The spectral catalogue of INTEGRAL gamma-ray bursts: results of the joint IBIS/SPI spectral analysis

We present the updated INTEGRAL catalogue of gamma-ray bursts (GRBs) observed between December 2002 and February 2012. The catalogue contains the spectral parameters for 59 GRBs localized by the INTEGRAL Burst Alert System (IBAS). We used the data from the two main instruments on board the INTEGRAL satellite: the spectrometer SPI (SPectrometer on INTEGRAL) nominally covering the energy range 18 keV - 8 MeV, and the imager IBIS (the Imager on Board the INTEGRAL Satellite) operating in the range from 15 keV to 10 MeV. For the spectral analysis we applied a new data extraction technique, developed in order to explore the energy regions of highest sensitivity for both instruments, SPI and IBIS. It allowed us to perform analysis of the GRB spectra over a broad energy range and to determine the bursts spectral peak energies. The spectral analysis was performed on the whole sample of GRBs triggered by IBAS, including all the events observed in period December 2002 - February 2012. The catalogue contains the trigger times, burst coordinates, positional errors, durations and peak fluxes for 28 unpublished GRBs observed between September 2008 and February 2012. The light curves in 20 - 200 keV energy band of these events were derived using IBIS data. We compare the prompt emission properties of the INTEGRAL GRB sample with the BATSE and Fermi samples.

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 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.