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Astron. Astrophys. 338, 781-794 (1998)


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Heavy obscuration in X-ray weak AGNs

R. Maiolino 1, M. Salvati 1, L. Bassani 2, M. Dadina 2, R. Della Ceca 3, G. Matt 4, G. Risaliti 5 and G. Zamorani 6

1 Osservatorio Astrofisico di Arcetri, Largo E.Fermi 5, I-50125, Firenze, Italy (maiolino@arcetri.astro.it; salvati@arcetri.astro.it)
2 Istituto Tecnologie e Studio Radiazioni Extraterrestri, CNR, Via Gobetti 101, I-40129 Bologna, Italy (loredana@botes1.tesre.bo.cnr.it; dadina@terra.tesre.bo.cnr.it)
3 Osservatorio Astronomico di Brera, Via Brera 28, I-20121 Milano, Italy (rdc@brera.mi.astro.it)
4 Dipartimento di Fisica, Università di Roma III, Via della Vasca Navale 84, I-00146, Roma, Italy (matt@haendel.fis.uniroma3.it)
5 Dipartimento di Astronomia, Università di Firenze, Largo E.Fermi 5, I-50125, Firenze, Italy (risaliti@arcetri.astro.it)
6 Osservatorio Astronomico di Bologna, Via Zamboni 33, I-40126 Bologna, Italy, (zamorani@astbo3.bo.astro.it)

Received 13 March 1998 / Accepted 23 July 1998

Abstract

We present observations in the 0.1-100 keV spectral band of 8 Seyfert 2 galaxies, obtained by means of BeppoSAX. These sources were selected according to their [OIII] optical emission line flux, to avoid biases against obscuration on the pc scale. All sources were detected. All of them are weak X-ray emitters, and most of them are characterized by prominent iron lines at 6.4-7 keV (EW[FORMULA] eV) and by a flat continuum, indicative of heavy obscuration along our line of sight (NH [FORMULA] 1025 cm-2 in most cases). These results 1) provide further evidence in favor of the unified scenario, and 2) indicate that the average obscuration of type 2 AGNs is very likely much higher than deduced by former X-ray surveys. These findings have important implications for the synthesis of the X-ray background.

Key words: X-rays: galaxies – galaxies: Seyfert – galaxies: active

Send offprint requests to: R. Maiolino

© European Southern Observatory (ESO) 1998

Online publication: September 17, 1998

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