A Cutoff in the X-Ray Fluctuation Power Density Spectrum of the Seyfert 1 Galaxy NGC 3516
A Cutoff in the X-Ray Fluctuation Power Density Spectrum of the Seyfert 1 Galaxy NGC 3516
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DOI：
10.1086/306980
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发表时间：
1998-10
期刊：
影响因子：
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通讯作者：
R. Edelson;K. Nandra
中科院分区：
文献类型：
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作者：
R. Edelson;K. Nandra
在1997年3月至7月期间，Rossi X射线计时探测器观测到明亮的、强变的Seyfert 1星系NGC 3516，每隔约12.8小时观测一次，持续了4.5个月，中间几乎连续观测了4.2天（由于南大西洋异常通道而不是地球掩星而中断）。随后每约4.3天进行一次持续监测。这些数据被用来构建一个活跃星系的第一个确定的X射线波动功率密度谱（PDS），跨越四十多年的可用时间频率。PDS没有显示出任何严格或准周期性的迹象，但确实显示出幂律斜率从短时间尺度的-1.74逐渐变平到长时间尺度的-0.73。这是迄今为止对PDS中长期预测的截止日期的最清晰的观察。对应于该截止时间频率的特征性变异性时间尺度约为1个月。虽然目前还不清楚如何在物理尺寸或工艺方面解释这个时间尺度，但有几个有希望的候选模型。PDS看起来类似于银河系黑洞候选者，如天鹅座X-1，这表明这两类具有非常不同的光度和假定的黑洞质量（相差超过105倍）的物体可能具有相似的X射线产生过程和结构。
During 1997 March-July, the Rossi X-Ray Timing Explorer observed the bright, strongly variable Seyfert 1 galaxy NGC 3516 once every ~12.8 hours for 4.5 months and nearly continuously (with interruptions due to South Atlantic Anomaly passage but not Earth occultation) for a 4.2 day period in the middle. These were followed by ongoing monitoring once every ~4.3 days. These data are used to construct the first well-determined X-ray fluctuation power density spectrum (PDS) of an active galaxy to span more than four decades of usable temporal frequency. The PDS shows no signs of any strict or quasi-periodicity but does show a progressive flattening of the power-law slope from -1.74 at short timescales to -0.73 at longer timescales. This is the clearest observation to date of the long predicted cutoff in the PDS. The characteristic variability timescale corresponding to this cutoff temporal frequency is ~1 month. Although it is unclear how this timescale may be interpreted in terms of a physical size or process, there are several promising candidate models. The PDS appears similar to those seen for Galactic black hole candidates such as Cyg X-1, suggesting that these two classes of objects with very different luminosities and putative black hole masses (differing by more than a factor of 105) may have similar X-ray generation processes and structures.