Related papers: The Blazar Emission Environment: Insight from Soft…

The Fermi, Swift and INTEGRAL satellites, together with ground based (especially Cherenkov) telescopes made possible a great progress in our understanding of relativistic jets. We can now start to attack the difficult questions of jet…

The high-frequency-peaked BL Lacertae object 1ES 0229+200 is a relatively distant (z = 0.1396), hard-spectrum (Gamma ~ 2.5), very-high-energy-emitting (E > 100 GeV) gamma-ray blazar. Very-high-energy measurements of this active galactic…

Cosmic Ray (CR) interactions with the dense gas inside Giant Molecular Clouds (GMCs) produce neutral pions, which in turn decay into gamma rays. Thus, the gamma ray emission from GMCs is a direct tracer of the cosmic ray density and the…

The Burst Alert Telescope (BAT) onboard Swift detected bright emission from 15--195 keV from the source SWIFT~J0746.3+2548 (J0746 in the following), identified with the optically-faint (R ~ 19), z=2.979 quasar SDSS J074625.87+244901.2. Here…

The Galactic high-mass X-ray binary and jet source (microquasar) LSI +61 303 has recently been detected at TeV gamma-ray energies by the MAGIC telescope. We have applied a time-dependent leptonic jet model to the broadband spectral energy…

Context. Blazars are powerful active galactic nuclei (AGNs) radiating prominently in the whole electromagnetic spectrum, from the radio to the X-ray and gamma-ray bands. Their emission is dominated by synchrotron and inverse-Compton…

For High frequency BL Lac objects (HBLs) like H1426+428, a significant fraction of their TeV gamma-rays emitted are likely to be absorbed in interactions with the diffuse IR background, yielding $e^\pm$ pairs. The resulting $e^\pm$ pairs…

Because of the short duty-cycles and observation-time constraints, studies of bright TeV (E>100 GeV) blazars are mostly restricted to flaring episodes or rather short (days to few weeks) multiwavelength campaigns. At the same time,…

The expected opacity of the intergalactic space limits the mean free path of TeV gamma rays to dozens of Megaparsecs. However, TeV photons from numerous more distant sources have been detected. This might be interpreted, in each particular…

Advances in the capabilities of X-ray, gamma-ray and TeV telescopes have brought new information on the physics of relativistic jets, which are responsible for the blazar "phenomenon". In particular the broad band sensitivity of the…

Relativistic jets from blazars are known to be sources of very-high-energy gamma rays (VHEGRs). During their propagation in the intergalactic space, VHEGRs interact with pervasive cosmological photon fields such as the extragalactic…

We propose a scenario for self-consistent interpretation of GeV - TeV spectrum of a distant blazar PKS 1424+240. In this scenario, ultra-high energy (UHE) protons are assumed to exist in the blazar jet and produce gamma rays through…

TeV gamma-rays from the BL Lac object 1ES1959+650 have been measured during the years 2000 and 2001 with a significance of 5.2 sigma at a value of 5.3% of the Crab flux and in May 2002 during strong outbursts with > 23 sigma at a flux level…

From the early days in gamma-ray astronomy, locating the origin of GeV emission within the core of an active galactic nucleus (AGN) persisted as an open question; the problem is to discern between near- and far-site scenarios with respect…

Very high energy (VHE; $E \geq$ 100GeV) $\gamma-$ray from cosmological distances are attenuated by the extragalactic background light (EBL) in the IR to UV band. By contrasting measured versus intrinsic emission, the EBL photon density can…

In this first systematic attempt to characterise the intranight optical variability (INOV) of TeV detected blazars, we have monitored a well defined set of 9 TeV blazars on total 26 nights during 2004-2010. In this R (or V)-band monitoring…

The TeV radio galaxy M87 is the first radio galaxy detected in the TeV regime. The structure of its jet, which is not pointing towards our line of sight, is spatially resolved in X-ray (by Chandra), optical and radio observations. In 2008,…

Galactic Gamma ray astronomy at very high energy (E > 30 TeV) is a vital tool in the study of the non-thermal universe. The interpretation of the observations in this energy region requires the precise modeling of the attenuation of photons…

Investigations that were carried out over the last two decades with novel and more sensitive instrumentation have dramatically improved our knowledge of the more violent physical processes taking place in galactic and extra-galactic…

X-ray absorption of high-redshift quasars is enigmatic, because it remains unclear where in the universe the absorbing gas is. If absorption occurs near the high-z host, it could help us understand early stages of galaxy formation. If it is…