Journal Article

An X-ray view of the <i>INTEGRAL</i>/IBIS blazars

S. Gianní, A. De Rosa, L. Bassani, A. Bazzano, T. Dean and P. Ubertini

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 411, issue 4, pages 2137-2147
Published in print March 2011 | ISSN: 0035-8711
Published online March 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.17725.x
An X-ray view of the INTEGRAL/IBIS blazars

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The aim of this work is a broad-band study, using the INTEGRAL, Swift and XMM–Newton satellites, of a sample of nine blazars (seven flat-spectrum radio quasars and two BL Lacertae objects) with redshift (z) up to about 4. The spectral analysis has shown clear evidence of a flattening of the continuum towards low energies (E < 3 keV observer frame). This behaviour is well reproduced, with both an absorbed power-law model (NH∼ 1020–1023 cm−2 in the rest frame of the sources) and a broken power-law continuum model (with an energy break below 3 keV in the observer frame). No Compton reflection features, Fe Kα line or hump at high energies have been detected, with the exception of the source IGR J22517+2218, which shows the presence of a weak iron line. In this paper, we also investigate a possible correlation between the absorption column density NH and the redshift. We confirm the existence of an NHz trend, with the higher absorption at z > 2 for a larger sample compared to previous results. A distribution of NH and the photon index Γ is also presented. The hard X-ray data allow us to detect highly absorbed sources (with NH≥ 1023 cm−2 in the rest frame of the source) characterized by a photon-index distribution peaking at harder values (Γ∼ 1.4) with respect to those obtained with XMM data only (Γ∼ 2).

Keywords: galaxies: active; quasars: general; X-rays: galaxies

Journal Article.  7349 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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