J ul 2 00 1 Multiwavelength Monitoring of the Narrow - Line Seyfert 1 Galaxy Akn 564 . I . ASCA Observations and the Variability of the X - ray Spectral Components

We present a 35 day ASCA observation of the Narrow-Line Seyfert 1 galaxy Akn 564, yielding an on-source exposure ∼ 1 Ms. The ASCA observation was part of a multiwavelength AGN Watch monitoring campaign. The soft X-ray light curve binned to 256 s reveals trough-to-peak flux variations up to a factor of ∼ 16 and changes in the fractional amplitude of variability across the observation. Akn 564 shows small variations in photon index across the observation, with Γ in the range 2.45–2.72. The presence of the soft hump component below 1 keV, previously detected in ASCA data, is confirmed. Time-resolved spectroscopy with ∼ daily sampling reveals a distinction in the variability of the soft hump and power-law components over a timescale of weeks, with the hump varying by a factor of ∼ 6 across the 35-day observation compared to a factor 4 in the power-law. This difference in the long-term amplitudes of variation causes changes in the softness ratio across the observation. Flux variations in the power-law component are measured down to a timescale of ∼ 1000 s and accompanying spectral variability suggests the soft hump is not well-correlated with the power-law on such short timescales. However, some correlated events are observed in the soft hump, UV flux and hard X-ray flux when all are sampled daily. No significant UV to X-ray lags are found, with upper limits ∼ 1 day. – 2 – We detect Fe Kα and a blend of Fe Kβ plus Ni Kα, the line energies indicating an origin in highly ionized gas. Variability measurements constrain the bulk of the Fe Kα line to originate within ∼ a light week of the nucleus. The large EW of the emission lines may be due to high metallicity in NLS1s, supporting some evolutionary models for AGN.