The BeppoSAX High Energy Large Area Survey (HELLAS) has surveyed about 85 deg(2) of sky in the 5-10 keV band down to a flux of 4-5 x 10(-14) erg cm(-2) s(-1). The source surface density of 16.9 +/- 6.4 deg(-2) at the survey limit corresponds to a resolved fraction of the 5-10 keV X-ray background (XRB) of the order of 20-30 per cent. Hardness ratio analysis indicates that the spectra of a substantial fraction of the HELLAS sources (at least one-third) are harder than a alpha (E) = 0.6 power law. This hardness may be caused by large absorbing columns. The hardness ratio analysis also indicates that many HELLAS sources may have a spectrum more complex than a single absorbed power law. A soft component, superimposed on a strongly cut-off power law, is likely to be present in several sources.
Fiore, F., Giommi, P., Vignali, C., Comastri, A., Matt, G., Perola, G.c., et al. (2001). The BeppoSAX High Energy Large Area Survey (HELLAS) - II. Number counts and X-ray spectral properties. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 327(3), 771-780 [10.1046/j.1365-8711.2001.04736.x].
The BeppoSAX High Energy Large Area Survey (HELLAS) - II. Number counts and X-ray spectral properties
Matt G;LA FRANCA, Fabio;
2001-01-01
Abstract
The BeppoSAX High Energy Large Area Survey (HELLAS) has surveyed about 85 deg(2) of sky in the 5-10 keV band down to a flux of 4-5 x 10(-14) erg cm(-2) s(-1). The source surface density of 16.9 +/- 6.4 deg(-2) at the survey limit corresponds to a resolved fraction of the 5-10 keV X-ray background (XRB) of the order of 20-30 per cent. Hardness ratio analysis indicates that the spectra of a substantial fraction of the HELLAS sources (at least one-third) are harder than a alpha (E) = 0.6 power law. This hardness may be caused by large absorbing columns. The hardness ratio analysis also indicates that many HELLAS sources may have a spectrum more complex than a single absorbed power law. A soft component, superimposed on a strongly cut-off power law, is likely to be present in several sources.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
