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 \sim 19 mag source that shows broad Lyman- \alpha , Si iv , He ii , C iv , and C iii ] emission lines at redshift z = 2.40 \pm 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 \sim 1.6 ) and a hint of spectral curvature below \sim 2 keV , possibly due to intrinsic absorption ( N _ { H } \sim 7 \times 10 ^ { 22 } cm ^ { -2 } ) local to the source .
Alternatively , a slope change ( \Delta \Gamma \sim 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 \sim 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 .