We present the results from ASCA and OSSE simultaneous observations of the Seyfert 1.5 galaxy MCG+8-11-11 performed in August–September 1995 .
The ASCA observations , split into two pointings of \sim 10 ksec each , indicate a modest flux increase ( \sim 20 \% ) in 3 days , possibly correlated to a softening of the 0.6–9 keV spectrum .
The spectrum obtained combining data from both the observations is well described by a hard power law ( \Gamma \sim 1.64 \pm 0.03 ) absorbed by a column density slightly larger than the Galactic value .
An iron line at 6.4 keV of EW \sim 400 eV is also required by the data .
The simultaneous OSSE data are characterized by a much softer power law with photon index \Gamma = 3.0 ^ { +0.9 } _ { -0.8 } , strongly suggesting the presence of a spectral break in the hard X/soft \gamma - ray band .
In order to better investigate the complex hard X-ray spectrum of this source , a total spectrum has been produced by summing over all the observations of MCG+8-11-11 performed by OSSE so far .
A joint fit to the complete OSSE data sets and our ASCA data clearly shows an exponential cut–off of the power law at \sim 300 keV ( e –folding energy ) , as well as a quite strong reflection component .
MCG+8-11-11 is then one of the few Seyfert galaxies where a spectral break in the underlying continuum is detected unambiguously , fitting well in the X–ray/ \gamma - ray description of co–added spectra of Seyfert galaxies ( Zdziarski et al .
1995 ) .
Though the break could be due to downscattering of X–rays on cold e ^ { + } e ^ { - } –pairs in a non–thermal plasma , the inferred low compactness of this source favours instead thermal or quasi–thermal electron Comptonization in a structured corona as the leading process of high energy radiation production .