Compton processes in the bright AGN MCG +8-11-11

Abstract

We present preliminary results on the hard X-ray emission properties of the Seyfert 1.5 galaxy MCG +8−11−11, as observed by INTEGRAL and SWIFT. All the INTEGRAL IBIS/ISGRI data available up to October 2009 have been analysed together with two SWIFT/XRT snapshot observations performed in August and October 2009, quasi-simultaneously to INTEGRAL pointed observations of MCG +8−11−11. No correlation is observed between the hard Xray flux and the spectral slope, while the position of the high-energy cut-off is found to have varied during the INTEGRAL observations. This points to a change in the temperature of the Comptonising medium from a minimum value of kT e = 30 − 50 keV to values larger than 100-150 keV. There is no significant detection of Compton reflection, with a 3σ upper limit of R < 0.2, and no line has been detected at 112 keV, as previously claimed from HEAT observations (F 112 keV < 2.4 × 10 −4 ph cm −2 s −1 ). The variability behaviour of MCG +8−11−11 is found to be similar to that shown by IC 4329A, with different temperatures of the electron plasma for similar flux levels of the source, while other bright Seyfert galaxies present different variability patterns at hard X-rays, with spectral changes correlated to flux variations (e.g. NGC 4151).

Long-term variability of AGN at hard X-rays

“…At the same time, pointed observations with Suzaku, INTEGRAL, and NuSTAR will continue to investigate the spectral variability in bright and well studied AGN, as already successfully done in a number of sources (Reeves et al 2007;Itoh et al 2008;Terashima et al 2009;Fukazawa et al 2011;Beckmann et al 2007b;Soldi et al 2010Soldi et al , 2011bLubiński et al 2010). …”