The BeppoSAX High Energy Large Area Survey

IV. On the soft X-ray properties of the hard X-ray-selected HELLAS sources

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

Corresponding author: C. Vignali, vignali@kennet.bo.astro.it

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.