Simultaneous Chandra and RXTE observations of the nearby bright Seyfert 2 galaxy NGC4945

Astrophysics, abstract
astro-ph/0301383

From: Chris Done <chris.done@durham.ac.uk>

Date: Mon, 20 Jan 2003 10:35:32 GMT   (134kb)

Authors:
Chris Done,
Greg M.Madejski,
Piotr T. Zycki,
Lincoln J. Greenhill

Comments: Accepted in ApJ

We analyze recent simultaneous Chandra/RXTE observations of the Seyfert 2
galaxy NGC 4945. The unprecedented spatial resolution of Chandra means we are
able to separate the spectra of the nucleus, starburst and superwind regions,
while the RXTE data extend the spectrum to higher energies. The extreme
absorbing column of $N_Hsim 4 imes 10^{24}$ cm$^{-2}$ means that the nucleus
is only seen directly above 8–10 keV, while the lower energy spectrum from the
nuclear region in Chandra is dominated by reflection. By contrast, the
superwind is dominated by emission from hot plasma, but the starburst region
contains both hot plasma and reflection signatures. To form a reflected
spectrum requires that the starburst region contains clumps of cool, optically
thick material, perhaps star forming cores, which are irradiated by 7–10 keV
photons from the nucleus. Since photons of this energy are obscured along the
line sight then this confirms the result of Madejski et al. (2000) that the
extreme absorbtion material is disk-like rather than a torus. However, the
IR/optical limits on the lack of high excitation emission lines show that by
contrast the lower energy photons from the nucleus are obscured in all
directions. We discuss the complex absorption structure revealed by these
observations, and propose an an overall source geometry in which the nucleus is
completely embedded in material with $N_Hsim 10^{23}$ cm$^{-2}$

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