Search Publications
A Hubble Diagram for Quasars
Risaliti, Guido; Lusso, Elisabeta; Bisogni, Susanna
The cosmological model is at present not tested between the redshift of the farthest observed supernovae (z 1.4) and that of the Cosmic Microwave Background (z 1,100). Here we introduce a new method to measure the cosmological parameters: we show that quasars can be used as “standard candles” by employing the non-linear relation between their intr…
The MEXSAS2 Sample and the Ensemble X-ray Variability of Quasars
Serafinelli, Roberto; Middei, Riccardo; Chiaraluce, Elia +1 more
We present the second Multi-Epoch X-ray Serendipitous AGN Sample (MEXSAS2), extracted from the 6th release of the XMM Serendipitous Source Catalogue release (XMMSSC-DR6), cross-matched with Sloan Digital Sky Survey quasar catalogues DR7Q and DR12Q. Our sample also includes the available measurements for masses, bolometric luminosities, and Eddingt…
Catalog of 3<z<5.5 quasar candidates selected among XMM-Newton sources and its spectroscopic verification
Khorunzhev, Georgii; Sazonov, Sergey; Burenin, Rodion +1 more
We have compiled a catalog of 903 quasar candidates (including known quasars) at 3<z<5.5 selected among X-ray sources from the XMM-Newton serendipitous survey (3XMM-DR4 catalog). We used photometric SDSS, 2MASS and WISE data to select the objects. The surface number density of objects in our sample exceeds that in the SDSS spectroscopic quas…
Gaia space mission and quasars
Zwitter, Tomaž
Quasars are often considered to be point-like objects. This is largely true and allows for an excellent alignment of the optical positional reference frame of the ongoing ESA mission Gaia with the International Celestial Reference Frame. But presence of optical jets in quasars can cause shifts of the optical photo-centres at levels detectable by G…
Multi-frequency databases for AGN investigation - Results and perspectives
La Mura, Giovanni; Berton, Marco; Chen, Sina +5 more
Active Galactic Nuclei (AGNs) are characterized by emission of radiation over more than 10 orders of magnitude in frequency. Therefore, the execution of extensive surveys of the sky, with different types of detectors, is providing the attractive possibility to identify and to investigate the properties of AGNs on very large statistical samples. Th…