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Issue A&A
Volume 370, Number 3, May II 2001
Page(s) 900 - 908
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20010286



A&A 370, 900-908 (2001)
DOI: 10.1051/0004-6361:20010286

The BeppoSAX High Energy Large Area Survey

IV. On the soft X-ray properties of the hard X-ray-selected HELLAS sources
C. Vignali1, 2, A. Comastri2, F. Fiore3, 4 and F. La Franca5

1  Dipartimento di Astronomia, Università di Bologna, Via Ranzani 1, 40127 Bologna, Italy
2  Osservatorio Astronomico di Bologna, Via Ranzani 1, 40127 Bologna, Italy
3  Osservatorio Astronomico di Roma, Via Frascati 33, 00044 Monteporzio, Italy
4  BeppoSAX Science Data Center, Via Corcolle 19, 00131 Roma, Italy
5  Dipartimento di Fisica, Università degli Studi "Roma Tre", Via della Vasca Navale 84, 00146 Roma, Italy

(Received 13 December 2000 / Accepted 16 February 2001)

Abstract
We present a comprehensive study of the soft X-ray properties of the BeppoSAX High-Energy Large Area Survey (HELLAS) sources. A large fraction (about 2/3) of the hard X-ray selected sources is detected by ROSAT. The soft X-ray colors for many of these objects, along with the 0.5-2 keV flux upper limits for those undetected in the ROSAT band, do imply the presence of absorption. The comparison with the ROSAT Deep Survey sources indicates that a larger fraction of absorbed objects among the HELLAS sources is present, in agreement with their hard X-ray selection and the predictions of the X-ray background synthesis models. Another striking result is the presence of a soft (additional) X-ray component in a significant fraction of absorbed objects.


Key words: surveys -- galaxies: active -- galaxies: nuclei -- galaxies: starburst X -- rays: galaxies

Offprint request: C. Vignali, vignali@kennet.bo.astro.it

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© ESO 2001


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