spectrum of hard X-ray selected QSOs.
It has been almost 40 years since Giacconi et al. (1962) discovered the X-ray Background (XRB), the first cosmic background detected. Nevertheless its origin is still not fully understood. At a flux limit of ∼ 10 −15 erg cm −2 s −1 70 −80 % o
Sorry, we are unable to provide the full text but you may find it at the following location(s):
http://citeseerx.ist.psu.edu/v... (external link)
http://arxiv.org/pdf/astro-ph/... (external link)