表征ALMA线偏振镶嵌的精度
Characterizing the accuracy of ALMA linear-polarization mosaics
摘要：
我们使用阿塔卡玛大型毫米/亚毫米阵列（ALMA）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，我们测量了blazar的偏振11 $\times$ 11网格均匀间隔偏移点覆盖的半峰全宽（FWHM）地区的主要光束。在将从3C 279的轴上指向导出的校准解决方案应用于所有轴上和离轴数据之后，我们发现在所有频率下穿过初级光束的剩余偏振误差是相似的：线偏振分数$P_\textrm{frac}$和偏振位置角$χ$的残差为$\lesssim$ 0.001（$\lesssim$为斯托克斯$I$的0.1%）和$\lesssim$ 1 $^\circ$;误差增大到$\sim$ 0.003 ~ 0.005由于（线性偏振）$Q$和$U$图中的不对称光束图案，在FWHM附近的$\sim$ 1-5（$\sim$ 0.3-0.5%的斯托克斯$I$）和$\sim$ 1-5 $^\circ$。我们在圆偏振（Stokes $V$）图中看到了预期的双叶“光束斜视”图案。其次，为了测试偏振精度在一个典型的ALMA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，我们将ALMA马赛克与Orion-KL的档案1.3 mm CARMA偏振马赛克进行比较，发现偏振模式具有良好的一致性。
英文摘要：
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$\times$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 $P_\textrm{frac}$ and polarization position angle $χ$ are $\lesssim$0.001 ($\lesssim$0.1% of Stokes $I$) and $\lesssim$1$^\circ$ near the center of the primary beam; the errors increase to $\sim$0.003-0.005 ($\sim$0.3-0.5% of Stokes $I$) and $\sim$1-5$^\circ$ 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 CARMA polarization mosaic of Orion-KL and find good consistency in the polarization patterns.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
