C. Otani, T. Kii, C.S. Reynolds, A. C. Fabian, K. Iwasawa, K. Hayashida, H. Inoue, H. Kunieda, F. Makino, M. Matsuoka, Y. Tanaka
We present the results of a 4-day ASCA observation of the Seyfert galaxy MCG-6-30-15, focusing on the nature of X-ray absorption by the warm absorbe r, characterized by the K-edges of highly ionized oxygen, Ovii and Oviii. We have confirmed that the column density of Oviii chan ges on a timescale of ~ 10(4) s when the X-ray continuum flux decreases. A significant anti-correlation of the column density with the continuum flux gives direct evidence that the warm absorber is photoionized by the X-ray continuum. From the timescale of the variation of the Oviii column density, we have estimated that it originates from gas within a radius of about 10(17) cm of the central engine. In contrast, the depth of the Ovii edge shows no response to the continuum flux, which indicates that it originates in gas at larger radii. Our results strongly suggest that there are two warm absorbing regions: one is located near or within the Broad Line Region; the other is associated with the outer molecular torus, scattering medium or Narrow Line Region.