2002A&A...382L...1P

We present a power spectrum analysis of the long ASCA observation of Ark 564 in June/July 2001. The observed power spectrum covers a frequency range of ∼3.5 decades. We detect a high frequency break at ∼2x10^–3Hz. 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., 2001ApJ...550L..15P), the observed power spectra of Ark 564 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 Ark 564.