We present results of an infrared-to-X-ray study of 76 bright soft X-ray selected Seyfert galaxies discovered in the ROSAT All-Sky Survey. These objects are characterized by steep X-ray spectra in the 0.2-2.0 keV bandpass with power law energy spectral indices in the range of 1.3 to 8 and a lack of internal absorption by neutral hydrogen. Our sample selection based on hardness ratio yields a me...

The spectrum of the diffuse isotropic component of cosmic X-rays over the 13–180 keV range was determined by the UCSD/MIT Hard X-Ray and GammaRay instrument (HEAO A4) on the High Energy Astronomical Observatory–1 (HEAO–1). The instrument consists of a complex of actively shielded and collimated scintillation counters, including the Low Energy Detector set from which the data reported here were ...

We investigate the γ-ray and X-ray properties of the flat spectrum radio quasar (FSRQ) 4C 50.11 at redshift z = 1.517. The Fermi Large Area Telescope (LAT) data indicate that this source was in an active state since 2013 July. During the active period, the γ-ray flux increased by more than a factor of three and two distinct flares were detected with the variability timescale as short as several...

The X-ray background from 0.1 to 7 keV has been studied using high spectral and spatial resolution data from the ASCA Solid-state Imaging Spectrometers and ROSAT Position Sensitive Proportional Counter. Analysing both the diffuse background radiation and resolved sources, we have carried out a series of joint spectral fits of the ASCA and ROSAT data. As found previously with ASCA data alone, th...

We present a study of the X-ray coronal emission from the active binary VY Ari, using data from both the Low Energy Concentrator Spectrometer (LECS) and the Medium Energy Concentrator Spectrometer (MECS) instruments onboard the X-ray satellite BeppoSAX. Using these instruments, the X-ray spectrum of VY Ari can be studied across two full decades of energy, from 0.1 to 10 keV. The spectrum is wel...

The GALPROP model for cosmic-ray (CR) propagation produces explicit predictions for the angular distribution of Galactic diffuse γ-rays. We compare our current models with EGRET spectra for various regions of the sky. This allows a critical test of alternative hypotheses for the observed GeV excess. We show that a population of hard-spectrum γ-ray sources cannot be solely responsible for the ex...

The unidentified TeV gamma-ray source MGRO J1908+06/HESS J1908+063 was observed with the VERITAS Imaging Atmospheric Cherenkov Array during October 2007 and May-June 2008. This extended source is located on the galactic plane at a galactic longitude of 40.45 degrees and has a hard TeV spectrum with an index of Γ≈2.08 [1]. The Very High Energy (VHE) gamma-ray flux was measured by H.E.S.S. out to...

Preliminary analysis of the X-ray spectrum of NGC 1068 obtained by the RGS spectrometer on board XMM-Newton is presented. A physically consistent model is developed in order to quantitatively describe the reprocessing of the central AGN continuum source into the discrete X-ray emission observed in Seyfert 2 galaxies. All the important atomic processes are taken into account, including photoexci...

We review the current observational status of the M87 jet at radio, optical, and X-ray frequencies. Special attention is paid to the radio morphology, the radio-to-X-ray spectrum, measurement of proper motions, and optical evidence for a counter-jet. The problem of jet confinement is discussed, as well as models for the radio-to-X-ray spectrum and the related problem of particle lifetimes. Fina...