INTEGRAL observations of six AGN in the Galactic Plane

Abstract

We present results on approximately one year of INTEGRAL observations of six AGN detected during the regular scans of the Galactic Plane. The sample is composed by five Seyfert 2 objects (MCG -05-23-16, NGC 4945, the Circinus galaxy, NGC 6300, ESO 103-G35) and the radio galaxy Centaurus A. The continuum emission of each of these sources is well represented by a highly absorbed (N H > 10 22 cm -2 ) power law, with average spectral index Γ = 1.9 ± 0.3. A high energy exponential cut-off at E c ∼ 50 keV is required to fit the spectrum of the Circinus galaxy, whereas a lower limit of 130 keV has been found for NGC 4945 and no cut-off has been detected for NGC 6300 in the energy range covered by these INTEGRAL data. The flux of Centaurus A was found to vary by a factor of ∼2 in 10 months, showing a spectral change between the high and low state, which can be modelled equally well by a change in the absorption (N H from 17 to 33 x 10 22 cm -2 ) or by the presence of a cut-off at ≥120 keV in the low state spectrum. A comparison with recently reprocessed BeppoSAX/PDS data shows a general agreement with INTEGRAL results. The high energy cut-off in the hard X-ray spectra appears to be a common but not universal characteristic of Seyfert 2 and to span a wide range of energies.