1,299 research outputs found
The Missing X-ray Background
The fraction of the hard X-ray background (XRB) resolved into individual
sources by the deep Chandra and XMM-Newton surveys strongly depends on the
adopted energy range and decreases with increasing energy. As a consequence,
the nature of the sources of the even harder (>10 keV) XRB remains
observationally poorly constrained. I will briefly discuss the need for X-ray
observations above 10 keV.Comment: to appear in the proceedings of 'Multiwavelength AGN surveys'
(Cozumel, December 8-12 2003), ed. R. Maiolino and R. Mujic
ASCA spectroscopy of the luminous infrared galaxy NGC6240: X-ray emission from a starburst and a buried active nucleus
We present an X-ray spectral study of the prototype far-infrared galaxy
NGC6240 from ASCA. The soft X-ray spectrum (below 2 keV) shows clear signatures
of thermal emission well described with a multi-temperature optically-thin
plasma, which probably originates in a powerful starburst. Strong hard X-ray
emission is also detected with ASCA and its spectrum above 3 keV is extremely
flat with a prominent iron K line complex, very similar to that seen in the
Seyfert 2 galaxy NGC1068 but about an order of magnitude more luminous
[L(3-10keV)=1.4E42 erg/s]. The hard X-ray spectrum indicates that only
reflected X-rays of an active galactic nucleus (AGN) buried in a heavy
obscuration [N(H)>2E24 cm-2] are visible. This is evidence for an AGN in
NGC6240 emitting possibly at a quasar luminosity and suggests its significant
contribution to the far-infrared luminosity.Comment: 9 pages, 6 Postscript figures, to appear in MNRA
The contribution of AGN to the X-ray background: the effect of iron features
The contribution of the iron emission line, commonly detected in the X-ray
spectra of Seyfert (Sey) galaxies, to the cosmic X-ray background (XRB)
spectrum is evaluated in the framework of the XRB synthesis models based on AGN
unification schemes. To derive the mean line properties, we have carried out a
search in the literature covering a sample of about 70 AGN. When adopting line
parameters in agreement with the observations, it turns out that the maximum
contribution of the iron line to the XRB is less than 7% at a few keV. This is
still below the present uncertainties in the XRB spectrum measurements.Comment: 21 LaTeX pages with 5 Postscript figures. Accepted for publication in
New Astronom
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