High-redshift blazar identification for Swift j1656.3-3302

We report on the high-redshift blazar identification of a new gamma-ray source, Swift J1656.3-3302, detected with the BAT imager onboard the Swift satellite and the IBIS instrument on the INTEGRAL satellite. Follow-up optical spectroscopy has allowed us to identify the counterpart as an R similar to 19 mag source that shows broad Lyman-alpha, Si IV, He II, C IV, and CIII] emission lines at redshift z = 2.40 +/- 0.01. Spectral evolution is observed in X-rays when the INTEGRAL/IBIS data are compared to the Swift/BAT results, with the spectrum steepening when the source gets fainter. The 0.7-200 keV X-ray continuum, observed with Swift/XRT and INTEGRAL/ IBIS, shows the power law shape typical of radio loud (broad emission line) active galactic nuclei (with a photon index Gamma similar to 1.6) and a hint of spectral curvature below similar to 2 keV, possibly due to intrinsic absorption (N-H similar to 7 x 10(22) cm(-2)) local to the source. Alternatively, a slope change (Delta Gamma similar to 1) around 2.7 keV can describe the X-ray spectrum equally well. At this redshift, the observed 20-100 keV luminosity of the source is similar to 10(48) erg s(-1) (assuming isotropic emission), making Swift J1656.3-3302 one of the most X-ray luminous blazars. This source is yet another example of a distant gamma-ray loud quasar discovered above 20 keV. It is also the farthest object, among the previously unidentified INTEGRAL sources, whose nature has been determined a posteriori through optical spectroscopy.