Spectral Variability and Iron Line Emission in the ASCA Observations of the Seyfert 1 Galaxy NGC 4051

Matteo Guainazzi, Tatehiro Mihara, Chiko Otani, Masaru Matsuoka
1996 Nippon Tenmon Gakkai obun kenkyu hokoku  
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 ∼ 8 on time scales ∼ 10^4 s, with a typical doubling time ∼ 500 s. The spectrum is characterized by a strong emission excess over the extrapolated power law at energies E < 1 keV. Absorption edges due to ionized oxygen species OVII and OVIII are detected together with an emission-like feature at E ∼ 0.93 keV. The OVII
more » ... dge undergoes significant variability on a timescale as low as ∼ 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 > 2.3 keV) power law reflected by an infinite plane-parallel cold slab, a photon index change (ΔΓ = 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 ∼ 6.1 keV) and broad (σ > 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 ∼ 1.5 are required.
doi:10.1093/pasj/48.6.781 fatcat:ydidej44mbfvvj3bcm2n4so4mu