Unveiling the High Energy Tail of 1E 1740.7-2942 With INTEGRAL

The microquasar 1E 1740.7-2942 is observed with INTEGRAL since Spring 2003. Here, we report on the source high-energy behavior by using the first three years of data collected with SPI and IBIS telescopes, taking advantage of the instruments complementarity. Light curves analysis showed two main states for 1E 1740.7-2942: the canonical low/hard state of black hole candidates (BHCs) and a "dim" state, characterized by an ~20 times fainter emission, detected only below 50 keV and when summing more than 1 Ms of data. For the first time the continuum of the low/hard state has been measured up to ~600 keV with a spectrum that is well represented by a thermal Comptonization plus an additional component necessary to fit the data above 200 keV. This high-energy component could be related to nonthermal processes as already observed in other BHCs. Alternatively, we show that a model composed of two thermal Comptonizations provides an equally representative description of the data: the temperature of the first population of electrons results as (kT _e)₁~ 30 keV while the second, (kT _e)₂, is fixed at 100 keV. Finally, searching for 511 keV line showed no feature, either narrow or broad, transient or persistent.

INTEGRAL is an ESA project with instruments and science data center funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Spain, and Switzerland), Czech Republic and Poland with participation of Russia and USA.