Broadband X-ray spectra of two low-luminosity active galactic nuclei NGC 1566 and NGC 4941 observed with Suzaku.
KAWAMURO T., UEDA Y., TAZAKI F. and TERASHIMA Y.
Abstract (from CDS):
We report the first broadband X-ray spectra of the low-luminosity active galactic nuclei (LLAGNs), 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 ∼1041–42 erg/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-Kα line, and a scattered component (for NGC 4941). We do not significantly detect a broad iron-Kα line 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 = 0.45–0.10+0.13 in NGC 1566 and Ω/2π = 0.64–0.27+0.69 in NGC 4941. Comparison of the equivalent width of the narrow iron-Kα line with a model prediction based on a simple torus geometry constrains its half-opening angle to be θoa≃ 60°-70° 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 ∼ 1042–43 erg/s but decreases toward lower luminosities.
galaxies: active - galaxies: individual (NGC 1566, NGC 4941) - X-rays: galaxies