We report on two XMM- Newton observations of the bright narrow-line Seyfert 1 galaxy Ark 564 taken one year apart ( 2000 June and 2001 June ) .
The 0.6–10 keV continuum is well described by a soft blackbody component ( kT \approx 140–150 eV ) plus a steep power law ( \Gamma \approx 2.50–2.55 ) .
No significant spectral changes are observed between the two observations , although the X-ray flux in the second observation is \approx 40–50 per cent lower .
In both observations we detect a significant absorption edge at a rest-frame energy of \approx 0.73 keV , corresponding to O vii .
The presence of the absorption feature is confirmed by a simultaneous Chandra grating observation in 2000 June , although the best-fitting edge threshold is at a slightly lower energy in the Chandra data , possibly because of a different parameterisation of the underlying X-ray continuum .
We find tentative evidence for a broad iron emission line in the 2000 June observation .
The results from an analysis of the power spectral density ( PSD ) function are also presented .
The present XMM- Newton data support the idea that the PSD shows two breaks , although the location of the high-frequency break requires further constraints .