High-redshift blazar identification for Swift J1656.3-3302
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.
Cite
@article{arxiv.0801.2976,
title = {High-redshift blazar identification for Swift J1656.3-3302},
author = {N. Masetti and E. Mason and R. Landi and P. Giommi and L. Bassani and A. Malizia and A. J. Bird and A. Bazzano and A. J. Dean and N. Gehrels and E. Palazzi and P. Ubertini},
journal= {arXiv preprint arXiv:0801.2976},
year = {2009}
}
Comments
9 pages, 5 figures, 2 tables. Accepted for publication on Astronomy & Astrophysics, main journal