X-ray power density spectrum of the narrow-line Seyfert 1 galaxy Arakelian564

Beginning in 1999 January, the bright, strongly variable narrow-line Seyfer t 1 (NLS1) galaxy Akn 564 has been observed by RXTE once every similar to4. 3 days. It was also monitored every similar to 3.2 hr throughout 2000 July. These evenly sampled observations have allowed the first quantitative comp arison of long- and short-timescale X-ray variability in an NLS1 galaxy and the derivation of an X-ray power density spectrum (PDS). The variability a mplitude in the short-timescale light curve is very similar to that in the long- timescale light curve, in marked contrast to the stronger variability on longer timescales, which is characteristic of "normal" broad-line Seyfe rt 1 (BLS1) galaxies. Furthermore, the Akn 564 PDS power law cuts off at a frequency of 8.7 x 10(-7) Hz, corresponding to a timescale of similar to 13 days, significantly shorter than that seen in the PDS of NGC 3516, a BLS1 galaxy of comparable luminosity. This result is consistent with NLS1 galaxi es showing faster (as opposed to larger amplitude) variations than BLS1 gal axies, providing further evidence that NLS1 galaxies harbor lower mass blac k holes than BLS1 galaxies of similar luminosity, accreting at a correspond ingly higher relative rate.