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arXiv · 0801.2976

High-redshift blazar identification for Swift J1656.3-3302

N. Masetti·E. Mason·R. Landi·P. Giommi·L. Bassani·A. Malizia·A. J. Bird·A. Bazzano·A. J. Dean·N. Gehrels·E. Palazzi·P. Ubertini
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Abstract

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.

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N. Masetti, E. Mason, R. Landi, P. Giommi, L. Bassani, A. Malizia, A. J. Bird, A. Bazzano, A. J. Dean, N. Gehrels, E. Palazzi, P. Ubertini. 2008-01-18. High-redshift blazar identification for Swift J1656.3-3302. https://doi.org/10.1051/0004-6361:20078901

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