The imminent availability of large arrays of large light collectors deployed to exploit atmospheric Cherenkov radiation for gamma-ray astronomy at more than 100 GeV, motivates the growing interest in application of intensity interferometry in astronomy. Indeed, planned arrays numbering up to one hundred telescopes will offer close to 5,000 baselines, ranging from less than 50 m to more than 100...

ARGO−YBJ is a “full coverage” air shower detector under construction at the YangBaJing Laboratory (4300 m a.s.l., Tibet, P.R. of China). Its main goals are γ-ray astronomy and cosmic ray studies. In this paper we present the capabilities of ARGO−YBJ in detecting the emission from Gamma Ray Bursts (GRBs) at energies E > 10 GeV .

Cosima is the Geant4-based simulator of the medium-energy gamma-ray astronomy library MEGAlib. Within the MEGAlib framework, Cosima is designed to be a simple, fool-proof interface to Geant4 and to enable the simulation of most of the measurement scenarios encountered by X-ray and gamma-ray detectors in space and on Earth.

We have undertaken near-continuous monitoring of the Seyfert 1 galaxy NGC 7469 in the X-ray with RXTE over a ∼ 30 d baseline. The source shows strong variability with a root-mean-square (rms) amplitude of ∼ 16 per cent, and peak–to–peak variations of a factor of order 2. Simultaneous data over this period were obtained in the ultraviolet (UV) using IUE, making this the most intensive X-ray UV/X...

Recent ROSAT studies have identified a significant population of Active Galactic Nuclei (AGN) that are notably faint in soft X-rays relative to their optical fluxes. Are these AGN intrinsically X-ray weak or are they just highly absorbed? Brandt, Laor & Wills have systematically examined the optical and UV spectral properties of a well-defined sample of these soft X-ray weak (SXW) AGN drawn fro...

We present a new X-ray selected high redshift quasar CXOCY J125304.0090737 at z = 4.179, discovered by the Calán-Yale Deep Extragalactic Research (CYDER) Survey. This quasar is the fifth X-ray selected high redshift radio quiet quasar (z > 4) found so far and also the second faintest. Here, we present its observed properties which are characterized by its relative faintness, hardness and X-ray ...

Very high-energy (VHE) gamma-ray astronomy has undergone a transformation in the last few years, with telescopes of unprecedented sensitivity having greatly expanded the source catalogue. Such progress makes the detection of a gamma-ray burst at the highest energies much more likely than previously. This paper describes the facilities currently operating and their chances for detecting gamma-ra...

We present a detailed analysis of week-long simultaneous observations of the blazar Mrk 421 at 2–60 keV X-rays (RossiXTE) and TeV γ-rays (Whipple and HEGRA) in 2001. Accompanying optical monitoring was performed with the Mt. Hopkins 48" telescope. The unprecedented quality of this dataset enables us to establish the existence of the correlation between the TeV and X-ray luminosities, and also t...