Related papers: ROXA: a new multi-frequency selected large sample …
We present results of a variability study in the optical band of 44 newly identified blazar candidates behind the Magellanic Clouds. Our sample contains 27 flat spectrum radio quasars (FSRQs) and 17 BL Lacertae objects (BL Lacs). However,…
In recent years, blazar surveys at radio and X-ray energies have greatly increased our understanding of this type of active galaxy. The combination of multi-wavelength data has shown that blazars follow a well defined sequence in terms of…
We use optical data from the Palomar Transient Factory (PTF) and the Catalina Real-Time Transient Survey (CRTS) to study the variability of gamma-ray detected and non-detected objects in a large population of active galactic nuclei (AGN)…
Machine learning based approaches are emerging as very powerful tools for many applications including source classification in astrophysics research due to the availability of huge high quality data from different surveys in observational…
We searched for gamma-ray blazar candidates among the 382 unidentified hard X-ray sources of the 3rd Palermo BAT Catalog (3PBC) obtained from the analysis of 66 months of SWIFT-BAT survey data and listing 1586 sources. We adopted a recently…
AIMS: We present the optical classification and redshift of 348 X-ray selected sources from the XMM-Newton Bright Serendipitous Survey (XBS) which contains a total of 400 objects (identification level = 87%). About 240 are new…
The SRG/eROSITA All-Sky Survey (eRASS) is expected to contain ~100 quasars that emitted their light when the universe was less than a billion years old, i.e. at z>5.6. By selection, these quasars populate the bright end of the AGN X-ray…
We present some first results on the variability, polarization and general properties of radio sources selected in a blind survey at 20 GHz, the highest frequency at which a sensitive radio survey has been carried out over a large area of…
This talk focuses on the statistical properties of X-ray selected BL Lacertae objects (XBLs) whose catalogue has been compiled. It consists of 312 sources from different X-ray surveys, unambiguously identified to mid-2010. Results of the…
Blazars are the most abundant class of known extragalactic very-high-energy (VHE, E>100 GeV) gamma-ray sources. However, one of the biggest difficulties in investigating their VHE emission resides in their limited number, since less than 60…
BL Lac objects are an extreme type of active galactic nuclei (AGNs) that belong to the largest population of $\gamma$-ray sources: blazars. This class of AGNs shows a double-bumped spectral energy distribution that is commonly described in…
In the last two decades, very-high-energy gamma-ray astronomy has reached maturity: over 200 sources have been detected, both Galactic and extragalactic, by ground-based experiments. At present, Active Galactic Nuclei (AGN) make up about…
We present simultaneous multifrequency radio observations for a complete subsample of 26 XBLs from the Einstein Extended Medium-Sensitivity Survey, obtained with the Very Large Array (VLA). Spectra are computed using fluxes at 20, 6 and 3.6…
Using survey data, we have re-evaluated the correlation of flat spectrum radio sources with EGRET sources in the Northern sky. A likelihood analysis incorporating the radio and X-ray properties and the Gamma-ray source localization is used…
Hard X-ray properties of beamed AGN have been published in the 105-month Swift/BAT catalog, but there have not been any studies carried out so far on a well-defined, radio-selected sample of low-peaked blazars in the hard X-ray band. Using…
We present new, simultaneous, multifrequency observations of 45 out of the 55 candidate High Frequency Peakers (HFP) selected by Dallacasa et al. (2000), carried out 3 to 4 years after a first set of observations. Our sub-sample consists of…
The parsec-scale radio properties of blazars detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope have been investigated using observations with the Very Long Baseline Array (VLBA). Comparisons between LAT…
We present the first catalog of active galactic nuclei (AGN) detected by the LAT, corresponding to 11 months of data collected in scientific operation mode. The First LAT AGN Catalog (1LAC) includes 671 gamma-ray sources located at high…
All but three (M87, BL Lac and 3C 279) extragalactic sources detected so far at very high energy (VHE) gamma-rays belong to the class of high-frequency peaked BL Lac (HBL) objects. This suggested to us a systematic scan of candidate sources…
The Fermi Large Area Telescope (LAT) is currently the most important facility for investigating the GeV $\gamma$-ray sky. With Fermi LAT more than three thousand $\gamma$-ray sources have been discovered so far. 1144 ($\sim40\%$) of the…