Search Publications
The high energy X-ray probe (HEX-P): probing the physics of the X-ray corona in active galactic nuclei
Nardini, Emanuele; Ricci, Claudio; Walton, Dominic J. +27 more
The hard X-ray emission in active galactic nuclei (AGN) and black hole X-ray binaries is thought to be produced by a hot cloud of electrons referred to as the corona. This emission, commonly described by a power law with a high-energy cutoff, is suggestive of Comptonization by thermal electrons. While several hypotheses have been proposed to expla…
The high energy X-ray probe (HEX-P): studying extreme accretion with ultraluminous X-ray sources
Maitra, Chandreyee; Mori, Kaya; Wolter, Anna +25 more
Introduction: Ultraluminous X-ray sources (ULXs) represent an extreme class of accreting compact objects: from the identification of some of the accretors as neutron stars to the detection of powerful winds travelling at 0.1–0.2 c, the increasing evidence points towards ULXs harbouring stellar-mass compact objects undergoing highly super-Eddington…
Eight Years of TIGRE Robotic Spectroscopy: Operational Experience and Selected Scientific Results
Nazé, Yaël; Rauw, Gregor; Jack, Dennis +4 more
TIGRE (Telescopio Internacional de Guanajuato Robótico Espectroscópico) has been operating in fully robotic mode in the La Luz Observatory (Guanajuato, Mexico) since the end of 2013. With its sole instrument, HEROS, an échelle spectrograph with a spectral resolution R ∼20,000, TIGRE has collected more than 48,000 spectra of 1,151 different sources…
Cosmology with quasars: predictions for eROSITA from a quasar Hubble diagram
Lusso, Elisabeta
The effort for understanding the matter and energy content of the Universe and its evolution relies on different probes, such as cosmic background radiation, cluster lensing, supernovae. Yet, we are still far from grasping what dark matter is made of, and what the physical origin of dark energy is. Our group has developed a technique that makes us…
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…
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…