Long-term variability of the low-luminosity active galactic nucleus of M81
Long-term variability of the low-luminosity active galactic nucleus of M81
复制标题
M81低光度活动星系核的长期变化
DOI：
10.1046/j.1365-8711.2001.04086.x
复制
发表时间：
2000
影响因子：
4.8
通讯作者：
K. Makishima
中科院分区：
文献类型：
--
作者：
N. Iyomoto;K. Makishima
利用16次ASCA观测，研究了M81低亮度活动星系核的长期x射线变化率，跨度为5.5年。该物体在5.5年期间呈现出3倍的变化因子。每次观测中，源强度相对恒定，通常持续一天，但在第15次观测中发现了30%的日内变化率。功率谱密度（PSD）以“前向”方式估计，频率范围为10−8.2-10−4.3 Hz（周期范围为0.25 d-5.5 yr），利用结构函数和广泛的蒙特卡罗模拟，以克服非常稀疏和不均匀的数据采样。假设PSD在“破裂频率”fb以下为白色，在fb以上随∝f−α下降，其中f为频率，α为正参数，则1/fb≥800 d， α=1.4±0.2可以很好地描述M81光曲线。
Long-term X-ray variability of the low-luminosity active galactic nucleus of M81 was studied, using 16 ASCA observations spanning 5.5 yr. The object exhibits a factor of 3 variation over the 5.5 yr. The source intensity was relatively constant within each observation which lasted typically for one day, but intra-day variability by 30 per cent was detected on the 15th observation. The power-spectral density (PSD) was estimated in a ‘forward’ manner, over a frequency range of 10−8.2–10−4.3 Hz (period range of 0.25 d–5.5 yr), by utilizing the structure function and extensive Monte Carlo simulations in order to overcome the very sparse and uneven data samplings. When the PSD is assumed to be white below a ‘break frequency’fb and falls off as ∝ f−α above fb, where f is frequency and α is a positive parameter, the M81 light curve is well described with 1/fb≥800 d and α=1.4±0.2.