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On the Exotic Hard X-ray Source Populations in the Hellas2XMM survey
C. Vignali, M. Mignoli
Recent hard X-ray surveys have proven to be effective in discovering large numbers of X-ray sources that, despite the likely association with active nuclei, appear to be characteri…
Type II quasar candidates in the Sloan Digital Sky Survey: evidence for X-ray obscuration
C. Vignali, D. M. Alexander, A. Comastri
Recent X-ray surveys with Chandra and XMM-Newton have found several genuine Type II quasars, the long sought-after population of high-luminosity (high-redshift) Seyfert 2 galaxies,…
The HELLAS2XMM 1dF Survey: a window on exotic hard X-ray selected sources
C. Vignali
Recent Chandra and XMM-Newton surveys have confirmed that the cosmic X-ray background is mostly due to accretion onto super-massive black holes, integrated over cosmic time. Here w…
The HELLAS2XMM 1dF survey: on the nature of high X-ray to optical flux ratio sources
F. Fiore, M. Brusa, F. Cocchia +12
We present results from the photometric and spectroscopic identification of 122 X-ray sources discovered by XMM-Newton in the 2-10 keV band (the HELLAS2XMM 1dF sample). One of the…
X-rays from the First Massive Black Holes
W. N. Brandt, C. Vignali, D. P. Schneider +7
X-ray studies of high-redshift (z > 4) active galaxies have advanced substantially over the past few years, largely due to results from the new generation of X-ray observatories. A…
X-ray emission from the most luminous z>4 Palomar Digital Sky Survey Quasars: the Chandra view
C. Vignali, W. N. Brandt, D. P. Schneider +2
We present the results obtained from exploratory Chandra observations of nine high-redshift (z=4.09-4.51) quasars, selected from among the optically brightest Palomar Digital Sky S…