  0.1-10 MeV observations of the black hole microquasar Cygnus X-1 have shown
the presence of a spectral feature in the form of a power law in addition to
the standard black body and Comptonization components observed by INTEGRAL.
This so-called "high-energy tail" has recently been shown to be strong in its
hard spectral state and interpreted as high-energy part of the emission from a
compact jet. This result was, however, obtained from a data set dominated by
hard state observations. In the soft state, only upper limits on the presence
and hence the potential parameters of a high-energy tail could be derived.
Using an extended data set we aim at obtaining better constraints on the
properties of this spectral component in both states. We make use of data
obtained from 15 years of observations with the INTEGRAL satellite. The data
set is separated into the different states and we analyse stacked
state-resolved spectra obtained from the X-ray monitors, the gamma-ray imager,
and the gamma-ray spectrometer onboard. A high-energy component is detected in
both states confirming its earlier detection in the hard state and its
suspected presence in the soft state with INTEGRAL. We first characterize the
high-energy tail components in the two states through a model-independent,
phenomenological analysis. We then apply physical models based on hybrid
Comptonization. The spectra are well modeled in all cases, with a similar
goodness of the fits. While in the phenomenological approach the high-enery
tail has similar indices in both states, the fits with the physical models seem
to indicate different properties. We discuss the potential origins of the
high-energy components in both states, and favor an interpretation where the
part of the high-energy component is due to a compact jet in the hard state and
hybrid Comptonization in either a magnetised or non-magnetised corona in the
soft state.
