Characterizing the Accuracy of ALMA Linear-polarization Mosaics
Characterizing the Accuracy of ALMA Linear-polarization Mosaics
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DOI：
10.1088/1538-3873/ab99cd
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发表时间：
2020-06
影响因子：
3.5
通讯作者：
C. Hull;P. Cortés;V. J. M. L. Gouellec;J. Girart;H. Nagai;K. Nakanishi;S. Kameno;E. Fomalont;C. Brogan;G. Moellenbrock;R. Paladino;E. Villard
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文献类型：
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作者：
C. Hull;P. Cortés;V. J. M. L. Gouellec;J. Girart;H. Nagai;K. Nakanishi;S. Kameno;E. Fomalont;C. Brogan;G. Moellenbrock;R. Paladino;E. Villard
我们使用阿塔卡玛大型毫米/亚毫米阵列（阿尔马）的线性偏振马赛克的准确性。首先，我们在波段3、5、6和7（分别为3 mm、1.6 mm、1.3 mm和0.87 mm）观测到明亮的高度线偏振的blazar 3C 279。在每个波段，我们在一个11 × 11的网格上测量blazar的偏振，网格上的均匀间隔的偏移点覆盖了主光束的半峰全宽（FWHM）区域。在将3C 279的轴上指向导出的校准解应用于所有的轴上和离轴数据之后，我们发现在所有频率下穿过主光束的剩余偏振误差是相似的：线偏振分数Pfrac和偏振位置角χ的剩余误差是1.001（Stokes I的约0.1%）和在初级光束中心附近的约1°;误差增大到0.003 ~ 0.005（线偏振）Q和U图中的非对称光束图案导致在FWHM附近的（斯托克斯I的约0.3%-0.5%）和（斯托克斯I的约1°-5°）。我们在圆偏振（斯托克斯V）图中看到预期的双叶“光束斜视”图案。其次，为了测试偏振精度在一个典型的阿尔马项目，我们进行了观测的连续线性偏振朝向Kleinmann-Low星云在猎户座（猎户座-KL）使用几个马赛克图案在波段3和6。我们发现，镶嵌后，残余的离轴误差减少重叠的多个点的结果。最后，我们比较了阿尔马马赛克与档案1.3毫米组合阵列的研究毫米波天文偏振马赛克的猎户座-KL，发现良好的一致性的偏振模式。
We characterize the accuracy of linear-polarization mosaics made using the Atacama Large Millimeter/submillimeter Array (ALMA). First, we observed the bright, highly linearly polarized blazar 3C 279 at Bands 3, 5, 6, and 7 (3 mm, 1.6 mm, 1.3 mm, and 0.87 mm, respectively). At each band, we measured the blazar’s polarization on an 11 × 11 grid of evenly spaced offset pointings covering the full-width at half-maximum (FWHM) area of the primary beam. After applying calibration solutions derived from the on-axis pointing of 3C 279 to all of the on- and off-axis data, we find that the residual polarization errors across the primary beam are similar at all frequencies: the residual errors in linear polarization fraction Pfrac and polarization position angle χ are ≲0.001 (≲0.1% of Stokes I) and ≲ 1° near the center of the primary beam; the errors increase to ∼0.003–0.005 (∼0.3%–0.5% of Stokes I) and ∼1°–5° near the FWHM as a result of the asymmetric beam patterns in the (linearly polarized) Q and U maps. We see the expected double-lobed “beam squint” pattern in the circular polarization (Stokes V) maps. Second, to test the polarization accuracy in a typical ALMA project, we performed observations of continuum linear polarization toward the Kleinmann–Low nebula in Orion (Orion-KL) using several mosaic patterns at Bands 3 and 6. We show that after mosaicking, the residual off-axis errors decrease as a result of overlapping multiple pointings. Finally, we compare the ALMA mosaics with an archival 1.3 mm Combined Array for Research in Millimeter-wave Astronomy polarization mosaic of Orion-KL and find good consistency in the polarization patterns.