A Variability Study of the Seyfert 2 Galaxy NGC 6300 withXMM‐Newton

We present the results of timing analysis of the XMM-Newton observation ofthe Seyfert 2 galaxy NGC 6300. The hard X-ray spectrum above 2 keV consists ofa Compton-thin-absorbed power law, as is often seen in Seyfert 2 galaxies. Weclearly detected rapid time variability on a time scale of about 1000 s fromthe light curve above 2 keV. The excess variance of the time variability(sigma2_RMS) is calculated to be ~0.12, and the periodogram of the light curveis well represented by a power law function with a slope of 1.75. In contrastwith previous results from Seyfert 2 nuclei, these variability characteristicsare consistent with those of Seyfert 1 galaxies. This consistency suggests thatNGC 6300 has a similar black hole mass and accretion properties as Seyfert 1galaxies. Using the relation between time variability and central black holemass by Hayashida et al. (1998), the black hole mass of NGC 6300 is estimatedto be ~2.8x10^5 Mo. Taking uncertainty of this method into account, the blackhole mass is less than 10^7 Mo. Taking the bolometric luminosity of 3.3x10^43erg/s into consideration, this yields an accretion rate of > 0.03 of theEddington value, and comparable with estimates from Seyfert 1 galaxies usingthis method. The time variability analysis suggests that NGC 6300 actually hasa Seyfert 1 nucleus obscured by a thick matter, and more generally provides anew pillar of support for the unified model of Seyfert galaxies based onobscuration.Comment: 11 pages, 6 figures, accepted for publication in Ap