Spectral Variability and iron line emission in the ASCA Observations of the Seyfert 1 Galaxy NGC4051

We present the results of an extensive analysis of the ``ASCA'' AO2 observation of the Seyfert 1 galaxy NGC4051. The target exhibits broadband [0.5--10 keV] variability by a factor $\sim 8$ on time scales $\sim 10^4 s$, with a typical doubling time $\sim 500 s$. The spectrum is characterized by a strong emission excess over the extrapolated power law at energies $E \le 1 keV$. Absorption edges due to ionized oxygen species OVII and OVIII are detected together with an emission-like feature at $E \sim 0.93 keV$. The OVII edge undergoes significant variability on a timescale as low as $\sim 10^4 s$, whilst no contemporary variability of the OVIII feature is detected. Typical variability time scales place constraints on the location and the density of the absorbing matter. In the self-consistent hypothesis of a high energy ($E \ge 2.3 keV$) power law reflected by an infinite plane-parallel cold slab, a photon index change ($\Delta \Gamma = 0.4$) has also been observed; a natural explanation can be found in the framework of non-thermal Comptonization models. The iron line is redshifted (centroid energy $E \sim 6.1 keV$) and broad ($\sigma > 0.2 keV$); multicomponent structure is suggestive of emission from a relativistic accretion disk; however if the disk is not ionized a contribution by a molecular torus or an iron overabundance by a factor $\sim 1.5$ are required.Comment: 17 pages, latex, 12 figures. To be published in Publication of Astronomical Society of Japa

Detection of Iron Emission Line from the Galaxy Cluster Including the Radio Galaxy 3C220.1 at z=0.62

We have detected an emission line feature at 4 keV in the X-ray emission from a sky region including the distant radio galaxy 3C220.1(z=0.62) obtained with ASCA. The line energy is 6.1 - 7.0 keV (90% confidence) in the rest frame of 3C220.1. Within the present statistics, the observed spectra are consistent with two different models: a non-thermal model consisting of a power-law continuum plus a 6.4 keV iron emission line, and a Raymond-Smith thin-thermal emission model of kT ~6 keV with a metal abundance of ~0.5 solar. However, because of the large (~ 500 eV) equivalent width of the line, a significant fraction of the X-ray emission is likely to arise from the hot intracluster gas associated with the galaxy cluster that includes 3C220.1. The spectral parameters of the thermal emission are consistent with the luminosity-temperature relation of nearby clusters.Comment: 15 pages, 5 ps figures, accepted for publication in the Astrophysical Journa