################################################################################### This README file contains a description of the 11x11 ALMA beam-polarization EOC test observations toward the (point-source) blazar 3C 279; the calibration and imaging scripts; the test datasets; the calibration and imaging procedure; and the data products. The purpose of these tests was to image a polarized, continuum point source at multiple positions within the primary beam to map the response within the field of view equivalent to a single pointing (see the "COMMENTS" section below for more information). All spectral windows of all observations contain continuum emission. The observations were taken in Mar 2015 (Band 3), May 2015 (Bands 6, 7) and Nov 2016 (Band 5). The approximate spatial resolutions are 3.3 x 2.5'' (Band 3), 1.0 x 0.6'' (Band 5), 1.2 x 0.9'' (Band 6), and 0.8 x 0.6'' (Band 7). The Stokes I values in all images are set to 1; all other values (Stokes Q, U, V, and rms noise levels) are reported with respect to the Stokes I peak value of 1. The 11x11 images, and a complete description and discussion of these data, have been published in Hull et al. 2020, PASP (https://arxiv.org/abs/2006.03671). The Calibrated Data and Reference Images provided here were produced using CASA version 5.6.1. Additional information can be found below in the "COMMENTS" section of this README. ################################################################################### 11x11_Scripts.tar contains the calibration/imaging and plotting scripts: # Script for calibration and imaging beamCrossRedux.py # Script for producing 11x11 plots: beamCrossPlots.py 11x11_UncalibratedData.tar contains the raw ASDM datasets. Observations in each band comprise 3 ASDMs. Each set of 3 ASDMs are located in subdirectories labeled by band: # Band 3 B3-3/ uid__A002_X9b98ec_X94d uid__A002_X9b98ec_Xb98 uid__A002_X9b98ec_Xde3 # Band 5 B5-1/ uid__A002_Xba6edb_X31db uid__A002_Xba6edb_X3988 uid__A002_Xba6edb_X3d57 # Band 6 B6-1/ uid__A002_Xa018c4_X743 uid__A002_Xa018c4_Xa3d uid__A002_Xa018c4_Xdc7 # Band 7 B7-1/ uid__A002_Xa018c4_X3b92 uid__A002_Xa018c4_X3de3 uid__A002_Xa018c4_X402a The onAxisRedux function of beamCrossRedux.py derives calibration tables from the on-axis data only (i.e., with the source at the phase center), and produces the following calibrated dataset containing only on-axis data: onaxis.cal.ms 11x11_ReferenceImages.tgz contains the reference images for each band. These images are 4-plane Stokes IQUV image cubes normalized to Stokes I=1, produced using only the data observed on-axis (i.e., from onaxis.cal.ms): 3c279.B3.IQUV.clean.selfcal1.image.fits 3c279.B5.IQUV.clean.selfcal1.image.fits 3c279.B6.IQUV.clean.selfcal1.image.fits 3c279.B7.IQUV.clean.selfcal1.image.fits These on-axis reference images can be re-created by running the onAxisRedux function of beamCrossRedux.py. Next, the offAxisRedux_onAxisCal function of beamCrossRedux.py applies all of the on-axis calibration tables to all off-axis data in the following dataset: concat.ms.split The offAxisRedux_onAxisCal function of beamCrossRedux.py also produces the 11 x 11 - 1 = 120 off-axis images from the full dataset (i.e., concat.ms.split). Next, all of the images are analyzed by the offAxisImageAnalysis function of beamCrossRedux.py. Finally, the results of this analysis are used to create the 11x11 beam plots (shown in Hull et al. 2020, PASP; https://arxiv.org/abs/2006.03671) using the beamPlots function of beamCrossPlots.py. --------------------------------------------------------------- Publications making use of these data must include the following statement in the acknowledgement: "This paper makes use of the following ALMA data: ADS/JAO.ALMA#2011.0.00009.E. 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." In addition, publications from North American authors must include the standard NRAO acknowledgement: "The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc." ################################################################################### COMMENTS: These observations were taken to measure the polarization errors across the primary beam of the ALMA 12m antennas at Bands 3, 5, 6, and 7, with the goal of characterizing the accuracy of ALMA polarization observations in a single-pointing observation. These results are relevant not only for interpreting single-pointing observations, but also for understanding the effects of off-axis errors in mosaicked polarization observations. All of these observations are toward the highly polarized blazar 3C 279. 