Testing and confirming the thermal Comptonization model for black hole X-ray emission in the low/hard state with three simultaneous XMM-INTEGRAL observations of 1E 1740.7-2942

Hard X-ray spectra of black hole binaries in the low/hard state are well modeled by thermal Comptonization of soft seed photons by a corona-type region with kT ∼ 50{ }keV and optical depth around 1. Previous spectral studies of 1E{ }1740.7-2942 including both the soft and the hard X-ray bands were always limited by gaps in the spectra or by a combination of observations with imaging and non-imaging instruments. In this study we have used three rare (almost) simultaneous observations of 1E{ }1740.7-1942 by two ESA's satellites, XMM-Newton and INTEGRAL, combining spectra from 4 different imaging instruments with no data gaps. We were able to test the Comptonization scenario to explain the X-ray spectra of 1E{ }1740.7-2942 in the low/hard state. Our analysis also shows that for two of the three observations, models including Compton reflection can addequately fit the data. This is in agreement with previous reports in the literature. Our observations can also be described by a more detailed Comptonization model. We also find, in one occasion, the presence of an iron K-edge absorption feature, previously observed by Suzaku. According to our broadband analysis, we found a rich spectral variability in 1E{ }1740.7-2942 spectra at the low/hard state. We attempted to address the causes of this variations with our limited sample. It would be interesting to confirm this, helping in constraining the physical models, by more simultaneous soft/hard observations of the system. As we highlight here, the combined use of both XMM-Newton and INTEGRAL is very suitable to achieve such a goal.