View source for 3C286 Polarization

[[Category:ALMA]][[Category:Polarization]][[Category:Continuum]]
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== Data Reduction and Imaging Tutorials ==

This tutorial has been split into calibration and imaging pages: 

# <font size = 3>'''[[3C286_Band6Pol_Calibration | Calibration]]'''</font size>
#: This section of the tutorial steps you through inspection and calibration of the visibility (u-v) data. To complete this part, you will need the data in the 3C286_Band6_UncalibratedData directory.
# <font size = 3>'''[[3C286_Band6Pol_Imaging | Imaging]]'''</font size>
#: This part of the tutorial focuses on constructing images from the fully calibrated visibility data. If you wish to skip calibration and proceed directly to this part of the tutorial, you will need the fully-calibrated visibility data in the 3C286_Band6_CalibratedData directory.

For information on obtaining the latest version of CASA, see [https://casa.nrao.edu the CASA home page].

For help getting started with CASA, see [[Getting_Started_in_CASA]].

To learn how to extract the CASA commands into an executable python script, see [[Extracting_scripts_from_these_tutorials]].

Guide history for past CASA versions:
* Calibration: [[3C286_Band6Pol_Calibration_for_CASA_5.4|[5.4]]] [[3C286_Band6Pol_Calibration_for_CASA_5.1|[5.1]]] [[3C286_Band6Pol_Calibration_for_CASA_4.3|[4.3]]]
* Imaging: [[3C286_Band6Pol_Imaging_for_CASA_5.4|[5.4]]] [[3C286_Band6Pol_Imaging_for_CASA_5.1|[5.1]]] [[3C286_Band6Pol_Imaging_for_CASA_4.3|[4.3]]]

==Obtaining the Data==

Calibrated data is provided if you wish to skip the Calibration section and start with Imaging.

To download the most recent calibrated data and image products for this guide here:
* https://bulk.cv.nrao.edu/almadata/public/casaguides/3C286_Band6_6.6.1
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*: ''3C286_Band6_CalibratedData'' [~3 GB]
*:: The fully calibrated u-v data in CASA Measurement Set (MS) format, ready for imaging. 
*: ''3C286_Band6_ReferenceImages'' [~5 MB]
*:: The final total intensity and polarization images.

To download the raw data, click on the region closest to your location:
* [http://almascience.nrao.edu/almadata/sciver/3C286Band6 North America]
* [http://almascience.eso.org/almadata/sciver/3C286Band6 Europe]
* [http://almascience.nao.ac.jp/almadata/sciver/3C286Band6 East Asia]

Here you will find:
:: ''3C286_Band6_UncalibratedData'' [~6 GB]
::: The raw data files in ALMA Science Data Model (ASDM) format.
:: '''The calibrated data and products found with the raw data are for an older version of CASA.'''

==Science Target Overview==

[[File:3c286_14_48.png|400px|thumb|right| '''Figure 1''' Maps of 3C286 at 1.4 and 4.8 GHz. (Akujor & Garrington 1995)]]
[[File:VLA_3c286.png|300px|thumb|right| '''Figure 2''' 3C286 map at 8.4 GHz. The jet to the W of the core is highly polarized with E-vectors parallel to the jet axis at 8.4 GHz. (Akujor & Garrington 1995)]]

These SV observations have been taken with the aim of testing ALMA polarization capabilities at Band 6 (233 GHz, 1 mm). 

The target observed is 3C286: a bright, compact, steep-spectrum radio quasar at a redshift of 0.849 (e.g. [http://adsabs.harvard.edu/cgi-bin/bib_query?2010MNRAS.405.2302H Hewett & Wild et al. 2010]).
Radio imaging with the Very Large Array (VLA) at subarcsecond resolution has revealed an extended structure composed of three misaligned bright 
features. The linear polarization emission is dominated by the two brightest features (see Figure 1), and the electric vector position angle is oriented nearly parallel to the axis of the jet like structure between them ([http://adsabs.harvard.edu/abs/1995A%26AS..112..235A Akujor & Garringon 1995]).

This source has been widely used as calibrator for linear polarization observations at centimeter wavelengths because of its extremely stable polarization angle (33º at frequencies < 10 GHz).  At higher frequencies, however, the polarization angle slowly increases from 33º below 10 GHz to 36º at 45 GHz (VLA results from [http://adsabs.harvard.edu/abs/2013ApJS..206...16P Perley & Butler 2012]).  Recent results from IRAM, CARMA, and now ALMA are characterizing the polarization of 3C286 at the much higher frequencies of the millimeter regime.

Details of the ALMA results can be found in the Imaging portion of this guide at the end of the '''[[3C286_Band6Pol_Imaging#Image_visualization_and_analysis | Image Visualization and Analysis]]''' section, where we also compare the results with available measurements from IRAM and CARMA.

==ALMA Data Overview==

This CASA Guide shows the calibration and imaging steps for the ALMA Science Verification data 
in full polarization targeting the quasar 3C286. 

The ALMA Science Verification observations consist of three Executions over 1 observing session on July 1st, 2014. The data from each Execution is saved in ASDM format, as follows:
# uid___A002_X85c183_X10a
# uid___A002_X85c183_X51a
# uid___A002_X85c183_X822
 
All four cross correlation (XX, XY, YX, and YY) measurements were observed using a spectral setup with
four 2 GHz spectral windows of 64 channels each (TDM mode with 31.25 MHz resolution
per channel). To calibrate the instrumental polarization, we sampled a polarized
source (J1337-1257) as a function of paralactic angle every 30 minutes for 5 minutes
per sample. The strongly polarized source 3C279 was also observed as a bandpass calibrator; however, 
it can also be used to check the instrumental polarization calibration.

'''Using the data for publication'''

The following statement should be included in the acknowledgment of papers using the datasets listed above:

"This paper makes use of the following ALMA data: ADS/JAO.ALMA#2011.0.00017.SV. 
ALMA is a partnership of ESO (representing its member states), NSF (USA) and 
NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan), and KASI (Republic of Korea), 
in cooperation with the Republic of Chile. The Joint ALMA Observatory is 
operated by ESO, AUI/NRAO and NAOJ."

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==How to use this casaguide==

For both portions of the guide, we will provide you with the full CASA commands needed to carry out each step.  

<source lang="python">
# In CASA
The commands you need to execute 
will be displayed in regions 
like this.  
</source>

Simply copy and paste the commands into your CASA terminal.  You may also type the commands in by hand if desired, but be mindful of typos.  Note that you may need to hit Enter twice in order for the process to start running.  Also note that copying and pasting multiple commands at a time may not work, so only copy and paste the contents of one region at a time.  

Occasionally we will also show output to the CASA logger:

<pre style="background-color: #fffacd;">
This output will be displayed 
in regions like this.
</pre>

For a brief introduction to the different ways CASA can be run, click [http://casaguides.nrao.edu/index.php?title=EVLA_Spectral_Line_Calibration_IRC%2B10216#How_to_Use_This_casaguide here].
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