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首页> 外文期刊>The Astrophysical journal >THE SPECTRUM AND VARIABILITY OF CIRCULAR POLARIZATION IN SAGITTARIUS A~* FROM 1.4 TO 15 GHz
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THE SPECTRUM AND VARIABILITY OF CIRCULAR POLARIZATION IN SAGITTARIUS A~* FROM 1.4 TO 15 GHz

机译：1.4至15 GHz时射手A〜*的圆极化的光谱和变异性

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摘要

We report here multiepoch, multifrequency observations of the circular polarization in Sagittarius A~*, the compact radio source in the Galactic center. Data taken from the Very Large Array (VLA) archive indicate that the fractional circular polarization at 4.8 GHz was -0.31%, with an rms scatter of 0.13%, from 1981 to 1998, in spite of a factor of 2 change in the total intensity. The sign remained negative over the entire time range, indicating a stable magnetic field polarity. In the summer of 1999, we obtained 13 epochs of VLA A-configuration observations at 1.4, 4.8, 8.4, and 15 GHz. These observations employ a new technique that produces an error of 0.05% at 1.4, 4.8, and 8.4 GHz and 0.1% at 14.9 GHz. In 1999 May, September, and October, we obtained 11 epochs of Australia Telescope Compact Array (ATCA) observations at 4.8 and 8.5 GHz. In all three data sets, we find no evidence of linear polarization greater than 0.1%, in spite of strong circular polarization detections. Both VLA and ATCA data sets support three conclusions regarding the fractional circular polarization: (1) the average spectrum is inverted, with a spectral index α ≈ 0.5 +- 0.2; (2) the degree of variability is roughly constant on timescales of days to years; and (3) the degree of variability increases with frequency. We also observed that the largest increase in fractional circular polarization was coincident with the brightest flare in total intensity. Significant variability in the total intensity and fractional circular polarization on a timescale of 1 hr was observed during this flare, indicating an upper limit to the intrinsic size during outburst of 70 AU at 15 GHz. The fractional circular polarization at 15 GHz reached -1.1%, and the spectral index was strongly inverted (α ～ 1.5) during this flare. We tentatively conclude that the spectrum has two components that match the high- and low-frequency total intensity components.
机译：我们在此报告人马座A〜*（银河系中心的紧凑型无线电源）的圆极化的多历时，多频观测。从甚大阵列（VLA）档案中获取的数据表明，尽管总强度变化了2倍，但从1981年到1998年，4.8 GHz时的圆圆分数为-0.31％，均方根散射为0.13％。 。该符号在整个时间范围内保持负值，表明磁场极性稳定。在1999年夏天，我们在1.4、4.8、8.4和15 GHz处获得了13个VLA A配置观测值。这些观察结果采用了一种新技术，该技术在1.4、4.8和8.4 GHz处产生0.05％的误差，在14.9 GHz处产生0.1％的误差。在1999年5月，9月和10月，我们获得了4.8 GHz和8.5 GHz的11个澳大利亚望远镜紧凑阵列（ATCA）观测值。在所有三个数据集中，尽管有很强的圆极化检测，但我们都没有发现线性极化大于0.1％的证据。 VLA和ATCA数据集都支持关于圆圆分数偏振的三个结论：（1）平均光谱是倒置的，光谱指数为α≈0.5±0.2。 （2）变异程度在几天到几年的时间尺度上大致恒定； （3）可变程度随频率增加。我们还观察到，分数圆极化的最大增加与总强度最亮的耀斑同时发生。在爆发过程中，在1小时的时间尺度上观察到了总强度和部分圆极化的显着变化，这表明在15 GHz时70 AU爆发期间本征尺寸的上限。在该耀斑中，15 GHz时的分数圆极化达到-1.1％，光谱指数强烈反转（α〜1.5）。我们初步得出结论，频谱具有两个与高频和低频总强度分量匹配的分量。

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