Detection of an X-ray periodicity in the Seyfert galaxy IRAS18325-5926
  We report the detection of a 58 ks (16 hr) periodicity in the 0.5-10 keV X-ray light curve of the Seyfert galaxy IRAS18325-5926 (Fairall49), obtained from a 5-day ASCA observation. Nearly 9 cycles of the periodic variation are seen; it shows no strong energy dependence and has an amplitude of about 15 per cent. Unlike most other well-studied Seyfert galaxies, there is no evidence for strong power-law red noise in the X-ray power spectrum of IRAS18325-5926. Scaling from the QPOs found in Galactic black hole candidates suggests that the mass of the black hole in IRAS18325-5926 is (6-40) million solar masses. 
K. Iwasawa, A.C. Fabian, W.N. Brandt, H. Kunieda, K. Misaki, C.S.   Reynolds and Y. Terashima