Optical monitoring and spectral analysis of the Seyfert galaxy NGC1275

Abstract

In this paper, we present VRI photometric observations of NGC1275 obtained by using the 1.56 m telescope at Shanghai Observatory (ShAO), China, during the period of Nov. 2005 to Feb. 2014. Our observations show that the maximum variabilities at three bands are $\Delta m_{V}=1.03 \pm 0.09\mbox{ mag}$, $\Delta m_{R}=0.82\pm 0.08\mbox{ mag}$ and $\Delta m_{I}=0.95 \pm 0.03\mbox{ mag}$; and the time scales are $\Delta t_{1}=2.97\mbox{ days}$ and $\Delta t_{2}=5.99\mbox{ days}$. We use the VRI observations to obtain optical spectral indices ($\alpha$), and investigate the relationship between spectral indices ($\alpha$) and VRI flux densities ($F_{V,R,I}$). Our results show that, at V band, there is a clear anti-correlation between $\alpha$ and $F_{V}$: $\alpha = -(0.07\pm 0.003)F_{V} + (3.18\pm 0.08)$, with a correlation coefficient $r = -0.76$ and a chance probability $p < 0.01~\%$; at R band, there is anti-correlation between $\alpha$ and $F_{R}$: $\alpha = -(0.04 \pm 0.003)F_{R} + (2.64\pm 0.09)$ with $r = -0.45$, $p < 0.01~\%$; but there is no correlation at I band, $\alpha = (1.13\pm 0.008)F_{I} + (0.13 \pm 0.003)$, with $r = 0.08$ and $p = 31.9~\%$.