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Containerized Automated Radio Astronomy Calibration (CARACal) pipeline
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Allow use of 3C286/J1331+3030 as primary calibrator #1364

Open ktrehaeven opened 3 years ago

ktrehaeven commented 3 years ago

Hi

My meerkat observation has J1331+3030 as both the primary and secondary calibrator. It is a polarised source so caracal doesn't handle it well as a primary calibrator. A1795_raw_vis1-obsinfo.txt

o-smirnov commented 2 years ago

@francescaLoi can you point out where the 3C286 model is set up in polcal?

francescaLoi commented 2 years ago

These are the properties of J1331+3030 as taken from Perley&Butler 2017 + updated polarization properties from NRAO web site (https://science.nrao.edu/facilities/vla/docs/manuals/obsguide/modes/pol, Table 7.2.7).

"3C138": {"standard": "manual",
                                       "fluxdensity": [8.33843],
                                       "spix": [-0.4981, -0.1552, -0.0102, 0.0223],
                                       "reffreq": "1.47GHz",
                                       "polindex": [0.078],
                                       "polangle": [-0.16755],
                                       "rotmeas": 0.0},

I suggest to check carefully the results since there are some differences between the resulting polarization properties and those constrained with the JVLA, i.e. the input model. I suspect that this could have an impact on the flux scale.

o-smirnov commented 2 years ago

Thanks, but that's 3C138 not 3C286?

francescaLoi commented 2 years ago

sorry, I copied the wrong part :) 

"3C286": {"standard": "manual",
                                       "fluxdensity": [14.7172],
                                       "spix": [-0.4507, -0.1798, 0.0357],
                                       "reffreq": "1.47GHz",
                                       "polindex": [0.098],
                                       "polangle": [0.575959],
                                       "rotmeas": 0.0},
ktrehaeven commented 8 months ago

Hi @bennahugo can you please advise whether 3C286 can be used as a primary calibrator in L band and if the above model is sufficient?

bennahugo commented 8 months ago

No it can't be used as primary calibrator without significantly biasing polarization measurements and introducing dynamic-range limiting gain errors on the two polarizations.

This is because the ionosphere is the main limiting driver of error on the fractional Q (which is seen in bandpass calibration for linear feeds).

Re the model: The above model is incorrect - the source intrinsically depolarises towards the low end of L-band, with a continuous changing RM below 1.1 GHz. However the model is there only to set an initial condition for crosshand phase calibration. No model is needed for crosshand phase calibration in the linear basis (it is sufficient just to run clearcal to set a unity model) (assuming no amplitude adjustments are made).

On Thu, Jan 11, 2024 at 12:59 PM ktrehaeven @.***> wrote:

Hi @bennahugo https://github.com/bennahugo can you please advise whether 3C286 can be used as a primary calibrator in L band and if the above model is sufficient?

— Reply to this email directly, view it on GitHub https://github.com/caracal-pipeline/caracal/issues/1364#issuecomment-1886873516, or unsubscribe https://github.com/notifications/unsubscribe-auth/AB4RE6VC4EUI5YYMFOVOBTLYN7AXZAVCNFSM5C3FM672U5DIOJSWCZC7NNSXTN2JONZXKZKDN5WW2ZLOOQ5TCOBYGY4DOMZVGE3A . You are receiving this because you were mentioned.Message ID: @.***>

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Benjamin Hugo

ktrehaeven commented 8 months ago

What about just for Stokes I imaging?

bennahugo commented 8 months ago

Not really -- the unmodelled Q introduces substantial time and frequency variable gain errors

On Thu, Jan 11, 2024 at 1:13 PM ktrehaeven @.***> wrote:

What about just for Stokes I imaging?

— Reply to this email directly, view it on GitHub https://github.com/caracal-pipeline/caracal/issues/1364#issuecomment-1886911397, or unsubscribe https://github.com/notifications/unsubscribe-auth/AB4RE6S7E36BYFC5NSH7JXDYN7CN3AVCNFSM5C3FM672U5DIOJSWCZC7NNSXTN2JONZXKZKDN5WW2ZLOOQ5TCOBYGY4TCMJTHE3Q . You are receiving this because you were mentioned.Message ID: @.***>

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Benjamin Hugo

bennahugo commented 8 months ago

Here is a better model for the EVPA and fraction. However, it still does not account for ionospheric errors induced in the forward modelling step: image image image