3C 279 was observed both on-axis (i.e., with the source at the phase center) as well as off-axis in a square grid of 11x11 offset pointings covering approximately the FWHM of the primary beam at each band. The data were calibrated using a scheme very similar to the current ALMA polarization calibration scheme. Calibration tables were derived from the on-axis data only, but were applied to all on- and off-axis data. The calibration and imaging script beamCrossRedux.py performs all of the calibration and imaging, and image analysis (i.e., fitting using the CASA task IMFIT to extract IQUV fluxes). The plotting script uses these results to plot the polarization error maps across the primary beam at each of the observed bands (3,5,6,7). As these data are test data taken in manual mode, the calibration and imaging procedure is much different from a normal, standard ALMA observation. Note that no WVR or TSYS are applied to these data during the calibration process. There is also no independent flux calibrator, as 3C 279 was the target, and was exceptionally bright at all bands during the 2015-2016 observations. Furthermore, all fluxes at all bands are normalized to an on-axis Stokes I flux of 1. As our primary goal was simply to characterize variations in the Stokes IQUV fluxes (and the associated variations in polarization fraction and position angle) of 3C 279 in the off-axis positions relative to the on-axis positions, the simple calibration method coded in beamCrossRedux.py was sufficient. The background behind and purpose of the observations, the calibration procedure, the imaging procedure, and results and interpretation of the 11x11 images of the Stokes V (squint) data and the errors in Stokes Q, Stokes U, polarization position angle, and polarization fraction are discussed in detail in Hull et al. 2020, PASP (https://arxiv.org/abs/2006.03671). ################################################################################### HOW TO EXECUTE THE CALIBRATION SCRIPT To calibrate the data, produce on- and off-axis images, and analyze the images, you will need to execute beamCrossRedux.py in the following manner. (1) Place this script in a directory, and create a subdirectory for the data. This subdirectory should be named "B3-3" (for Band 3), "B5-1" (Band 5), "B6-1" (Band 6) or "B7-1" (Band 7) (2) Copy raw ASDMs into the data subdirectory (3) cd into the data subdirectory Note that steps (1) and (2) above are taken care of automatically in the structure of 11x11_UncalibratedData.tgz. I.e., when you untar that file, the UIDs for each band are all located in their respective, properly named directories. Then execute the following commands in CASA (version <= 5.6.1). Replace "band" with "B3_3", "B5_1", "B6_1", or "B7_1" (without quotes) for Bands 3, 5, 6, or 7, respectively. [CASA]> execfile('../beamCrossRedux.py') [CASA]> setup(band) [CASA]> S = onAxisRedux(band) [CASA]> offAxisRedux_onAxisCal(band, S) [CASA]> offAxisImageAnalysis(band) S is the IQUV source model, which is returned by the function onAxisRedux and used by the function offAxisRedux_onAxisCal. Note that the calibration script uses CLEAN (not TCLEAN) to produce all of the images that are later analyzed. If desired, TCLEAN can be substituted for CLEAN, although this will require modification of some parameters. HOW TO EXECUTE THE IMAGING SCRIPT To produce the 11x11 plots published in Hull et al. 2020, PASP (https://arxiv.org/abs/2006.03671), you will need to execute beamCrossPlots.py in the following manner: (1) Place this script in the directory where your data subdirectory is located (2) Check that the *peak*.txt files were successfully copied by beamCrossRedux.py (see above into the directory where this script is located (3) cd into the data subdirectory Then execute the following commands in an iPython 2.7 session. Replace "band" with "B3_3", "B5_1", "B6_1", or "B7_1" (without quotes) for Bands 3, 5, 6, or 7, respectively. [py2.7]> run ../beamCrossPlots.py [py2.7]> beamPlots(band)