  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-band 19 mag
source that shows broad Lyman-alpha, Si IV, He II, C IV, and C III] 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
around 1.6) and a hint of spectral curvature below 2 keV, possibly due to
intrinsic absorption (N_H about 7e22 cm-2) local to the source. Alternatively,
a slope change (of about 1 in terms of photon index) 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 about 1e48 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.
