Soft gamma-ray emission from the V404 Cygni outburst observed with INTEGRAL/PICsIT

Abstract

V404 Cygni during its 2015 outburst was the brightest source ever observed by INTEGRAL in the soft gamma-ray band. This made possible to detect the source with the IBIS high energy detector PICsIT in many single pointings (≈1 h long) allowing to study the evolution of the gamma-ray emission over the whole event period. In general, the PICsIT flux in the 255-340 keV band correlates with the hard X-ray flux measured by INTEGRAL/ISGRI, although we observe a saturation of the gamma-ray emission from the source. The spectra extracted for several short periods of the outburst were modelled with a Comptonization model. The plasma temperature remains stable despite a variation of the Compton parameter. We found a strong Compton reflection and a hint for a non-thermal emission occurring during some phases of the outburst. Our preliminary analysis do not show a presence of the positron annihilation line in the V404 Cygni spectra from the 2015 outburst.