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AGN emission processes of NGC 4945 in the X-rays and gamma-rays
Menzel M.-L., Beckmann V., Mattana F.
Dans The Extreme and Variable High Energy Sky - INTEGRAL conference "The Extreme and Variable High Energy Sky", Chia Laguna : Italie (2011) - http://hal.archives-ouvertes.fr/hal-00657216
Physique/Astrophysique/Phénomènes cosmiques de haute energie
Planète et Univers/Astrophysique/Phénomènes cosmiques de haute energie
AGN emission processes of NGC 4945 in the X-rays and gamma-rays
M.-L. Menzel1, V. Beckmann1, F. Mattana1
1 :  APC - UMR 7164 - AstroParticule et Cosmologie
CNRS : UMR7164 – IN2P3 – Observatoire de Paris – Université Paris VII - Paris Diderot – CEA : DSM/IRFU
APC - UMR 7164, Université Paris Diderot, 10 rue Alice Domon et Léonie Duquet, case postale 7020, F-75205 Paris Cedex 13
NGC 4945 has an outstanding role among the Seyfert 2 active galatic nuclei (AGN) because it is one of the few non-blazars which have been detected in the gamma-rays. Here, we analyse the high energy spectrum using Suzaku, INTEGRAL and Fermi data. We reconstruct the spectral energy distribution in the soft X-ray to gamma-ray domain in order to provide a better understanding of the processes in the AGN. We present two models to fit the high-energy data. The first model assumes that the gamma-ray emission originates from one single non-thermal component, e.g. a shock-induced pion decay caused by the starburst processes in the host galaxy, or by interaction with cosmic rays. The second model describes the high-energy spectrum by two independent components: a thermal inverse Compton process of photons in the non-beamed AGN and a non-thermal emission of the gamma-rays. These components are represented by an absorbed cut-off power law for the thermal component in the X-ray energy range and a simple power law for the non-thermal component in the gamma-rays. For the thermal process, we obtain a photon index of Gamma=1.6, a cut-off energy of Ec ~ 150 keV and a hydrogen column density of NH = 6e24 1/cm**2. The non-thermal process has a photon index of Gamma=2.0 and a flux of F(0.1-100 GeV) = 1.4e-11 erg/cm**2/sec. The spectral energy distribution gives a total unabsorbed flux of F(2 keV - 100 GeV) = 5e-10 erg/cm**2/sec and a luminosity of L(2 keV - 100 GeV) = 9e41 erg/sec at a distance of 3.7 Mpc. It appears more reasonable that the gamma-ray emission is independent from the AGN and could be caused e.g. by shock processes in the starburst regions of the host galaxy.

The Extreme and Variable High Energy Sky
Communications avec actes

INTEGRAL conference "The Extreme and Variable High Energy Sky"
Chia Laguna

Astrophysics - High Energy Astrophysical Phenomena
6 pages, 2 figures, proceedings of the INTEGRAL conference "The Extreme and Variable High Energy Sky", held on September 19-23, 2011 in Chia Laguna (Italy); accepted for publication in Proceedings of Science, SISSA, PoS(Extremesky 2011)075