paper

Broad Band X-Ray Spectra of Two Low-luminosity Active Galactic Nuclei NGC 1566 and NGC 4941

arXiv:1305.2912 · doi:10.1088/0004-637X/770/2/157

Abstract

We report the first broad band X-ray spectra of the low luminosity active galactic nuclei (LLAGN) NGC 1566 (type 1.5) and NGC 4941 (type 2) observed with Suzaku and Swift/BAT covering the 0.5-195 keV band. Both targets have hard X-ray luminosities of ~ 10^{41-42} ergs/s in the 15-55 keV band. The spectra of the nucleus are well reproduced by a sum of partially or fully covered transmitted emission and its reflection from the accretion disk, reprocessed emission from the torus accompanied by a strong narrow iron-Kαline, and a scattered component (for NGC 4941). We do not significantly detect a broad iron-Kαline from the inner accretion disk in both targets, and obtain an upper limit on the corresponding solid angle of Ω/2π< 0.3 in NGC 1566. The reflection strength from the torus is moderate, Ω/2π=0.45^{+0.13}_{-0.10} in NGC 1566 and Ω/2π=0.64^{+0.69}_{-0.27} in NGC 4941. Comparison of the equivalent width of the narrow iron-Kαline with a model prediction based on a simple torus geometry constrains its half-opening angle to be θ_oa ~ 60-70 degree in NGC 4941. These results agree with the obscured AGN fraction obtained from hard X-ray and mid-infrared selected samples at similar luminosities. Our results support the implication that the averaged covering fraction of AGN tori is peaked at L 10^{42-43} ergs/s but decreases toward lower luminosities.

11 pages, 6 figures, accepted for publication in ApJ

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