (3) I get the two IFs following a consistent slope. With these data though I am getting something that I am having trouble making much sense of. If you refer to the '0420_mismatch.png' file I attach, you can see that the two IFs are not exactly being consistent with one another.
An oversight when observing, I had the pointing mode set to 'point' and not 'dwell' in the schedule file for both 0420-014 and 1934-638. Hence, when tracking these sources all data were being flagged. I can get around this in miriad by using atlod with the caldata keyword, and subsequently manually flagging the pointing update data. I don't think is related to what I am seeing in the attached plot, but thought I'd share just to be sure.
I am wondering if anyone has any suggestions on what to do? Is this is as good as it is going to get, or is there something else that I should be doing?