Strange problem in 1934-638

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saracmbr
Posts: 38
Joined: Fri Jan 20, 2012 3:40 pm

Strange problem in 1934-638

Post by saracmbr »

Hello every one,
I'm currently calibrating my first calibrator which is in CABB mode in 16cm. After running mfcal and gpcal I noticed that the time-phase diagram is showing strange pattern.
Also the real-imag diagram for stokes I is odd. The amplitude is steep which I think it should not be like this.
I looked at the raw data and it is the same.
Dose anyone know what is the resson for this problem and how I can correct for that?
Any help is deeply appreciated.

Thanks,

Sara
Attachments
real-imag.jpg
real-imag.jpg (40.21 KiB) Viewed 66612 times
Red Hat Enterprise Linux 5 (3)-2012-01-20-14-30-45.png
Red Hat Enterprise Linux 5 (3)-2012-01-20-14-30-45.png (84.98 KiB) Viewed 66612 times
The time-phase for one baseline
The time-phase for one baseline
Red Hat Enterprise Linux 5 (3)-2012-01-19-15-53-35.png (100.99 KiB) Viewed 66612 times
ste616
Site Admin
Posts: 220
Joined: Thu Feb 04, 2010 3:27 pm
Location: Paul Wild Observatory Narrabri NSW

Re: Strange problem in 1934-638

Post by ste616 »

Hi Sara,

Actually, the amplitude is supposed to be very steep. The amplitude of 1934-638 changes from a peak of about 15 Jy at 1.2 GHz down to about 9 Jy at 3.1 GHz. This is because it is a gigahertz-peaked spectrum (GPS) source (perhaps the archetypal GPS!). You can look at the spectral shape of 1934-638 using the Miriad task calplot.

From your plots, your reduction looks fine, although the phase seems to have a jump (from your third image) at a UTC time of 01:41 - it looks like a pcal was done at that time. You should flag all the data before the pcal and redo your calibration steps.

And let us know if you run into further trouble!
cheers
Jamie Stevens
ATCA Senior System Scientist
saracmbr
Posts: 38
Joined: Fri Jan 20, 2012 3:40 pm

Re: Strange problem in 1934-638

Post by saracmbr »

Hi Jamie,

I made it right by working on the spectrum. As my bandpass and flux calibrator are 1934-638, after GPcopy the bandpass to my secondary calibrator and running gpboot, Do I need to run mfboot on my 1934 and secondary calibrator as well ?

to calibrate my source do I just need to gpcopy calibration tables from my secondary tables into my source? In this case dose my source have a good bandpass shape ?

Many Thanks,

Sara
ste616
Site Admin
Posts: 220
Joined: Thu Feb 04, 2010 3:27 pm
Location: Paul Wild Observatory Narrabri NSW

Re: Strange problem in 1934-638

Post by ste616 »

Hi Sara,

When you solve for the bandpass using 1934-638, the bandpass will have the correct shape and amplitude. So you won't need to use mfboot to correct the bandpass shape. You may find though that mfboot will more accurately correct for amplitude than gpboot will, especially when the fractional bandwidth is large.

To calibrate your source, all you need to do is copy the solution from the phase calibrator after it has been calibrated against 1934-638. Then your source will have the correct bandpass shape and amplitude, and the right flux scale.
cheers
Jamie Stevens
ATCA Senior System Scientist
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