Dr Piotr Lubinski
ISDC
"Extreme flux states of NGC 4151 observed with the current X-ray satellites"

A comprehensive spectral analysis of all INTEGRAL data taken for the brightest Seyfert 1
galaxy NGC 4151 is presented. To constrain better the spectral models we used also all
contemporary data collected by the RXTE, XMM-Newton, Swift and Suzaku satellites. An
inspection of the historical data on NGC 4151 shows that its 20--100 keV emission remains
within the limits measured by INTEGRAL since almost 40 years, despite long-time variation
in the optical flux. Because majority of INTEGRAL observations was made when the object was
at very bright or very dim hard X-ray state, we were able to determine the range of the
plasma parameters and strength of reflection with an unprecedented precision.
Comptonization model applied to the bright state gave plasma temperature in the range
45--65 keV and plasma optical depth in the range 1.4-3.1, depending on the assumed geometry
of the system. For the dim state corresponding values are in the range 200--400 keV and
0.15--0.55. In addition, it was possible to disentangle for the first time for any AGN the
reflection strength associated with the close and distant reprocessing medium. These values
are equal to ~0.2/2pi and ~0.35/2pi, respectively. Preliminary interpretation of the
results favours a model with a hot inner accretion flow (plasma) and a cold outer disc of
relatively large inner radius. The spectral models obtained for NGC 4151 are compared with
the hard X-ray spectra of other AGNs and BH binaries.