A variability study of the Seyfert 2 galaxy NGC 6300 with XMM-Newton

We present the results of timing analysis of the XMM-Newton observation of the Seyfert 2 galaxy NGC 6300. The hard X-ray spectrum above 2 keV consists of a Compton-thin absorbed power law, as is often seen in Seyfert 2 galaxies. We clearly detected rapid time variability on a timescale of about 1000 s from the light curve above 2 keV. The excess variance of the time variability (sigma(rms)(2)) is calculated to be similar to 0.12, and the periodogram of the light curve is well represented by a power-law function with a slope of 1.75. In contrast to previous results from Seyfert 2 nuclei, these variability characteristics are consistent with those of Seyfert 1 galaxies. This consistency suggests that NGC 6300 has a black hole mass and accretion properties similar to Seyfert 1 galaxies. Using the relation between time variability and central black hole mass by Hayashida et al., the black hole mass of NGC 6300 is estimated to be similar to 2.8 x 10(5) M-circle dot. Taking the uncertainty of this method into account, the black hole mass is less than 10(7) M-circle dot. Taking the bolometric luminosity of 3.3 x 10(43) ergs s(-1) into consideration, this yields an accretion rate of > 0.03 of the Eddington value, comparable to estimates from Seyfert 1 galaxies using this method. The time variability analysis suggests that NGC 6300 actually has a Seyfert 1 nucleus obscured by thick matter and more generally provides a new pillar of support for the unified model of Seyfert galaxies based on obscuration.