We present the results of a 3.3 yr project to monitor the flux density of Sagittarius A* at 2.0, 1.3, and 0.7 cm with the Very Large Array. Between 2000.5 and 2003.0, 119 epochs of data were taken with a mean separation between epochs of 8 days. After 2003.0, observations were made roughly once per month for a total of nine additional epochs. Details of the data calibration process are discussed, including corrections for opacity and elevation effects, as well as changes in the flux density scales between epochs. The fully calibrated light curves for Sgr A* at all three wavelengths are presented. Typical errors in the flux density are 6.1%, 6.2%, and 9.2% at 2.0, 1.3, and 0.7 cm, respectively. There is preliminary evidence for a bimodal distribution of flux densities, which may indicate the existence of two distinct states of accretion onto the supermassive black hole. At 1.3 and 0.7 cm, there is a tail in the distribution toward high flux densities. Significant variability is detected at all three wavelengths, with the largest amplitude variations occurring at 0.7 cm. The rms deviation of the flux density of Sgr A* is 0.13, 0.16, and 0.21 Jy at 2.0, 1.3, and 0.7 cm, respectively. During much of this monitoring campaign, Sgr A* appeared to be relatively quiescent compared with results from previous campaigns. At no point during the monitoring campaign did the flux density of Sgr A* more than double its mean value. The mean spectral index of Sgr A* is α = 0.20 ± 0.01 (where Sν ∝ να), with a standard deviation of 0.14. The spectral index appears to depend linearly on the observed flux density at 0.7 cm with a steeper index observed during outbursts. This correlation is consistent with the expectation for outbursts that are self-absorbed at wavelengths of 0.7 cm or longer and inconsistent with the effects of simple models for interstellar scintillation. Much of the variability of Sgr A*, including possible time lags between flux density changes at the different wavelengths, appears to occur on timescales less than the time resolution of our observations (8 days). Future observations should focus on the evolution of the flux density on these time-scales.
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机译：我们提出了一个3.3年计划的结果，以非常大的阵列监视射手座A *在2.0、1.3和0.7 cm处的通量密度。在2000.5到2003.0之间，获取了119个时期的数据，每个时期之间的平均间隔为8天。在2003.0之后，每月大约进行一次观测，总共增加了9个纪元。讨论了数据校准过程的详细信息，包括对不透明度和高程影响的校正，以及历元之间通量密度标度的变化。给出了所有三个波长下Sgr A *的完全校准光曲线。在2.0、1.3和0.7厘米处，通量密度的典型误差分别为6.1％，6.2％和9.2％。有通量密度双峰分布的初步证据，这可能表明在超大质量黑洞上存在两种不同的积聚状态。在1.3和0.7 cm处，在朝向高通量密度的分布中有一条尾巴。在所有三个波长处都检测到显着的变化，最大的幅度变化发生在0.7厘米处。在2.0、1.3和0.7厘米处，Sgr A *的通量密度的均方根偏差分别为0.13、0.16和0.21 Jy。在此监视活动的大部分时间内，Agr *与以前的活动相比似乎相对静止。在监测活动期间，Sgr A *的通量密度从未超过其平均值的两倍。 Sgr A *的平均光谱指数为α= 0.20±0.01（其中Sνννα），标准偏差为0.14。光谱指数似乎线性依赖于在0.7 cm处观察到的通量密度，而在爆发过程中观察到的指数更陡。这种相关性与对在0.7厘米或更长的波长处自吸收的爆发的期望相符，并且与星际闪烁的简单模型的效果不一致。 Sgr A *的大部分可变性，包括在不同波长处的通量密度变化之间可能存在的时间滞后，似乎发生在小于我们观察结果的时间分辨率（8天）的时间尺度上。未来的观察应集中在这些时间尺度上通量密度的变化。
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