Suzaku wide-band X-ray Spectroscopy of the Seyfert 2 AGN in NGC 4945

摘要

Suzaku observed a nearby Seyfert 2 galaxy NGC4945, which hosts one of thebrightest active galactic nuclei above 20 keV. Combining data from the X-rayCCD camera (XIS) and the Hard X-ray Detector (HXD), the AGN intrinsic nuclearemission and its reprocessed signals were observed simultaneously. Theintrinsic emission is highly obscured with an absorbing column of $\sim 5\times 10^{24}$ cm$^{-2}$, and was detectable only above $\sim 10$ keV. Thespectrum below 10 keV is dominated by reflection continuum and emission linesfrom neutral/ionized material. Along with a neutral iron K$\alpha$ line, aneutral iron K$\beta$ and a neutral nickel K$\alpha$ line were detected for thefirst time from this source. The neutral lines and the cold reflectioncontinuum are consistent with both originating in the same location. TheCompton down-scattered shoulder in the neutral Fe-K$\alpha$ line is $\sim 10%$in flux of the narrow core, which confirms that the line originates fromreflection rather than transmission. The weakness of the Compton shoulder alsoindicates that the reflector is probably seen nearly edge-on. Flux of theintrinsic emission varied by a factor of $\sim 2$ within $\sim 20$ ks, whichrequires the obscuring material to be geometrically thin. Broadband spectralmodeling showed that the solid angle of the neutral reflector is less than afew $\times 10^{-2} \times 2\pi$. All this evidence regarding the reprocessedsignals suggests that a disk-like absorber/reflector is viewed from a nearedge-on angle.