Related papers: Blazars distance indications from Fermi and TeV da…

High-energy photons from cosmological emitters suffer attenuation due to pair production interactions with the extragalactic background light (EBL). The collective emission of any high-energy emitting cosmological population will exhibit an…

The diffuse meta-galactic radiation field at ultraviolet to infrared wavelengths - commonly labeled extragalactic background light (EBL) - contains the integrated emission history of the universe. Difficult to access via direct observations…

As a bright gamma-ray source, 3C 66A is of great interest to the high-energy astrophysics community, having a potential for placing cosmological constraints on models for the extragalactic background light (EBL) and the processes which…

The emission of very-high-energy photons (VHE, E>100 GeV$) in blazars is closely connected to the production of ultra-relativistic particles and the role of these gamma-ray sources as cosmic particle accelerators. This work focuses on a…

The Extragalactic Background Light (EBL) is the integrated light from all the stars that have ever formed, and spans the IR-UV range. The interaction of very-high-energy (VHE: E>100 GeV) gamma-rays, emitted by sources located at…

We present results of observations in the UV to near-IR range for eight blazars, three of which have been recently discovered at Very High Energies (VHE) and five appearing as interesting candidates for VHE {\gamma}-ray detection. We focus…

Recent gamma-ray observations of the blazar 1ES 1101-232 (redshift z=0.186) reveal that the unabsorbed TeV spectrum is hard, with spectral index $\alpha \lesssim 0.5$ [$F(\nu) \propto \nu^{-\alpha}$]. We show that simple one-zone…

Observations of very-high-energy (VHE, E > 250 GeV) gamma-ray emission from several blazars at z > 0.1 have placed stringent constraints on the elusive spectrum and intensity of the intergalactic infrared background radiation (IIBR).…

PG 1553+113 is a very-high-energy (VHE, $E>100\,\mathrm{GeV}$) $\gamma$-ray emitter classified as a BL Lac object. Its redshift is constrained by intergalactic absorption lines in the range $0.4<z<0.58$. The MAGIC telescopes have monitored…

Very-high energy (VHE) emission has been detected from PKS 0447-439 with the H.E.S.S. Cherenkov telescope array. This blazar is one of the brightest hard-spectrum extragalactic objects in the Fermi bright source list. Its detection with…

The diffuse extragalactic background light (EBL) is formed by ultraviolet (UV), optical, and infrared (IR) photons mainly produced by star formation processes over the history of the Universe, and contains essential information about galaxy…

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…

The blazar 1ES 1101-232 was observed with the High Energy Stereoscopic System (H.E.S.S.) of Atmospheric Cherenkov Telescopes (ACT) in 2004 and 2005, for a live time of 43 hours. VHE (E > 10^11 eV) gamma-rays were detected for the first time…

The Fermi Large Area Telescope (LAT) Collaboration has recently released the Third Catalog of Hard Fermi-LAT Sources (3FHL), which contains 1556 sources detected above 10 GeV with seven years of Pass 8 data. We investigate the source count…

Spectra of the brightest blazars detected by the Fermi Gamma-ray Space Telescope Large Area Telescope cannot be described by a simple power law model. A much better description is obtained with a broken power law, with the break energies of…

The extragalactic $\gamma$-rays sky observed by Fermi-Large Area Telescope (LAT) is dominated by blazars. In the fourth release of the Fermi-LAT Point Source Catalog (4FGL), are sources showing a multifrequency behavior similar to that of…

We study the origin of the extragalactic diffuse gamma-ray background using the data from the Fermi telescope. To estimate the background level, we count photons at high Galactic latitudes |b|>60 degrees. Subtracting photons associated to…

We compute the contribution of blazars (Flat Spectrum Radio Quasars and BL-Lacs) to the Fermi-LAT Extragalactic gamma-ray Background, assuming a gamma-ray luminosity function proportional to the luminosity function of radio galaxies and the…

Blazars with redshifts z<0.1 are likely candidates for detection at energies in the range 300 GeV - 50 TeV with Cerenkov telescopes and scintillator arrays. We present gamma-ray flux predictions for a sample of 15 nearby flat-spectrum radio…

The extragalactic background light (EBL), the cumulative radiation from all extragalactic sources, traces galaxy formation and cosmic evolution. High-energy $\gamma$ rays attenuated via pair production with EBL photons are a powerful probe…