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We present the results obtained from exploratory Chandra observations of nine high-redshift (z=4.09-4.51) quasars, selected from among the optically brightest Palomar Digital Sky Survey quasars known. Their broad-band spectral energy…
We discuss production of very high energy (VHE) gamma-rays in large scale extragalactic jets of FR I sources. Based on recent optical and X-ray observations of these objects we evaluate their VHE emission in a framework of one electron…
The cosmological nature of gamma-ray bursts (GRBs) implies that a small portion of them could be gravitationally lensed by foreground objects during their propagation. The gravitational lensing effect on the GRB prompt emission and on-axis…
SAX J1819.3-2525 is a nearby X-ray transient which exhibited a fast and large X-ray outburst on Sep. 15, 1999 (Smith et al. 1999). The Wide Field Cameras and the Narrow Field Instruments (NFI) on board BeppoSAX observed SAX J1819.3-2525 at…
BeppoSAX observed several galactic binary X-ray pulsars during the Science Verification Phase and in the first year of the regular program. The complex emission spectra of these sources are an ideal target for the BeppoSAX instrumentation,…
We study the detectability and characterization of electron beams as they leave their acceleration site in the low corona toward interplanetary space through their nonthermal X-ray bremsstrahlung emission. We demonstrate that the largest…
The LAT instrument on the Fermi Gamma-Ray Space Telescope is performing an all-sky survey from 20 MeV to 300 GeV with unprecedented statistics and angular resolution. This is providing a wealth of new information on the non-thermal emission…
We present calculations of the heliospheric SWCX emission spectra and their contributions in the ROSAT 1/4 keV band. We compare our results with the soft X-ray diffuse background (SXRB) emission detected in front of 378 identified shadowing…
We report on the detection of cosmic shear on angular scales of 1.3-6.5 arcmin using 45 independent empty fields observed with the Very Large Telescope (VLT). This result confirms previous measurements obtained with the CFH Telescope at the…
We present results from continued Chandra X-ray imaging and spectroscopy of a flux-limited sample of flat spectrum radio-emitting quasars with jet-like extended structure. X-rays are detected from 24 of the 39 jets observed so far. We…
A general scaling of the evolution of an exploding liquid jet under an ultra short and intense X-ray pulse from a X-ray free electron laser (XFEL) is proposed. A general formulation of the conservation of energy for blasts in vacuum…
GRB 980329 is the brightest gamma-ray burst detected so far with the Wide Field Cameras aboard BeppoSAX, both in gamma-rays and X-rays. With respect to its fluence (2.6 X 10**-5 erg/s/cm**2 in 50 to 300 keV) it would be in the top 4% of…
We describe a new approach to studying the intergalactic and circumgalactic medium in the local Universe: direct detection through narrow-band imaging of ultra-low surface brightness visible-wavelength line emission. We use the…
It has been suggested that the peculiar properties of the luminous Type Ic supernova SN 1998bw and its low-energy gamma-ray burst GRB 980425 may be understood if they originated in a standard gamma-ray burst explosion viewed far from the…
We discuss the possibility that gamma-ray bursts may result from cosmological relativistic blob emitting neutron star jets that precess past the line of sight. Beaming reduces the energy requirements, so that the jet emission can last…
Cosmic rays are the highest energy particles found in nature. Measurements of the mass composition of cosmic rays between 10^{17} eV and 10^{18} eV are essential to understand whether this energy range is dominated by Galactic or…
Very-high-energy (VHE) photons around TeV energies from a gamma-ray burst (GRB) jet will play an essential role in the multi-messenger era, with a fair fraction of the events being observed off-axis to the jet. We show that different energy…
Measurements of the intensity of the cosmic X-ray background (XRB) carried out over small solid angles are subject to spatial variations due to the discrete nature of the XRB. This cosmic variance can account for the dispersion of XRB…
We present an analytic model for measuring the jet core angle ($\theta_c$) and viewing angle ($\theta_{obs}$) of off-axis gamma-ray bursts independently of the jet angular structure outside of the core. We model the images of off-axis jets…
The X-ray properties of the haloes of disk galaxies formed in fully cosmological, hydro/gravity simulations are discussed. The results are found to be consistent with observational X-ray detections and upper limits. Disk galaxy haloes are…