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

Potential origin of the state-dependent high-energy tail in the black hole microquasar Cygnus X-1 as seen with INTEGRAL