Related papers: Optical Spectroscopy of Blazars for the Cherenkov …
The VERITAS array of 12-m atmospheric-Cherenkov telescopes is used in an intensive observation program focused on the discovery of VHE (E > 100 GeV) gamma-ray-emitting blazars. Since VERITAS began full-scale operation in 2007, more than…
Astrophysical models for the high-energy emission of blazars are reviewed. Blazars ejecting relativistic radio jets at small angles to the line-of-sight are the only type of active galactic nuclei (AGN) discovered above 100 MeV. The…
Within the framework of our program of assessment of the nature of unidentified or poorly known INTEGRAL sources, we present here spectroscopy of optical objects, selected through positional cross-correlation with soft X-ray detections…
The extragalactic gamma-ray sky is dominated by the emission arising from blazars, one of the most peculiar classes of radio-loud active galaxies. Since the launch of Fermi several methods were developed to search for blazars as potential…
(abridged) Hard X-ray surveys performed by the INTEGRAL satellite have discovered a conspicuous fraction (up to 30%) of unidentified objects among the detected sources. Here we continue our identification program by selecting probable…
Blazars are a subclass of active galactic nuclei (AGN) that emit non-thermal radiation through relativistic jets, characterized by rapid flux and polarization variability. High synchrotron-peaked blazars (HSPs) and extreme high…
Blazars are active galactic nuclei (AGN) whose relativistic jets point nearly to the line of sight. Their compact radio structure can be imaged with very long baseline interferometry (VLBI) on parsec scales. Blazars at extremely high…
The rapid variability observed in very-high-energy (VHE) sources-such as pulsars, gamma-ray bursts (GRBs), and flares from active galactic nuclei (AGN)-can be used to detect or constrain a potential violation of Lorentz invariance (LIV).…
We present the results of our identification of eight objects from a preliminary catalogue of X-ray sources detected in the 4-12 keV energy band by the Mikhail Pavlinsky ART-XC telescope aboard the SRG observatory during its first all-sky…
The VERITAS array of Cherenkov telescopes was used to observe ~130 blazars from 2007 to 2012. Of these, 25 were detected as very-high-energy (VHE; E > 100 GeV) sources. We present here the results of the analysis of 65 VERITAS non-detected…
The VERITAS array of 12-m atmospheric-Cherenkov telescopes in southern Arizona is currently the world's most-sensitive detector of astrophysical very high energy (VHE; E>100 GeV) gamma rays. Approximately 25 blazars are known to emit VHE…
The radiation mechanism of very high energy $\gamma$-ray emission from blazars and crucial parameters like magnetic field, and size of the emitting region are not well understood yet. To understand the above mentioned properties of blazars,…
Blazars are a class of active galactic nuclei (AGNs) known for their very rapid variabilty in the high energy regions of the electromagnetic spectrum. Despite this known fast variability, X-ray observations have generally not revealed…
The Cherenkov Telescope Array Observatory (CTAO) will enable detailed studies of Active Galactic Nuclei (AGN) in the very-high-energy (VHE) regime, as the next-generation ground-based gamma-ray observatory, designed to enhance sensitivity…
The maximum number density of Active Galactic Nuclei (AGNs), as deduced from X-ray studies, occurs at z<~1, with lower luminosity objects peaking at smaller redshifts. Optical studies lead to a different evolutionary behaviour, with a…
The understanding of acceleration mechanisms in active galactic nuclei (AGN) jets and the measurement of the extragalactic-background-light (EBL) density are closely linked and require the detection of a large sample of very-high-energy…
The BL Lac object 3C66A is one of the most luminous extragalactic sources at TeV $\gamma$-rays (VHE, i.e. $E >100$ GeV). Since TeV $\gamma$-ray radiation is absorbed by the extragalactic background light (EBL), it is crucial to know the…
The number of discovered TeV sources populating the extragalactic sky in 2017 is nearly 70, mostly blazars located up to a redshift ~1. Ten years ago, in 2007, less than 20 TeV emitters were known, up to a maximum redshift of 0.2. This is a…
The ANTARES telescope is well-suited for detecting astrophysical transient neutrino sources as it can observe a full hemisphere of the sky at all times with a high duty cycle. The background due to atmospheric particles can be drastically…
We recently started a systematic search of low-energy counterparts of the unidentified gamma-ray sources (UGSs) listed in the Fermi-Large Area Telescope (LAT) First Source Catalog (1FGL) and the Fermi-LAT 2-Year Source Catalog (2FGL).} The…