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∼ 19 mag source that shows broad Lyman-α, 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 Γ ∼ 1.6) and a hint of spectral curvature below ~2 keV, possibly due to intrinsic absorption (NH ∼ 7× 10 22 cm-2) local to the source. Alternatively, a slope change (Δ Γ ∼ 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 ~1048 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.
Partly based on X-ray observations with INTEGRAL, an ESA project with instruments and science data centre funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Switzerland, Spain), Czech Republic and Poland, and with the participation of Russia and the USA, and on optical observations collected at ESO (La Silla, Chile) under programme 079.A-0171(A).- Publication:
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Astronomy and Astrophysics
- Pub Date:
- March 2008
- DOI:
- 10.1051/0004-6361:20078901
- arXiv:
- arXiv:0801.2976
- Bibcode:
- 2008A&A...480..715M
- Keywords:
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- quasars: emission lines;
- quasars: individual: J1656.3-3302;
- galaxies: high-redshift;
- galaxies: active;
- X-rays: galaxies;
- astrometry;
- Astrophysics
- E-Print:
- 9 pages, 5 figures, 2 tables. Accepted for publication on Astronomy &