Unveiling the high energy tail of 1E 1740.7-2942 with INTEGRAL

TL;DR

This study analyzes three years of INTEGRAL data on microquasar 1E 1740.7-2942, revealing its high energy behavior, spectral states, and the first measurement of its continuum up to 600 keV, with implications for thermal and non-thermal processes.

Contribution

First detailed high-energy spectral analysis of 1E 1740.7-2942 up to 600 keV, identifying spectral states and modeling the continuum with thermal and non-thermal components.

Findings

Detected two main spectral states: low/hard and dim.

Measured the continuum spectrum up to ~600 keV.

No 511 keV annihilation line detected.

Abstract

The microquasar 1E 1740.7-2942 is observed with Integral since Spring 2003. Here, we report on the source high energy behaviour 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 and a ``dim'' state, characterised by a ~ 20 times fainter emission, detected only below 50 keV and when summing more than 1Ms 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 non-thermal processes as already observed in other black-hole candidates. Alternatively, we show that a model composed by two thermal Comptonizations provides an equally representative description of the data: the temperature of the first population of electrons results as (kTe)_1 ~ 30 keV while the second, (kTe)_2, is fixed at 100 keV. Finally, searching for 511 keV line showed no feature, either narrow or broad, transient or persistent.