Sgr A* 位置漂移的限制
Limits on the Position Wander of Sgr A*
摘要：
我们目前的测量与VLBA的变化的质心位置的Sgr A* 相对于背景类星体在7毫米波长。我们发现，在50和100分钟之间的时间尺度和113 +/- 50微弧秒之间的时间尺度，没有长期趋势的平均质心漂移71 +/- 45微弧秒。这些都足以开始限制Sgr A* 的无线电可变性的热点模型的可行性。可以排除轨道半径大于15 GM_SgrA */c^2的热点，这些热点贡献了总7 mm通量的30%以上。然而，较近或较不明亮的热点仍然不受约束。由于在我们的观测期间，Sgr A* 的分数变异性在小时的时间尺度上约为20%，因此Sgr A* 的射电变异性的热点模型与这些限制保持一致。改进的Sgr A* 的质心位置的监测有可能把显着的约束的存在和形态的不均匀性在一个超大质量黑洞吸积流。
英文摘要：
We present measurements with the VLBA of the variability in the centroid position of Sgr A* relative to a background quasar at 7-mm wavelength. We find an average centroid wander of 71 +/- 45 micro-arcsec for time scales between 50 and 100 min and 113 +/- 50 micro-arcsec for timescales between 100 and 200 min, with no secular trend. These are sufficient to begin constraining the viability of the hot-spot model for the radio variability of Sgr A*. It is possible to rule out hot spots with orbital radii above 15GM_SgrA*/c^2 that contribute more than 30% of the total 7-mm flux. However, closer or less luminous hot spots remain unconstrained. Since the fractional variability of Sgr A* during our observations was ~20% on time scales of hours, the hot-spot model for Sgr A*'s radio variability remains consistent with these limits. Improved monitoring of Sgr A*'s centroid position has the potential to place significant constraints upon the existence and morphology of inhomogeneities in a supermassive black hole accretion flow.
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