Letter to the Editor

Detection of a high frequency break in the X-ray power spectrum of Ark 564

¹ IESL, Foundation for Research and Technology-Hellas, PO Box 1527, 711 10 Heraklion, Crete, Greece
² Physics Department, University of Crete, PO Box 2208, 710 03 Heraklion, Greece
³ Max–Planck–Institut für extraterrestrische Physik, Giessenbachstrasse, 85740 Garching, Germany
⁴ Cosmic Radiation Laboratory, RIKEN, 2-1 Hirosawa, Wako-shi, Saitama 351-01, Japan

Corresponding author: I. E. Papadakis, jhep@physics.uoc.gr

Received: 22 October 2001
Accepted: 10 December 2001

Abstract

We present a power spectrum analysis of the long ASCA  observation of   in June/July 2001. The observed power spectrum covers a frequency range of ~3.5 decades. We detect a high frequency break at ~ Hz. The power spectrum has an rms of ~30% and a slope of ~-1 and ~-2 below and above the break frequency. When combined with the results from a long RXTE observation (Pounds et al. [CITE]), the observed power spectra of  and Cyg X-1 (in the low/hard state) are almost identical, showing a similar shape and rms amplitude. However, the ratio of the high frequency breaks is very small (~10^3-4), implying that these characteristic frequencies are not indicative of the black hole mass. This result supports the idea of a small black hole mass/high accretion rate in .