The black hole system 1E${thinspace}$1740.7$-$2942 is usually the brightest hard X-ray source (above 20 keV) near the Galactic Center, but presents some epochs of low emission (below the INTEGRAL detection limit, for example). In this work, we presen
t the results of studies on 1E${thinspace}$1740.7$-$2942 over 10 years, using the instruments ISGRI/IBIS and JEM-X, both on board the INTEGRAL observatory. We fit the spectra with both the compTT and cutoffpl models. According to the fits and taking the mean value over the 10 years, we have obtained a plasma temperature in the range $sim$20$,-,$90$thinspace$ keV, and an average powerlaw index of 1.41 ($sigma$=0.25). We have also made a Lomb$,-,$Scargle periodogram of the flux in the 50$,-,$20${thinspace}$keV band and found two tentative periods at 2.90 and 3.99${thinspace}$days. We present here the preliminary results of this ongoing work.
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 $kT$thinspace$sim 50${thinspace}keV and optical depth around 1. Previous spectral studies of
1E{thinspace}1740.7$-$2942, including both the soft and the hard X-ray bands, were always limited by gaps in the spectra or by a combination of observations with imaging and non-imaging instruments. In this study, we have used three rare nearly-simultaneous observations of 1E{thinspace}1740.7$-$1942 by both XMM-Newton and INTEGRAL satellites to combine spectra from four different imaging instruments with no data gaps, and we successfully applied the Comptonization scenario to explain the broadband X-ray spectra of this source in the low/hard state. For two of the three observations, our analysis also shows that, models including Compton reflection can adequately fit the data, in agreement with previous reports. We show that the observations can also be modeled by a more detailed Comptonization scheme. Furthermore, we find the presence of an iron K-edge absorption feature in one occasion, which confirms what had been previously observed by Suzaku. Our broadband analysis of this limited sample shows a rich spectral variability in 1E{thinspace}1740.7$-$2942 at the low/hard state, and we address the possible causes of these variations. More simultaneous soft/hard X-ray observations of this system and other black-hole binaries would be very helpful in constraining the Comptonization scenario and shedding more light on the physics of these systems.
Studies of the long-term spectral variations have been used to constrain the emission processes of black hole candidates. However, a common scenario which is able to explain the emission from soft to hard X-rays has been proposed only recently. Here,
we use XMM and INTEGRAL data on 1E 1740.7-2942 in order to demonstrate that Comptonization plays an important role in producing high energy photons, as predicted by the current modeling scenario.
