Related papers: Optical depth for VHE gamma-rays from distant sour…
Very high energy (VHE) gamma-rays undergo pair production with low energy photons of background radiation fields. This leads to an attenuation of the primary gamma-ray flux of extragalactic sources in the interaction with the extragalactic…
The Extragalactic Background Light (EBL) as an integrated light from outside of our Galaxy includes information of the early universe and the Dark Ages. We analyzed the spectral data of the astrophysical diffuse emission obtained with the…
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…
Recently, a new method to constrain the distances of blazars with unknown redshift using combined observations in the GeV and TeV regimes has been developed. The underlying assumption is that the Very High Energy (VHE, E > 100 GeV) spectrum…
The radio galaxy M87 is a variable very-high energy (VHE) gamma-ray source, exhibiting three major flares reported in 2005, 2008, and 2010. Despite extensive studies, the origin of the VHE gamma-ray emission is yet to be understood. In this…
The unexpectedly hard spectra measured by HESS for the BLLacs 1ES 1101-232 and H 2356-309 has allowed an upper limit on the Extragalactic Background Light (EBL) to be derived in the optical/near-infrared range, which is very close to the…
The attenuation of very high energy (VHE) photons by the extragalactic background light (EBL) prevents the observation of high redshift flat spectrum radio quasars (FSRQs). However, the correlation of VHE spectral index with source redshift…
Gamma rays of ~TeV energies from distant sources suffer attenuation due to pair production off of ~1 micron EBL photons. We may exploit this process in order to indirectly measure the EBL and constrain models of galaxy formation. Here,…
The propagation of high energy (HE, $E_\gamma>100$ MeV) and very high-energy gamma-rays (VHE, $E_\gamma>100$ GeV) in the extra-galactic photon field leads to pair-production and consequently energy- and distance-dependent attenuation of the…
We present an analysis of the intrinsic (unattenuated by the extragalactic background light, EBL) power-law spectral indices of 128 extragalactic sources detected up to z~2 with the Fermi-Large Area Telescope (LAT) at very high energies…
Energy spectra of gamma-ray blazars may contain an imprint from the cosmic infrared background radiation due to gamma-ray absorption (pair-production) by soft photons constituting the extragalactic background light (EBL). The signature of…
We calculate the gamma-ray spectrum of a distant blazar, PKS 1424+240, located at redshift z > 0.6035, where the optical depth to primary gamma rays of the highest observed energies is \tau > 5. The spectral shape agrees well with what is…
In a project aimed at measuring the optical Extragalactic Background Light (EBL) we are using the shadow of a dark cloud.We have performed, with the ESO VLT/FORS, spectrophotometry of the surface brightness towards the…
Photons with very high energy up to TeV (VHE) emitted from active galactic nuclei (AGNs) provide some invaluable information of the origin of $\gam$-ray emission. Although 66 blazars have been detected by {\it EGRET}, only three low…
VHE (Very High Energy, E>100 GeV) radiation emitted at cosmological distances will pair produce on low-energy diffuse extragalactic background radiation before ever reaching us. This prevents us from directly seeing most of the VHE emission…
We assess the constraints imposed by the observed extragalactic background light (EBL) on the cosmic history of star formation and the stellar mass density today. The logarithmic slope of the galaxy number-magnitude relation from the…
We study the possible detection of and properties of very high-energy (VHE) gamma-ray emission (in the energy band above 100 GeV) from high redshift sources. We report on the detection of VHE gamma-ray flux from blazars with redshifts…
The Extragalactic Background Light (EBL) captures the total integrated emission from stars and galaxies throughout the cosmic history. The amplitude of the near-infrared EBL from space absolute photometry observations has been controversial…
The VERITAS collaboration has approved long-term observations on several distant, hard-spectrum blazars. We present first results from VERITAS long-term observations of 1ES1218+304, 1ES0229+200, and 1ES0414+009. Gamma-ray observations of…
We report the observation in the GeV band of the blazar 1ES 0229+200, which over recent years has become one the primary sources used to put constraints on the Extragalactic Background Light (EBL) and Extragalactic Magnetic Field (EGMF). We…